Title: Engine with variable cam timing and control advantageously using humidity sensor
Abstract: A system and method for utilizing a humidity sensor with an internal combustion engine of a vehicle is described. Specifically, information from the humidity sensor is used to adjust a desired air-fuel ratio to reduce engine misfire while improving vehicle fuel economy. Further, such information is also used to adjust timing and/or lift of the valve in the engine cylinder. Finally, diagnostic routines are also described.
Patent Number: 6,918,362 Issued on 07/19/2005 to Cullen
| Inventors:
|
Cullen; Michael J. (Northville, MI)
|
| Assignee:
|
Ford Global Technologies, LLC (Dearborn, MI)
|
| Appl. No.:
|
678500 |
| Filed:
|
October 2, 2003 |
| Current U.S. Class: |
123/90.15; 123/90.19; 123/90.16; 123/677; 123/678; 123/679; 123/568.22; 701/109; 701/105; 701/102 |
| Intern'l Class: |
F01L 001/34 |
| Field of Search: |
123/9015,901.1,901.6,901.9,902.7,903.1,568.22,677-679
701/101-105,109
|
References Cited [Referenced By]
U.S. Patent Documents
| 5241937 | Sep., 1993 | Kanehiro et al.
| |
| 5609126 | Mar., 1997 | Cullen et al.
| |
| 6062204 | May., 2000 | Cullen.
| |
| 6101993 | Aug., 2000 | Lewis et al.
| |
| 6557540 | May., 2003 | Mianzo et al.
| |
| 6575148 | Jun., 2003 | Bhargava et al.
| |
| 6581447 | Jun., 2003 | Strohrmann et al.
| |
| 6581571 | Jun., 2003 | Kubesh et al.
| |
| 6728625 | Apr., 2004 | Strubhar et al.
| |
| 2002/0046741 | Apr., 2002 | Kakuho et al.
| |
Other References
U.S. Appl. No. 10/678,197, filed Oct. 2, 2003, Cullen.
U.S. Appl. No. 10/678,409, filed Oct. 2, 2003, Cullen.
U.S. Appl. No. 10/678,411, filed Oct. 2, 2003, Cullen.
|
Primary Examiner: Denion; Thomas
Assistant Examiner: Riddle; Kyle M.
Attorney, Agent or Firm: Lippa; Allan J., Alleman Hall McCoy Russell & Tuttle LLP
Claims
1. A method for adjusting engine operation of a vehicle having a humidity sensor,
the method comprising:
determining a parameter indicative of ambient humidity outside of the vehicle
based on said sensor;
varying a desired cylinder valve condition based at least as said parameter indicative
of ambient humidity varies;
adjusting a control signal to adjust said cylinder valve based on said desired
cylinder valve condition; and
determining degradation of said sensor based on a signal.
2. The method of claim 1 wherein said desired cylinder valve condition is a desired
cylinder valve lift.
3. The method of claim 1 wherein said desired cylinder valve condition is a desired
cylinder intake valve lift.
4. The method of claim 1 wherein said desired cylinder valve condition is a desired
cylinder exhaust valve lift.
5. The method of claim 1 wherein said desired cylinder valve condition is a desired
cylinder valve timing.
6. The method of claim 1 wherein said desired cylinder valve condition is a desired
cylinder intake valve timing.
7. The method of claim 1 wherein said desired cylinder valve condition is a desired
cylinder exhaust valve timing.
8. The method of claim 1 wherein said desired cylinder valve condition is a desired
cylinder cam timing.
9. The method of claim 1 wherein said desired cylinder valve condition is a desired
cylinder intake valve cam timing.
10. The method of claim 1 wherein said desired cylinder valve condition is a
desired cylinder exhaust valve cam timing.
11. The method of claim 1 wherein said desired cylinder valve condition is a
desired cylinder intake and exhaust valve cam timing.
12. A method for adjusting engine operation of a vehicle having a humidity sensor,
the engine having a cylinder with a valve, the method comprising:
determining a parameter indicative of ambient humidity outside of the vehicle
based on said sensor;
determining a desired cylinder cam timing based at least on said parameter and
an engine operating condition;
adjusting a control signal to adjust said cylinder valve based on said desired
cylinder cam timing; and
determining degradation of said humidity sensor based at least on a measured signal.
13. The method recited in claim 12 wherein said parameter is absolute humidity.
14. The method recited in claim 12 wherein said parameter is relative humidity.
15. The method recited in claim 12 further comprises setting said desired cam
timing to a nominal value if said humidity sensor has degraded.
16. An article of manufacture having a computer readable storage medium with
a computer program encoded therein for adjusting engine operation of a vehicle
having a humidity sensor, the engine having a cylinder with at least an adjustable
valve, the article comprising:
code for determining a parameter indicative of ambient humidity outside of the
vehicle based on said sensor;
code for determining a desired cylinder cam timing that varies based at least
on said parameter and an engine operating condition;
code for adjusting a control signal to adjust said cylinder valve based on said
desired cylinder cam timing; and
code for determining degradation of said sensor based at least on a measured signal.
Description
FIELD OF THE INVENTION
The field of the present invention relates generally to the control of engine
operation to reduce engine misfire conditions while maximizing engine fuel economy
for passenger vehicles driven on the road.
BACKGROUND OF THE INVENTION
Vehicle engines use various sensors to provide information that is then used
to control engine operations for a variety of reasons. One example, U.S. Pat. No.
6,575,148, describes using a specific humidity sensor to modify the engine air-fuel
ratio as well as other engine parameters.
The inventors of the present invention have recognized a disadvantage with such
an approach. In particular, such a system fails to consider engine misfire effects
on the achievable fuel economy performance in controlling engine air-fuel ratio.
Furthermore, when such an engine uses variable cam or valve timing,
variations in humidity can further exacerbate engine misfires due to the combined
effect of cam timing variation and humidity on engine combustion.
Specifically, the inventors of the present invention have recognized
that the achievable valve timing varies as ambient humidity varies. Thus, if valve
timing is optimized for low humidity (as much dilution as possible to maximize
fuel economy in low humidity conditions), an increase in humidity may cause a change
in the mixture dilution thereby increasing potential for engine misfire. Alternatively,
when cam timing is set for a worst case of high humidity, thereby reducing engine
misfires, this can result in less vehicle economy and increased emissions on low
humidity days. As such, operation according to prior approaches results in either
increased engine misfires, or lost vehicle fuel efficiency and increased emissions.
SUMMARY OF THE INVENTION
The above disadvantages are overcome by a method for adjusting engine operation
of a vehicle having a humidity sensor. The method comprises:
- determining a parameter indicative of ambient humidity outside of the
vehicle based on said sensor;
- determining a desired cylinder valve condition based at least on said
parameter; and
- adjusting a control signal to adjust said cylinder valve based on said
desired cylinder valve condition.
By setting the valve conditions for engine operation based on humidity, it is
possible to provide increased fuel economy and reduced emissions. In this way,
operation of the vehicle's engine is improved across various conditions by taking
into account variations of ambient humidity and its effect on engine misfire and
residual fraction. As such, increased vehicle fuel economy and reduced vehicle
emissions and misfires can be achieved, even with lean air-fuel operation.
In other words, in one example, during low humidity conditions, the method allows
additional adjustment of valve timing thereby providing increased fuel economy.
Likewise, during high humidity conditions, the method reduces engine misfire by
operating with valve timing adjustment based on humidity. In this way, operation
of the vehicle's engine is optimized in various conditions and takes into account
variations of ambient humidity and its effect on engine misfire. As such, increased
vehicle fuel economy and reduced vehicle emissions and misfires can be achieved.
Note that various types of humidity sensors can be used to provide information
to the engine control, such as an absolute humidity sensor, a relative humidity
sensor, or various others. Also note that various types of engine misfire parameters
can be used to adjust the engine valves.
DESCRIPTION OF THE FIGURES
FIGS. 1A, 1B, and 5 are schematic diagrams of an engine wherein
the invention is used to advantage; and
FIGS. 2-4, 6-7 and 8A-8B are high level flow charts
illustrating operation according to an example embodiment of the invention.
DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
Referring to FIG. 1A, internal combustion engine
10, further described
herein with particular reference to FIG. 1B, is shown coupled to torque converter
11 via crankshaft
13. Torque converter
11 is also coupled
to transmission
15 via turbine shaft
17. Torque converter
11
has a bypass clutch (not shown) which can be engaged, disengaged, or partially
engaged. When the clutch is either disengaged or partially engaged, the torque
converter is said to be in an unlocked state. Turbine shaft
17 is also known
as transmission input shaft. Transmission
15 comprises an electronically
controlled transmission with a plurality of selectable discrete gear ratios. Transmission
15 also comprise various other gears, such as, for example, a final drive
ratio (not shown). Transmission
15 is also coupled to tire
19 via
axle
21. Tire
19 interfaces the vehicle (not shown) to the road
23.
Internal combustion engine
10 comprising a plurality of cylinders,
one cylinder of which is shown in FIG. 1B, is controlled by electronic engine controller
12. Engine
10 includes combustion chamber
30 and cylinder
walls
32 with piston
36 positioned therein and connected to crankshaft
13. Combustion chamber
30 communicates with intake manifold
44
and exhaust manifold
48 via respective intake valve
52 and exhaust
valve
54. Exhaust gas oxygen sensor
16 is coupled to exhaust manifold
48 of engine
10 upstream of catalytic converter
20.
Intake manifold
44 communicates with throttle body
64 via throttle
plate
66. Throttle plate
66 is controlled by electric motor
67,
which receives a signal from ETC driver
69. ETC driver
69 receives
control signal (DC) from controller
12. Intake manifold
44 is also
shown having fuel injector
68 coupled thereto for delivering fuel in proportion
to the pulse width of signal (fpw) from controller
12. Fuel is delivered
to fuel injector
68 by a conventional fuel system (not shown) including
a fuel tank, fuel pump, and fuel rail (not shown).
Engine
10 further includes conventional distributorless ignition system
88 to provide ignition spark to combustion chamber
30 via spark plug
92 in response to controller
12. In the embodiment described herein,
controller
12 is a conventional microcomputer including: microprocessor
unit
102, input/output ports
104, electronic memory chip
106,
which is an electronically programmable memory in this particular example, random
access memory
108, and a conventional data bus.
Controller
12 receives various signals from sensors coupled to
engine
10, in addition to those signals previously discussed, including:
measurements of inducted mass air flow (MAF) from mass air flow sensor
110
coupled to throttle body
64; engine coolant temperature (ECT) from temperature
sensor
112 coupled to cooling jacket
114; a measurement of throttle
position (TP) from throttle position sensor
117 coupled to throttle plate
66; a measurement of turbine speed (Wt) from turbine speed sensor
119,
where turbine speed measures the speed of shaft
17, and a profile ignition
pickup signal (PIP) from Hall effect sensor
118 coupled to crankshaft
13
indicating and engine speed (N).
Continuing with FIG. 1B, accelerator pedal
130 is shown communicating
with the driver's foot
132. Accelerator pedal position (PP) is measured
by pedal position sensor
134 and sent to controller
12.
In an alternative embodiment, where an electronically controlled throttle is
not
used, an air bypass valve (not shown) can be installed to allow a controlled amount
of air to bypass throttle plate
62. In this alternative embodiment, the
air bypass valve (not shown) receives a control signal (not shown) from controller
12.
In addition, an absolute, or relative, humidity sensor
140 is shown for
measuring humidity of the ambient air. This sensor can be located either in the
inlet air stream entering manifold
44, or measuring ambient air flowing
through the engine compartment of the vehicle. Further, in an alternative embodiment,
a second humidity sensor (
141) is shown which is located in the interior
of the vehicle and coupled to a second controller
143 that communicates
with controller
12 via line
145. The diagnostic routines described
below herein can be located in controller
12, or controller
143,
or a combination thereof. Further note that the interior humidity sensor can be
used in a climate control system that controls the climate in the passenger compartment
of the vehicle. Specifically, it can be used to control the air-conditioning system,
and more specifically, whether to enable or disable the air-conditioning compressor
clutch which couples the compressor to the engine to operate the compressor.
As will be appreciated by one of ordinary skill in the art, the specific routines
described below in the flowcharts may represent one or more of any number of processing
strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading,
and the like. As such, various steps or functions illustrated may be performed
in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the
order of processing is not necessarily required to achieve the features and advantages
of the invention, but is provided for ease of illustration and description. Although
not explicitly illustrated, one of ordinary skill in the art will recognize that
one or more of the illustrated steps or functions may be repeatedly performed depending
on the particular strategy being used. Further, these Figures graphically represent
code to be programmed into the computer readable storage medium in controller
12.
Referring now to FIG. 2, an example routine is described for controlling
engine fuel injection based on humidity. First, in step
210, the routine
determines whether current conditions are for a cold engine start (versus a warm
re-start). In other words, the routine determines based on various factors such
as, for example: engine coolant temperature, time since engine start, engine speed,
whether current conditions represent the starting of the engine during non warmed-up
conditions or combinations thereof. When the answer to step
210 is yes,
the routine continues to step
212. In step
212, the routine determines
an initial lean air-fuel ratio set-point. This set-point, or desired lean air-fuel
ratio, is used as described below herein to provide a balance between engine fuel
economy and reduced emissions. In particular, this desired lean air-fuel ratio
is determined based on various engine operating parameters, such as, for example:
engine coolant temperature (ect), engine air flow (or engine load, or engine torque),
measured vehicle emission such as NOx, time since engine start (atmr1) and various
other parameters or combinations thereof. In one example, the desired air-fuel
ratio (lean
-AF
-desired) is determined as described in the
equation 1 below.
Note that this desired air-fuel ratio is modified below depending on humidity,
and in this particular example, ambient humidity. While the exact relationship
between cam timing and the desired lean air-fuel ratio can vary from engine to
engine, various testing can be performed to quantify this effect and also take
into account the effect of variable cam timing, in combination with humidity, on
the desired lean air-fuel ratio. In this alternate embodiment, equation 1 would
be modified to include a desired lean air-fuel ratio based on variable cam timing
position as well.
The present inventors herein have also recognized that the effect of humidity
on the residual fraction is substantially linear with humidity in some cases. As
such, as described below herein, a linear modifier to the desired lean air-fuel
ratio can be utilized. Note however, that various other modifications can be used
depending on the particular effect of humidity on the lean air-fuel ratio that
can be achieved while reducing engine misfires.
Continuing with FIG. 2, in step
214 the routine determines an ambient
humidity value. In one example, this is the ambient humidity measured from one
or both of the humidity sensors. In another example, information from a humidity
sensor, in combination with various other sensors, can be used to provide a modified,
or estimated, humidity value. Then, in step
216, the routine calculates
a lean air-fuel ratio limit that reduces engine misfires based on the humidity
and engine operating conditions. Next, step
218, the desired lean air-fuel
ratio, (determined in step
212) is read, taking into account any other modifications
of the desired lean air-fuel ratio due to other engine systems (such as, for example:
temperature modifications, engine speed modifications, or various others).
In step
220, the routine determines whether the lean air-fuel ratio is
greater than the limit calculated in step
216. If so, the desired lean air-fuel
ratio is clipped to the limit in step
222. In this way, it is possible to
adjust the lean air-fuel ratio based on an engine misfire parameter taking into
account humidity. The result is that improved engine fuel economy and reduced emissions
can be achieved across a variety of ambient humidities, without sacrificing engine misfires.
In an alternate embodiment, the desired lean air-fuel ratio is adjusted to produce
the desired lean air-fuel ratio taking into account potential engine misfires.
In this case, the adjustment as described in equation 2 below.
where, hum-obs=ambient humidity,
NOMHUM=calibratable nominal humidity for which base schedule is optimized,
usually 50 grams,
FNAFHUM (N,load) is the change in A/F desired over the range of humidity, and
N=RPM, or speed of the engine.
In this case, the measured humidity variation from a nominal humidity value (NOMHUM)
is used as a linear adjustment to a humidity function (FNAFHUM) that is calculated
as a function of current engine operating conditions of engine speed and engine
load. This function represents, in one example, a change in the desired lean air-fuel
ratio over the range of potential humidity experienced in an operating vehicle.
Note also that this equation 2 can be modified to include an adjustment to the
lean air-fuel ratio based on the deviation of the measured humidity from a nominal
humidity value multiplied by a function dependent on variable cam timing position.
Continuing with FIG. 2, in step
224, the routine adjusts the fuel
injection amount to the engine based on the clipped desired lean air-fuel ratio.
Note that this adjustment can be in either an open loop or closed loop feedback
control system. In particular, the fuel injection amount can be adjusted based
on the desired lean air-fuel ratio as well as feedback from exhaust gas oxygen
sensors located in the vehicle's exhaust.
Referring now to FIG. 3, an alternate embodiment of the present invention
is described for adjusting a desired lean air-fuel ratio based on humidity outside
of the vehicle. In this example, the engine is operated at a lean air-fuel ratio
during various operating conditions in addition to engine warm-up conditions after
a cold engine start. In particular, in step
310, the routine determines
whether lean operation has been enabled after the engine warm up condition. If
the answer to step
310 is YES, the routine continues to step
312.
In step
312, the routine determines whether stratified operation is requested.
Note that stratified operation can be used in directly injected engines where
the fuel injector is located to directly inject fuel into the engine cylinder.
If the answer to step
312 is YES, the routine continues to step
314
to calculate a desired lean air-fuel ratio based on engine speed as described in
equation 3.
Alternatively, if homogenous lean operation is selected, then the
desired lean air-fuel ratio is calculated based on equation 4 in step
316
using an alternate function of speed and load.
Next, in step
318, the ambient humidity is read from the sensor, and
optionally modified based on other sensor parameters and operating conditions.
Then, in step
320, the routine adjusts the desired lean air-fuel ratio based
on humidity to account for reduced engine misfire as indicated in equation 5.
Next, in step
322, the routine determines whether the adjusted desired
lean air-fuel ratio from step
320 has been adjusted past the stoichiometric
point. In other words, the routine determines whether the adjustment based on the
humidity (to the desired lean air-fuel ratio) has caused the desired lean air-fuel
ratio to be adjusted to a rich value. If such conditions have been indicated, then
in step
324 the desired air-fuel ratio is clipped to the stoichiometric
value to reduce inadvertent rich operation. This is indicated as described in equation 6.
Continuing with FIG. 3, in step
326 the routine adjusts the fuel
injection into the engine based on the clipped adjustment of desired lean air-fuel
ratio as described above. In this way, improved fuel economy, reduced engine misfires,
and reduced emissions are achieved. Finally, if lean operation is not enabled and
the answer to step
310 is no, the routine continues to step
328 to
operate the engine to oscillate about the stoichiometric value, or to operate rich
as desired by engine operating conditions.
Note that the adjustment of fuel injection based upon the desired air-fuel ratio
can further take into account feedback from exhaust gas oxygen sensors. In other
words, the desired air-fuel ratio, along with feedback from the oxygen sensor,
are used in combination to maintain the actual air-fuel ratio at or near the desired
value, and to track changes in the desired value due to, for example, changes in humidity.
Referring now to FIG. 4, a routine is described for adjusting cam timing
(and thus valve timing) based on humidity, specifically ambient humidity. Note
that this embodiment is directed to changing valve timing by changing cam timing
via a single overhead cam. However, various other valve timing mechanisms can be
used. For example, the routine could also adjust intake or exhaust valve lift,
intake or exhaust valve timing (e.g., via an electromechanical valve actuator),
intake or exhaust valve cam timing, or adjust a dual equal cam timing which adjusts
both intake and exhaust valve timing.
As described above, in internal combustion engines, it is desirable to schedule
camshaft timing for best fuel economy and emissions. This typically occurs at a
cam timing corresponding to high residual fraction (RF), sometimes termed internal
EGR (Exhaust Gas Re-circulation). The extent of residual fraction is also referred
to as the charge "dilution" level. Countering this use of high dilution is the
tendency for misfire when the dilution interferes with spark ignition. As such,
the optimal VCT for fuel economy and emissions is usually lies on one side of the
misfire limit.
Ambient humidity also causes dilution of the engine cylinder charge mixture.
Thus if the VCT timing was optimized for low humidity, resulting in being right
on the edge of misfire, the addition of humidity would push the dilution over the
edge into a potential misfire condition. To avoid this, engines are typically calibrated
with the VCT timing schedule for a worst case high humidity day, avoiding misfires.
This, of course, results in less than best fuel economy on lower humidity days.
Therefore a humidity sensor, such as an internal or ambient humidity sensor,
can be used as described herein. Specifically, if the VCT timing schedule is adjusted
for humidity, then the optimal timing for fuel economy can be delivered at a variety
of humidity levels, while reducing misfire.
Note that cam timing can be controlled as described in U.S. Pat. No. 5,609,126,
which is incorporated by reference in its entirety herein. However, it is adjusted
as described with regard to FIG. 4. An engine with variable cam timing is shown
in FIG. 5.
Referring now specifically to FIG. 4, the desired cam timing from step
225 of U.S. Pat. No. 5,609,126 is calculated as described below and adjusted
based on humidity. First, in step
410, the routine calculates a nominal
cam timing (cam
-nom) based on speed (n) and load. Then, in step
412,
the routine calculates an adjustment in cam timing (vct
-hum
-adj)
based on the deviation of measured humidity (hum
-obs) from a nominal
value (NOMHUM). The adjustment is a function of engine parameters, such as engine
speed and load as indicated in FIG. 4. Note that, as above, by using the deviation
from a nominal value, it is potentially possible to reduce the calibration effort
if a standardized function FNVCTHUM can be predetermined based on engine features.
Note again that a linear adjustment is used, however various others can also be
used based on experimental testing of the particular engine application.
Then, in step
414, the routine calculates the adjusted desired cam timing
(vct
-adjusted) based on nominal cam timing and cam timing adjustment
as shown in FIG. 4. Then, in step
416, the routine clips the adjusted values
to the maximum and/or minimum available cam timing at the present engine operating conditions.
In this way, it is possible to provide improved emissions and fuel economy that
is not compromised due to variations in ambient humidity.
An alternative embodiment of internal combustion engine
10 is shown in
FIG. 5. The engine is controlled by electronic engine controller
12. In
this embodiment, engine
10 includes a variable valve adjustment mechanism,
which in this example is a variable cam timing mechanism. As in FIG. 1, engine
10 includes combustion chamber
30 and cylinder walls
32 with
piston
36 positioned therein and connected to crankshaft
40. Combustion
chamber
30 is shown communicating with intake manifold
44 and exhaust
manifold
48 via intake valve
52 and exhaust valve
54, respectively.
Intake manifold
44 is shown communicating with throttle body
64 via
throttle plate
62. Throttle position sensor
70 measures position
of throttle plate
62. Exhaust manifold
48 is shown. Intake manifold
44 is also shown having fuel injector
80 coupled thereto for delivering
liquid fuel in proportion to the pulse width of signal FPW from controller
12.
Fuel is delivered to fuel injector
80 by a conventional fuel system (not
shown) including a fuel tank, fuel pump, and fuel rail (not shown). Alternatively,
the engine may be configured such that the fuel is injected directly into the cylinder
of the engine, which is known to those skilled in the art as a direct injection
engine. Also, as in FIG. 1, an electronically controlled throttle plate can be used.
Distributorless ignition system
88 provides ignition spark
to combustion chamber
30 via spark plug
92 in response to controller
12. Two-state exhaust gas oxygen sensor
16 is shown coupled to exhaust
manifold
48 upstream of catalytic converter
20. Sensor
16
provides signal EGO to controller
12 which converts signal EGO into two-state
signal EGOS. A high voltage state of signal EGOS indicates exhaust gases are rich
of a reference air/fuel ratio and a low voltage state of converted signal EGO indicates
exhaust gases are lean of the reference air/fuel ratio.
Controller
12 is shown in FIG. 1 as a microcomputer including:
microprocessor unit
102, input/output ports
104, read-only memory
106, random access memory
108, and a conventional data bus. Controller
12 is shown receiving various signals from sensors coupled to engine
10,
in addition to those signals previously discussed, including: engine coolant temperature
(ECT) from temperature sensor
112 coupled to cooling sleeve
114;
a measurement of mass air flow measurement (MAF) from mass flow sensor
116
coupled to intake manifold
44; and a profile ignition pickup signal (PIP)
from Hall effect sensor
118 coupled to crankshaft
40. In one aspect
of the present invention, engine speed sensor
119 produces a predetermined
number of equally spaced pulses every revolution of the crankshaft.
Camshaft
130 of engine
10 is shown communicating with rocker
arms
132 and
134 for actuating intake valve
52 and exhaust
valve
54. Camshaft
130 is directly coupled to housing
136.
Housing
136 forms a toothed wheel having a plurality of teeth
138.
Housing
136 is hydraulically coupled to an inner shaft (not shown), which
is in turn directly linked to camshaft
130 via a timing chain (not shown).
Therefore, housing
136 and camshaft
130 rotate at a speed substantially
equivalent to the inner camshaft. The inner camshaft rotates at a constant speed
ratio to crankshaft
40. However, by manipulation of the hydraulic coupling
as will be described later herein, the relative position of camshaft
130
to crankshaft
40 can be varied by hydraulic pressures in advance chamber
142 and retard chamber
144. By allowing high pressure hydraulic fluid
to enter advance chamber
142, the relative relationship between camshaft
130 and crankshaft
40 is advanced. Thus, intake valve
52 and
exhaust valve
54 open and close at a time earlier than normal relative to
crankshaft
40. Similarly, by allowing high pressure hydraulic fluid to enter
retard chamber
144, the relative relationship between camshaft
130
and crankshaft
40 is retarded. Thus, intake valve
52 and exhaust
valve
54 open and close at a time later than normal relative to crankshaft
40.
Teeth
138, being coupled to housing
136 and camshaft
130,
allow for measurement of relative cam position via cam timing sensor
150
providing signal VCT to controller
12. Teeth
1,
2,
3,
and
4 are preferably used for measurement of cam timing and are equally
spaced (for example, in a V-8 dual bank engine, spaced 90 degrees apart from one
another), while tooth
5 is preferably used for cylinder identification,
as described later herein. In addition, Controller
12 sends control signals
(LACT,RACT) to conventional solenoid valves (not shown) to control the flow of
hydraulic fluid either into advance chamber
142, retard chamber
144,
or neither.
Relative cam timing is measured using the method described in U.S. Pat.
No. 5,548,995, which is incorporated herein by reference. In general terms, the
time, or rotation angle between the rising edge of the PIP signal and receiving
a signal from one of the plurality of teeth
138 on housing
136 gives
a measure of the relative cam timing. For the particular example of a V-8 engine,
with two cylinder banks and a five toothed wheel, a measure of cam timing for a
particular bank is received four times per revolution, with the extra signal used
for cylinder identification.
Referring now to FIG. 6, a routine is described for taking default action
in response to degradation of the humidity sensor. First, in step
610, the
routine determines whether the humidity sensor has degraded as described below
herein with particular reference to FIG. 7.
Next, in step
612, the routine determines whether the sensor has degraded
beyond a predetermined level. When the answer to step
612 is YES, the routine
continues to step
614. In step
614, the routine sets the measured
humidity sensor value in the control code (hum
-obs) to the nominal humidity
value (NOMHUM). In this way, default settings are used to control various engine
operating conditions, such as, for example: engine air-fuel ratio, engine air-fuel
ratio limit values, variable cam timing, exhaust gas recirculation, valve lift,
and any combination or subcombination of these parameters. In particular, since
the control routines are structured using the deviation of measured humidity from
a nominal value, this allows for simplified routines in the case of default operation.
In other words, as described above, the only action that need be taken in response
to a degraded humidity sensor is to set the measured reading to the nominal value.
In this way, the routines controlling the various engine operations simply operate
as if there were no humidity sensor. In this way, smooth engine operation can be
achieved even with humidity sensor degradation, thereby allowing continued engine operation.
Note that in one example, not only are default settings used to control the
variable cam timing and air-fuel ratio limit value if the humidity sensor degrades,
but other parameters as well, such as EGR. Specifically, as described in U.S. Pat.
No. 6,062,204, (which is incorporated by references herein in its entirety), EGR
is scheduled based on humidity. However, if sensor degradation has occurred, then
the humidity value used for EGR can be set to a level that reduces engine misfires,
such as, for example, 50. Alternatively the equation for EGR can be modified according
to the following formula:
Referring now to FIGS. 7,
8A, and
8B, routines are described
for determining degradation of the humidity sensor
140. One diagnostic approach
described herein has two humidity sensors with sufficiently different wiring, location,
and plant manufacturing batch number that they are very unlikely to degrade simultaneously.
One diagnostic routine then consists of verifying that the sensors have the same
reading, as described below. When the sensors are in separate locations in the
vehicle, certain gates can be applied to narrow the diagnostic to certain operating
regions where high correlation is expected, such as described in FIGS. 8A and 8B.
Specifically, in this example, the two humidity sensors are labeled hum1 and hum2
herein for ease. I.e., sensor
140 provide hum 1 (or hum
-obs)
and sensor
141 provides hum2.
Referring now to FIG. 7, a routine is described for monitoring the sensors
140, and/or
141. Note that the term HUM
-DELTA is the calibratable
delta between the two sensors to indicate degradation has occurred. For example,
it can be set to 10 grains.
First, in step
710, the routine determines whether monitoring of the
humidity sensor(s) has been enabled as described below in two alternative embodiments
(FIGS. 8A and 8B). If monitoring has been enabled, then in step
720 the
routine determines whether the absolute value of (hum1-;hum2 is greater than HUM
-DELTA.
If so, degradation is indicated in step
730. Otherwise, sensor operability
is indicated in step
740.
A first embodiment to determine whether to enable humidity sensor monitoring
is
now described with regard to FIG. 8A. Here, the diagnostic is performed upon entering
preselected engine operating conditions, such as: at key-on after a long soak (engine
off) time. In this embodiment, the second sensor can be a vehicle interior humidity
sensor as described in FIG. 1. Note that for a short soak, or for vehicle running
operation, the interior sensor may read high due to a sweaty driver or other source
of water vapor in the vehicle. Or, it may be low due to the action of an air conditioning
system. As such, after a long soak, a more reliable comparison is possible. Even
then, however, multiple vehicle trips can be used to increase the reliability of
detection. In this way, the monitoring is enabled during selected conditions where
both sensors should read similar values, and thus improved detection can be achieved.
Note that in an alternative embodiment, one (or both) humidity signal(s) can be
adjusted based on engine operating conditions to provide a more accurate comparison.
Referring now specifically to FIG. 8A, in step
810, the routine
determines whether the engine soak time is longer than a threshold (SOAK
-VALUE).
If so, in step
820, diagnosis is enabled.
Note that the engine soak timer is a sensor that indicates the time since the
car was last turned on. This could be based on a timer in controller
12,
for example. The routine of FIG.
8A, in one embodiment, operates only on
the first computer loop after a vehicle has the ignition key turned on.
A second embodiment performs the diagnostic on a continuous basis. This can be
used when such continuous monitoring may be needed to determine degradation throughout
vehicle operation. In this case the interior humidity sensor may not be used. Rather,
the second humidity sensor is installed in the vehicle in a location where it would
read close to the same air stream as the first sensor, whether it is in the engine
inlet airflow stream or the ambient stream. Again, the electrical circuits can
be designed to minimize the potential of common degradation of the sensors simultaneously.
Also, the routine of FIG. 8B can perform the reading of the sensors for diagnosis
when they have reached an equilibrium value by using filters, for example.
Referring now specifically to FIG. 8B, in step
830, the routine
determines whether the time since vehicle key on is greater than a threshold values
(TIME
-ON
-VALUE). If so, in step
840, diagnosis is
enabled. Thus, by using the key on time it is possible to obtain an accurate reading
from both sensors in order to perform the diagnosis.
Note that the routines can be used to monitor either sensor
141 or sensor
143, or both.
This concludes the description of the invention. The reading of it by those
skilled in the art would bring to mind many alterations and modifications without
departing from the spirit and the scope of the invention. Accordingly, it is intended
that the scope of the invention be defined by the following claims:
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