U.S. patent application number 11/074961 was filed with the patent office on 2006-09-14 for method and apparatus for determining rotary position.
Invention is credited to Murri H. Decker, David J. Trapasso.
Application Number | 20060201238 11/074961 |
Document ID | / |
Family ID | 36951611 |
Filed Date | 2006-09-14 |
United States Patent
Application |
20060201238 |
Kind Code |
A1 |
Trapasso; David J. ; et
al. |
September 14, 2006 |
METHOD AND APPARATUS FOR DETERMINING ROTARY POSITION
Abstract
A system for determining the angular position of a rotating
element such as an engine crankshaft. An encoder wheel is divided
into a plurality of equal-angle segments, each comprising a
peripheral tooth extending radially over a central angle
representing an angular percentage of each segment. The total angle
in each segment is a tooth dwell angle and a gap dwell angle. The
ratio of the tooth dwell angle to the total segment angle is the
duty cycle. A prime segment is given a first tooth dwell angle.
Each segment has a unique tooth dwell angle. As the wheel rotates,
a sensor begins timing at a first tooth rise and determines the
time to the first tooth fall and the time to the second tooth rise.
Since each duty cycle is unique, for a wheel having 45 degree
segments the system can determine the segment being interrogated
within 90 rotational degrees.
Inventors: |
Trapasso; David J.;
(Bloomfield, NY) ; Decker; Murri H.; (Phelps,
NY) |
Correspondence
Address: |
DELPHI TECHNOLOGIES, INC.
M/C 480-410-202
PO BOX 5052
TROY
MI
48007
US
|
Family ID: |
36951611 |
Appl. No.: |
11/074961 |
Filed: |
March 8, 2005 |
Current U.S.
Class: |
73/114.26 |
Current CPC
Class: |
G01D 5/246 20130101;
G01D 5/2451 20130101 |
Class at
Publication: |
073/117.3 |
International
Class: |
G01L 3/26 20060101
G01L003/26 |
Claims
1. An encoder system for determining the angular position of a
rotating device, comprising an encoder wheel mountable coaxially on
said device and having a plurality of angular segments subtending a
plurality of central angles of said wheel, each segment including a
tooth extending from a periphery of said wheel over a first
predetermined central angle of said wheel for causing a signal to
be prevented from generation and a gap between adjacent of said
teeth extending over a second predetermined central angle of said
wheel for causing a signal to be generated and wherein said first
and second predetermined central angles comprise the total central
angle of said segment, wherein said tooth extends over an angular
percentage of said respective segment, wherein said angular
percentage of said tooth defines a duty cycle for said segment, and
wherein each of said segment duty cycles is unique.
2. An encoder system in accordance with claim 1 wherein the central
angles of said plurality of segments are equal.
3. An encoder system in accordance with claim 1 wherein the number
of said segments is between 2 and 100.
4. An encoder system in accordance with claim 3 wherein the number
of said segments is 48, each segment having a central angle of
7.5.degree..
5. An encoder system in accordance with claim 1 wherein said
plurality of segments are arranged angularly on said wheel
according to increasing sizes of said unique duty cycles.
6. An encoder system in accordance with claim 1 wherein the size of
each duty cycle is in a range between greater than 0% and less than
100%.
7. An internal combustion engine comprising an encoder system for
determining the angular position of a rotating element of said
engine, said system including an encoder wheel having a plurality
of angular segments subtending a plurality of central angles of
said wheel, each segment including a tooth extending from a
periphery of said wheel over a first predetermined central angle of
said wheel for causing a signal to be prevented from generation and
a gap between adjacent of said teeth extending over a second
predetermined central angle of said wheel for causing a signal to
be generated and wherein said first and second predetermined
central angles comprise the total central angle of said segment,
wherein said tooth extends over an angular percentage of said
respective segment, wherein said angular percentage of said tooth
defines a duty cycle for said segment, and wherein each of said
segment duty cycles is unique.
8. An engine in accordance with claim 7 wherein said rotating
element of said engine is selected from the group consisting of
crankshaft, camshaft, camshaft phaser, and any combination
thereof.
9. An engine in accordance with claim 7 wherein the number of
segments in said wheel is an integral multiple of the number of
cylinders in said engine.
10. An encoder system for determining the angular position of a
rotating device, comprising an encoder wheel mountable coaxially on
said device and having a plurality of angular segments subtending a
plurality of central angles of said wheel, each segment including a
tooth for causing a signal to be prevented from generation and a
notch defined in said tooth for causing a signal to be generated,
wherein said tooth extends over an angular percentage of a segment
and said notch extends over the remaining angular percentage of
said segment, and wherein said angular percentage of said tooth
defines a duty cycle for said segment, and wherein each of said
segment duty cycles is unique.
11. An encoder system in accordance with claim 10 wherein said
tooth extends from the periphery of said wheel over a first
predetermined central angle of said wheel, and wherein said notch
is between adjacent of said teeth extending over a second
predetermined central angle of said wheel, and wherein said first
and second predetermined central angles comprise the total central
angle of said segment.
12. An encoder system in accordance with claim 10 wherein the
central angles of said plurality of segments are equal.
13. An encoder system in accordance with claim 10 wherein the
number of said segments is between 2 and 100.
14. An encoder system in accordance with claim 13 wherein the
number of said segments is 48, each segment having a central angle
of 7.5.degree..
15. An encoder system in accordance with claim 10 wherein said
plurality of segments are arranged angularly on said wheel
according to increasing sizes of said unique duty cycles.
16. An encoder system in accordance with claim 10 wherein the size
of each duty cycle is in a range between greater than 0% and less
than 100%.
17. A method for determining the angular position of a rotating
device, the method comprising: providing a wheel mounted coaxially
on the device; dividing the wheel into a plurality of segments,
each segment having a total segment angle comprising a tooth dwell
angle and a gap dwell angle; designating one of the segments as a
prime segment having a minimum tooth dwell angle; providing
succeeding segments relative to the prime segment with
progressively greater tooth dwell angles thereby establishing a
unique duty cycle for each segment, the duty cycle being the ratio
of the tooth dwell angle to the total segment angle, wherein the
primary segment includes a minimum duty cycle, and wherein one of
the segments other than the primary segment has a maximum duty
cycle; providing each of the segments with a segment identification
number, wherein the prime segment's identification number is zero,
and wherein the succeeding segments from the prime segment are
designated with progressively greater segment identification
numbers that are integers, determining a tooth dwell angle time for
a first segment as the wheel is rotating, the first segment being
one of the segments, the tooth dwell angle time for the first
segment starting at the beginning of the tooth dwell angle of the
first segment and ending at the end of the tooth dwell angle for
the first segment; determining a total segment angle time for the
first segment as the wheel is rotating, the total segment time for
the first segment starting at the beginning of the tooth dwell
angle for the first segment and ending at the end of the gap dwell
angle for the first segment; dividing the tooth dwell angle time by
the total segment angle time to establish a first apparent duty
cycle; establishing a first percent rotation by dividing the
difference between the first apparent duty cycle and the minimum
duty cycle by the difference between the maximum duty cycle and the
minimum duty cycle; determining the apparent segment identification
number of the first segment by subtracting 1 from the total number
of segments on the wheel, multiplying by the first percent
rotation, adding 0.5, and taking the resulting integer value, which
represents an actual segment identification number of the first
segment thereby determining the angular position of the rotating
device.
18. The method in accordance with claim 17 further comprising:
comparing the first apparent duty cycle with a nominal minimum duty
cycle and a nominal maximum duty cycle; and determining that the
first apparent duty cycle is greater than the nominal minimum duty
cycle and less than the nominal maximum duty cycle.
19. The method in accordance with claim 17 further comprising:
determining a tooth dwell angle time for a second segment as the
wheel is rotating, the second segment being one of the segments
other than the first segment, the tooth dwell angle time for the
second segment starting at the beginning of the tooth dwell angle
of the second segment and ending at the end of the tooth dwell
angle for the second segment; determining a total segment angle
time for the second segment as the wheel is rotating, the total
segment time for the second segment starting at the beginning of
the tooth dwell angle for the second segment and ending at the end
of the gap dwell angle for the second segment; dividing the tooth
dwell angle time of the second segment by the total segment angle
time of the second segment to establish a second apparent duty
cycle; establishing a second percent rotation by dividing the
difference between the second apparent duty cycle and the minimum
duty cycle by the difference between the maximum duty cycle and the
minimum duty cycle; determining the apparent segment identification
number of the second segment by subtracting 1 from the total number
of segments on the wheel, multiplying by the second percent
rotation, adding 0.5, and taking the resulting integer value, which
represents the apparent segment identification number of the second
segment thereby determining the angular position of the rotating
device; and confirming that the apparent segment identification
number for the second segment is an actual segment identification
of the second segment by determining that the modulus of the actual
segment identification number of the first segment plus 1 divided
by the total number of segments is equal to the apparent segment
identification number of the second segment.
20. The method in accordance with claim 19 further comprising:
comparing the second apparent duty cycle with the minimum duty
cycle and the maximum duty cycle; determining that the second
apparent duty cycle is one of less than the minimum duty cycle and
greater than the maximum duty cycle; and establishing the actual
segment identification number of the second segment as the modulus
of the actual segment identification number of the first segment
plus 1 divided by the total number of segments on the wheel.
21. The method in accordance with claim 19 further comprising:
determining that the modulus of the actual segment identification
number of the first segment plus 1 divided by the total number of
segments is not equal to the apparent segment identification number
of the second segment; establishing the actual segment
identification number of the second segment as the modulus of the
actual segment identification number of the first segment plus 1
divided by the total number of segments on the wheel.
22. The method in accordance with claim 17 wherein the wheel is an
encoder wheel, the method further comprising: providing a timing
sensor that is associated with the encoder wheel; using the sensor
to determine the tooth dwell angle time for at least one of the
segments; and using the sensor to determine the total segment angle
time for at least one of the segments.
23. The method in accordance with claim 17 wherein the total
segment angles of each segment are equal.
24. The method in accordance with claim 17 wherein the number of
segments is between 2 and 100.
25. The method in accordance with claim 17 wherein the size of the
duty cycle of each segment is in a range between greater than 0%
and less than 100%.
26. A method for determining the angular position of a rotating
device, the method comprising: providing an encoder wheel mounted
coaxially on the device; dividing the encoder wheel into a
plurality of segments, each segment having a total segment angle
comprising a tooth dwell angle and a gap dwell angle; providing
each of said plurality of segments with a unique tooth dwell angle
thereby establishing a unique duty cycle for each segment, the duty
cycle being the ratio of the tooth dwell angle to the total segment
angle, each of the unique duty cycles being stored in a memory;
determining a tooth dwell angle time for a first segment as the
wheel is rotating, the first segment being one of the segments, the
tooth dwell angle time for the first segment starting at the
beginning of the tooth dwell angle of the first segment and ending
at the end of the tooth dwell angle for the first segment;
determining a total segment angle time for the first segment as the
wheel is rotating, the total segment time for the first segment
starting at the beginning of the tooth dwell angle for the first
segment and ending at the end of the gap dwell angle for the first
segment; dividing the tooth dwell angle time by the total segment
angle time to establish a first apparent duty cycle, wherein the
first apparent duty cycle is compared with at least one of the
unique duty cycles stored in memory; and matching the first
measured duty cycle with one of the stored unique duty cycles to
identify the first segment and thereby determine the angular
position of the rotating device.
27. The method in accordance with claim 26 further comprising:
providing a timing sensor that is associated with the encoder
wheel; using the sensor to determine the tooth dwell angle time for
at least one of the segments; and using the sensor to determine the
total segment angle time for at least one of the segments.
28. The method in accordance with claim 26 wherein each of the
unique duty cycles stored in memory have a tolerance range
associated therewith, and wherein the first apparent duty cycle is
matched with one of the unique duty cycles if the first apparent
duty cycle falls within one of the tolerance ranges for the unique
duty cycles.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method and apparatus for
determining the dynamic angular position of a rotary element with
respect to a reference position; more particularly, to encoder
sensing systems for determining the angular position of the
crankshaft of an internal combustion engine; and most particularly,
to such a system wherein a position determination can be-made
within a small fraction of a single revolution of the
crankshaft.
BACKGROUND OF THE INVENTION
[0002] Position sensors are required for modern automobile engine
control systems to detect the angular position of the crankshaft. A
vehicle's engine controller uses this information to calculate the
optimal times to fire fuel injectors and, for spark ignited
engines, ignition discharge. The information is also useful for
diagnosing malfunctions such as misfire, which typically is done by
detecting a rapid change in angular velocity.
[0003] Prior art sensors for measuring rotary position typically
incorporate encoders, resolvers, or potentiometers. In the hostile
environment of automotive engines, incremental encoders of some
form are typically used. Other types of position sensors are
typically analog in nature and have poor noise immunity and/or
drift with temperature changes, and sometimes have wear-prone
brushes. Encoders have the advantage of being simple and reliable
even when subjected to temperature extremes. They require only a
single timer/counter channel of a vehicle's controller to function
and therefore are also inexpensive.
[0004] An incremental encoder is typically constructed as a series
of spaced-apart features such as alternating teeth and notches
around the circumference of a wheel connected to a rotating device
such as a crankshaft. The wheel may be formed as a part of the
apparatus, for example, an engine flywheel may be formed as an
encoder wheel. As the wheel spins, a pickup sensor mounted in close
proximity to the wheel detects each feature as it passes by the
pickup, for example, by chopping of an optical beam or variation in
magnetic field, and generates a square wave response. An index
pulse function is typically present to identify an absolute or
reference position of the wheel, such as top dead center of the No.
1 engine piston. This sometimes consists of two features more
closely spaced than the other features. The reference position also
may be established externally by a feature on an engine camshaft
which is synchronized to the crankshaft at one-half its angular
velocity.
[0005] A known problem exists in using prior art systems when
starting an engine. The index feature must be found in order to
synchronize the engine control system, which can require up to one
full revolution of the engine to locate the index feature on the
crankshaft or two full engine revolutions to locate the index
feature on the camshaft. This represents time delay in starting the
engine.
[0006] Although prior art absolute encoder technology is well
known, such an encoder system requires multiple inputs in a
controller for each bit of resolution desired. For example, an
encoder with three bits requires a more complex wheel, three wires,
connections, and inputs, adding to the cost while decreasing the
reliability. An encoder with three bits of resolution provides an
angular resolution of 360/2.sup.3 degrees, equals 45 degrees.
[0007] Another prior art technology uses a series of unevenly
spaced features and pulses. By searching for a pattern of spacing,
the position can be established in this fashion. Such a system
typically requires a plurality of pulses before the position can be
identified. Although this may be an improvement over waiting for an
index pulse, this system typically requires up to one-half an
engine revolution (180 degrees) before the position can be
established.
[0008] What is needed in the art is a method and apparatus for
determining rotary position of a rotatable element in a small
fraction of a single revolution, preferably within 45 degrees or
less.
[0009] It is a principal object of the present invention to
determine the rotary position of a rotatable element within a small
fraction of a single revolution of the element.
[0010] It is a further object of the invention to minimize the time
required for an internal combustion engine control system to
determine the angular position of the engine at start-up.
SUMMARY OF THE INVENTION
[0011] Briefly described, an encoder wheel is divided into a
plurality of equal-angle segments, for example eight segments of 45
degrees each. Each segment comprises a peripheral tooth extending
over a fixed central angle representing a percentage of the dwell
in each segment. Thus the total angle in each segment comprises a
tooth dwell angle and a gap dwell angle. The ratio of the tooth
dwell angle to the total segment angle (which segment angle is
known and is a constant for all segments) is the duty cycle. A
first segment is arbitrarily designated as a prime segment and is
given a minimum tooth dwell angle. The succeeding segments in the
counter-rotation direction are given progressively greater tooth
dwell angles. As the wheel begins to rotate, the sensor begins
timing at a first tooth rise and determines the time to the first
tooth fall (numerator of the duty cycle) and the time from the
first tooth rise to the second tooth rise (denominator of the duty
cycle). Since each duty cycle is unique and is independent of
rotation speed, for wheel having 45 degree segments, for example,
the system can determine the angular position of the wheel within
no more than 90 degrees of rotation and as few as 45 degrees of
rotation. The greater the segmental division of the wheel, the
smaller the revolution angle required to determine the angular
position, up to the reliable detection of the teeth.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
[0013] FIG. 1 is a table showing exemplary division of an encoder
wheel into eight segments, a duty cycle unique to each segment, and
the corresponding tooth and gap dwell angles;
[0014] FIG. 2 is a plan view of an encoder wheel constructed in
accordance with the table shown in FIG. 1;
[0015] FIG. 3 is an exemplary decoding algorithm suitable for use
with an encoder such as is shown in FIGS. 1 and 2; and
[0016] FIG. 4 is a flow chart showing a second embodiment of the
method of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] Referring to FIGS. 1 and 2, an exemplary encoder wheel 10 is
suitable for mounting on a rotating object whereof the angular
position must be determined at any given time. An especially
suitable use is for determining the angular position of a
crankshaft or a camshaft of an internal combustion engine 12 such
as a compression ignited (CI) engine or a spark ignited (SI)
engine. Wheel 10 is mounted coaxially with the appropriate shaft on
a standoff therefrom, as is known for prior art encoder wheels.
During rotation of wheel 10, peripheral region 14 of wheel 10 may
be interrogated conventionally as by a light beam, magnetic
coupling, or the like (not shown) to generate an intermittent
signal from a sensor (not shown) in known fashion.
[0018] Wheel 10 comprises a central hub portion 16 and peripheral
region 14. Wheel 10 is exemplarily divided into a plurality of
equal-angle segments, for example, eight segments of 45 degrees
each, labeled with segment identification numbers 0 through 7 in
FIG. 2. Each segment comprises a peripheral tooth 18 and a gap or
notch 19, each extending over a central angle representing a
percentage of the dwell in each segment, as shown in FIG. 1. Thus
the total angle in each segment comprises a tooth dwell angle 20
and a gap dwell angle 22. It will be understood and appreciated
that the tooth may cause a signal to be prevented from generation,
and the gap may cause a signal to be generated. Each of the
segments has a unique tooth dwell angle. For instance, in the
particular embodiment shown in FIG. 2, a first segment is
arbitrarily designated as a prime segment and is given a minimum
tooth dwell angle relative to the remaining segments. Each
succeeding segments in the counter-rotation direction are given
progressively greater tooth dwell angles. (Note that in use wheel
10 as shown in FIG. 1 is intended for rotation in a
counter-clockwise direction past a stationary source and sensor.)
In other words, when wheel 10 is stationary, succeeding segments in
the clockwise direction may be given progressively greater tooth
dwell angles relative to the minimum tooth dwell angle of the prime
segment. The ratio of the tooth dwell angle 20 to the total segment
angle, 45.degree., defines the duty cycle, which represents the
percentage of the time in a segment in which an interrogating beam
is occluded by the segment tooth.
[0019] In an engine application, the number of segments may be
governed by the number of cylinders. For example, four segments are
acceptable for a four-cylinder engine, but eight segments are
better for greater resolution (shorter rotation angle to segment
determination). Similarly, a six-cylinder engine may use a six- or
twelve-segment wheel (or higher multiples of six), and an
eight-cylinder engine may use an eight- or sixteen-segment wheel.
Of course, a 48-segment wheel having 7.5.degree. segments is
universally useful for four-, six-, eight-, twelve-, and
sixteen-cylinder engines.
[0020] The greater the segmental division of the wheel, the smaller
the revolution angle required to determine the angular position, up
to the reliable detection of the teeth. The practical number of
segments is determined in part by the diameter of the wheel (the
larger the better), the resolution of the sensor (optical is
generally better than magnetic), and the rotational uniformity of
the device being measured. For example, an eight-cylinder engine
runs more smoothly than a four-cylinder engine. If the encoder
teeth are cast as features on an engine flywheel, which has a
relatively large diameter, sixteen or even 32 segments may be
practical on an eight-cylinder engine when using a magnetic sensor.
A smooth-running system with a massive load driven by an electric
motor may practically have even more segments. In principle, more
than 100 segments are possible. Thus, the practical range of duty
cycles may be greater than 0% to just less than 100%.
[0021] In operation, as the wheel begins to rotate, the sensor
begins timing at a first tooth rise (onset of occlusion) and
determines the time to the first tooth fall (numerator of the duty
cycle) and also the time from the first tooth rise to the second
tooth rise (start of the next segment, and denominator of the duty
cycle). Since each duty cycle is unique and is independent of
rotation speed, for a 45 degree segment wheel the system can
determine the angular position of the wheel within less than 90
degrees of rotation. For example, if interrogation begins with the
beam occluded, the wheel must rotate through the remainder of that
tooth dwell angle plus the gap angle following it before reaching
the next tooth rise, at which point the determining algorithm, as
shown in FIG. 3, begins to identify which segment is currently
being interrogated. Although the duty cycle for each segment is
unique, because of variations in speed the measured duty cycle may
not correspond exactly to one of the unique duty cycles of the
segments. It is important, therefore, to confirm that the inferred
position is correct by comparing it to the last segment that was
identified.
[0022] At the sensing of a rising edge interrupt, the algorith
follows the following logic: [0023] 1) Calculate an Apparent (i.e.,
measured) Duty Cycle of the present segment by dividing the tooth
occlusion time (tooth dwell) by the measured period of the full
segment (time between consecutive rise interrupts). [0024] 2)
Determine whether the Apparent Duty Cycle of the present segment is
outside a nominal range of the wheel. Outside the nominal range of
the wheel would be less than a nominal minimum Duty Cycle (e.g., 5%
Duty Cycle) or greater than a nominal maximum Duty Cycle (e.g., 95%
Duty Cycle)). If the Duty Cycle of the present segment is outside
the nominal range of the wheel, then the method proceeds to an
error handling subroutine, wherein the actual present segment
number is computed to be equal to the modulus of the last Apparent
Segment Number plus 1 divided by the total number of segments per
revolution. If the Duty Cycle of the present segment is not outside
the nominal range of the wheel, the method proceeds to step #3.
[0025] 3) Calculate the Percent Rotation during the measured
occlusion time by taking the Apparent Duty Cycle minus the minimum
Duty Cycle of the wheel divided by the maximum Duty Cycle minus the
minimum Duty Cycle. The minimum Duty Cycle is the duty cycle of the
prime segment and the maximum Duty Cycle is the duty cycle of the
segment with the largest duty cycle relative to the other segments
(i.e., the duty cycle of segment identification number 7). [0026]
4) Calculate the Apparent Present Segment Number by subtracting 1
from the total number of segments per revolution, multiply by the
Percent Rotation, add 0.5, and take the integer value, which
represents the present segment identification number for the
present segment. Note that, for purposes of this calculation, the
segment identification numbers begin with 0 as best seen in FIG. 2.
[0027] 5) If the modulus (i.e., remainder) of the last segment
number plus 1 divided by the number of segments per revolution is
unequal to the Apparent Present Segment Number, then the method
proceeds to the error handling subroutine, wherein the actual
present segment number is computed to be equal to the modulus of
the last Apparent Segment Number plus 1 divided by the total number
of segments per revolution. The method then proceeds to step #6. If
the modulus is equal to the Apparent Present Segment Number, the
Apparent Present Segment Number is confirmed to be the actual
present segment number and the method proceeds to step #6. [0028]
6) Replace the last Actual Present Segment Number as set forth in
step #5 with the new Present Segment Number and return to step #1
for identifying the next segment.
[0029] The present invention may also include a second embodiment
that operates to determine the angular position of a rotating
device. In general, the alternative method establishes the Apparent
Duty Cycle of one of the segments and then matches the Apparent
Duty Cycle with one or more unique duty cycles associated with each
of the segments that are stored in a memory location. In other
words, the second embodiment comprises a look-up table including
the unique duty cycles associated with each of the segments on the
wheel that may be matched with the Apparent Duty Cycle to identify
the current position of the rotating device.
[0030] As best seen in FIG. 4, the method of the second embodiment
may provide an encoder wheel mounted coaxially on the device. The
encoder wheel is divided into a plurality of segments, wherein each
segment has a total segment angle comprising a tooth dwell angle
and a gap dwell angle. Each of the plurality of segments is
provided with a unique dwell angle thereby establishing a unique
duty cycle that corresponds to each segment. The segments may be
provided with progressively greater tooth dwell angles, but it will
be understood that such a progressive increase in tooth dwell
angles is not required so long as each segment has a unique duty
cycle. As stated above, the duty cycle is the ratio of the tooth
dwell angle to the total segment angle. In accordance with the
second embodiment, each of the unique duty cycles is stored in a
memory, such as a storage device.
[0031] In implementing the second method, a tooth dwell angle time
for a first segment is determined using a timing sensor as the
wheel is rotating, wherein the first segment is one of the segments
on wheel 10. The tooth dwell angle time for the first segment
starts at the beginning of the tooth dwell angle of the first
segment and ends at the end of the tooth dwell angle for the first
segment. A total segment angle time is then determined using the
sensor for the first segment as the wheel is rotating. The total
segment time for the first segment starts at the beginning of the
tooth dwell angle for the first segment and ends at the end of the
gap dwell angle for the first segment. The tooth dwell angle time
is then divided by the total segment angle time to establish a
first Apparent Duty Cycle. The first Apparent Duty Cycle is then
compared with at least one of the unique duty cycles of the
segments in the look-up table stored in memory. The first Apparent
Duty Cycle is then matched with one of the stored unique duty cycle
having an equivalent value to identify the first segment and
thereby determine the angular position of the rotating device.
[0032] The second embodiment also may include a tolerance range for
each of the unique duty cycles stored in the look-up table. The
tolerance range may be, for example, .+-.5.degree., or any other
degree range, so long as the tolerance ranges for different
segments do not overlap with one another so that they cover the
same duty cycle value. Therefore, if the Apparent Duty Cycle is not
equivalent to one of the stored unique duty cycles, but falls
within a tolerance range for one of the unique duty cycles, then
the Apparent Duty Cycle will be matched with the unique duty cycle
that corresponds to the tolerance range that the Apparent Duty
Cycle falls within.
[0033] The method and apparatus of the present invention for
determining rotary position of a rotating object can be useful in a
wide variety of applications.
[0034] As disclosed above, engine uses with crankshafts can
regulate timing of fuel injection and spark ignition, and can
detect mis-firings, resulting in faster starting of engines and
lower hydrocarbon emissions at start-up.
[0035] When used on an engine's camshaft in addition to the
crankshaft, the two sensors can cross-check each other for onboard
diagnostics, and redundancy allows each to function alone in event
of failure of the other. This feature also allows a vehicle to be
driven until it can be serviced. In small or less expensive
engines, the crankshaft encoder may be eliminated in favor of a
single camshaft encoder.
[0036] The present encoder system may be mounted on the wheels of a
vehicle. Rough road surface can cause instantaneous variations in
wheel rotational velocity that can be detected and quantified to
permit, for example, auto-adjustment of vehicle suspension.
Further, low tire inflation pressure can be detected, as a
low-inflation tire has a functionally smaller diameter and thus
will indicate an excessive rotation rate relative to the other
tires. Further, the present encoder system can be useful in
managing an antilock braking system by measuring the actual
rotational velocity and velocity variations of any wheel.
[0037] The present encoder wheel, when mounted on the rotor of a
camshaft phaser can be useful in managing the action of the
phaser.
[0038] Further, a low-cost (single bit) servo actuator feedback
sensor employing an encoder wheel in accordance with the invention
can detect rotation automatically in either direction and therefore
can be used to determine the position of motorized actuators for
vehicle windows, doors, antennas, headlamps, and wipers, and can
easily be applied to hydraulic actuators rather than electric
actuators.
[0039] In the field of consumer electronics, a rotary position
sensor can be useful in managing the action of a video cassette
recorder, a digital video disk player or recorder, a garage door
opener, and the like.
[0040] The wheel embodiment 10 discussed above is essentially an
optical beam chopper or a magnetic field chopper. Obviously,
however, the invention fully anticipates and embraces encoder
wheels formed not with alternative teeth and gaps but rather with
alternating signal means such as magnets, fluorescent materials,
radioactive materials, and the like, all of which may act to
generate an alternating signal in an appropriate associated
sensor.
[0041] Note that an encoder wheel in accordance with the invention
may be inherently unbalanced rotationally, that is, the geometric
center of wheel hub 16 is not necessarily coincident with the
center of mass of wheel 10. Hence, it may be necessary to balance
the wheel itself in known fashion to compensate for the unbalancing
effect of the teeth, for example, by shortening the radii of gaps
19 such that the wheel has equal radius to the center of mass in
each segment, when the wheel is to be used in critical, high-speed
applications such as on a crankshaft or a camshaft.
[0042] While the invention has been described by reference to
various specific embodiments, it should be understood that numerous
changes may be made within the spirit and scope of the inventive
concepts described. Accordingly, it is intended that the invention
not be limited to the described embodiments, but will have full
scope defined by the language of the following claims.
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