U.S. patent application number 15/405664 was filed with the patent office on 2018-07-19 for hybrid transmission having electro-magnetically actuated pawl clutch.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Norman Jerry Bird, Jacob Klaser.
Application Number | 20180202502 15/405664 |
Document ID | / |
Family ID | 62716589 |
Filed Date | 2018-07-19 |
United States Patent
Application |
20180202502 |
Kind Code |
A1 |
Klaser; Jacob ; et
al. |
July 19, 2018 |
Hybrid Transmission Having Electro-Magnetically Actuated Pawl
Clutch
Abstract
An electro-magnetically actuated pawl clutch is adapted to
establish a fixed overdrive ratio in a powersplit type hybrid
gearing arrangement. The electro-magnetically actuated clutch
includes an inner race splined to the transmission input shaft and
an outer race fixed to a first gear that is supported for rotation
about the input shaft. The inner race includes two magnetically
separated toothed rings. Electrical current in a non-rotating coil
establishes a magnetic field in the inner race. The magnetic field
causes a set of pawls to pivot with respect to the outer race and
to engage at least one of the toothed rings. The pawls and teeth
are designed such that, when engaged, the outer race can rotate
faster than the inner race but cannot rotate slower. The first gear
meshes with a second gear fixed to the transmission output
shaft.
Inventors: |
Klaser; Jacob; (Royal Oak,
MI) ; Bird; Norman Jerry; (Plymouth, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
62716589 |
Appl. No.: |
15/405664 |
Filed: |
January 13, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02T 10/62 20130101;
Y10S 903/91 20130101; F16D 41/12 20130101; B60Y 2400/427 20130101;
F16D 27/118 20130101; B60K 6/365 20130101; B60K 6/44 20130101; F16D
27/102 20130101; B60Y 2200/92 20130101 |
International
Class: |
F16D 27/118 20060101
F16D027/118; F16D 41/12 20060101 F16D041/12; B60K 6/365 20060101
B60K006/365; B60K 6/44 20060101 B60K006/44 |
Claims
1. An electro-magnetically actuated clutch comprising: a
non-rotating electromagnet coil; a toothed inner race supported for
rotation about the coil, the inner race having left and right
magnetically conductive rings magnetically separated from one
another; an outer race supported for rotation about the inner race;
and a magnetically conductive pawl supported for rotation with the
outer race and pivotable into engagement with the left and right
rings in response to current in the coil.
2. The electro-magnetically actuated clutch of claim 1 wherein the
left and right rings both have teeth.
3. The electro-magnetically actuated clutch of claim 2 wherein the
teeth of a first of the left and right rings is offset from the
teeth of a second of the left and right rings such that an
engagement force is distributed disproportionately to the first of
the left and right rings.
4. The electro-magnetically actuated clutch of claim 1 wherein the
inner race has a tooth profile configured to prevent relative
rotation between the inner and outer races in one direction in
response to engagement of the pawl while permitting relative
rotation in an opposite direction with the pawl engaged.
5. The electro-magnetically actuated clutch of claim 1 wherein the
outer race is not magnetically conductive.
6. A clutch comprising: an electromagnetic coil; left and right
magnetically conductive rings each having a cylindrical surface
adjacent to the coil, at least one of the left and right rings
having a toothed surface opposing the cylindrical surface, the left
and right rings magnetically separated from each other; a race
supported for rotation with respect to the rings; and a
magnetically conductive pawl pivotable with respect to the race
into engagement with at least one of the left and right rings in
response to current in the coil.
7. The clutch of claim 6 wherein: the electromagnetic coil is
non-rotating; and the left and right rings and the race are
supported for rotation.
8. The clutch of claim 6 wherein: the electromagnetic coil is
radially inside the left and right rings; and the race is radially
outside the left and right rings.
9. The clutch if claim 6 wherein the left and right rings are
fixedly coupled to one another.
10. A transmission comprising: an electromagnet coil fixed to a
transmission case; left and right magnetically conductive rings
each fixedly coupled to an input shaft and magnetically separated
from one another; an outer race supported for rotation with respect
to the input shaft; and a magnetically conductive pawl supported
for rotation with the outer race and pivotable into engagement with
at least one of the left and right rings in response to current in
the coil.
11. The transmission of claim 10 further comprising: a planetary
carrier fixedly coupled to the input shaft; a plurality of planet
gears supported for rotation with respect to the planet carrier; a
sun gear meshing with the planet gears and driveably connected to a
generator; and a ring gear meshing with the planet gears and
driveably connected to a transmission output.
12. The transmission of claim 11 further comprising a motor
driveably connected to the transmission output.
13. The transmission of claim 12 wherein the outer race is
driveably connected to the transmission output.
14. The clutch of claim 6 wherein the left and right rings both
have a toothed surface opposing the cylindrical surface.
15. The clutch of claim 14 wherein the teeth of a first of the left
and right rings is offset from the teeth of a second of the left
and right rings such that an engagement force is distributed
disproportionately to the first of the left and right rings.
Description
TECHNICAL FIELD
[0001] This disclosure relates to the field of vehicle clutches.
More particularly, the disclosure pertains to an
electro-magnetically actuated pawl clutch used within a hybrid
electric powertrain.
BACKGROUND
[0002] Many vehicles are used over a wide range of vehicle speeds,
including both forward and reverse movement. Some types of engines,
however, are capable of operating efficiently only within a narrow
range of speeds. Consequently, transmissions capable of efficiently
transmitting power at a variety of speed ratios are frequently
employed. When the vehicle is at low speed, the transmission is
usually operated at a high speed ratio such that it multiplies the
engine torque for improved acceleration. At high vehicle speed,
operating the transmission at a low speed ratio permits an engine
speed associated with quiet, fuel efficient cruising.
[0003] Some transmissions, called discrete ratio transmissions, are
configured to establish a finite number of speed ratios between an
input shaft and an output shaft. When the currently selected ratio
is no longer appropriate, a discrete ratio transmission must shift
to a different one of the available speed ratios. Other
transmissions, called continuously variable transmissions (CVTs),
are capable of establishing any speed ratio between lower and upper
limits. CVTs are capable of making frequent fine speed ratio
adjustments which are not perceivable by vehicle occupants.
[0004] Many transmissions use hydraulically actuated friction
clutches to establish various power flow paths. Hydraulic actuation
is suited for clutches that selectively couple rotating elements to
one another because pressurized hydraulic fluid can be routed from
a stationary housing to rotating components between seals.
Therefore, the hydraulic actuator can rotate with one of the
rotating elements. When there are multiple hydraulically actuated
clutches, the clutches often share an engine drive pump and share
many of the valve body components used to regulate the
pressure.
[0005] Hybrid vehicle transmissions improve fuel economy by
providing energy storage. In a hybrid electric vehicle, for
example, energy may be stored in a battery. The battery may be
charged by operating the engine to produce more power than
instantaneously required for propulsion. Additionally, energy that
would otherwise be dissipated during braking can be captured and
stored in the battery. The stored energy may be used later,
allowing the engine to produce less power than instantaneously
required for propulsion and thereby consuming less fuel.
SUMMARY OF THE DISCLOSURE
[0006] An electro-magnetically actuated clutch includes a
non-rotating electromagnet coil, a toothed inner race, an outer
race, and a magnetically conductive pawl. The toothed inner race,
which is supported for rotation about the coil, has left and right
magnetically conductive rings which are magnetically separated from
one another. The outer race, which may be magnetically
non-coductive, is supported for rotation about the inner race. The
pawl is supported for rotation with the outer race and is pivotable
into engagement with the left and right rings in response to
current in the coil. Both rings may have teeth. The teeth of one of
the rings may be offset from the teeth of the other ring such that
a majority of the engagement force is distributed to one ring.
[0007] A clutch includes an electromagnetic coil, left and right
magnetically conductive rings, a race supported for rotation with
respect to the rings, and a magnetically conductive pawl. The
electromagnetic coil may be non-rotating while the rings and the
race are supported for rotation. The left and right rings each have
a cylindrical surface adjacent to the coil and a toothed surface
opposing the cylindrical surface. The electromagnetic coil may be
radially inside the rings. The left and right rings are
magnetically separated from each other but may be fixedly coupled
to one another. The race is supported for rotation with respect to
the rings and may be radially outside the rings. The pawl is
pivotable with respect to the race into engagement with the left
and right rings in response to current in the coil.
[0008] A transmission includes an electromagnetic coil, left and
right magnetically conductive rings, an outer race, and a
magnetically conductive pawl. The coil may be fixed to a
transmission case. The rings are both fixedly coupled to an input
shaft and are magnetically separated from one another. The outer
race is supported for rotation with respect to the input shaft. The
pawl is supported for rotation with the outer race and is pivotable
into engagement with the left and right rings in response to
current in the coil.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic diagram of a gearing arrangement for a
hybrid electric powertrain.
[0010] FIG. 2 is a pictorial view of an electro-magnetically
actuated clutch suitable for use in the gearing arrangement of FIG.
1.
[0011] FIG. 3 is a cutaway view of the clutch of FIG. 2.
[0012] FIG. 4 is an exploded view of the clutch of FIG. 2.
[0013] FIG. 5 is a cross section of the clutch of FIG. 2.
[0014] FIG. 6 is a detailed cross-sectional view of the clutch of
FIG. 2 in a disengaged state.
[0015] FIG. 7 is a detailed cross-sectional view of the clutch of
FIG. 2 in an engaged state.
DETAILED DESCRIPTION
[0016] Embodiments of the present disclosure are described herein.
It is to be understood, however, that the disclosed embodiments are
merely examples and other embodiments can take various and
alternative forms. The figures are not necessarily to scale; some
features could be exaggerated or minimized to show details of
particular components. Therefore, specific structural and
functional details disclosed herein are not to be interpreted as
limiting, but merely as a representative basis for teaching one
skilled in the art to variously employ the present invention. As
those of ordinary skill in the art will understand, various
features illustrated and described with reference to any one of the
figures can be combined with features illustrated in one or more
other figures to produce embodiments that are not explicitly
illustrated or described. The combinations of features illustrated
provide representative embodiments for typical applications.
Various combinations and modifications of the features consistent
with the teachings of this disclosure, however, could be desired
for particular applications or implementations.
[0017] A group of rotating elements are fixedly coupled to one
another if they are constrained to rotate as a unit in all
operating conditions. Rotating elements can be fixedly coupled by
spline connections, welding, press fitting, machining from a common
solid, or other means. Slight variations in rotational displacement
between fixedly coupled elements can occur such as displacement due
to lash or shaft compliance. In contrast, two rotating elements are
selectively coupled by a shift element when the shift element
constrains them to rotate as a unit whenever it is fully engaged
and they are free to rotate at distinct speeds in at least some
other operating condition. Two rotating elements are coupled if
they are either fixedly coupled or selectively coupled. Two
rotating elements are driveably connected if a series of gears and
shafts is capable of transmitting power from one to the other and
establishes a fixed speed ratio between the two elements.
[0018] FIG. 1 schematically illustrates a kinematic arrangement for
a power-split type hybrid electric vehicle. Power is provided by
engine 10 which is fixedly coupled to planet carrier 12 via
transmission input shaft 11. A set of planet gears 14 are supported
for rotation with respect to carrier 12. Sun gear 16 and ring gear
18 are each supported for rotation about the same axis as carrier
12 and each mesh with the planet gears 14. Generator 20 is fixedly
coupled to sun gear 16. Layshaft gear 22 is fixedly coupled to ring
gear 18 and meshes with layshaft gear 24. Layshaft gear 24 is
fixedly coupled to layshaft gears 26 and 28 via shaft 30. Layshaft
gear 32 meshes with layshaft gear 28 and is fixedly couple to motor
34. Layshaft gear 26 meshes with layshaft gear 36 which is the
input to differential 38. Differential 38 drives wheels 40 and 42
allowing slight speed differences as the vehicle turns a
corner.
[0019] Generator 20 and motor 34 are both reversible electric
machines. The terms generator and motor are used merely as labels.
Both machines are capable of converting electrical power to
mechanical power or converting mechanical power to electrical
power. For example, each machine may be a synchronous motor in
combination with a three phase inverter. Both machines are
electrically connected to battery 44. In some circumstances, engine
10 may generate more power than is delivered to the vehicle wheels
40 and 42 with the excess power stored in battery 44. In other
circumstances, power may flow from battery 44 permitting engine 10
to produce less power than the instantaneous demand of the vehicle.
For example, the engine 10 may be off while power to propel the
vehicles comes from battery 44.
[0020] The powertrain of FIG. 1 can be operated in a continuously
variable mode with battery 44 neither providing nor absorbing
power. The torque applied to generator 20 and the torque applied to
layshaft gear 22 are both related to the torque generated by engine
10 based on the number of teeth on sun gear 16 and the number of
teeth on ring gear 18. Specifically,
T gen = N sun N sun + N ring T eng ##EQU00001## T gear 22 = N ring
N sun + N ring T eng ##EQU00001.2##
where T.sub.eng is the torque generated by engine 10, T.sub.gen is
the torque absorbed by the generator 20, T.sub.gear22 is the torque
absorbed by gear 22, N.sub.sun is the number of teeth on sun gear
16, and N.sub.ring is the number of teeth on ring gear 18. The
engine speed is a weighted average of the generator speed and the
speed of gear 22.
.omega. eng = N sun N sun + N ring .omega. gen + N ring N sun + N
ring .omega. gear 22 ##EQU00002##
[0021] When the vehicle is moving slowly, gear 22 rotates slowly
and generator 20 rotates faster than engine 10. Power generated by
the engine is split by the planetary gear set. A portion of the
power is transmitted mechanically to shaft 30 from carrier 12 to
ring gear 18 to gear 22 to gear 24. The remaining power is
transmitted from sun 16 to generator 20 which converts the power to
electrical power. Motor 34 converts the electrical power to
mechanical power which is transmitted to shaft 30 by gear 32 and
28. Although both power transfer paths are subject to some
parasitic losses, conversions between electrical power and
mechanical power typically involve more power loss than purely
mechanical transfer. As the ratio of the speed of shaft 30 to the
speed of engine 10 increases, a point is reached at which generator
10 is stationary. At this ratio, all of the power is transferred
mechanically. At higher overdrive ratios, generator 20 rotates in
the opposite direction as engine 10 and acts as a motor. Power
circulates from generator 20 through the mechanical power flow path
to shaft 30, through gears 28 and 32 to motor 34 which acts as a
generator. The parasitic losses associated with the circulation of
power tend to make operation at overdrive ratios inefficient.
[0022] The powertrain of FIG. 1 includes an additional power flow
path to provide efficient power transfer at overdrive speed ratios.
Specifically, layshaft gear 46 is supported for rotation about
transmission input shaft 11. Layshaft gear 48 is fixedly coupled to
shaft 30 and meshes with layshaft gear 46. Clutch 50 selectively
couples layshaft gear 46 to shaft 11. When clutch 50 is engaged,
power is transferred mechanically from engine 10 to shaft 30 via
gears 46 and 48. In this fixed ratio mode of operation, battery 44
can provide additional power via either generator 20 or motor 34 or
can be charged via either electrical machine. Use of the fixed
ratio mode for steady state cruising significantly reduces fuel
consumption because both the engine and the transmission operate
efficiently.
[0023] Since clutch 50 is the only clutch in the powertrain of FIG.
1, use of a hydraulically actuated clutch would require addition of
a pump and valve body. Therefore, a different method of actuating
clutch 50 is desired. FIGS. 2 through 4 illustrate an
electro-magnetically actuated pawl clutch suitable for selectively
coupling gear 46 to shaft 11.
[0024] FIG. 2 is a pictorial view of an electromagnetic clutch
suitable for use in the hybrid powertrain of FIG. 1. An inner race
includes two rings 52 and 54. As applied to the hybrid powertrain
of FIG. 1, each of these rings is fixedly coupled to input shaft
11. An outer race 54 is fixedly coupled to gear 46. A plurality of
pawls 58 are retained in the outer race and rotate with the outer
race. In the disengaged state illustrated in FIG. 2, the pawls are
tucked into the outer race so as not to contact the inner race. In
this state, relative rotation between the inner race and the outer
race in either direction may occur. Springs may bias the pawls
toward this disengaged position. The outer surfaces of the rings of
the inner race have teeth 60. When the clutch is in an engaged
state, the pawls 58 pivot into engagement with this these teeth.
The tooth profile is ramped on one side such that relative rotation
is permitted in one direction but not in the other. In the
orientation shown in FIG. 2, when the inner race rotates clockwise
relative to the outer race, the ramped profile of the teeth push
the pawl back toward outer race. However, the teeth preclude
counter-clockwise rotation of the inner race relative to the outer
race. (A few degrees of rotation may occur before a pawl
catches.)
[0025] FIG. 3 shows a cut-away pictorial view of clutch 50. The
left and right inner race rings are joined by a plurality of posts
62. The pawls are retained axially in the outer race 56 by a
retainer 64. An electro-magnetic coil is radially inside and
concentric with the inner and outer races. The coil includes a
magnetically conductive coil housing 66 having a U-shaped cross
section. Electrical windings 68 are wrapped circumferentially in
the gap of the coil housing. When the windings are energized with
current, a magnetic field is established in the coil housing. One
side of the U is axially aligned with the left inner race ring
while the other side of the U is axially aligned with the right
inner race ring. The radial clearances between the coil housing 66
and the left and right rings 54 and 52 are set as small as
practical consistent with free rotation. Rings 52 and 54 are made
of magnetically conductive material while the posts 62 separating
them are made of magnetically non-conductive material. Thus, when
the coil is energized, one ring becomes a magnetic North pole and
the other ring becomes a magnetic South pole. The pawls are made of
a magnetically conductive material such that they are attracted to
the left and right rings when the coil is energized, engaging the
clutch. Once the pawls come into contact with the left and right
rings, they complete the magnetic circuit. With the magnetic
circuit thus complete, other than the two small air gaps, little
power is required to maintain the pawls in this state. FIG. 4 is an
exploded view showing the assembly of clutch 50.
[0026] FIG. 5 is a cross section of the clutch as installed in the
kinematic arrangement of FIG. 1. The coil 66 is fixedly coupled to
a transmission housing 70. A stationary coild is advantageous
because no slip rings or other measures are required to convey
electrical power to the windings. The inner race is fixedly coupled
to input shaft 11. Notice that left ring 54 is wider than right
ring 52. The two rings may be circumferentially offset slightly
such that the torque is reacted entirely or almost entirely through
the left ring 54. In this way, the non-magnetic posts 62 do not
need to transmit appreciable torque. Right ring 52 serves a
magnetic function but does not carry significant mechanical load.
Outer race 56 is fixedly coupled to gear 46 which is supported for
rotation about input shaft 11. In alternative embodiments, the
toothed rings may form an outer race and the pawls may be retained
in an inner race. In that case, the coil would be located radially
outside the outer race. The tooth profile would be on the radially
inward surface of the outer race while a cylindrical surface of
each ring faces outward adjacent to the coil. FIGS. 6 and 7 show
the pawl in the disengaged and engaged positions respectively.
[0027] Friction clutches are capable of transmitting torque between
elements that are rotating at different speeds. The transmitted
torque tends to bring the components to the same speed. A pawl
clutch, on the other hand, selectively couples elements by
establishing a positive engagement as opposed to frictional
engagement. As a result, a pawl clutch can only transmit torque
between elements that are rotating at the same speed. Engaging a
pawl clutch when the elements are at different speeds would produce
a sudden change in speeds which is likely to be unpleasant to
vehicle occupants and may even cause transmission components to
fail. Therefore, control of element speeds at the time of clutch
engagement is important.
[0028] When the vehicle is at low speed, the transmission of FIG. 1
is operated in the continuously variable mode. No current is
supplied to coil 68 so clutch 50 is disengaged. When the controller
determines that operation in the fixed ratio overdrive mode is
preferable, the controller first transitions to a more overdrive
speed ratio than the fixed ratio. Then, the controller commands
current to coil 68 causing the pawls to pivot. The clutch does not
engage immediately because gear 46 is rotating faster than shaft 11
in this condition. The controller, still controlling the speed
ratio in the continuously variable mode, gradually permits the
engine speed to increase. Once the fixed ratio is reached, clutch
50 will engage.
[0029] While exemplary embodiments are described above, it is not
intended that these embodiments describe all possible forms
encompassed by the claims. The words used in the specification are
words of description rather than limitation, and it is understood
that various changes can be made without departing from the spirit
and scope of the disclosure. As previously described, the features
of various embodiments can be combined to form further embodiments
of the invention that may not be explicitly described or
illustrated. While various embodiments could have been described as
providing advantages or being preferred over other embodiments or
prior art implementations with respect to one or more desired
characteristics, those of ordinary skill in the art recognize that
one or more features or characteristics can be compromised to
achieve desired overall system attributes, which depend on the
specific application and implementation. As such, embodiments
described as less desirable than other embodiments or prior art
implementations with respect to one or more characteristics are not
outside the scope of the disclosure and can be desirable for
particular applications.
* * * * *