Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Descr~tion
Accelerator Padal Position tensor
Technical Field
The present invention relates generally to a
system for detecting the position of a control pedal
and producing an electrical signal in responsive to the
position of the control pedal and, more particularly,
to a system for detecting the position of an
accelerator pedal of a work vehicle and producing a
pulse-width-modulated signal correlative to a desired
engine speed.
Backaround Art
In the past, the most common means of
communicating a desired engine speed to an engine has
been a mechanical linkage from the accelerator pedal to
the engine throttle valve. However, modern engines are
equipped with electronic engine controllers and it is
desirable to replace the mechanical linkage with an
electronic equivalent. More particularly, it is
desirable to provide a pedal position sensor for
delivering an electrical signal which is responsive to
the position of the pedal.
It is common in the art to utilize a
a pedal mounted potentiometer to produce an analog
signal in response to the position of an accelerator
pedal. The engine controller receives the analog
signal and calculates a desired engine speed based on
an empirical derived relationship. In order to
eliminate unnecessary mechanical devices, it is
preferable to mount the sensor directly on the pedal.
In such a location, the potentiometer is subject to a
variety of extreme conditions including serious
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vibration, dust, etc. Therefore, it is possible for a
fragile electrical device, such as a potentiometer, to
malfunction and produce a signal which is not
indicative of the actual pedal position.
U.S. patent number 4,519,360 which issued on
May 28, 1985 to Murakami and U.S. patent number
4,603,675 which issued on August 5, 1986 to 3unigiger
et al. provide systems for detecting when a
potentiometer adapted to sense pedal position is
malfunctioning. More specifically, both systems
indicate when the engine throttle remains open even
though the accelerator pedal is fully released.
Tn order to perform this function, both systems require
an extra sensor for detecting when the accelerator
pedal is fully released. However, even these systems
are further subject to inaccuracies induced by
electromagnetic interference and wiring harness
degradation.
More particularly, electromagnetic
interference can interfere with the analog signal
produced by the potentiometer thereby providing an
inaccurate signal to the engine controller. The
greater the distance between the pedal mounted
potentiometer and the engine controller, the more
likely it is that interference will affect the analog
signal. Filters in the engine controller can be used
to remove electromagnetic interference from an
oscillating portion of the analog signal; however,
filters cannot correct for any change in a DC voltage
offset induced by the electromagnetic interference.
The engine controller can not be programmed to
distinguish between a DC offset caused by
electromagnetic interference and one correctly
representing the accelerator pedal position.
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In addition, the above mentioned extreme
conditions can also lead to a degradation of the wiring
harness used to connect the potentiometer to the engine
controller. For example, moisture can induce
conductivity between individual wires in the wiring
harness, and over time the resistance of individual
wires in the wiring harness can change. This wiring
harness degradation can induce inaccuracies in the
signal received by the engine controller similar to
those caused by electromagnetic interference.
Other systems currently address the above
mentioned problems by combining a pedal sensing
potentiometer and a conditioning circuit in a single
signal generating apparatus. The conditioning circuit
modifies the analog signal delivered by the
potentiometer and produces a pulse-width-modulated
signal in response to the accelerator pedal position.
Due to the close proximity of the potentiometer and the
conditioning circuit, the effects of electromagnetic
interference on the analog signal delivered to the
conditioning circuit are negligible. Furthermore, the
engine controller can be programmed to recognize
invalid waveforms in the pulse-width-modulated signal
which are caused by electromagnetic interference and
wiring harness degradation.
To date, signal generating units having both
a potentiometer arid conditioning circuit in a single
unit are not pedal mounted. Therefore, a mechanical
linkage is used to connect the accelerator pedal to the
signal generating apparatus. Due to the unit s remote
location, installation and maintenance are made
difficult, expense is incurred, and a mechanical
linkage is once more required by such systems.
The present invention is directed to
addressing the above mentioned problems with an
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apparatus that can be easily mounted directly on an
accelerator pedal. other aspects, objects and
advantages can be obtained from a study of the
drawings, the disclosure, and the appended claims.
While the present invention is described for use with
an accelerator pedal it is recognized that such an
apparatus could be adapted for use with numerous other
control pedals.
Disclosure of The Invention
In accordance with one aspect of the present
invention, there is provided a signal generating
apparatus for delivering a pulse-width-modulated signal
responsive to the position of a mavable mechanical
member. A circuit board has a potentiometer mounted on
a first side and a conditioning circuit mounted on a
second side. The potentiometer has a movable wiper
portion in movable contact with a stationary portion.
The movable wiper is further connected to and movable
with the movable mechanical member. The conditioning
circuit is electrically connected to the stationary
portion so that the conditioning circuit produces the
pulse-width-modulated signal in response to the
position of the movable wiper on the stationary
portion.
Description of The Drawings
Fig. 1 is a diagrammatic side view of a pedal
mounted sensor adapted to deliver a signal in response
to the position of the pedal.
Fig. 2 is a diagrammatic sectional partial
view taken along line II-IT of Fig. 1.
Fig. 3 is a diagrammatic sectional partial
view taken along line III-III of Fig. 2.
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Fig. 4 is a diagrammatic sectional partial
view taken along line IV-IV of Fig. 2.
Fig. 5 is a functional block diagram of an
embodiment of the pedal mounted position sensor of Fig.
1.
Best Mode for Carrying Out The Invention
Fig. 1 illustrates the relationship between
an accelerator pedal unit 12 of a work vehicle (not
shown) and a signal generating apparatus 10. The
signal generating apparatus 10 produces a
pulse-width-modulated signal having a duty factor
responsive to the position of the pedal 14, and
delivers the signal to an engine controller 16. The
pedal 14 is illustrative and the signal generating
apparatus 10 can be adapted for use with other movable
mechanical members. In a preferred embodiment the
accelerator pedal unit 12 is a series WM-516
manufactured by Williams Precision Controls of
Portland, Oregon, and includes the pedal 14, a hinge
18, a baseplate 20, a lever 22, and a pin 24. The base
plate 20 has a horizontal portion 26 rigidly attached
to the vehicle frame 28 by anchor bolts 30a-30c, for
example. The base plate 20 further includes an angled
portion 32 which is fixed relative to the vehicle frame
28. The pedal 14 is pivotally movable about the hinge
18 relative to the work vehicle frame 28. Preferably
the hinge 18 can be positioned on the base plate
horizontal portion 26 as shown; however, the hinge 18
can also be rigidly attached to the vehicle frame 28.
The pedal 14 is movable between a first
position corresponding to engine idle speed and a
second position corresponding to maximum engine speed.
A pedal return spring (not shown) biases the pedal 14
to the first position. The pin 24 is positioned on the
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pedal lower portion 34 and is rotatable relative to and
in response to pivotal movement of the pedal 14 by the
lever 22. The lever 22 has first and second end
portions 23,25. The lever first end portion 23 is
fixedly connected to the pin 24 and the lever second
end portion 25 includes a roller 36 in contact with and
movable along the base plate angled portion 32 in
response to movement of the pedal 14.
zn a preferred embodiment, a pair of connecting
bolts 38a,38b are used to attach the signal generating
apparatus 10 to the pedal 14. However, it is
foreseeable to accomplish this connecting function
using adhesives or other fasteners. The signal
generating apparatus 10 is electrically connected to a
source of positive battery voltage, to ground, and to
the engine controller 16 by respective wires 40, 42,
and 44.
Referring now to Figs. 2, 3, and 4, a circuit
board 46 has first and second sides 48,50. A rotatable
potentiometer 52 has a movakile wiper 54 in movable
contact with a stationary portion 56. The
potentiometer is positioned on the circuit board first
side 48, and delivers a DC voltage in responsive to the
position of the pedal 14 shown in Fig. 1. The
potentiometer stationary portion 56 includes a
resistive strip 58 and a conductive strip 64. The
resistive strip is connected between a first voltage
source 60 and a higher potential second voltage source
62 by respective wires 61 and 63. Preferably the
resistive strip 58 and the conductive strip 64 are
screen printed on the circuit board first side 48p
however, it is foreseeable to position the strips 58,64
on the circuit board first side 48 using methods such
as etching, insert molding, compression molding, etc.
The movable wiper 54 is of negligible resistance and
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effectively forms a short circuit from the resistive
strip 58 to the conductive strip 64. Thus, the entire
conductive strip 64 is maintained at DC voltage
potential correlative to the position of the movable
wiper 54 on the resistive strip 58. One skilled in the
art will recognize that the potentiometer 52 could be
replaced, for example, by a variable capacitance or
inductance device.
A conditioning circuit 66 is located on the
circuit board second side 50 and is electrically
connected to the conductive strip 64 by a wire 68. The
conditioning circuit 66 receives the DC voltage
delivered by the potentiometer 52 and delivers a
pulse-width-modulated signal having a duty factor
responsive to this DC voltage on the wire 44.
A housing 70 is of sufficient size to contain
the conditioning circuit 66, the circuit board 46 and
the potentiometer 52. In the preferred embodiment, the
housing 70 is constructed of polyetherimide, but the
housing 70 could be formed from numerous other
materials. An epoxy resin 74 filling the void 76
between the housing 70 and the circuit board 46
hermetically seals the conditioning circuit 66, circuit
board 46 and potentiometer 52 within the housing 70.
The housing 70 and epoxy resin 74 support the circuitry
and protect against possible malfunctions such as short
circuits and broken wires within the signal generating
apparatus 10.
The housing 70 includes a molded rotor 78
having a first end 80 integrally engaging and movable
with the pin 24, shown in Fig. 1, and a second end 82
fixedly connected to the movable wiper 54. Thus, when
the pin 24 rotates, the movable wiper 54 moves along
the resistive strip 58 causing the potentiometer 52 to
deliver a DC voltage correlative to the position of the
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pin 24. The molded rotor 78 can be constructed of any
one of numerous nonconductive materials but is
preferably polyetherimide. A return spring 84 has a
first end 86 connected to the molded rotor second end
82 and a second end 88 connected to the housing 70, and
is adapted to bias the molded rotor 78 to a preselected
position.
Turning now to Fig 4., a block diagram
illustrates the functional aspects of the signal
generating apparatus 10. These functional aspects are
common in the industry; therefore, the exact circuitry
will not be defined. A voltage preregulator 90 filters
noise from and regulates the battery voltage to a level
usable by the remaining electrical circuitry of the
signal generating apparatus 10. In the preferred
embodiment, battery voltage ranges from approximately
+9 to +32 volts and the preregulator 90 delivers
approximately a +10 volt signal. A voltage regulator
92 receives this preregulated voltage and delivers the
first voltage potential on the wire 61 and the second
voltage potential on the wire 63. In the preferred
embodiment the first voltage source 60 is +0.7 volts
and the second voltage source 62 is +5.7 volts;
however, it is recognized that numerous other voltages
may be chosen without departing from the invention. In
the preferred embodiment, the voltage preregulator 90
and voltage regulator 92 are both located on the
circuit board second side 48.
As previously stated, the resistive strip 58
is connected between the first and second voltage
sources 60,62. The movable wiper 54 forms a short
circuit from the resistive strip 58 to the conductive
strip 64, causing the potentiometer 52 to deliver a DC
voltage signal correlative to the position of the
movable wiper 54 on the resistive strip 58. A wire 68
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connects the conductive strip 64 to the conditioning
circuit 66 such that the DC voltage signal delivered by
the potentiometer 52 is received by the conditioning
circuit 66,
In the preferred embodiment, the conditioning
circuit 66 includes a square wave generator 94, an
integrator 96, and a comparator 98. The square wave
generator 94 receives the preregulated voltage from the
voltage preregulator 90 and delivers a square wave
signal having a predetermined amplitude and base
frequency. The integrator 96 integrates this square
wave signal and delivers a triangular wave signal
having a predetermined amplitude and base frequency.
In the preferred embodiment the triangular wave signal
has an amplitude of +5 volts. The comparator 98
compares the triangular wave signal to the DC voltage
signal produced by the potentiometer 52 and delivers a
pulse-width-modulated signal having a duty factor
responsive to the DC voltage signal. It is foreseeable
that components other than those used in the preferred
embodiment could be used for generating the
pulse-width-modulated signal.
Industrial Applicability
Assume that the signal generating apparatus
10 is mounted on the accelerator pedal of a work
vehicle, not shown. Initially, the pedal 14 is biased
to a predetermined position by a pedal return spring
(not shown). At this predetermined position, an angle
(theta) between the lever 22 and the pedal 14 is obtuse
and the signal generating apparatus 20 produces a
pulse-width-modulated signal having a duty factor
representative of the initial pedal position. The
engine controller 16 receives the pulse-width-modulated
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signal and calculates a desired engine speed based on
the empirical relationship.
Subsequently, if a vehicle operator desires
an increase in the engine speed the operator applies a
force "F" to the accelerator pedal 14. As the operator
applies the force "F", the pedal 14 rotates relative to
the vehicle frame 28 about hinge 18 to a second
position. As the pedal 14 is displaced from the first
position to the second position, the lever 22 and pin
14 rotate relative to the pedal 14 in a preselected
direction such that the angle (theta) increases in
magnitude.
Rotation of the pin 24, causes the movable
wiper 54 to rotate along the resistive strip 58 between
first and second positions corresponding to the pedal
first and second positions, respectively. The movable
wiper 54 effectively forms a short circuit from the
resistive strip 58 to the conductive strip 64;
therefor, the entire conductive strip 64 has a DC
voltage potential correlative to the position of the
wiper 54 on the resistive strip 58. Thus, the
potentiometer 52 delivers a DC voltage signal over the
wire 68 responsive to the conductive strip voltage
potential.
The conditioning circuit 66 receives the DC
voltage signal from the potentiometer 52 and produces a
pulse-width-modulated signal having a duty factor
responsive to the DC voltage signal.
Because there is no appreciable distance
between potentiometer 52 and the conditioning circuit
66, the effects of electromagnetic interference on the
analog signal delivered to the conditioning circuit 56
are negligible. Additionally, in the event that
electromagnetic interference or wiring harness
degradation change the frequency or the DC level of
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pulse-width-modulated signals produced by the
conditioning circuit 66, the engine controller 16 can
be programmed to recognize invalid waveforms caused by
such interference and wiring harness degradation.
The engine controller 16 receives 'the
pulse-width-modulated signal and regulates the engines
speed in response to the duty factor of the
pulse-width-modulated signal. The engine controller 16
can be programmed to reduce the amount of fuel supplied
to the engine to a preselected minimum in response to
invalid waveforms in the pulse-width-modulated signal.
For instance, if any of the wires 40,42,44 break,
short, or become disconnected, a high signal is
continuously delivered by the signal generating
apparatus 10. The engine controller 16 in turn can be
programmed to reduce the amount of fuel supplied to the
engine to a preselected minimum upon receiving a
continuous high signal for a predetermined period of
time.
Other aspects, objects, and advantages of
this invention can be obtained from a study of the
drawings, the disclosure, and the appended claims.
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