Apparatus for generating electrically distinguishable bipolar signals using a magnetic sensor and an oval wheel with teeth and notches in its minor and major axis

This specification discloses an apparatus and method for providing electrically distinguishable signals occurring as a function of the position of a moving element. It is possible to identify a sub group of electrical signals from the remaining electrical signals or from the entire group. The electrical signals can be used altogether to determine a variable such as revolutions per minute of the movable element or, particular ones of the electrically distinguishable signals can be used for initiating a function such as the firing of spark plugs.

FIELD OF THE INVENTION 
This invention relates to an apparatus and method for generating pulses 
and, in particular, generating pulses indicating the rotational movement 
and position of a shaft. 
DESCRIPTION OF THE PRIOR ART 
It is known in automotive vehicles to have a rotating wheel provide signals 
representative of the rotation of a crank shaft of an engine. In 
particular, the wheel can have a number of radially protruding teeth which 
produce a signal each time they go past the receiver. Thus, determining 
the number of teeth which pass the detector during a given time period can 
be used to determine the revolutions per minute of the crank shaft. 
Further, the occurrrence of a pulse generated by a tooth indicates that 
the rotational position of the wheel, and thus the crank shaft, is at one 
of those positions indicated by the teeth on the wheel. 
Signals can also be generated which characterize one particular angular 
reference position of the crank shaft. Such signals are necessary, for 
example, to initiate ignition. Although each one of the teeth on the wheel 
may indicate that an ignition should take place, the reference position is 
necessary to indicate when the sequence of cylinder firing should start. 
To generate a reference signal, it is known to make use of an additional 
wheel having a single protruding tooth and an additional detecting device 
for detecting the single tooth. Thus, a signal indicating a particular 
reference position occurs when the receiver detects passing of the single 
tooth. Such an arrangement is undesirable because there is the additional 
expense of the wheel having a single tooth and the detector as well as the 
assembly of the two additional components. The positioning of the wheel 
with the single tooth with respect to the other wheel must be done 
carefully so that there is an accurate angular relationship between the 
two wheels. 
The prior art also teaches attempts at avoiding the necessity for two 
separate wheels and the attendant disadvantages. In a wheel having a 
plurality of teeth, one tooth is longitudinally cut to provide two tooth 
portions with a gap therebetween. If the spacing between adjacent uncut 
teeth is equal to the width of a tooth, the presence of the cut tooth with 
the gap can be detected by comparing the duration of the separation 
between adjacent teeth and the width of the immediately proceeding tooth. 
That is, the spacing separating a cut tooth and an adjacent tooth is 
greater than the width of one of the cut tooth portions. 
However, such a scheme also has disadvantages in that the width of a tooth 
must be sufficiently wide to be cut into two portions and still provide a 
signal. Thus, the minimum width of the tooth is determined by the ability 
of a manufacturing process to form two tooth portions out of a single 
tooth. Further, the counting technique used to determine the presence of a 
cut tooth is based upon a spacing between adjacent teeth equal to the 
width of each tooth. Thus, such a system may not be desirable where it is 
necessary to have relatively narrow pulses which are spaced further apart 
than the pulse width. Further, relatively elaborate circuitry is required 
to determine the occurrence of a split tooth. Still further, it would be 
desirable to be able to establish the position of the reference point 
without the need for detecting or recognizing any of the other positions 
denoting angular position. 
A further problem which has existed without a completely satisfactory 
solution is to provide a sufficiently accurate indication of revolutions 
per minute when only two angular positions of the wheel need be known to 
determine firing of the cylinders. For example, in a four cylinder engine, 
two cylinders are fired during each rotation of the wheel. Thus, although 
only two positions are required on the wheel, the variance when 
determining the revolutions per minute is sufficient that it is desirable 
to have additional reference positions on the wheel for more frequent and 
thus more accurate computation of crankshaft revolutions per minute. One 
problem has been that these additional reference positions create 
erroneous spark plug firings. While the signals designating the different 
reference positions should be different, they should be sufficiently alike 
in such parameters as magnitude that the apparatus used to detect one 
signal can easily and efficiently detect the other signal. These are some 
of the problems this invention overcomes. 
SUMMARY OF THE INVENTION 
This invention teaches a pulse generating apparatus and method for 
providing electrically distinguishable signals occurring as a function of 
position of a relatively movable element. For purposes of electrically 
distinguishing the signals, they need not have any particular relationship 
with respect to one another, can be placed in an arbitrary angular 
position with respect to one another and can be detected and distinguished 
without detection of any other signal. A particular problem which this 
invention solves is the use of a single wheel coupled to a rotating 
crankshaft for determining both the revolutions per minute of the 
crankshaft and determining when a cylinder should be fired. For example, 
two positions on a rotating wheel can be distinguished from two other 
positions on a rotating wheel. 
More specifically, the pulse generating means includes a transducer means 
located on the relatively movable element for generating the electrically 
distinguishable signals. A transducer receiving means is located in energy 
transfer coupling with respect to the transducer means for providing the 
electrically distinguishable signals in response to passage of the 
transducer means past the transducer receiving means. The transducer means 
includes teeth means for projecting toward the transducer receiving means 
for generating electrical signal of a first shape and a notch means for 
receding away from the transducer receiving means for generating an 
electrical signal of a second shape, distinguishable from the first shape.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a pulse generator 10 includes a transducer wheel 20 
operatively coupled by a magnetic field to a transducer receiver 30 which 
is electrically connected to the combination of an output voltage 
indicator 11 and a controller 12. Rotation of transducer wheel 20 produces 
a changing magnetic flux which is detected by transducer receiver 30 and 
communicated as a voltage to output voltage indicator 11 where the 
voltages are displayed. Controller 12 performs various functions in 
response to the signals indicated at output voltage indicator 11. For 
example, such functions can include computation of revolutions per minute 
of an engine crankshaft and initiating firing of a cylinder spark plug in 
an automobile engine. 
Transducer wheel 20 has a generally elliptical shape with a pair of teeth 
21 protruding from the periphery of the generally elliptical shape along a 
minor diameter 23 and a pair of notches 22 extending into the generally 
elliptical shape along a major diameter 24. Transducer wheel 20 rotates 
about a central axis 25 so that teeth 21 and notches 22 pass transducer 
receiver 30. Transducer wheel 20 is made of a ferro magnetic material so 
that it can influence a magnetic field established by transducer receiver 
30. 
More particularly, it is generally desirable to have the magnitude of the 
field influence be the same when a tooth 21 passes transducer receiver 30 
as when a notch 22 passes transducer receiver 30. This invention 
recognizes that a circular periphery having a notched indentation and a 
tooth extending down the circular boundary and rotating about a fixed axis 
would position the tooth closer to transducer receiver 30 than the notch. 
As a result, the effect produced by the tooth would be greater than that 
produced by the notch. In accordance with an embodiment of this invention, 
transducer wheel 20 is shaped so that notches 22 and teeth 21 pass 
approximately the same distance from transducer receiver 30 and produce an 
effect of substantially equal magnitude, even though of opposite polarity, 
on the magnetic flux. Thus, the particular relationship of the width of 
the tooth and the width of the notch depends, in part, on the magnetic 
properties of the material which forms the tooth in relation to the 
magnetic properties of the material which forms the notch. 
Teeth 21 are generally rectangular in shape and have an axis aligned with 
the radius of transducer wheel 20. Similarly, notches 22 are also 
rectangular in shape and have an axis along the radius of transducer wheel 
20. In order to make the increase in flux when a tooth 21 passes 
transducer receiver 30 substantially equal to the reduction in magnetic 
flux when notch 22 passes transducer receiver 30, it has been found that 
the width of notch is advantageously about 21/2 times the width of a tooth 
21 and that notch 22 extends longer in a radial direction than a tooth 21. 
The curve of the periphery of transducer wheel 20 between a tooth 21 and 
adjacent notch 22 is curved so that as transducer wheel rotates, the 
change in magnetic flux adjacent transducer receiver 30 is substantially 
constant thereby producing a substantially constant output voltage. 
Accordingly, since the periphery of transducer wheel 20 adjacent wheel 21 
is further from transducer receiver 30 than the portion of periphery of 
transducer wheel 20 adjacent notch 22, the rate of change of curvature 
adjacent to tooth 21 is greater than the rate of change of curvature 
adjacent notch 22. Additionally, the curvature between tooth 21 and 
adjacent notch 22 is advantageously smooth and without sudden changes in 
curvature which would cause abrupt fluctuations in the output voltage. 
Transducer receiver 30 detects the change in magnetic flux and has an 
electrical voltage output indicative of the rate of change of flux. More 
particularly, referring to FIG. 3, a reluctance type pickup measures the 
rate of change of flux and includes a permanent magnet 31, a pole piece 32 
positioned adjacent permanent magnet 31 and a wire coil 33 wound around 
pole piece 32. Changing magnetic flux in pole piece 32 induces a voltage 
in wire coil 33 and produces an electrical input for output voltage 
indicator 11. 
Referring to FIG. 4, a transducer receiver 30a includes a permanent magnet 
31a adjacent a semiconductor 36 which is fabricated so that magnetic flux 
adjacent semiconductor 36 causes a Hall effect and a shift of charge 
carriers within semiconductor 36 can be used to establish a voltage 
proportional to the flux. That is, in the Hall effect device of transducer 
receiver 30a the output voltage is proportional to the magnitude of the 
magnetic field. In contrast, in transducer receiver 30 shown in FIG. 3, 
the output voltage is a function of the rate of change of the magnetic 
flux. The transducer wheel used with either of the two transducer 
receivers can be the same. 
Referring to FIG. 2, the output of a device in accordance with FIG. 3 is 
shown. As can be seen from the wave form, the magnitude of the electrical 
signals in response to a passing of a tooth 21 and a notch 22 adjacent 
transducer receiver 30 alternate in sequence and are approximately equal 
in magnitude. However, the polarities are reversed with a tooth having a 
positive rise followed by a negative drop and a notch 22 having a negative 
drop followed by a positive rise. The magnitude of the signal going from a 
tooth 21 to a notch 22 is a small positive value because of the increasing 
amount of magnetic flux caused by an increased mass of transducer wheel 20 
adjacent transducer receiver 30. The opposite occurs when going from a 
notch 22 to a tooth 21. There is a decrease in magnetic flux and thus 
there is a small constant negative signal between the electrical signals 
caused by the decreasing diameters of transducer wheel 20 in the direction 
from notch 22 to tooth 21. 
Referring again to FIG. 1, controller 12 performs various functions in 
response to the electrical signals shown in the wave form of FIG. 2. For 
example, controller 12 can cause the firing of a spark plug in a cylinder 
of an automotive engine when the electrical signal in response to a tooth 
21 has a zero crossing. The occurrence of such a zero crossing typically 
would be set to occur 10.degree. before top dead center of the piston 
associated with the spark plug to be fired. Additionally, controller 12 
can compute the revolutions per minute by determining the number of zero 
crossings, both from teeth 21 and notches 22, during a given period of 
time. 
The availability of a differentiation between the electrical signals 
produced by the notches 22 and teeth 21 permits controller 12 to readily 
decide whether a spark plug should be fired. Nevertheless, the 
availability of electrical signals from notch 22, even though not used for 
firing of a cylinder, in addition to electrical signals produced by teeth 
21, increases the accuracy of the revolution per minute computation. 
Further, the fact that the magnitude of the signals from both teeth 21 and 
notches 22 can be substantially equal, simplifies the circuitry of 
controller 12 and permits it to handle both signals with equal ease. If 
one signal were substantially different from the other, the smaller signal 
would have a substantially worse signal to noise ratio compared to the 
other signal. This is particularly important when pulse generator 10, 
exists in an electrically noisy environment such as an automobile. 
Experimental data indicates that transducer wheel 20 can be an ellipse and 
that the particular shape of transducer wheel 20, notches 22 and teeth 21 
can depend upon the spacing of transducer receiver 20 the axis of rotation 
of transducer wheel 20. Typical parameters for pulse generator 10 include 
a tooth 21 having a width of 0.120 inches and a radial extension of 0.125 
inches. Typical dimensions for notch 22 includes a width of 0.30 inches 
and a radial depth of 0.35 inches. The thickness of transducer wheel 20 
can be about 0.20 inches and have a radius which corresponds to the 
following table wherein a tooth 21 is positioned 90.degree. from a notch 
22 which forms a reference position for angle, .theta., so that angle 
.theta. has a value of zero at notch 22 and a value of 90.degree. at tooth 
21. The magnitude of the radius at 0.degree. includes the radial 
indentation of notch 22, and the magnitude of the radius at 90.degree. 
includes the radial extension of tooth 21. 
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.theta. (in degrees) 
r (in inches) 
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0 2.110 
10 2.105 
20 2.099 
30 2.092 
40 2.083 
50 2.072 
60 2.059 
70 2.041 
80 2.017 
90 1.985 + .125 = 2.110 
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A typical transducer receiver can be a magnet made of alnico V having a 
generally cylindrical shape with a length of 1.0 inches and a diameter of 
0.31 inches. A generally cylindrical piece of soft iron abuts an end face 
of alnico magnet, is coaxial therewith, has a length of about 0.25 inches, 
a diameter of 0.156 inches, and has wound therearound about 3100 turns of 
wire. 
Various modifications and variations will no doubt occur to those skilled 
in the art. For example, the particular shape of the teeth and notches may 
be varied from those disclosed herein. These and all other variations 
which basically rely on the teachings through which this disclosure has 
advanced the art are properly considered within the scope of this 
invention.