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Claims  |
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What is claimed is:
1. An electrical odometer for use in a wheeled vehicle, comprising:
(a) means for generating a first series of electrical pulses which are
related to a given unit of distance traveled by the vehicle;
(b) means for conditioning said first series of pulses to provide a train
of shaped pulses which are effective to initiate a computer routine;
(c) a digital display adapted to serve as an odometer register;
(d) means for presetting said digital display to a start count and for
placing said start count in the memory of a computer; and
(e) electronic computer means for algebraically summing a predetermined
constant upon receiving respective ones of the train of shaped pulses,
with a present value in the computer memory being the same as the start
count, such that the instantaneous count which is held in the memory is
progressively updated as each shaped pulse is received, with the count
being displayed on the digital display being the same as the count stored
in the computer memory, and said predetermined constant being the actual
distance traveled between each consecutive pair of pulses in the train of
shaped pulses, and the predetermined constant being based upon all of the
relevant parameters which are associated with the vehicle on which the
odometer is mounted, with said parameters including vehicle wheel size,
tire inflation conditions, vehicle speed, and vehicle loading.
2. An electrical odometer for use in wheeled vehicles, comprising:
(a) a transducer coupled to the vehicle so that angular rotation of a wheel
produces a first series of discrete signals which are related to a given
unit of distance traveled by the vehicle;
(b) means for transforming said discrete signals into a pulse train of
electrical signals which vary periodically with said discrete signals,
with the waveform of said electrical signals being shaped for driving a
computer logic element;
(c) means for conditioning said pulse train to form a similar pulse train
consisting of trigger pulses, each having approximately equal duration;
(d) a digital display adapted to serve as an odometer register;
(e) means for presetting said digital display to a start count and for
placing said start count in the memory of a computer;
(f) electronic computer means for algebraically summing a predetermined
constant upon receiving respective ones of the train of trigger pulses,
with a preset value in the computer memory being the same as the start
count, such that the instantaneous count which is held in the memory is
progressively updated as each trigger pulse is received, with the count
being displayed on the digital display being the same as the count stored
in the computer memory, and said predetermined constant being the actual
distance traveled between each consecutive pair of pulses in the train of
trigger pulses, and the predetermined constant being based upon the
relevant parameters which are uniquely associated with the vehicle on
which the odometer is mounted;
(g) means for selectively starting and stopping the electronic computer
means while the vehicle is in motion, with stopping said computer means
being effective to permit presetting of the digital display to a start
count, and starting said computer means being effective so as to enable it
to respond to the trigger pulses; and
(h) means for selecting either a count-up mode or a count-down mode for the
computer means, whereby distance increments may be added to or subtracted
from the initial distance value in the digital display.
3. An electrical odometer for use in a wheeled vehicle, comprising:
(a) means for generating a first series of electrical pulses which are
related to a given unit of distance traveled by the vehicle;
(b) means for conditioning said first series of pulses to provide a train
of shaped pulses which are effective to initiate a computer routine;
(c) a digital display adapted to serve as an odometer register;
(d) means for presetting said digital display to a start count and for
placing said start count in the memory of a computer;
(e) electronic computer means for algebraically summing a predetermined
constant upon receiving respective ones of the train of shaped pulses,
with a preset value in the computer memory being the same as the start
count, such that the instantaneous count which is held in the memory is
progressively updated as each shaped pulse is received, with the count
being displayed on the digital display being the same as the count stored
in the computer memory;
(f) means for creating at least one dependent pulse train which is a
fraction of the first series of electrical pulses, with said dependent
pulse train being related to the first series of electrical pulses by a
factor which is a rational number, and the dependent pulse train being
synchronized with respect to the first series of electrical pulses; and
(g) selector means to establish whether the electronic computer means acts
in response to each of the first series of electrical pulses, or in
response to each pulse in the dependent pulse train, whereby the up-date
rate of the computer means may be selectively chosen.
4. The electrical odometer as claimed in claim 3 wherein there are at least
two dependent pulse trains derived from said series of first electrical
pulses, and further including selector means for selecting which one of
the dependent pulse trains is passed to the computer means at a given
time.
5. An electrical odometer for use in wheeled vehicles, comprising:
(a) a transducer for converting repetitive wheel rotations into a series of
discrete signals;
(b) a digital display for displaying distance values;
(c) means for manually entering an initial distance value into the digital
display;
(d) computer means for either adding or subtracting a calibration constant
to the distance value which is presented by the digital display, with said
calibration constant constituting the actual distance traveled between
each of the discrete signals generated by the transducer; and
(e) means for manually entering the calibration constant into the memory of
said computer means with a numeric keyboard, said calibration constant
being based upon all of the relevant parameters which are associated with
the vehicle on which the odometer is mounted, with said parameters
including vehicle wheel size, tire inflation conditions, vehicle speed,
and vehicle loading.
6. The electrical odometer as claimed in claim 5 and further including
means for adjustably establishing the rate at which the digital display is
updated as a result of movement by said wheeled vehicle.
7. An electrical odometer for use in wheeled vehicles, comprising:
(a) a transducer coupled to a wheel of the vehicle, such that angular
rotation of said wheel produces a series of discrete signals;
(b) means for transforming said discrete signals into a first pulse train
of electrical signals which vary periodically with said discrete signals,
with the waveform of said electrical signals being shaped for driving a
logic element;
(c) means for creating at least one dependent pulse train which is a
fraction of said first pulse train, with said dependent pulse train being
related to the first pulse train by a factor which is a rational number,
and the dependent pulse train being synchronized with respect to the first
pulse train;
(d) means for conditioning said dependent pulse train to form a similar
pulse train consisting of trigger pulses, each having approximately equal
duration;
(e) computer means for performing arithmetic operations and control
functions;
(f) means for selectively causing said computer means to perform an
arithmetic operation upon the occurrence of each trigger pulse;
(g) means for starting and stopping operation of said computer means;
(h) a digital display for displaying distance values;
(i) means for manually entering an initial distance value into the digital
display;
(j) means for selecting either a count-up mode or a count-down mode for the
computer means, whereby distance increments may be added to or subtracted
from the initial distance value in the digital display;
(k) means for storing a calibration constant into the memory of said
computer means, with said calibration constant corresponding to the actual
distance traveled between trigger pulses which are passed to said computer
means; and
(l) means for recalling said calibration constant from said memory and for
supplying said constant to the arithmetic part of the computer means,
whereby said digital display is sequentially changed by the calibration
constant upon the occurrence of each trigger pulse.
8. The electrical odometer as claimed in claim 7 wherein there are at least
two dependent pulse trains, each being a different fraction of the first
pulse train, and further including means for selecting which one of said
dependent pulse trains will be passed to the computer means at a given
time, whereby the update rate for said display may be determined by
switching from one of the dependent pulse trains to another.
9. The electrical odometer as claimed in claim 8 wherein two of the
dependent pulse trains differ by a factor of at least 16.
10. The electrical odometer as claimed in claim 7 wherein the means for
manually entering the initial distance value is a numeric keyboard.
11. The electrical odometer as claimed in claim 7 wherein the transducer is
coupled to a wheel of the vehicle through an element which is placed in
series with the standard speedometer cable of the wheeled vehicle, whereby
wheel rotation operates to simultaneously drive both the standard
speedometer cable and the electrical odometer.
12. The electrical odometer as claimed in claim 11 wherein the element that
is placed in series with the speedometer cable is adapted to be positioned
immediately adjacent the transmission of the wheeled vehicle, and said
element has treads that mate with the transmission housing.
13. An electrical odometer for use in a wheeled vehicle, comprising:
(a) means for generating a series of electrical pulses which are related to
actual distance traveled by the vehicle;
(b) a digital display adapted to serve as an odometer register, with said
register being adapted to visually reflect the distance traveled by the
wheeled vehicle from the time that said pulse-generating means is
activated;
(c) means for converting the electrical pulses generated by the
pulse-generating means into input signals for updating the digital
display; and
(d) means for permitting the rate at which said digital display is updated
to be changed at will by the vehicle operator through use of a switch
which is located in the vicinity of the digital display, and the
calibration accuracy being the same after a display rate has been changed
as it was before the display rate was changed. |
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Claims |
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Description |
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This invention relates generally to odometer systems for road vehicles, and
more particularly to an odometer system which is capable of being
calibrated by the vehicle operator at will in order to achieve accurate
distance measurements based upon a vehicle's travel.
Odometer systems for wheeled vehicles are well known, having been utilized
on bicycles, automobiles, trucks, motorcycles, etc. for many years. Among
those odometers which have been patented are those disclosed in U.S. Pat.
Nos. 2,634,914 to Lyon and 3,226,021 to Dusinberre et al. Among the more
recent systems are those which operate electrically, including those
described in U.S. Pat. Nos. 3,659,780 to Woodward, 3,780,272 to Rohner,
and 3,872,288 to Sampey. Because the state of the art of odometers has
been so well developed, it would be onerous to recite each and every
feature that has been suggested or disclosed in the many patents in this
field. However, this is not to say that there is no longer any room for
improvement in odometers; and, a recitation of two common problems
involving road vehicles will serve to illustrate some advantages of the
invention disclosed herein.
First, it should be appreciated that odometers of the prior art for any
given vehicle cannot be any more accurate than the underlying members upon
which a mileage indication is to be derived. Many prior art odometers have
employed levers, wheels, knobs and switches, etc., which inherently
contribute to a certain amount of inaccuracy--after many years of a
vehicle's use if not when it is new. For example, odometers for
American-made vehicles are typically driven through a system of reduction
gearing by the core of a conventional speedometer cable. The core of the
speedometer cable is, in turn, driven by either the transmission or a
front wheel. The nominal number of revolutions of the speedometer cable,
per mile of traveled distance, are specified by industry-wide standards
such as those established by the Society of Automotive Engineers. Such
specifications are very enlightening to the extent that they define
tolerances. For example, SAE J678 specifies that speedometer cable cores
driven by the transmission is being driven with a gear ratio that will
nominally produce 1000 revolutions of cable core for every mile of vehicle
travel. However, this SAE specification does allow a deviation from the
preferred 1000 revolutions of as much as minus 1 percent to plus 3.75
percent in order to accommodate practical gear-train drive ratios. The
extent to which design variations in individual gear trains may affect
accuracy of an odometer are, of course, difficult to predict.
In addition to accuracy limitations which are the result of design choices,
SAE specification 862b lists many variable factors affecting odometer
accuracy which are not controllable by design. These variable factors
produce variations in the wheel-rolling radius--which directly affects
odometer accuracy. For example, it is known that tires are elastic
members, and the rolling radius is subject to variation from tire to tire
as a result of manufacturing tolerances. But, even with respect to a
single tire there are other variations that arise from changes in
temperature, inflation pressures, wear and loading. Also, an automobile
tire will tend to change size due to aging after it is placed on a rim and
inflated. Such tire variations, plus differences in construction, material
and tread design, can result in a number of tire revolutions per mile
which is significantly different from the nominal value set by any agency
or engineer. Indeed, the number of revolutions per mile obtained from old
tires in comparison with their performance when they were new can be
nearly 3 percent.
Vehicle speed will also affect the accuracy of prior art odometers. An
average automobile tire experiences up to a 3 percent change in
revolutions per mile when the vehicle speed changes from 30 mph to 90 mph,
as a result of a change in rolling radius caused by centrifugal force. Of
course, the actual change in revolutions per mile resulting from speed
changes for any given tire will be dependent on the characteristics of
that particular tire. And, while some odometer errors may be controllable,
others--such as tire temperature--are not.
To illustrate how some errors may affect the accuracy of an odometer, let
it be assumed that there is a desire by a vehicle operator to synchronize
an odometer in his vehicle with the mileage markers on an interstate
highway. Furthermore, it will be assumed that any error in synchronization
should be as low as 0.2 miles. If the only source of error was that due to
the upper SAE design limit of 3.75 percent for the odometer drive, a
useful measurement criterion would be the maximum distance that could be
traveled without exceeding the error of 0.2 miles. The distance which
could be traveled would be 0.2 divided by 0.0375 or 5.33 miles. Thus, to
obtain synchronization with the mileage markers to within 0.2 miles would
require the operator to re-synchronize about every fifth mileage marker.
The present invention overcomes these accuracy problems by providing an
odometer system which can be easily and precisely calibrated by the driver
while the vehicle is in motion, simply by driving a course of any
precisely known distance and then using a simple arithmetical operational
procedure with a calculator or the like. Later, if the number of wheel
revolutions per mile should begin to vary as radically different operating
conditions are encountered, the odometer can be freshly calibrated by the
driver at any time.
In brief, the present invention derives the distance traveled from wheel
rotation, like most other odometers for road vehicles. The wheel rotation
information is converted into a series of electrical pulses, with each
pulse corresponding to a specific distance traveled. The pulse train is
then applied to a pulse rate divider which provides a means for selecting
the desired resolution and data update rate. The pulse train output from
the divider is shaped to provide a trigger pulse which is subsequently
applied to a microcomputer to initiate an arithmetic routine which causes
a constant (previously stored in memory) to be added to or subtracted from
the distance display register. The constant is a calibration constant
which would normally be derived by the user of the odometer, and it may be
very precise. Once a calibration constant has been derived for a
particular operational condition, the constant can be reentered in the
microcomputer at any time. A keyboard can also be used to preset an
initial reference distance, and to set the add or subtract function for
distance traveled. In one embodiment, the electrical pulses derived from a
transducer are conditioned and then passed directly to a computer
interface without being divided. In another embodiment, at least two
divide ratios are provided--and those two ratios differ by a factor of at
least 16, so that the update rate for the digital display may be changed
by a factor of 16 through the act of switching divide ratios.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram of the electrical odometer system of the
invention which includes a transducer and a circuit for generating a
series of trigger pulses which are operative to cause a computer means to
perform an arithmetic operation and to subsequently display a distance
value on a digital display;
FIG. 2 is a schematic diagram of a transducer section which is shown in
block form in FIG. 1, with an optical coupler device being used to convert
angular rotation into a series of discrete electrical signals;
FIG. 3 is a schematic diagram of the signal conditioner shown in block form
in FIG. 1, with the conditioned signal being characterized by a fast rise
time so as to improve compatibility with logic elements in the circuit;
FIG. 4 is a schematic diagram of the trigger pulse generator shown in block
form in FIG. 1, with said generator being advantageously used to improve
the response of the computer means and to simplify the computer interface
shown in FIG. 1;
FIG. 5 is a diagrammatic showing in the nature of a block diagram for a
typical digital calculator (which employs a microcomputer chip), a readout
(which is preferably a digital display), and a keyboard which is also used
to establish an initial distance value in the display;
FIG. 6 is a schematic diagram of a typical matrix keyboard used for the
calculator;
FIG. 7 is a perspective view of one embodiment of the invention showing a
possible spatial relationship between a keyboard, a digital display, and a
housing for the circuitry shown in FIG. 1;
FIG. 8 is a partially exploded, elevational view of one embodiment of a
transducer which is adapted to be connected immediately adjacent the
transmission of a wheeled vehicle such as an automobile where it is then
in series with the original speedometer cable.
FIG. 9 is a front elevation view of the rotative element which constitutes
the optical interrupter in the transducer shown in FIG. 8.
Referring initially to FIG. 1, a transducer 12 is provided which will
produce a series of discrete signals upon movement of the vehicle.
Typically, the transducer 12 is coupled to a wheel of the vehicle in which
the odometer is mounted, such that angular rotation of said wheel produces
the series of discrete signals. The transducer 12 can also be coupled to
the vehicle's drive shaft instead of a wheel, and it may be arranged so
that it is driven by the speedometer cable which is standard equipment on
all modern vehicles. The transducer may be any one of a variety of
well-known devices, including that shown in U.S. Pat. No. 3,406,775 to
Magnuski or U.S. Pat. No. 3,983,372 to Klaver. However, in order to foster
the accuracy which is a significant feature of this invention, it is
preferred that the transducer provide a relatively large number of
electrical pulses for each full revolution of the vehicle's wheel. In any
case, however, it is important that the number of electrical pulses
generated by the transducer 12 be directly proportional to the distance
traveled by the vehicle.
The output of transducer 12 is passed through suitable means 14 to a signal
conditioner 16, which converts the transducer pulses (which usually have
relatively low rise-times) into sharp rise-time pulses that are compatible
with a digital divider 20. The signal conditioner 16 also includes
circuitry (which will subsequently be described in connection with FIG. 3)
which provides substantial noise immunity to the divider 20.
The divider 20 is implemented by a binary counter, and provides exact scale
factors for controlling the rate at which data in the odometer is updated.
Such a divider is advantageous because usually a different update rate
will be selected for calibration than will be used for routine operation
of the odometer. A switch 22 is a multi-position switch, providing means
for the user to manually select a particular divide ratio so as to produce
a desired update rate. With the vehicle driving at a constant speed, the
output of each of the divider taps 24, 26, 28, 30 will normally be a
square wave whose period is a function of vehicle speed and the respective
division constant, e.g., 2, 4, 8.
The output of the divider 20 is passed through switch 22 and means 32 to a
trigger pulse generator 34, which converts the selected square wave into a
trigger pulse of nearly constant duration--which ultimately initiates an
addition or subtraction routine in a microcomputer 46.
An interface 42 is provided between the trigger pulse generator 34 and the
microcomputer 46, in order to provide a proper impedance for the generator
34 and to provide a suitable command signal for the microcomputer 46. The
trigger pulse generator 34 is connected to interface 42 through DPDT
switch 36 which has a stop contact 38 and a run contact 40. When the
switch 36 is in the stop position, the divider 20 is reset to zero by
switch contact 39 and conductor 41.
In the preferred embodiment, the microcomputer 46 and a keyboard 48, as
well as a display 50, are wired and packaged similarly to that of a common
four-function, hand-held electronic calculator having a memory and
automatic constant features. In addition to the arithmetic functions of a
microcomputer chip which is used in such calculators, the chip contains
the circuitry which is necessary for multiplexing the display and scanning
the keyboard, etc.
Having generally described the basic components of an electrical odometer
10 for use in wheeled vehicles, more detailed attention will now be given
to specific components of a preferred embodiment. Referring specifically
to FIG. 2, the transducer 12 is adapted to convert angular rotation of a
vehicle wheel (exemplified by the arrow 60) into a series of discrete
signals. In the embodiment shown, this is accomplished optically by
coupling an adapter to the readily accessible end of a speedometer cable,
so that rotation of the speedometer cable can be sensed without
interfering with the normal operation of said cable. That is, discrete
signals are derived from said cable for use in this invention, but the
cable continues to drive the speedometer which comes as standard equipment
from the vehicle manufacturer.
The transducer 12 includes an optical energy source 62, a phototransistor
switch 64, and an optical interrupter 66 positioned between elements 62,
64. The optical interrupter 66 is coupled to the speedometer cable in
order to rotate therewith. Suitable holes or slots in the interrupter 66
allow passage of optical energy from the source 62 to the phototransistor
64 when said holes become aligned with a direct path between elements 62,
64. The optical energy impinging on phototransistor 64 creates a current
flow from the positive voltage source to ground. This current flow
establishes a voltage drop across resistor 68 to provide a signal output.
Thus, for each revolution of the optical interrupter 66, the number of
output pulses will be equal to the number of holes or slots in the optical
interrupter. And, as will be explained more fully hereinafter, selection
of an optimum number of output pulses can enhance the accuracy of the
odometer 10.
Referring next to FIG. 3, the signal conditioner 16 includes a low-pass
filter section, three NAND logic elements, and an output section.
Resistors 70, 72 and capacitor 74 form a low-pass filter section, which
serves to reduce high-frequency noise and thereby improve over-all noise
immunity. Logic elements 76, 78 (which are preferably COSMOS logic
elements because of their high immunity to electrical noise) are connected
in a positive feedback arrangement, in order to provide a toggle action
which causes the logic state to be rapidly switched when the input signal
exceeds an upper threshold value. The feedback path is through diode 80
and resistor 82 and appropriate conductors. Once the input threshold is
exceeded, current which is fed back through the feedback network adds to
the current from the signal source. Logic gate 84 is used primarily as an
inverter to provide an appropriate output polarity. Resistor 88 is a
pull-up resistor which provides proper circuit loading; and, diode 86 acts
in conjunction with capacitor 90 to minimize opposite-polarity,
high-frequency transients coupling with the divider 20.
A preferred divider 20 is a conventional COSMOS 7-stage binary ripple
counter. The number of stages required for such a counter is determined by
the maximum divisor (i.e., divide ratio) which is required for a
particular embodiment. The divider/counter 20 is automatically reset to
zero and held there when switch 39 (FIG. 1) is in the stop position.
The output of a particular counter tap 24, 26, 28, 30 is a square wave when
the counters are being clocked at a constant rate. This square wave signal
must be conditioned to provide a trigger pulse whose duration is
relatively independent of the input clock rate. Such conditioning is
accomplished by the trigger pulse generator 34 shown in FIG. 4. The input
square wave is clamped to zero by diode 92, and the positive-going square
wave is applied across capacitor 96 in series with resistor 98. The
initial voltage drop across the capacitor 96 is zero; hence, the full
output voltage is initially dropped across resistor 98 to provide a pulsed
output signal. Immediately, however, capacitor 96 begins to charge as a
result of the positive signal being applied thereto, until essentially the
entire applied voltage is dropped across capacitor 96. The output signal
of generator 34 thereby approaches zero as the voltage across capacitor 96
approaches the applied voltage. The time constant, and hence the duration
of the trigger pulses, is dependent on the product of the values of
capacitor 96 and resistor 98, and may typically be about 0.1 sec. Resistor
94 provides component protection by establishing a discharge path for the
capacitor 96 when the circuit is disconnected.
The interface 42 (which receives the train of trigger pulses from generator
34) is preferably a solid state electronic switch which opens and closes
in synchronism with each trigger pulse. A suitable switch will provide a
high impedence input for minimizing distortion of the trigger pulse and
circuit loading. The interface switch 42 also provides a high on/off
resistance ratio, which is necessary for the switch-closure function that
is required to initiate computer operations. Turning next to FIGS. 5 and
6, there is depicted a typical interconnection between the microcomputer
46 (which preferably is a single LSI calculator chip), a keyboard 48 and
the display 50. A typical matrix keyboard schematic arrangement is shown
in FIG. 6. The switch contacts connect horizontal matrix lines to vertical
matrix lines when they are manually depressed, as in typical hand-held
calculator operation. In the preferred embodiment, the interface 42
provides a switch closure of two electrical contacts which are connected
in parallel with the contacts for the "equal" key, so as to provide remote
control of the equal key function. This is made possible by virtue of the
automatic constant features which are incorporated into conventional LSI
calculator chips. This automatic constant feature provides "repeat"
operation for any operant which has previously been keyed-in on the
keyboard. For example, if any number (such as the odometer calibration
constant) is keyed-in on a keyboard 48, subsequent closure of the equal
key will cause the display 50 to increment by the keyed-in number every
time that the contacts associated with the equal key are closed.
Similarly, if any number is to be subtracted from a displayed number,
repeated closures of the equal key contacts will cause the displayed
number to decrement by the keyed-in number each time the contacts are
closed. It will be seen, therefore, that in accordance with the circuit
described herein, each trigger pulse from the trigger generator 34 causes
a contact closure of the interface switch 42; this, in turn, causes the
calculator 46 to perform the previously keyed-in arithmetic function (plus
or minus the calibration constant) on the contents of display 50. Too,
each trigger pulse from generator 34 is directly dependent upon the
distance traveled. Therefore, if the keyed-in number (which is held in the
automatic constant register) is made equal to the calibration constant,
then subsequent applications of each trigger pulse will cause the distance
actually traveled by the vehicle to be added to (or subtracted from) the
display 50, according to whether the operator had selected either the plus
or minus operant.
In one working model of the circuitry described herein, the transistors and
capacitors--and their respective values--are given in Table 1, as well as
manufacturer's identifying numbers for other components of one embodiment
of the invention.
TABLE 1
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Diodes 80 1N914
86 1N914
92 1N914
Capacitors 74 0.1 MFD
90 0.001 MFD
96 0.1 MFD
Resistors 68 1 K.OMEGA.
70 100 K.OMEGA.
72 100 K.OMEGA.
82 33 K.OMEGA.
88 3.3 K.OMEGA.
94 330 K.OMEGA.
98 1 M.OMEGA.
Logic Elements 76 RCA CD4011
78 RCA CD4011
84 RCA CD4011
Divider RCA CD4024
Quad Switch 42 RCA CD4066
(interface)
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A suitable optical interrupter (62, 64) is a GE H13a1-2 or H13B. A suitable
calculator chip to serve the function of the microcomputer 46 would be a
Mostek MK 50321 N 8-digit calculator circuit; however, one prototype of
the invention was made with a commercially available Rockwell calculator
having therein an A5901 CA chip.
It is perhaps appropriate at this time to consider odometers in a
mathematical sense. Ideally, the distance registered by an odometer
(R.sub.b) at the instant that a vehicle is physically present at some
point b can be represented by the continuous integral
##EQU1##
where: R.sub.a is the initial registration at point a
ds is the incremental differenial distance in the direction of travel and
.+-. is selected depending whether the registration is increasing or
decreasing with travel.
If the distance function is allowed to be accumulated on an incremental
basis instead of continuously, then the registered distance would be given
by
##EQU2##
where: K is a constant
.DELTA.X.sub.i is the incremental distance in arbitrary units related to
the desired units by the constant K, and
R.sub.a is as in Equation (A).
In general, most mechanical odometers are based upon an implementation of
equation A, while most electronic odometers would likely implement some
form of equation B. In the present invention, .DELTA.X.sub.i is selected
as a constant parameter. The following equation may then be written.
##STR1##
Another form of this equation is
##EQU3##
Since X.sub.i is assumed to be held constant, both of the latter two
equations provide the same answer. However, the implementation of the two
forms is not identical. Implementation of equation C (which is used in the
present invention) employs addition for its arithmetic operation, whereas
the second form uses multiplication. Naturally, an operation must be
performed each time that the distance register is updated; and, since
microcomputer addition operations are faster than multiplication
operations, then the implementation of equation C minimizes the speed
requirement for a microcomputer 46. (For previous odometers which have not
used a microcomputer, the implementation of equation D has generally been
more advantageous.) A further advantage of the implementation of equation
C is that the interface electronics which provide an input to the
microcomputer 46 are relatively simple, because only simple trigger pulses
are required in order to perform the summation steps. On the other hand,
to implement equation D would require a relatively complex encoder.
The concept of the calibration constant as employed herein can perhaps best
be understood by describing an algorithm in the form of a procedure for
deriving a typical calibration constant. First, it will be assumed that at
least two display rates (fast and slow) are selectable with a particular
embodiment, and that one of these display rates may be manually selected
by the user through movement of a slide switch on the keyboard 48. Also,
it will be assumed that the faster display rate corresponds to a divide
ratio of 1/8, and that the slower display rate corresponds to a divide
ratio of 1/128. Referring next to an exemplary keyboard 48 shown in FIG.
7, the vehicle owner would first clear his odometer by pressing the clear
key C with the unit stopped. Assuming that he wishes to update his display
at the faster rate, he would move the slide switch to the right so that it
is adjacent F. This will cause the accumulation of the largest quantity of
trigger pulses in the shortest period of time. Next, the operator would
manually key in the plus key (to increment distance traveled from zero),
and the "1" key--so that each trigger pulse will increment the display by
1. When the vehicle reached the beginning of a known calibration course,
the operator would start his electronic odometer 10 by depressing the run
key R. The vehicle would then travel a known distance along the
calibration course at the operating speed for which the most accurate
calibration is desired. It does not make any difference whether the known
distance D is in feet, miles, kilometers or some other units, because the
calibration constant which is to be calculated will be in the same units.
At the end of the calibration course, the operator would depress stop key
S to halt the incrementing operation of the odometer.
In one example, a known distance D of 5 miles was traveled; and the
displayed value N on the display 50 was 1260. Advantageously using the
calculator which is available, the displayed value N could be entered in
the calculator memory by depressing memory key M. With the displayed value
N being stored, the operator would then enter--using the keyboard 48--the
known distance which was traveled during the calibration run. The operator
would then divide the traveled distance D by the value of N stored in
memory, to obtain the calibration constant for the divide ratio which had
been selected for calibration. The calculation is:
K.sub.1/8 =5.div.1260=0.00397
The result is numerically equal to the actual distance traveled for each
trigger pulse generated by pulse generator 34 when the divide ratio of 1/8
is selected as the desired update rate. A similar calibration constant
would be calculated for any other divide ratios, but it is not necessary
to re-run the course to do so. That is, the data obtained from the run
using 1/8 as the divide ratio can be used to calculate the other
calibration constants by using the relation between 1/8 and the new divide
ratio. For a divide ratio of 1/128, the calibration constant will be 16
times larger because 1/8 is 16 times larger than 1/128. Hence, K.sub.1/128
will be 0.06349. Both of these calibration constants would be recorded
somewhere for subsequent use by the vehicle operator.
Perhaps it should be mentioned here that it is not necessary for practice
of the invention to have more than one divide ratio for the incoming
signals from the transducer 12. However, if a person is ever bothered by
watching rapidly changing numerals in a display 50, it is convenient to be
able to slow down the rate of change of the display; having both a fast
and slow up-date rate satisfies this desire.
Actual operation of the odometer will perhaps be better understood from the
following description of some exemplary uses of the electronic odometer.
Let it be assumed that the odometer has been suitably calibrated as
described above, and that the calibration constant K has been stored in
memory. And, let it be assumed that the vehicle is about to be driven on a
trip of some known distance, and the operator would like to know
throughout the trip how much further he has to travel before reaching his
destination. In such a case, with the electronic odometer 10 being in its
stop mode, the distance to the destination would be entered on the display
50 using the keyboard 48. The operator would then depress the minus key,
and he would recall the stored calibration constant K by depressing key
RM. These two steps will set up the microcomputer 46 for subtracting the
calibration constant K from the displayed distance each time a pulse is
received at interface 42. With the electronic odometer suitably prepared,
the operator would simply depress run key R at the reference point where
the run is to start. As the vehicle continues to progress toward its
destination, the remaining distance to be traveled will be displayed and
updated throughout the trip.
In another example, let it be assumed that the electronic odometer 10 is to
be used to record the actual distance traveled from a starting point,
which will be arbitrarily established as zero. With the odometer in its
stop mode, the operator would enter zero with the keyboard. Next, he would
depress the plus key, and recall the calibration constant which had been
stored in memory by depressing key RM. These steps will set up the
microcomputer 46 for adding the calibration constant K to the displayed
distance each time that a trigger pulse is received at the interface 42.
Finally, the run key R is depressed, so that movement of the vehicle will
begin operation of the odometer 10. It should perhaps be noted here that
measuring traveled distance as a function of wheel rotation is obviously
more reliable than trying to establish traveled distance as a function of
some other parameter--such as engine operation. For example, if a person
should attempt to derive signals from the engine's distributor or the
like, then inaccuracy would creep into the computed distance every time
that the vehicle stopped at a traffic light or stop sign, etc. To the
extent that the engine might sometimes be running when the vehicle is not
in motion, any raw signal which is derived from the engine (instead of a
wheel) will have built-in opportunity for error.
In order to use the electronic odometer disclosed herein along a
location-referenced highway system (such as the U.S. Interstate Highway
system), the operator would first determine if reference markers are
numerically increasing or decreasing in his direction of travel. Next, the
operator would enter the number of a location marker which is to be used
as a starting reference, e.g., 535, meaning that the vehicle will be
located at mile marker 535 along a particular highway. If the location
markers are numerically increasing, the operator would depress the plus
key, and then depress the RM key to recall the calibration constant K from
memory. This procedure must be followed with the electronic odometer in
its stop mode, but the vehicle itself does not have to be stopped. Hence,
the vehicle operator may have determined back when he was at mileage
marker 534 that he wished to subsequently synchronize his odometer with
the road's mileage markers. Then, when his vehicle arrived at marker 535,
the operator would simply press run key R to start the distance
accumulation. Thereafter, the exact position of the vehicle along the
highway can be ascertained by simply looking at the display 50; and, the
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