Note: Descriptions are shown in the official language in which they were submitted.
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1 BACKGROUND OF THE INVENTION
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Field of the Invention
The invention relates to belt tensioning devices and
arrangements, and in particular to hydraulically actu~ted belt
tensioners and the arrangements thereof for use with an éndless
belt of the vehicle accessories drive system. More particularly,
the invention relates to an improved arrangement for tensioning
such a drive belt in which one of the vehicle accessories is
movably mounted to tension the belt which is drivingly engaged
therewith by a hydraulic actuated piston, in combination with a~
7~71:~
1 ratchet-pawl mechanism which limits mo~ement of said one acces-
sory in the opposite nontensioning direction.
Description of the Prior Art
There is the trend today in the automobile industry to
operate the various vehicle accessories, such as the power steer-
ing pump, oil and air pumps, air conditioning and alternator, by
a single endless belt driven by a pulley connected to the engine
crankshaft. This system is referred to as a "serpentine" drive
belt system. To ensure optimum operating efficiency for these
various accessories, it is necessary that the drive belt be
maintained at a predetermined tension to assure efficient per-
formance of the accessories, as well as satisfactory service
life for the belt. Due to the relatively greater length of the
single drive be]t which replaces the heretofore plurality of
smaller belts, there is a greater tendency for the belt to
stretch, which will affect the operating characteristics of the
driven accessories. There-fore, it is desirable that a belt
tensioning device and arrangement be used for these endless
belts to provide reliable service over an extended period of
time and to maintain a constant amount of tension thereon regard-
less of the amount of belt stretch.
Numerous devices and belt tensioning arrangements have
been proposed and used to accomplish this purpose. One type of
tensioning arrangement uses a tensioner having a bushing formed
of an elastomeric material which is placed in compression by
some mechanical means for continuously exerting a ~ensioning
force on the belt. Examples of these constructions and arrange-
ments are shown in U. S. Patent Nos. 3,975,965 and 4,14~,772.
These tensioner constructions, which use an elastomeric materialS
have the disadvantages in that the high load rate which they
exert on the belt results in the rapid loss of tensioning as
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1 the belt stretches, and this load rate limits the stroke of the
belt-engaged idler pulley to a shorter distance than desired.
Also, sudden acccleration and deceleration of the drive belt
can cause a whipping action to occur which creates a time lag
before full damping is achieved.
Numerous other types of belt tensioning devices and
arrangements use springs for applying and maintaining the
tensioning force on a belt-engaging idler pulley or chain-
engaging sprocket. Some examples of these types of construc-
tions and arrangements are shown in U. S. Patent Nos. 2,703,019,2,893,255, 3,483,763 and 3,965,768. Some of these various
spring-actuated devices use the biasing force of the spring in
combination with hydraulic-actuated members for regulating the
amount of tensioning force applied to the belt, depending on
whether the engine is running or shut off.
U. S. Patent No. Z,051,488 shows a chain tensioning
arrangement in which a hydraulic cylinder is actuated when the
engine is running to reduce the tensioning pressure which is
exerted on the drive chain by a biasing spring. This hydraulic
cylinder applies a counter force to the biasing action of the
spring when the engine is running in order to decrease the ten-
sioning force on the chain, whereupon the full biasing force of
the spring is exerted on the chain when the engine is off and
the hydraulic cylinder inactive. U. S. Patent No. 3,142,193
discloses another belt tensioning arrangement using a hydrau-
lically actuated bellcrank and belt-engaging pulley in which a
spring biases the pulley into tensioning engagement with the
belt until the engine is operating, whereupon the hydraulic-
actuated piston imparts a greater tensioning force to the pulley
through the bellcrank. When the engine stops, the piston
retracts and the spring maintains a lesser tensioning force on
1 the belt. U. S. Patent No. 4,077,272 discloses another belt
tensioning arrangement using both a spring and a hydraulic mem-
ber to achieve the ~esired tensioning characteristics. In this
arrangement, when the engine is running, hydraulic oil from the
S engine lubricating system forces a piston back into its cylinder
to overcome an internally mounted first spring so that only a
second spring acts on the belt tensioning pulley when the engine
is operating. When the engine is off, both springs act on the
belt tensioning pulley. U. S. Patent No. 3,132,596 shows a
belt tensioner using a hydrostatic snubber controlled by the
power steering pump of the vehicle, whereupon the snubber is
forced outwardly in direct relationship to the output pressure
of the power steering pump. This mechanism does not maintain a
constant pressure on the belt when the vehicle engine is both
on and off, and will apply different forces in relationship to
the engine speed.
Other types of tensioning devices and arrangements are
provided with some type of mechanical retaining means, usually a
ratchet-retaining mechanism, which limits the movement of the
belt tensioning member in an opposite nontensioning direction,
thereby maintaining a constant tensioning force on the endless
drive belt. Most of these known arrangements use a spring-biased
member in combination with the retaining means for achieving the
belt tensioning effect. Examples of these prior constructions
and arrangements are shown in U. S. Patent Nos. 2,051,488,
2,703,019, 3,631,734 and 3,812,733. Another known tensioning
arrangement having mechanical detent-ratchet retaining means
uses the weight of the vehicle accessory to achieve the tension-
ing force on the drive belt, and is shown in U. S. Patent No.
3,413,866.
Other known types of belt tensioners and tensioning
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1 arrangements will pivot one of the vehicle accessories toward
belt tensioning engagement either by springs, as shown in U. S.
Patent Nos. 3,768,324 and 3,924,483, or by a hydraulic snubberg
as shown in U. S. Patent No. 3,132,596. However, none of these
constructions use a mechanical ratchet-pawl retaining means to
limit the movement of the tensioning device in an opposite non-
tensioning direction except the arrangement of U. S. Patent No.
3,413,866, which relies entirely on the weight of the pivotally
mounted accessory, as discussed above, for achieving the desired
tensioning force on the belt.
Many of these prior devices are believed to perform
satisfactorily :Eor their intended purpose, but it is preferred
that the use of springs for effecting the tensioning force on a
drive belt or chain, either for applying or retracting a ten-
sioning member therefrom presents problems. The operatingcharacteristics of these springs will change over the life of
the spring and even in response to changes in ambient tempera-
ture. Also, as the drive belt stretches, the spring's biasing
effect changes, making it difficult to maintain a constant ten-
sioning force on the drive belt. Likewise, the springs maybecome rusted and corroded and break during the life of the
vehicle, presenting mechanical maintenance problems for the
vehicle owner.
Relying on the weight of the vehicle accessory for
applying the tensioning force on the belt will not provide a
constant tensioning force thereon since the amount of tensioning
force will increase as the vehicle accessory moves farther past
its center balanced position. Likewise, the amount of tension-
ing force is controlled entirely by the initial weight of the
accessory and its position past center, which may not provide a
su:Eficiently large tensioning force, as desired.
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1 Accordingly, it is desirable to provide a belt ten-
sioning arrangement for a vehicle accessory drive belt which
eliminates the use of springs for achieving, controlling and
maintaining the tensioning force on the belt, which arrangement
will maintain a constant predetermined tension on the belt
throughout the life of the belt regardless o~ whether the
engine is on or off or being driven at high or low speeds.
There is no known belt tensioning arrangement of which
I am aware which imparts and maintains a constant predetermined
tensioning force on the drive belt for the vehicle accessories
by pivotally moving one of the accessories which is driven by
the belt, toward a tensioning direction by a hydraulically
actuated piston, in combinat.ion with a mechanical mechanism to
prevent moveme`nt of the accessory in an opposite direction with-
out the use of any springs or similar biasing means, and whichmaintains this constant pressure on the belt whether the engine
is on or off or operating at various speeds.
SUMMARY OF THE INVENTION
Objectives of the invention include providing an
improved arrangement for tensioning the drive belt for vehicle
accessories which maintains a constant predetermined tensioning
force on the drive belt throughout the life of ~he belt and
regardless of whether the engine is on or off or operating at
various speeds and conditions; providing such a belt,tensioning
arrangement in which a hydraulically actuated piston pivotally
moves one of the vehicle accessories, preferably the alternator,
to tension the drive belt which is operatively drivingly engaged
therewith, in combination with a mechanical spring-biased
ratchet-pawl mechanism to limit or prevent movement of the
vehicle accessory in the opposite direction; providing such an
improved belt tensioning arrangement which is relatively
1 una~fected by rapid engine acceleration and deceleration and
changes in engine operating speeds; providing such an improved
belt tensioning arrangement which completely eliminates the use
of springs for imparting the belt tensioning force, which
springs are subject to breakage and changing operating charac-
teristics; and providing such an improved drive belt tensioning
arrangement which is of a relatively simple construction, which
reduces maintenance and repair problems, which achieves the
stated objectives in a simple, effective and relatively inexpen-
sive manner, and which solves problems and satisfies needs inthe art.
These objectives and advantages are obtained by the
improved arrangement for tensioning an endless drive belt for
vehicle engine accessories, the general nature of which may be
stated as including a vehicle accessory pivotally mounted with
respect to the vehicle engine and operatively engaged with and
driven by the endless drive belt; piston means operatively
engaged with the said vehicle accessory for pivotally moving
said accessory to a tensioning position and for applying a pre-
determined tensioning -force on the drive belt engaged therewith;
fluid supply means communicating with the piston means for
hydraulically actuating said piston means to pivot the vehicle
accessory to the belt tensioning position and to apply the pre-
determined tensioning force on the drive belt; and ratchet-pawl
means operatively engageable with the said accessory to maintain
said accessory in the belt tensioning position and to maintain
the predetermined tensioning force on the belt during a decrease
in hydraulic pressure on the piston means.
BRIEF DESCRIPTION OF THE DRAWING
A preferred embodiment of the invention - illustrative
of the best mode in which applicant has contemplated applying
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1 the principles - is set forth in the following description and
shown in the accompanying drawing, and is particularly and
distinctly pointed out and set Eorth in the appended claims.
Fig. l is a diagrammatic view looking toward the front
of an engine, illustrating an endless drive belt operatively
connected to and driving the vehicle accessories, having the
improved belt tensioning arrangement incorporated therein;
Fig. 2 is an enlarged fragmentary top plan view of the
pivotally mounted vehicle accessory and piston means looking in
the direction of arrows 2-2~ Fig l;
Fig. 3 is a fragmentary front elevational view looking
in the direction of arrows 3-3, Fig. 2;
Fig. 4 is an enlarged fragmentary sectional view taken
on line 4-4, Fig. 3;
Fig. 5 is an enlarged fragmentary front elevational
view of the upper portion of the arrangement shown in Fig. 3,
with portions shown in section; and
Fig. 6 is a left-hand end view of the drive belt
arrangement shown in Fig. 1, with portions of the engine shown
therein.
Similar numerals refer to similar parts throughout
the drawing.
DESCRIPTION OF THE PREFERRED EMBODIMENT
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Referring to Fig. 1 of the drawing, the imp,roved belt
tensioning arrangemen~ is shown diagrammatically in cooperation
with a vehicle accessories drive system. An improved hydraulic
belt tensioner construction used in the tensioning arrangement
is indicated generally at 1, and is shown in tensioning engage-
ment with an endless drive belt 2 of the power transmission belt
drive system. The drive system consists of a plurality of belt
pulleys or sheaves having configurations and diameters determined
1 by and associated with engine accessory components and their
locations relative to each other. The various pulleys are sup-
ported on their respective engine components which, in turn,
are mounted on an engine 3 (Fig. 6) in a usual manner known in
the art. Belt 2 operates in a single vertical plane, as shown
in Fig. 6, to eliminate binding and skewing o~ the belt.
The engine accessories drive system consists of a main
driving pulley 4 which is operatively connected to the main
drive shaft of the engine, a pulley 5 which is opera~ively con-
nected to the air conditioning motor, a pulley 6 which is opera-
tively connected to an alternator 7 which provides the electri-
cal power ~or the engine, a pulley 8 which is operatively
connected to the vehicle's power steering unit 9, a pulley 10
which is operatively connected to the engine air pump, and a
pulley 11 which is operatively connected to the engine water
pump. Alternator 7 is pivotally mounted on a bracket 12 by a
bolt 13, with bracket 12 being mounted on engine 3 by mounting
bolts 14. This mounting arrangement for alternator 7 enables
the hydraulic belt tensioner 1 to pivotally move alternator 7
about pivot bolt 13 in a counterclockwise direction (Fig. 1) ~or
tensioning belt 2 through its driving engagement with pulley 6.
Belt tensioner 1 includes as main components a hydrau-
lic cylinder 17, a piston 18, and a ratchet-pawl mechanism 19.
Cylinder 17 is pivotally mounted by a pin 20 on a bracket 21
~only a portion of which is shown), which is mounted on a fixed
position on engine 3. Another bracket 24 extends about cylinder
17 and is held in clamping engagement therewith by bot~om pivot
pin 20 and a top pin 22. Bracket 24 is in abutting engagement
with an annular shoulder 23 formed on the outer cylindrical wall
25 which forms cylinder 17 (Pigs. 4 and 5). Bracket 24, in
turn, is pivotally mounted on a mounting bracket 21.
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o
1 CylincLrical wall 25 of cylinder 17 forms a hollow
cylindrical-shaped interior chamber 26, The front open end of
chamber 2~ is closed by a disc-shaped end wall 27 havlng a
central opening 28 formed therein in which a bushing 29 is
mounted for slidably receiving and supporting a piston rod 30.
The opposite open end of cylinder chamber 2~ is closed by an end
cap 31 having a sealing O-ring 32 and an outer coupling boss 33.
End cap 31 may be secured in the open end of cylinder 17 by
peening or deforming adjacent metal areas of the end cap and
cylinder wall, indicated at 34, at spaced circumferential loca-
tions about the closure. An inlet passage 35 is formed through
boss 33 and communicates with cylinder chamber 26. The outer
end of passage 35 terminates in an internally threaded portion
36 for receiving a threaded coupler 37 of a flexible conduit 38
(Fig. 2). The opposite end of conduit 38 is attached to power
steering unit 9 for supplying a relatively high-pressure hydrau-
lic fluid to chamber 26 of cylinder 17.
Piston 18 includes a cylindrical rod 30 and a piston
head 40 (Fig. 4) mounted on one end thereof. A sealing ring 41
is mounted in an annular recess 42 of piston head 40 to provide
a sliding sealing engagement with the internal cylindrical sur-
face of cylinder wall 25. The outer end of rod 30 (Fig. 5) has
a reduced threaded portion 43 which is engaged in a complementary
threaded opening formed in the web wall 44 of a U-shaped clevis
45. Clevis 45 is pivotally mounted by a pin 47 to the top mov-
able portion of alternator 7. Pin 47 extends through an opening
formed in alternator flange 48 and through aligned openings
formed in the spaced legs 49 of clevis 45.
In accordance with one of the features o-f the inven-
tion, ratchet-pawl mechanism 19 is mounted on and is operatively
engageable with cylinder 17 and alternator 7 for providing a
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o
positlve mechanical ac-tion which limits movenlent of the
alternator away from its belt tensioning position upon a
change or loss of hydraulic pxessure in cylinder 17.
Mechanism 19 includes a ratchet bar 52 which is pivotally
mounted on the top of cylinder mounting bracket 24 by pin 22.
The extended end of bar 52 is formed with a series of angled
teeth 53.
An inverted generally U-shaped bracket 54 is
pivotally mounted on the top oE alternator flanye 48 by pin
47. Pin 47 extends through openings formed in the bottom
of a pair of spaced, vertically extending bracket legs 55O
Top and intermediate cross members 56 and 57 (Fig~ 5) extend
between legs 55. Intermediate cross member 57 provides a
guide support for the extended end of ratchet bar 52.
A pawl 59 is pivotally mounted on bracket 54
between bracket legs 55 by a pin 60 which extends there-
between and is located between cross members 56 and 57. Pawl
59 includes a ratchet teeth-engaging projection 61 and a
release lever 62. A coil spring 63 extends between top
cross member 56 and pawl 59, biasing pawl 59 toward engaged
position wherein projeckion 61 engages one of the ratchet bar
teeth 53.
The operation of the improved vehicle accessory
drive belt tensioning arrangement is set forth below. Cylinder
17 is connected by conduit 38 to a source of hydraulic fluid,
preferably to the power steering drive unit 9 which provides
a relatively high hydraulic pressure for actuation of pistion
18. This source of hydraulic fluid and pressure is preferably
over the relatively lower pressure available from the engine
lubricating system which would necessi-tate some type of a
fluid pump or special hydraulic cylinder construc-tion, such
as shown in my copending Canadian application, Serial No.
A, -
sb/-~
7~
365,306, filed November 24, 1980, to achieve sufficlent
pressure for actuation
lla -
sb/( ,
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1 o-f piston 18
Upon installation o~ belt 2, alternator 7 will ~e
manually rotated in a counterclockwise direction about bolt 13
to place sufficient tension on belt 2 for operation of the
vehicle accessories upo~ engine start-up. Immediately upon
engine start-up, hydraulic fluid and its corresponding pressure
is supplied to chamber 26 and applied to piston head 40,
slidably moving piston rod 30 outwardly from cylinder 17
rotating alternator 7 in a counterclockwise direction to ten-
sion belt 2.
The size of cylinder 17 and piston head 40 are deter-
mined in relationship to the known amount of hydraulic pressure
to be supplied thereto from power steering unit 9~ so that the
desired amount of belt tensioning force exerted by piston 18
can be achieved. Accordingly, this predetermined amount of
tension will be exerted on piston 18 upon a certain engine
operating condition being reached. Bracket 54 of the ratchet-
pawl mechanism 19 moves with the top of alternator 7 as piston
18 moves outwardly under the influence of the hydraulic pressure,
with pawl projection 61 sliding easily over and along ratchet
bar teeth 53 due to the particular slope of the teeth. Pawl
projection 61 prevents return movement of alternator 7 in a
clockwise direction upon a decrease or loss of hydraulic pres-
sure in cylinder 17, thereby maintaining alternator 7 in its
furthermost belt tensioning position
As belt 2 stretches, the predetermined hydraulic force
exerted on piston 18 will pivot alternator 7 farther in a
counterclockwise direction to maintain the constant ~ensioning
force on belt 2. Pawl projection 61 again permits clevis 45 and
pawl mounting bracket 54 to move in a counterclockwise direction
along ratchet bar teeth 53. Projection 61 will permit these
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1 components and alternator 7 to move in a clockwise direction a
distance no greater than the pitch between adjacent tceth 53.
Thus, ~he prede~ermined tensioning force for which hydraulic
belt tensioner 1 was designed and constructed will always be
maintained on belt 2 regardless of the engine operating condi-
tion, speed of the vehicle, etc., due to alternator 7 being
prevented from movement in the nontensioning direction.
The improved belt tensioner and its arrangement enable
maintenance to be performed easily on any of the vehicle acces
sories or on drive belt 2 by manual upward movement of pawl
release lever 62 which disengages projection 61 from teeth 53.
This enables alternator 7 to be pivoted in a clockwise direction
until belt 2 has sufficient slack for its removal from one or
all of the accessories. No hydraulic pressure will be acting on
piston 18 since this work will be performed when the engine is
off, whereupon no pressure is supplied through conduit 38 to
cylinder 17.
The improved hydraulic belt tensioner 1 and its
arrangement have a number of advantageous features. This
arrangement prevents backing off or slackening of belt 2 in the
event of even partial hydraulic pressure or fluid loss and during
engine shutdown due to the mechanical locking feature of ratchet-
pawl mechanism 19. Alternator 7 preferably will operate through-
out a range closely adjacent to the vertical positioning of
alternator 7; i.e., alternator 7 is shown in a genera~ly vertical
position in Fig. 1, and throughout the belt life will move
throughout an angle of approximately 20, or 10 on each side of
vertical. Thus, this limited angular movement of alternator 7
about the horizontal axis of bolt 13 does not rely on nor is it
affected by the weight of the alternator for tensioning of the
belt, as in some prior art tensioning arrangements. Likewise,
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l clue to ~his limited angular movement about the vertical, piston
rod 30 will move generally in a horizontal direction parallel
with ratchet bar 52, eliminating binding of the various ratchet
and piston components throughout the entire angular movement of
alternator 7.
Another advantage of the improved arrangement and belt
tensioner construction l is the relatively simple~and inexpen-
sive construction of cylinder 17 and its piston 18, including
the ratchet-pawl mecha:nism 19. These various components are of
an extremely simple and inexpensive design, easily manufactured
in mass quantities, and can be mounted on the engine by a single
bracket 21. Also, the use of check valves and other hydraulic
control.means as in prior constructions have been eliminated,
thereby reduclng the cost of the piston for use by those car
manufacturers and suppliers desiring such a type of tensioner
construction. Furthermore, this improved arrangement eliminates
the use of an idler pulley and its mounting bracket since one
of the vehicle accessories is used for the tensioning function,
thereby eliminating additional components.
Accordingly, the improved belt tensioner construction
and its arrangement for tensioning the drive belt for the
vehicle accessories is simplified, provides an effective, safe,
inexpensive and efficient means which achieves all of the enu-
merated objectives~ provides for eliminating difficulties
encountered with prior tensioning devices and arrangements~ and
solves problems and obtains new results in the art.
In the foregoing description, certain terms have been
used for brevity, clearness and understanding, but no unneces-
sary limitations are to be implied therefrom beyond the require-
ments of the prior art, because such terms are used for descrip-
tive purposes and are intended to be broadly construed.
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1 Moreover, the description and illustration of the
invention is by way of example, and the scope of the invention
is not limited to the exact details of the construction shown
or described.
Having now described the features, discoveries and
principles of the invention, the manner in which the improved
belt tensioning means is constructed, assembled and operated,
the characteristics of the new construction and arrangement, and
the advantageous, new and useful results obtained; the new and
useful structures, devices, elements, arrangements, parts, and
combinations are set forth in the appended claims.
