Note: Descriptions are shown in the official language in which they were submitted.
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INSTALLATION SHAFT ASSEMBLY
Field of the Invention
[0001] The present invention relates generally to tensioners, and more
particularly, to
an installation shaft assembly for a tensioner.
Background of the Invention
[0002] Belt tensioners are known in the art for use in automotive applications
and are
utilized to apply a load to the belt or chain to maintain a desired amount of
tension on
the belt drive to drive various components attached to the belt system.
Additionally,
belt tensioners are utilized in a non-synchronized belt drive system to
prevent belt
slippage and power transmission loss. Tensioners are commonly utilized in
accessory
drive systems, and timing belt or timing chain systems of an automobile.
[0003] Typical belt tensioners include a tensioner arm, which is fitted with
an idler
pulley that is mounted on a ball bearing assembly. The tensioner arm if
pivotally
mounted on a pivot shaft. A coil spring is wrapped coaxially around the pivot
shaft
for pre-tensioning the tensioner arm enabling the idler pulley to exert a
force on the
belt. In this manner, the force of the coil spring applies a load to the belt
while the
idler pulley deflects and takes up slack in the length of the belt or chain.
[0004] In certain applications, there is a limited amount of space that is
available for
mounting the tensioner on the engine. This is particularly true for timing
belt
applications where volume on the engine is at a premium. In these
applications, a
double eccentric type of tensioner is commonly used. A first eccentric has the
same
function as the tensioner arm. A second eccentric or installation shaft
adjusts the
tensioner during installation to pre-apply the desired load on the belt.
[0005] When the tensioner is installed on an engine, the position of the
tensioner
needs to be adjusted to correspond with a nominal installation. The tensioner
is
fixedly mounted to an engine surface after proper orientation and positioning
of the
tensioner. An adjusting or installation shaft assembly is utilized to position
the
tensioner, as well as to maintain a proper belt tension. Examples of belt
tensioners for
motor vehicles and methods for installing the belt tensioner to the engine
include:
United States Patent Nos. 5,919,107; 6,149,542; 6,364,795; 6,375,588; and
6,464,604.
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[0006] At present, installation shafts can be manufactured as a one piece
construction,
although most are of two piece construction, utilizing known methods such as
injection molded sintered metal, die cast aluminum, and die cast zinc. While
these
parts seem simple enough, die casting and pressing shapes such as the
installation
shaft, which have a very long length to diameter ratio, are difficult to make,
require
expensive tooling, and have extremely high tooling capital and maintenance
costs
associated with them.
[0007] Alternatively, installation shafts can made employing a two piece
stamped
steel design. An installation plate and a cylindrical guide tube are staked
together to
form the installation shaft. The staking tools, required to join or stake the
upper
installation plate to the lower guide tube, are again relatively expensive,
and require
detailed set-up costs, as well as constant maintenance order to maintain joint
integrity.
[0008] Further, staked installation shafts may have inconsistencies with
respect to
engagement of the multiple pieces due to variations in part size, and
variations
introduced from the staking operation. Such variations may result in differing
forces
needed when installing the tensioner onto an engine, resulting in improper
installation
or damage to the tensioner.
[0009] While the process and theory of staking seems simple enough, it
ultimately
requires that the material to be joined be struck (impacted) and deformed just
enough,
but not too much, in order to hold a part together, and to maintain the
required
clamping force without fracturing or jamming surrounding components. The
clamping
force of a stake can vary wildly with minor variations in material properties
(carbon
content, hardness, grain structure, flow characteristics), tolerance stack-up
of each
component within the joint, which determines ultimate striking force,
compression
depth, and material flow characteristics, as well as other factors such as
staking tool
condition, press condition and deflection, initial press set-up, and a myriad
of other
factors.
[0010] If an eccentric installation shaft is staked too hard within the pivot
shaft, too
much material will be displaced by the staking die, or punch, and the
eccentric shaft
will become fused to the pivot shaft. The eccentric will now either stick when
rotated,
or not rotate at all when turned with a reasonable amount of force, ultimately
failing
to rotate freely. When installed onto the engine, an operator or installation
machine
(i.e. an automated torque wrench) will apply a force to the eccentric
installation shaft
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via an installation tool, in order to try to push or rotate the tensioner into
the belt, and
to align the tensioner arm pointer to the nominal belt mark indicated on the
stamped
steel base plate. If the installation eccentric does not rotate (i.e. is fully
seized) within
the pivot shaft due to too high a staking force, either the installation
operation will
cease when the torque limit is exceeded, or if no such limits exist, the
installation
plate can be plastically deformed, or worst, sheared off from the vertical
tube portion.
If the tensioner partially binds (i.e. is partially seized) within the pivot
shaft, the
installation procedure will overshoot and undershoot the nominal belt mark, as
the
majority of torque applied to the installation eccentric will be directed to
overcoming
sporadic friction between the eccentric and pivot shaft interface, and not be
employed
in forcing the tensioner into the belt.
[0011] If the eccentric installation shaft is staked too lightly, too little
material will be
displaced by the staking die, or punch, and the eccentric installation shaft
will slide
freely from the pivot shaft, and allow the tensioner to fall apart either
during shipping,
during handling, or during actual installation onto the engine. A tensioner
"explosion"
during installation may shut the engine assembly line down, as each part would
them
have to be located and identified, to insure that it has not become trapped
within the
timing drive system where belt tooth skip or chain skip would result if a part
were to
be ingested by the timing drive..
[0012] Therefore, it remains desirable to provide a tensioner installation
shaft that is
economical to manufacture, as well as provides a reliable and efficient means
for
installing and positioning a tensioner onto an internal combustion engine.
Summary of the Invention
[0013] The disadvantages of the prior art may be overcome by providing a
tensioner
assembly with a one piece stamped installation shaft assembly.
[0014] It is desirable to provide an installation shaft assembly that is
stamped from a
single sheet of metal and formed to incorporate both the guide tube and the
installation plate.
[0015] According to one aspect of the invention there is provided a tensioner
for a
synchronous or non-synchronous drive system of a motor vehicle engine. The
tensioner has a mounting plate with a cylindrical pivot shaft and an anchor
spaced
from the pivot shaft. A tensioner arm is rotatable mounted on the pivot shaft.
The
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tensioner arm has a first axis of rotation. A pulley is rotatably supported on
the
tensioner arm. The pulley has a second axis of rotation spaced from and
extending
generally parallel to the first axis of rotation. A coil spring operably
extends between
the mounting plate and the tensioner arm to bias the tensioner arm in a take
up
direction. An installation shaft is rotatably mounted within the pivot shaft
and
rotatable about the first axis of rotation. The installation shaft has an
aperture for
receiving a bolt for affixing the tensioner to a motor vehicle engine. The
aperture has
a center that is offset from the first axis of rotation. The installation
shaft has a guide
portion and an integrally formed plate portion. The plate portion extends
transversely
from the guide portion. The guide portion extends into the pivot shaft. A
distal end
of the guide portion engages the pivot shaft in a manner enabling rotational
movement
and which prevents axial movement therebetween. The guide portion is
configured to
maintain offsetness of a distal end of the guide portion as the offsetness of
the center
of the aperture when the tensioner is installed on an engine.
Brief Description of the Drawings
[0016] Exemplary embodiments of the invention will now be described in
conjunction with the following drawings wherein like numeral represent like
elements, and wherein:
[0017] Figure 1 is a perspective view of a tensioner assembly incorporating
the
installation shaft assembly according to one embodiment of the invention;
[0018] Figure 2 is a plan view of the tensioner assembly of Figure 1;
[0019] Figure 3 is a partially exploded view of the tensioner assembly and
installation
shaft assembly according to one embodiment of the invention;
[0020] Figure 4 is a partial fragmentary, exploded perspective view of the
installation
shaft assembly according to one embodiment of the invention;
[0021] Figure 5 is a perspective view of the installation shaft prior to
forming; and
[0022] Figure 6 is a perspective view of another alternative embodiment of the
installation shaft of the present invention;
[0023] Figure 7 is a second embodiment of a tensioner incorporating
installation shaft
of the present invention, wherein the tensioner has the distal end of the coil
spring
anchored to the engine;
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[0024] Figure 8 is schematic view of an initial step of assembly of a
tensioner of
incorporating installation shaft of Figure 6;
[0025] Figure 9 is a schematic view of a subsequent step of assembly following
Figure 8; and
[0026] Figure 10 is a schematic view of a finished assembly.
Detailed Description of the Preferred Embodiments
[0027] Referring to Figures 1-3, a tensioner is shown at 10 for tensioning a
belt
driven by a motor vehicle engine. The tensioner 10 includes a base plate 20, a
pivot
shaft 34, a tensioner arm 16, a pulley 12 and a bearing 14. The pulley 12 is
rotatably
supported by ball bearing race assembly 14. The bearing 14 and pulley 12 are
rotatably mounted on cast aluminum tensioner arm 16 having an eccentric bore
18
enabling translation of the pulley 12 to tension the belt. Tensioner arm 16
rotates
about a first axis of rotation defined by the center of the eccentric bore 18.
The pulley
12 rotates about a second axis of rotation that is spaced from and extends
parallel to
the first axis of rotation.
[0028] Base plate 20 is seated adjacent a base of the tensioner arm 16 for
mounting
and aligning the tensioner 10 on the engine. Base plate 20 is formed to
incorporate a
tab 11 having features representing the free arm stop position, the load stop
position,
and optionally various belt marking positions, namely nominal belt mark,
change belt
mark, as well as a tang 21 for fixing the end of coil spring 15. In addition,
the
mounting plate 20 has an anchor 23 extending generally perpendicular to the
plane of
the mounting plate 20 and configured to engage a recess in the engine block to
maintain orientation of the tensioner 10. Other forms of anchors are well
known in
the art and include a two prong structure that engages a bolt or post on the
engine.
[0029] Coil spring 15 acts between the mounting plate 20 and the tensioner arm
16 to
bias the tensioner arm 16 and pulley 12 in a take up direction into engagement
with
the belt. The tensioner arm 16 includes a pointer 22 that moves pivotally
relative to
the base plate 20 for alignment with a nominal position indicator on the base
plate 20
=
during installation of the tensioner 10 on the engine.
[0030] Referring to Figure 4, the pivot shaft 34 includes an elongated
cylindrical
shank portion 36 defining a center bore 38 extending between a proximal end 40
and
a distal end 42. A collar 44 projects radially from the proximal end 40 of the
shank
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portion 36. A counter bore 46 is formed in the proximal end 40 of the shank
portion
36 to define a radial shoulder 48. The tensioner arm 16 has an inner sleeve or
pivot
bushing 45 that is made from an organic polymeric material, such as Nylon,
which is
then is mounted on the shank portion 36. In this manner, tensioner arm 16 is
able to
rotate relative to the base 20.
[0031] The tensioner 10 has an installation shaft 32 for assembling the
tensioner 10
and for facilitating installation of the tensioner 10 onto the engine and
tensioning of
the belt. The installation shaft 32 of the present invention is preferably
formed as a
one piece stamped steel member and includes a generally planar plate portion
50
connected to a generally C-shaped guide portion 52 by a bent neck portion 54
extending therebetween. The plate portion 50 includes a key hole 56,
preferably
hexagonally shaped, and a bolt hole 58 for receiving a mounting bolt 59
therethrough.
The key hole 56 is spaced from the bolt hole 58, providing leverage to more
easily
rotate installation shaft 32 during installation. Bolt hole 58 has a diameter
that is less
than the inside diameter of center bore 38 of pivot shaft 34. Plate portion 50
has two
tabs 51, 53 which maintains the orientation of plate portion 50 during
operation.
[0032] The guide portion 52 extends generally perpendicular to the plate
portion 50
and extends arcuately about the first axis of rotation defined by the bolt
hole 58. The
axis of rotation of the guide portion 52 defined by the center of center bore
38, the
first axis of rotation which is offset from the axis of the center of the bolt
hole 58.
The outside diameter of the guide portion is slightly less than the inside
diameter of
the center bore 38 of the pivot shaft 36, enabling the installation shaft 32
to fit within
and frictionally engage the center bore 38 and rotate therein.
[0033] A pair of diagonally opposed flexible locking fingers 60 extend
longitudinally
from the end of the guide portion 52 to a distal end 62. The distal end 62 of
each
locking finger 60 includes a radially projecting hook portion 64 for engaging
with the
shoulder 48 on the pivot shaft 34. The locking fingers 60 are biased to engage
with
the shoulder in a snap fit and lock the installation shaft 32 to the pivot
shaft 34. The
locking fingers 60 thus hold the installation shaft 32 to the tensioner
assembly 10
during transport and assembly onto the vehicle engine.
[0034] The installation shaft 32 further includes a tab 66 positioned between
the
locking fingers 60 and similarly extending longitudinally from the end of the
guide
portion 52. An embossment 68 projects radially inwardly from the tab 66 into
the
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axis defined by the bolt hole 58. The height of the embossment 68 is of the
order of
the amount of offsetness between the center of the bolt hole 58 and the center
bore 38.
The embossment 68 engages the bolt 59 to ensure that the perpendicularity of
the
installation shaft 32 as the installation shaft 32 is rotated during the
installation
process.
[0035] The one piece installation shaft 32 of the present invention is formed
from a
single unitary member, preferably made of steel, as shown in Figure 5, which
is
stamped and bent, or formed, into the installation shaft 32 as shown in Figure
4. The
stamping and forming processes of the one piece installation shaft are cost
effective
and eliminate the potential for failure in the joining of the plate portion 50
to the guide
portion 52. Furthermore, the critical distance between the bottom of the=
plate portion
50 and the hook structure 64 of the fingers 60 can be readily controlled in
the
stamping and forming process to ensure proper alignment and engagement with
the
ledge 48 of the pivot shaft 34 during assembly.
[0036] Referring again to Figure 3, the installation shaft 32 is inserted into
the bore
18 in the tensioner 10 from the side opposite the pivot shaft 34. The guide
portion 52
is inserted through the center bore 38 of the pivot shaft 34 until the hook
structure 64
of the flexible locking fingers 60 engage the shoulder 48 of the pivot shaft
34 locking
the shafts 32, 34 together. The flexible locking fingers 60 project slightly
radially
outwardly and are flexed inwardly by engagement with the inside surface of the
center bore 38 during assembly, providing a "push and click" assembly
procedure.
The counter bore 46 allows the fingers 60 to spring radially outwardly for
engagement
with the shoulder 48 to automatically interlock the installation shaft 32 and
pivot shaft
34.
[0037] The stamped one piece installation shaft 32 provides controlled
tolerances, in
particular, providing a consistent predetermined distance between the
underside of the
plate portion 50 and the hook structure 64 for proper engagement with the
shoulder 48
on the pivot shaft 34. It is desirable to provide this predetermined distance
slightly
greater than the distance between the underside of the collar 44 and the
distal end 42
of the pivot shaft 34 in order to allow the installation shaft 32 to rotate
relative to= the
pivot shaft 34 for proper installation of the tensioner 10 onto the engine.
[0038] To assemble a tensioner 10 of the present invention, the steel mounting
plate
20 is stamped. The pivot shaft 34 and the base plate 20 are staked together to
form a
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permanent, fixed joint. A plastic spring support 13 and coil spring 15 are
then inserted
loosely over the pivot shaft 34. The spring support 13 cradles the end of the
coil
spring 15 and provides frictional damping. The lowermost end of the coil
spring 15 is
hooked into the tang 21 of the base plate. The tensioner arm 16, pivot bushing
45,
bearing 14 and pulley 12 are then installed over the pivot shaft. The
tensioner arm 16
is rotated to locate the upper spring tang of the coil spring 15 until the
coil spring 15
engages a hookup feature in the tensioner arm 16. The coil spring 15 is wound
in the
coil direction (i.e. winds the spring "up"), to the point at which the
tensioner arm
= pointer 22 corresponds to the NOMINAL BELT MARK on the base plate. The
tensioner arm 16 is then pushed down, so that the tensioner arm 16 rests on
the spring
support 13. A plastic thrust washer 25 is positioned over the top of the pivot
shaft 34.
The eccentric installation shaft 32 is inserted into the central bore 38 of
the pivot shaft
34. The installation plate 50 is pressed against the thrust washer 25 to hold
the
tensioner assembly 10 together axially. Optionally, a staking tool or mandrel
is
inserted into the base of the pivot shaft 34 to deform the fingers 60 and/or
tab 66 to
permanently retain the eccentric shaft 32 within the pivot shaft 32 and hold
the
tensioner assembly 10 together axially while allowing relative rotational
movement
between the installation shaft 32 and the pivot shaft 34. The coil spring 15
urges the
tensioner arm 16 to unwind and abut against the FREE ARM belt stop.
[0039] Referring to Figure 7, a second embodiment of a tensioner incorporating
the
installation shaft 32 of the present invention. In this embodiment, the pivot
shaft is
mounted directly onto the engine block without the aid of a mounting plate.
The
remote end of the coil spring 15' is anchored to the engine. In this view, the
embossment 68 clearly illustrates the support that is provided to the bolt 59
to
properly maintain vertical alignment of the tensioner.
[0040] Referring to Figure 6, there is shown another alternative embodiment of
the
installation shaft 32 of the present invention, wherein like numerals
represent the
same or similar parts. The installation shaft 32 remains a one piece stamped
member
having an integrally formed plate portion 50 and guide portion 52
interconnected by a
bent neck portion 54. The guide portion 52 is bent to into a C-shape forming
an
arcuate guide sleeve. An embossment 68 projects radially from the guide
portion 52
into the axis defined by the bolt hole 58. However, the installation shaft 32
of the
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=
alternative embodiment does not include the locking fingers 60 extending from
the
guide portion 52.
[0041] Referring to Figures 8 to 10, a staking tool 61 is required to deform
the distal
end of the guide portion 52 to form a circumferentially extending hook
structure 64'
or structures 64' to interconnect the installation shaft 32 and the pivot
shaft 34. The
interconnection allows relative rotational movement between installation shaft
32 and
the pivot shaft 34 while ensuring that the installation shaft is axially
locked onto the
pivot shaft 34, preventing accidental disassembly.
[0042] In each of the embodiments, the tensioner 10 is now fully assembled and
held
together by the interlocking connection between the installation shaft 32 and
pivot
shaft 34 for shipping and installation onto the engine of the vehicle.
Finally, a fully
detailed explanation of the installation and adjustment of the tensioner 10 is
set forth
by way of example in United States Patent No. 5,919,107.
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