U.S. patent application number 10/043749 was filed with the patent office on 2003-07-10 for magnetorheological fluid fan drive design for manufacturability.
Invention is credited to Kennedy, Lawrence Craig, Smith, Anthony L..
Application Number | 20030127297 10/043749 |
Document ID | / |
Family ID | 21928693 |
Filed Date | 2003-07-10 |
United States Patent
Application |
20030127297 |
Kind Code |
A1 |
Smith, Anthony L. ; et
al. |
July 10, 2003 |
MAGNETORHEOLOGICAL FLUID FAN DRIVE DESIGN FOR MANUFACTURABILITY
Abstract
An improved magnetorheological (MR) fluid fan drive design is
disclosed. A critical area in the design of such fan drives is the
gap for MR fluid between the rotor ring and the corresponding
structure of the stator. The stator member must confine the MR
fluid in the gap and the applied magnetic field for the fluid and
the field coil close to it. In this disclosure a ferrous alloy
stator insert is made as one piece and cast within a larger
aluminum alloy stator body. A slot for the rotor ring is cut
through stator insert separating it into two pieces that remain
supported by the aluminum body. The magnetically permeable insert
pieces confine the fluid and the magnetic field at the fluid gap
around the rotor, and one of the stator insert pieces supports the
field coil next to the gap.
Inventors: |
Smith, Anthony L.; (Troy,
MI) ; Kennedy, Lawrence Craig; (Commerce Township,
MI) |
Correspondence
Address: |
Generl Motors Corporation
Legal Staff
Mail Code 482-C23-B21
P.O. Box 300
Detroit
MI
48265-3000
US
|
Family ID: |
21928693 |
Appl. No.: |
10/043749 |
Filed: |
January 9, 2002 |
Current U.S.
Class: |
192/21.5 ;
192/58.2 |
Current CPC
Class: |
F16D 37/02 20130101;
F16D 2037/004 20130101; F16D 37/008 20130101 |
Class at
Publication: |
192/21.5 ;
192/58.2 |
International
Class: |
F16D 037/02 |
Claims
1. A viscous fluid, fan clutch for a fan drive assembly, said
viscous fluid clutch comprising a rotor assembly comprising (i) an
input shaft having a fan drive end, (ii) a cast metal hub attached
to said shaft at said fan drive end, coaxial therewith, and
extending radially to a circular perimeter and (iii) a ferrous
metal, rotor ring having a first edge incorporated into the
perimeter of said cast hub, coaxial with said input shaft, and
extending axially to a second edge in a direction from the drive
end of said input shaft; a bearing having inner and outer races and
fixed on its inner race to said input shaft; a circular fan housing
coaxial with said input shaft and fixed to the outer race of said
bearing, said housing extending radially past said rotor ring and
defining a viscous fluid gap between said housing and rotor; and a
fan drive cover assembly comprising (i) an annular non-ferrous
metal fan cover body with an edge in sealing engagement with said
fan housing outboard of said rotor, and (ii) a circular ferrous
metal fan drive cover insert having a circumferential surface in
sealing engagement with the inner annular surface of said fan cover
body, and a flat surface spaced axially from the end of said input
shaft; said fan cover insert initially being made as a single
piece, said nonferrous fan cover body being cast against the
circumferential surface of said fan cover insert in forming said
fan drive cover assembly and said assembly being thereafter
machined axially through the radially outer portion of said fan
cover insert to separate a fan cover insert ring portion from a fan
cover insert wheel portion and to form a slot through said fan
cover insert into said fan cover body to receive said rotor and
thereby to define a gap on both radial surfaces and around said
second edge of said rotor between slot surfaces of said fan cover
insert for a viscous fluid.
2. A viscous fluid, fan clutch drive assembly as recited in claim 1
comprising integral portions on each of said fan cover insert ring
portion and said fan cover wheel portion for mechanical
interlocking with said cast fan cover body.
3. A viscous fluid, fan clutch for a fan drive assembly as recited
in claim 1, further comprising an annular coil body with coil
windings for generating an electromagnetic field in said gaps, said
coil body being sealed against said flat surface of said insert
with a coil cover and spaced from said end of said input shaft and
coaxial therewith.
4. A viscous fluid, fan clutch for a fan drive assembly as recited
in claim 3 in which said annular coil body comprises a nomnmagnetic
sealing material between said coil cover and said insert body
surface to prevent a magnetic field shunt between said coil cover
and said insert.
5. A viscous fluid fan clutch for a fan drive assembly as recited
in claim 1 in which said ferrous metal rotor ring comprises
discontinuous, central, circumferential slots.
6. A viscous fluid, fan clutch for a fan drive assembly as recited
in claim 5 in which said rotor ring further comprises a perforated
rim for interlocking mechanical and heat transfer contact with said
cast hub.
7. A viscous fluid, fan clutch for a fan drive assembly as recited
in claim 1 in which said circular fan housing engages said hub in a
noncontact labyrinth seal against viscous fluid intrusion into said
bearing.
8. A viscous fluid, fan clutch for a fan drive assembly as recited
in claim 1 in which the sealing engagement between said fan cover
body and said fan housing comprises both a labyrinth seal structure
and a molded seal.
9. A viscous fluid, fan clutch for a fan drive assembly as recited
in claim 1 in which the viscous fluid gap between said fan housing
and said rotor interconnects with the viscous fluid gap at the
outer radial surface of said rotor and said fan drive cover.
10. A viscous fluid, fan clutch for a fan drive assembly as recited
in claim 9 in which said fan housing, fan cover assembly, hub and
rotor cooperate to form a continuous viscous fluid gap around both
inner and outer surfaces of said rotor.
11. A viscous fluid, fan clutch for a fan drive assembly as recited
in any of claims 1-10 in which said viscous fluid comprises a
magnetorheological fluid.
Description
TECHNICAL FIELD
[0001] This invention pertains to making viscous clutch assemblies.
More particularly, this invention pertains to the design of robust
and more readily manufacturable, continuously controllable,
magnetorheological fluid fan drive assemblies.
BACKGROUND OF THE INVENTION
[0002] U.S. Pat. Nos. 5,960,918; 6,032,772; 6,102,177; and
6,173,823, each entitled "Viscous Clutch Assembly," describe
clutches for a vehicle cooling fan assembly that use a
magnetorheological (MR) fluid as the viscous material operating in
a gap between the engine driven rotor and the fan carrying stator.
The assembly further includes a coil for creating an
electromagnetic field in the gap to vary the yield stress of the MR
fluid and, thus, the speed of the fan.
[0003] U.S. Pat. Nos. 5,667,715 entitled "Magnetorheological Fluid"
and 6,149,832 entitled "Stabilized Magnetorheological Fluid
Compositions" describe viscous fluids suitable for use in the
viscous clutch assemblies. Often these fluids comprise suitable,
finely divided iron particles suspended in a nonpolar vehicle. The
fluids are formulated to resist particle separation even under high
separation force applications and they typically function as
Bingham fluids. In an ambient gravitational field, but in the
absence of a magnetic field, they display a shear stress that
increases generally linearly as the shear rate on the fluid is
increased. When magnetorheological Bingham fluids are subjected to
a magnetic field, the shear stress vs. shear rate relationship is
increased so that substantially more shear stress is required to
commence shear of the fluid. This characteristic is very useful in
controlling the transfer of torque between a rotor and stator in a
viscous fluid clutch assembly.
[0004] In engine driven fan drive systems of the type described the
speed of the fan is continuously variable by varying the magnetic
flux in the MR fluid. Such variable speed fan drive assemblies
provide vehicle fuel economy improvement, noise reduction,
powertrain cooling improvement and cost reduction. After evaluation
and testing of fan drive assemblies such as those described in the
above four patents for a specific truck application it is realized
that further improvements could be made. It is an object of this
invention to provide improvements in the design of certain fan
drives for the purpose of their ease of manufacture and robustness
of operation.
SUMMARY OF THE INVENTION
[0005] As described in the "Viscous Clutch Assembly" patents
identified above, a fan drive assembly has an engine driven input
shaft with an attached hub and rotor assembly. This input assembly
applies torque to a fan drive assembly using a viscous fluid,
preferably a magnetorheological fluid such as those described in
the above cited patents. Accordingly, the input and output
structures are designed with complementary rotating portions that
fit closely together with a thin layer of torque transmitting, MR
fluid between them.
[0006] Also positioned close to this fluid gap is an electric coil
for generating a variable magnetic field in the fluid to vary its
yield stress and, thus, the torque transmitted from the input
shaft/rotor assembly to the fan drive. A separate computer based
controller determines the voltage or current flow applied to the
coil. Experience with such fan drive mechanisms reveals the
advantage of careful design of the complementary fluid gap forming
portions of the input and fan drive assemblies and the means taken
to seal in the MR fluid. This invention provides several such
related improvements enhancing the ease with which the fan drive is
made and the robustness of the drive.
[0007] In accordance with a preferred embodiment of the invention,
a viscous fluid clutch for a vehicle cooling fan drive comprises a
driving shaft/rotor assembly enclosed by a fan housing and a fan
cover assembly. The fan housing is carried on the driving torque
input shaft but separated from the shaft with respect to torque
transmission by a bearing. A fan cover assembly that is attached to
the fan housing includes a clutch stator insert that receives the
rotor and the MR fluid for the transmission of torque.
[0008] The fan cover assembly includes a fan cover body, a fan
cover insert and an annular coil body with coil windings. The coil
body is carried on the circular, ferrous metal fan cover insert
that, in turn, is preferably cast in place within the fan cover
body. This assembly is co-axial with the input shaft.
[0009] The fan cover insert has a larger diameter than the coil and
the outer region of the insert contains a slot in which the rotor
is received during assembly of the drive. The slot and the rotor
ring leave gaps on both sides of the rotor for the MR fluid. And
the magnetic permeability of the ferrous composition on both sides
of the slot confines the magnetic field of the coil on the MR fluid
in the gaps.
[0010] One important feature of the invention is the method by
which the fan cover assembly is made. The fan cover insert is made
as a single round, disc-like precursor piece, preferably by hot
forging a steel billet. The fan cover body is cast around the hot
forged insert precursor using a suitable aluminum alloy. Anchoring
features are formed on the fan cover insert to prevent separation
from the cover body. Further processing of this composite part
includes machining a circular slot through the insert for the
rotor. This operation divides the round insert into two parts, both
of which are anchored in the aluminum body portion of the
composite. The separated portions of the insert define a slot for
the rotor and MR fluid and provide magnetically permeable regions
to concentrate the magnetic field in the fluid.
[0011] Additional machining of the fan cover insert provides a
circular channel to receive the coil body and to provide a passage
for the coil leads to a non-rotating assembly for supplying power
to the coil. Additional machining of the fan cover body provides
for improved sealing engagement with the fan housing member.
[0012] Other objects and advantages of the invention will become
more apparent from a detailed description of preferred embodiments
which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a side elevation view, partly in section, of a fan
drive in accordance with the invention.
[0014] FIG. 2 is a side view, in section, of the ferrous metal
(steel) insert, as initially made, of the stator portion of the
drive shown in FIG. 1.
[0015] FIG. 3 is a side view in section of the insert of FIG. 2
cast into an aluminum cover assembly.
[0016] FIG. 4 is a side view, in section, of the cover member of
FIG. 3 after machining.
[0017] FIG. 5 is an assembly view of the fan drive shown in FIG.
1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] Reference is first made to FIG. 1 in which a fan drive
assembly is shown in side sectional view.
[0019] The complete drive assembly is indicated at 10. It comprises
an input shaft 12. Input shaft 12 is suitably made of steel and it
is driven by the engine of the vehicle, e.g., using the water pump
pulley. Accordingly, the speed of the input shaft is engine speed
or proportionately higher in accordance with the pulley ratio for
the water pump.
[0020] Affixed to the end 14 of input shaft 12 is a hub 16 for
rotor 18. Hub 16 has a central rim 20 tightly engaging the end 14
of input shaft 12. Hub 16 then extends radially to enclose the rim
portion 22 of rotor 18. Rotor 18 is preferably made of a
magnetically permeable ferrous material such as a low carbon steel
alloy. The hub is made of aluminum and, as will be described
further below, is cast so that it encloses the rim portion 22 of
rotor 18. The hub 16 also has a plurality of holes 23 to reduce the
weight of the hub.
[0021] Thus, input shaft 12, hub 16 and rotor 18 constitute an
input shaft/rotor assembly for the vehicle fan drive 10.
[0022] Ball bearing 26 is affixed at its inner race 28 to shaft 12.
Affixed to the outer race 30 of ball bearing 26 is an aluminum fan
housing 31. Fan housing 31 has a radially inner rim portion 32
which extends around the front edge of bearing 26. Additionally,
the housing 31 has a neck portion 34 that lies radially and axially
close to, but spaced from, the rim portion 20 of hub 16 to form a
labyrinth sealing path to prevent MR fluid from entering the
bearing 26.
[0023] The fan housing 31 is isolated by bearing 26 from torque
application by input shaft 12.
[0024] Still referring to FIG. 1 a fan cover assembly 38 includes a
cast aluminum fan cover body 40, a fan cover insert 42, coil body
44 and coil cover 46.
[0025] Fan cover insert 42 is preferably made of magnetically
permeable ferrous material such as a low carbon steel alloy. As
seen in FIG. 1 it includes an inner wheel portion 48 and an outer
ring portion 50. As will be described in more detail in connection
with FIGS. 2, 3, and 4, fan cover insert 42 is preferably initially
made as one piece and then machined so that ring portion 50 is
separated from wheel portion 48.
[0026] Fan cover body 40 comprises a plurality of boltholes 52 for
attachment of fan hub 180 and bolts 182 (see also FIG. 5) and fan
blades which are not shown in these figures. Fan housing 31 and fan
cover body 40 each contain corner structures at their area of
contact, generally 54, so as to provide a labyrinth sealing surface
between them and to provide a pilot surface for radial alignment of
fan cover assembly 38 with fan housing 31. Further, fan cover body
40 has a circular pocket 56 to provide for a polymeric sealant 57
to be molded in pocket 56 between fan cover body 40 and fan housing
31.
[0027] In the operation of fan drive assembly 10, rotor 18 rotates
in a slot 60 through fan cover insert 42. The inner wheel portion
48 of fan cover insert 42, thus, defines a gap 62 with the inner
surface of rotor 18, and the outer ring portion 50 of fan cover
insert 42 defines a gap at 64 with the outer surface of rotor
18.
[0028] In the FIG. 1 sectional view, coil body 44 sits in a
circular channel 66 in fan cover insert 42. The other side of coil
body 44 is enclosed by a round coil cover 46. The coil body 44 is
clamped by fan cover insert 42 at area of contact 69 and by coil
cover 46 at area of contact 67. Areas of contact 67 and 69 must
form a seal to prevent leakage of MR fluid. A suitable electrically
insulating, non-magnetic encapsulating material 65 (a commercial
material from DuPont called Zenite is suitable) applied around the
coil body 44 has a protrusion 68 that prevents a shunt in the
magnetic field between the coil cover 46 and the inner wheel
portion 48. Coil cover 46 is spot welded to inner wheel portion 48
at locations not shown.
[0029] In order to simplify its manufacture and to prevent a shunt
in the magnetic field, a series of discontinuous slots 70 are
formed in rotor 18. Furthermore, to improve the bond between the
rotor 18 and the cast hub 16 a series of holes 71 are formed in the
rim portion 22 of rotor 18 to provide interlocking contact between
the cast aluminum hub 16 and the rotor 18 which increases the
mechanical strength between them. Joining these parts by insert
casting, rather than pressing and pinning, for example, improves
heat transfer between them by essentially eliminating contact
thermal resistance.
[0030] Coil body 44 has a diametric arm 72 through which coil leads
73 are led into the central post region 74 of insert 42. Post 74
also carries a bearing. not shown, which carries a non-rotating
slip ring assembly 76. Slip ring assembly includes slip rings,
brushes, brush holders, a retaining clip and a Hall effect sensor
and target to measure fan speed. These features are known and used
in the art and, therefore, are not illustrated to simplify FIG.
1.
[0031] Leading to the slip ring assembly 76 is a tether 78
terminated by an electrical connector 80 through which electrical
power is conducted to slip assembly 76 and the leads 73 of the coil
body 44. The electrical connector 80 interfaces to the vehicle
electrical harness. When electrical power is applied to the coil
body 44 a magnetic field is formed in the gaps 62 and 64 between
the rotor 18 and the insert wheel portion 48 and insert ring
portion 50. A suitable MR fluid 88 is provided in gaps 62, 64 and
its yield stress increased for torque transmission by the
application of the magnetic field. Accordingly, input shaft 12 and
the connected hub 16 and rotor 18 are turning at an input speed
determined by the engine or the water pump pulley system. As power
is provided to the coil body 44, the formation of the magnetic
field causes a yield stress increase in the MR fluid 88 enabling
torque to be transferred between the rotor 18 and fan cover insert
portions 50 and 48 to thereby drive the fan cover assembly 38.
[0032] In addition to the design provisions that provide improved
sealing of the MR fluid 88 within the drive assembly there are
features of the invention which improve the manufacturability of
the fan cover assembly 38.
[0033] A fan cover insert precursor piece 142 is shown at
succeeding stages of its transformation to a fan cover insert 42 in
FIGS. 2, 3, and 4. In FIG. 2 the insert precursor 142 is shown in
its initially formed condition. Preferably, the insert precursor
142 is formed as a single wheel-like piece by hot forging a
suitable steel alloy blank. As thus formed, insert precursor 142
includes a central hub portion 174 which ultimately becomes the
coil lead post 74 of fan cover insert 42. Insert precursor 142 also
includes a lip portion 176 for later contact with a cast around fan
cover body 40. Following hot forging, lip 176 is further formed or
machined outwardly to anchor fan cover body 40 from axial
separation.
[0034] The outer ring portion 150 of insert precursor 142 is formed
with four lugs 152 (two shown in the sectional views of FIGS. 2-4)
spaced at ninety degrees on its circumferential portion for
subsequent interlocking mechanical engagement with cast aluminum
cover body 40. Also formed on the body of fan cover insert
precursor 142 are four fillets 184 (two shown in FIGS. 2-4) spaced
at ninety degrees at the base of lip 176. Like lugs 152, fillets
184 are for locking the later cast, fan cover body precursor 140
from separation from fan cover insert 42.
[0035] Referring now to FIG. 3 the aluminum fan cover body
precursor 140 is seen cast in place around the steel insert
precursor 142. The fan cover body precursor 140 is seen cast around
the lugs 152 on the ring portion 150 of insert precursor 142. The
fan cover body precursor is also cast over fillets 184. Thus,
cast-in-place fan cover body precursor 140 is anchored against
axial and radial separation from fan cover insert precursor 142 by
lugs 152 and fillets 184. The slight outward curvature of lip 176
also serves to retain fan cover body 40 against fan cover insert
42.
[0036] FIG. 4 shows the fan cover insert 42/fan cover body 40
composite structure after machining of the corresponding precursor
portions of FIG. 3. An important difference is that slot 60 has
been cut completely through the single piece precursor body 142
insert body to form fan cover insert ring portion 50 and fan cover
insert wheel portion 48 as separate pieces. The advantage of this
separation is to prevent shunting of the magnetic field in the gaps
62, 64 and to provide end clearance for the rotor 18. As seen in
FIGS. 1 and 4, the now separate ring 50 and wheel 48 portions of
the fan cover insert 42 are held in place by the cast around fan
cover body 40. Upon assembly of the fan drive, slot 60 receives the
rotor structure 18 as shown in FIG. 1.
[0037] The shape of fan cover insert 42 and its higher melting
composition permits the fan cover body 40 to be cast around
portions of it. This is an important feature of the invention
because fan cover insert precursor 142 is formed as a single piece
and fan cover body precursor 140 is cast around it before the
insert precursor 142 is machined into two pieces. The manufacture
of the fan cover insert wheel 48 and insert ring 50 are greatly
simplified because they remain held in place by fan cover member 40
and do not require handling or complex handling effort during
assembly of the fan drive 10. The four lugs 152 help to retain
insert ring 50 in the fan cover member 40 and fillets 184 and lip
176 help to retain fan cover insert wheel 48 in the fan cover
member 40. Also, cutting slot 60 after the insert casting process
allows for more precise geometric tolerances to be maintained with
respect to the relative positions of the slot 60, insert wheel
portion 48 and insert ring portion 50.
[0038] A further comparison of FIGS. 3 and 4 shows the machining of
the precursor composite 142, 140 to form the lead post 74, a
circular channel 66 in insert wheel 48 for the coil body 44 and
sealant pocket 56 in cover 40.
[0039] FIG. 5 is an exploded assembly view of the fan drive
assembly 10. FIG. 5 thus complements the FIG. 1 side sectional view
of the assembly 10. FIG. 5 includes fan hub 180 and self tapping
bolts 182 for attaching hub 180 and blades, not shown, to fan cover
assembly 38, specifically fan cover body 40 at bolt holes 52 (FIG.
1).
[0040] FIG. 5 better illustrates the cooling fins 33 on fan housing
31 and cooling fins 45 on fan cover body 40. Although a "lockup"
condition between rotor and stator is possible the viscous fluid
clutch typically operates with a difference in speed (termed slip)
between the input shaft/rotor assembly and the fan housing/cover
assemblies. When slipping, the shearing of the MR fluid in the gaps
produces heat in the drive assembly and the cooling fins help to
dissipate it.
[0041] During assembly and operation of the fan drive assembly 10
the MR fluid 88 typically stays in gaps 62 and 64 since the MR
fluid 88 is a Bingham fluid which has a non-zero yield stress with
no fluid shear. However, in the event the MR fluid 88 slumps when
the fan drive assembly is not rotating, the reservoir 86 is sized
such that there will not be MR fluid intrusion into the bearing
26.
[0042] Thus, a vehicle fan drive assembly has been developed and
described that is relatively easy to manufacture. It also provides
improved sealing of the MR fluid within the drive and better
confinement of the magnetic field in the region between rotor and
stator where the fluid is intended to function. The invention has
been described in terms of specific embodiments but it is apparent
that other forms of the invention could be adapted by those skilled
in the art. Accordingly the scope of the invention is to be
considered limited only by the following claims.
* * * * *