U.S. patent number 3,783,314 [Application Number 05/316,945] was granted by the patent office on 1974-01-01 for signal generating mechanism.
This patent grant is currently assigned to The Ford Motor Company. Invention is credited to Charles C. Kostan.
United States Patent |
3,783,314 |
Kostan |
January 1, 1974 |
SIGNAL GENERATING MECHANISM
Abstract
A signal generating mechanism is disclosed for producing an
electrical signal having a frequency proportional to the angular
velocity of a rotating shaft. The signal generating mechanism may
be used in the distributor for a breakerless ignition system for a
multi-cylinder internal combustion engine, in which case the
frequency of the alternating signal is equal to the rate at which
ignition sparks are to be generated. The signal generating
mechanism includes a lower plate and bushing through which the
rotating shaft passes. A non-adjustable stator assembly is formed
by a hub positioned around the bushing, the hub having an upper
plate attached to it on which is affixed a permanent magnet. A
stator is positioned on the permanent magnet and has an extending
pole-piece that passes through an electrical pickup coil. An
armature, or rotor, is formed by a toothed-wheel that is affixed to
the rotating shaft. The teeth of the toothed-wheel come into and go
out of alignment with the portion of the stator pole-piece that
extends through the electrical coil.
Inventors: |
Kostan; Charles C. (Detroit,
MI) |
Assignee: |
The Ford Motor Company
(Dearborn, MI)
|
Family
ID: |
23231397 |
Appl.
No.: |
05/316,945 |
Filed: |
December 20, 1972 |
Current U.S.
Class: |
123/146.5A;
123/617 |
Current CPC
Class: |
G01P
3/488 (20130101); F02P 7/0675 (20130101); F02P
7/0677 (20130101) |
Current International
Class: |
G01P
3/488 (20060101); H02K 21/38 (20060101); G01P
3/42 (20060101); F02P 7/067 (20060101); F02P
7/00 (20060101); H02K 21/00 (20060101); H02k
011/00 () |
Field of
Search: |
;310/68R,68C,69,70,154
;123/148 ;315/218 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Miller; J. D.
Assistant Examiner: Hickey; Robert J.
Attorney, Agent or Firm: Keith L. Zerschling et al.
Claims
Based upon the foregoing description of the invention, what is
claimed is:
1. A signal generating mechanism for producing an alternating
electrical signal having a frequency proportional to the angular
velocity of a rotating shaft, said signal generating mechanism
comprising, in combination: a lower plate fixed relative to said
rotating shaft, said lower plate having an opening therein; an
annular bushing affixed in said lower plate opening, said bushing
extending above said lower plate, said shaft passing through said
bushing; a stator assembly, said stator assembly including an
annular hub positioned around the portion of said bushing extending
above said lower plate, said hub being rotatable about said
bushing, an upper plate parallel to said lower plate and affixed to
said hub, a permanent magnet attached to said upper plate, said
magnet being polarized to produce a magnetic field having a
direction through said magnet that is perpendicular to said upper
plate, a stator positioned on said permanent magnet, said stator
having a pole-piece, and an electrical coil positioned on said
stator pole-piece; and a rotor attached to said shaft for rotation
therewith, said rotor having at least one tooth positioned to come
into and go out of alignment with said stator pole-piece; whereby
rotation of said rotor produces an alternating electrical signal
across the terminals of said electrical coil having a frequency
proportional to the angular velocity of said rotating shaft.
2. A signal generating mechanism for producing an alternating
electrical signal having a frequency proportional to the angular
velocity of a rotating shaft, said signal generating mechanism
comprising, in combination: a lower plate fixed relative to said
rotating shaft, said lower plate having an opening therein; an
annular ferromagnetic bushing affixed in said lower plate opening,
said bushing extending above said lower plate, said shaft passing
through said bushing; a stator assembly, said stator assembly
including an annular ferromagnetic hub positioned around the
portion of said bushing extending above said lower plate, said hub
being rotatable about said bushing, a ferromagnetic upper plate
parallel to said lower plate and affixed to said hub, a permanent
magnet polarized to produce a magnetic field having a direction
through said magnet that is perpendicular to said upper plate, a
ferromagnetic stator positioned on said permanent magnet, said
stator and said permanent magnet being non-adjustably secured to
said upper plate, said stator having a pole-piece extending
radially towards said shaft axis, and an electrical coil positioned
on said pole-piece, said pole-piece extending through said
electrical coil; and a ferromagnetic rotor affixed to said shaft
for rotation therewith, said rotor having a plurality of teeth
positioned to come into and to go out of alignment with said
pole-piece of said stator during rotation of said shaft; whereby
rotation of said shaft produces an alternating signal across the
terminals of said electrical coil.
3. The signal generating mechanism of claim 2 wherein a gap exists
between a tooth of said rotor that is in alignment with said
pole-piece, said gap being within the dimensional range from 0.062
of an inch to 0.023 of an inch.
4. A signal generating mechanism for producing an alternating
electrical signal, which comprises, in combination: a housing; a
shaft rotatably journalled in said housing; a lower plate secured
to said housing, said lower plate having an opening therein and
being positioned perpendicular to said shaft; a ferromagnetic
bushing affixed in said lower plate opening, said bushing extending
above said lower plate and having lubrication grooves on the
radially exterior portion thereof, said shaft passing through said
bushing; a ferromagnetic sleeve on the portion of said shaft
passing through said bushing, said sleeve being rotatable about
said shaft; a centrifugal mechanism interconnecting said sleeve and
said shaft for controlling rotation of said sleeve about said
shaft; a toothed ferromagnetic rotor secured to said sleeve for
rotation therewith, the teeth of said rotor extending radially
outward from the axis of said shaft; a stator assembly, said stator
assembly including an annular ferromagnetic hub positioned around
the portion of said bushing extending above said lower plate, said
hub being rotatable about said bushing, a ferromagnetic upper plate
parallel to said lower plate and affixed to said hub for rotation
therewith, an arcuately-shaped permanent magnet positioned on said
upper plate, said permanent magnet having a north pole and a south
pole, an imaginary line interconnecting said north and south poles
being perpendicular to said upper plate, said permanent magnet
being made from a ceramic ferrite material, a ferromagnetic stator
positioned on said permanent magnet, said stator and permanent
magnet being non-adjustably secured to said upper plate, said
stator having a pole-piece positioned to permit said rotor teeth to
come into and to go out of alignment with it, and an electrical
coil surrounding said pole-piece of said stator, said electrical
coil being helically wound and having an axis perpendicular to the
axis of said shaft; and means connected to said upper plate of said
stator assembly for controlling the rotation of said stator
assembly about said bushing.
5. The signal generating mechanism of claim 4 wherein a gap exists
between a tooth of said rotor that is in alignment with said
pole-piece, said gap being within the dimensional range from 0.062
of an inch to 0.023 of an inch.
Description
BACKGROUND OF THE INVENTION
This invention relates to a signal generating mechanism for
producing an alternating electrical signal having a frequency
proportional to the angular velocity of a rotating shaft. More
particularly, the invention relates to a signal generating
mechanism particularly suitable for use in a distributor for a
breakerless ignition system for a multi-cylinder internal
combustion engine.
Common past and present practice in ignition systems for
multi-cylinder internal combustion engines has been to employ a set
of breaker points in a distributor to generate sparks as required
by the engine. Electronic ignition systems eliminating these
breaker points recently have been developed. These electronic
breakerless ignition systems require a signal generating mechanism
capable of indicating the times or instants at which it is desired
to generate sparks in the various engine combustion chambers. A
common feature of such signal generating devices is that they
produce an electrical signal having a frequency proportional to the
angular velocity of a rotating shaft, the shaft usually being the
shaft in a distributor which rotates at an angular velocity equal
to that of the engine's cam shaft.
Although various signal generating mechanisms have been proposed
for use with multi-cylinder internal combustion engines, the
present invention is directed to the type which employs a
toothed-wheel affixed to the rotating shaft. The toothed-wheel
forms the armature, or rotor, of an alternating signal generator.
The stator assembly of the alternating signal generator includes an
electrical pickup coil through which a stator pole-piece passes.
The teeth of the toothed-wheel come into and go out of alignment
with the stator pole-piece to vary the flux produced by a permanent
magnet having a magnetic circuit including the stator and its
pole-piece and the rotating toothed-wheel. This produces an
alternating electrical signal across the terminals of the
electrical coil. This alternating signal, in turn, may be coupled
to a breakerless ignition system capable of producing sparks in
relation to the alternating signal, for example, at one or more
selected points in the signal waveform.
SUMMARY OF THE INVENTION
In accordance with the invention, a signal generating mechanism for
producing an alternating electrical signal having a frequency
proportional to the angular velocity of a rotating shaft comprises
a lower plate that is fixed relative to the rotating shaft. The
lower plate has an annular opening therein and a bushing is affixed
in the annular opening. The shaft passes through the bushing. A
stator assembly is positioned above the lower plate. The stator
assembly includes a hub which is positioned around a portion of the
bushing affixed to the lower plate. Attached to the hub is an upper
plate, parallel with the lower plate, on which is positioned a
permanent magnet having a magnetic field that is perpendicular to
the upper plate. The stator assembly further includes the stator
itself, which is positioned in contact with the permanent magnet,
the permanent magnet being located intermediate the stator and the
upper plate. The stator has a pole-piece which passes through and
supports an electrical coil the axis of which is perpendicular to
the shaft axis. An armature, or rotor, is formed by a toothed-wheel
that is affixed to the shaft for rotation therewith. The
toothed-wheel is concentric with the shaft axis and the teeth of
the toothed-wheel are positioned to come into and to go out of
alignment with the pole-piece of the stator.
Rotation of the shaft and the toothed-wheel attached to it produces
a voltage across the terminals of the electrical coil. This voltage
is determined in accordance with the well known equation E= -N
d.phi./dt where E is the electromotive force produced across the
terminals of the electrical coil, N is the number of turns in the
electrical coil and d.phi./dt is the time rate of change of
magnetic flux.
The entire stator assembly is non-adjustably secured together,
thus, eliminating screw adjustments or the like. Prior art devices
have required adjustments of this type to obtain voltage signals of
a desired level. The elimination of such adjustments simplifies the
manufacture of the signal generating mechanism and eliminates the
possibility of maladjustment during use of the device
The invention will be better understood by reference to the
detailed description which follows and to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view, the section being taken along the line
1--1 of FIG. 2, of an ignition distributor for a multi-cylinder
internal combustion engine, the distributor including a signal
generating mechanism for producing an alternating electrical signal
having a frequency proportional to the angular velocity of the
rotatable distributor shaft;
FIG. 2 is a plan view of the distributor of FIG. 1;
FIG. 3 is a sectional view of the distributor, the section being
taken along the line 3--3 in FIG. 1, and illustrates a centrifugal
weight mechanism for timing advance;
FIG. 4 is an enlarged plan view of the stator assembly used in the
signal generating mechanism of the distributor of FIG. 1;
FIG. 5 is an enlarged elevational view, partially in section, of
the stator assembly of FIG. 4;
FIG. 6 is an enlarged pictorial view of the stator assembly of
FIGS. 4 and 5; and
FIG. 7 is an illustration of the alternating signal waveform that
may be produced by the signal generating mechanism in the ignition
system distributor.
DETAILED DESCRIPTION
With particular reference now to FIGS. 1 through 3, there is shown
an ignition system distributor 10 for supplying sparks to a
multi-cylinder internal combustion engine. The distributor 10
includes a housing 12 having a cylindrical bearing 14 positioned
therein. A shaft 16 is rotatably journalled within the bearing 14.
The shaft 16 is driven by a gear 20 that, in use, meshes with
another gear (not shown), driven by the internal combustion engine.
The shaft 16 has a reduced-diameter portion 18, and both the
larger-diameter and reduced-diameter portions of the shaft contain
grooves for lubrication purposes.
A ferromagnetic sleeve 22 fits over the reduced-diameter portion 18
of the shaft 16. The sleeve 22 is retained on the shaft 16 with a
wire retainer 24. The sleeve 22 is rotatably mounted on the
reduced-diameter portion 18 of the shaft 16, and this rotation
relative to the shaft is controlled by a centrifugal advance
mechanism of the usual design.
The centrifugal advance mechanism, generally designated by the
numeral 26, comprises a plate 28 affixed to the shaft 16 and a
plate 30 affixed to the sleeve 22. In the usual manner, the plates
28 and 30 are coupled together by means of springs 32 and 34. In
order for the plate 30 and sleeve 22 to rotate about the plate 26
and shaft 16, the force of the springs must be overcome. When the
shaft 16 rotates, a pair of weights 36 and 38, pivotally connected
to the plate 28, exert a force that acts against that of the
springs 32 and 34 and tends to rotate the plate 30 and sleeve 22
with respect to the shaft 16. The magnitude of this force is
proportional to the shaft angular velocity. This provides a
centrifugal advance in the ignition timing. For the purpose of the
present invention, the sleeve 22 may be regarded as a part of the
shaft 16 with which it rotates.
The ignition system distributor 10 is shown without the usual cap
and high-voltage distribution rotor. It should be understood that
these elements would be present in a complete distributor
installation. The distributor cap would be of the usual
configuration in which a plurality of electrical contacts would be
connected by high-voltage leads to spark plugs for the
multi-cylinder internal combustion engine. The high-voltage
distribution rotor would be secured to the sleeve 22 and would
rotate with it to distribute voltage from the high-voltage side of
an ignition coil to the electrical leads to the various spark
plugs.
The ignition system distributor 10 includes a signal generating
mechanism of the invention, generally designated by the numeral 40,
for producing an alternating electrical signal having a frequency
proportional to the angular velocity of the rotating shaft 16 and
sleeve 22. Preferably, the alternating signal generating mechanism
has a frequency equal to the rate at which sparks are to be
generated by the ignition system. Typically, this frequency is
equal to the speed of the shaft in revolutions per second times the
number of cylinders in the internal combustion engine.
The signal generating mechanism 40 illustrated in the drawings is
intended for an 8-cylinder engine. It comprises a toothed-wheel 42,
hereinafter referred to as a rotor, and a stator assembly 44. The
rotor 42 is attached to the sleeve 22 for rotation therewith by
means of a roll pin 46. Also, the position of the rotor 42 on the
axis of the sleeve 22 is determined by a rotor ring retainer 48.
The rotor 42 may be made from a sintered high-permeability material
and has eight radially extending teeth 50, these corresponding in
number to the number of cylinders in the engine. Preferably, to
achieve a desirable signal, the teeth extend radially outward a
distance of from about five to 15 times the dimension of the
air-gap 51 between the rotor and stator. Also, it is preferred that
the air-gap 51 have a dimension ranging from a maximum of 0.062 in.
to a minimum of 0.023 in., the midpoint of this range being most
satisfactory. In this connection, it should be noted that similar
signal generating mechanisms of the prior art were limited to
air-gap dimensions ranging from about 0.006 in. to 0.001 in. and
required adjustment means to maintain this dimension.
The stator assembly 44 is located and positioned by means of a
lower plate 52 that has an annular opening therein in which an
annular bushing 54, made from a ferromagnetic material, is fixed.
The shaft 16 and associated sleeve 22 pass through the bushing 54
and rotate freely within it. The lower plate 52 is positioned
perpendicularly to the axis of the shaft and is secured to the
distributor housing 12 by a plurality of screws 56. The bushing 54
has a portion which extends above the lower plate 52. This upwardly
extending portion of bushing 54 has lubrication grooves 53 on its
radially outward exterior that are filled with grease during the
assembly of the mechanism.
The stator assembly 44 may best be seen in the enlarged views of
FIGS. 4 through 6. It includes an annular hub 58, also made from a
ferromagnetic material, that is positioned around the bushing 54 so
that the stator assembly may rotate about the bushing. A wire ring
retainer 60 (FIG. 1) is used to hold the stator assembly 44 in
position on the bushing 54. The stator assembly 44 comprises the
hub 58, an irregularly shaped, ferromagnetic upper plate 62
positioned parallel to the lower plate 52, a permanent magnet 64, a
stator 66 and an electrical pickup coil 68.
The upper plate 62 of the stator assembly is securely staked in
locations 70 to the hub 58. A pin 72 extends upwardly from the
upper plate 62. In FIG. 2, it may be seen that a rod 74 of a vacuum
motor 76, used in addition to the centrifugal timing mechanism 26
for ignition-timing advance and retard, is pivotally connected to
the pin 72 on the upper plate 62. The rod 74 controls rotation of
the hub 58, and the remainder of the stator assembly 44, about the
bushing 54.
The permanent magnet 64 has an arcuate shape. Preferably, it is
made from a ferrite material, such as sintered ceramic strontium
ferrite. It is preferred that the permanent magnet 64 be magnetized
at assembly of the signal generating mechanism. Its magnetic field
should be oriented such that its direction through the magnet is
perpendicular to the upper plate 62. Accordingly, the upper surface
78 of the permanent magnet 64 may be made a south pole and the
lower surface, that is, the surface in contact with the upper plate
62, may be made a north pole. In such case, an imaginary line
interconnecting these poles is perpendicular to the upper plate 62.
The permanent magnet 64 preferably is magnetized to an induction of
about 3600 gauss.
The stator 66 and the permanent magnet 64 are non-adjustably
secured to the upper plate 62 of the stator assembly with rivets 80
and 82. To avoid impact damage to the permanent magnet, a spin-type
riveting process may be used. The stator 66 is made from a
ferrogmagnetic material and preferably is made from a
sintered-iron, high-permeability, low-carbon material having a
minimum density of about 6.8 grams per cubic centimeter. The stator
66 has a generally arcuate shape but also has a pole-piece 86 of
rectangular cross-section extending through the central region of
the electrical coil 68 and radially toward the axis of the shaft
16. The teeth 50 of the rotor 42 come into and go out of alignment
with the pole-piece 86 of stator 66 as the shaft 16 and its sleeve
22 rotate. It should be noted that the axis of rotation of the
stator assembly 44 about the bushing 54 is the same as the axis of
shaft 16, and, thus, the air gap between the rotor teeth and
pole-piece does not change during ignition timing changes.
The electrical pickup coil 68 is supported by and surrounds the
stator pole-piece 86 and preferably is formed from a helical
winding of from about 4,000 to 4,075 turns of gauge number 39
(American Wire Gauge) copper wire and may have a resistance of from
600 to 700 ohms. Preferably, the electrical pickup coil 68 is
encapsulated by molding in a suitable insulating material. The
pickup coil 68 has leads 90 and 92 connected to the electrical
winding terminals that extend out of the coil encapsulation
material. Also, the pickup coil has a hook 94 attached to it. A
spring clip 96 is connected to the hook 94 and to the stator
pole-piece 86 to hold the electrical pickup coil on the pole-piece
86 in a secure manner. The axis of the coil 68 is perpendicular to
the axis of the shaft 16.
In FIG. 2, it may be seen that the wires 90 and 92 enter and pass
through a grommet 98, preferably made from a molded polyvinyl
chloride material, to a connector 100. The grommet 98 contains a
third wire 102 that is connected by one of the screws 56 to the
lower plate 52 to establish an electrical ground. The wire 102
extends out of the grommet 98 and into the connector 100. The wire
102 is a ground lead.
In operation, the rotor 42 preferably turns in the counterclockwise
direction indicated in FIG. 2 by the arrow on one of its teeth. As
the rotor 42 rotates, the magnetic flux changes to produce a time
varying voltage across the electrical leads 90 and 92 of the
electrical coil 68. This voltage or EMF is produced in accordance
with the aforementioned equation E= -N d.phi./dt.
The magnetic circuit is illustrated by the dotted line 104 in FIG.
6. This magnetic circuit includes the stator 66 and its pole-piece
86, the toothed rotor 42 and shaft 16 (not shown in FIG. 6), and
the upper plate 62 that is in contact with the bottom surface of
the permanent magnet 64.
With reference in particular to FIGS. 2 and 7, wherein one of the
teeth 50 of the rotor 42 is in alignment with the pole-piece 86 of
the stator 66, let it be assumed that the rotor is turning in a
counterclockwise direction. At this instant with the tooth in
alignment with the pole-piece 86, there is no change in flux with
respect to time and the generated voltage is zero. This corresponds
to the time t = 0 of FIG. 7. As the tooth moves out of alignment
with the pole-piece 86 of the electrical coil, a voltage is
generated across the coil leads 90 and 92 due to the change in
magnetic flux. This flux change, and consequently the generated
voltage, reaches a maximum and then decreases to zero at a time t =
T/2 corresponding to the time when the pole-piece 86 is midway
between two of the teeth 50 of the rotor 42. Continued rotation of
the rotor 42 produces a change in magnetic flux that generates a
voltage of opposite polarity. This voltage increases until it once
again becomes zero at time t = T when the next tooth 50 is in
alignment with the pole-piece 86. Thus, an alternating signal is
generated having a frequency proportional to the angular velocity
of the rotating shaft of the distributor.
* * * * *