Note: Descriptions are shown in the official language in which they were submitted.
;9
1 BACKGROUND OF THE INVENTION
_ _ _ _
Field of the Invention
, . . _
The invention relates to belt tensioning devices and
arrangements, and in particular to hydraulically actuated belt
tensioning devices for use with the endless drive belts o the
drive systems for vehicle accessories. More particularly, the
invention relates to a belt tensioner having an impro,ved self-
contained hydraulic fluid supply and pump assembly operated by
an idler pulley mounted thereon and driven by the endless belt
to maintain a predetermined constant tensioning force on the
endless drive belt regaTdless of ~he engine operating condition
by pivotal movement of one of the vehicle accessories.
Description o the Prior ~rt
_ _
There is ~he trend today in the automobile industry
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~ 7~ ~ ~
1 to operate the various vehicle accessories, such as the power
steering pump, oil and air pumps, air conditioning and alterna-
tor, by a single endless ~elt driven by a pulley connected to
the engine crankshaft. This system is referred to as a "ser-
pentine" drive belt system. To ensure optimum operating effi-
ciency for these various accessories, it is necessary that the
drive belt be maintained at a predetermined tension to assure
efficient performance of the accessories as well as satis-
factory service life for the belt. Due to the relatively
greater length for the single drive belt which replaces the
heretofore plurality of smaller belts, there is a greater ten-
dency for the belt to stretch, which will af~ect the operating
characteristics of the driven accessories. Therefore, it is
desirable that an automatic belt tensioning device 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 regardless of the amount of belt stretch with-
out requiring any maintenance or manual adjustment.
Numerous devices have been proposed and used to
2~ accomplish this purpose. One type of tensioner uses a bushing
formed of an elastomeric material which is placed in compression
by some mechanical means for continuously exerting a tensioning
force on the belt. Examples of these constructions are shown
in United States Patent Nos. 3~975,965 and 4,144,772. These
tensioner constructions, which use an elastomeric material, have
the disadvantages in that the high load rate which they exert
on the belt results in the rapid loss of tensioning as the belt
stretches, and ~his load rate limits the stroke of the belt-
engaged idler pulley to a shor~er distance than desired. Also,
sudden acceleration and deceleration of the drive belt can cause
a whipping action to occur which creates a time lag before full
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1 damping is achieved.
Numerous other types of belt tensioning devices use
springs for applying and/or maintaining the entire tensioning
force on a belt-engaging idler pulley or chain-engaging
sprocket. Some examples of these types o~ constructions are
shown in United States Patent Nos. 2,703,019~ 2,893,255,
3,413,866, 3,63:L,734, 3,768,324, 3,812,733, 3,924,4~3 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.
United States Patent No. 2,051,488 shows a chain
tensioning device 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 tensioning 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. United States Patent
No. 3,142,193 discloses another belt tensioner 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, wheTeupon the hydraulic
actuated piston imparts a greater tensioning force ~o the pul-
ley through the bellcrank. When the engine stops, the piston
retracts and the spring maintains a lesser tensioning force on
the belt. United States Patent No. 4,077,272 discloses another
belt tensioner using both a spring and a hydraulic member to
achieve the desired tensioning characteristics. In this
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1 devioe~ when the ~nl~ine is runnin~, hydraulic oil from the
en~in~ lubric~ing system forces fl p~5t:0n back into it:~ cylin
der to o~fercomo an ~ntern~lly mounted flrst spring 50 that
only ~ second spring ~cts or the ~elt ten3ienlng pu:lley wh~n
the engirle ls ope~ating. Wh~n the engine is o~f~ both springs
~ct on the belt tensionin~ pulley, Uni~e~ S~at~s Pate~ o.
3~13~,596 shows a bel~ tcn~ioner using a hydrost~ic snubb~r
controlled by the power steering pump of *h~ Y0hiC}.~ " whereupor
th~ snubber is orcad ou~wardly in direct relation~h~p to the
lQ olltput pressur~ of th~ power steering pump. This m~chanism
does not,maintn~n R constan~ pro~sur~ on thc bel~ when the .`
v~hicle engin~ 15 bo~h on and of~, and w~l apply dif~ere~t
"
forces in r~lationship to ~he eng~n~ sp~ed~
Many o~ these devices are belielr~d to perform satis- -
actorily ~or ~heir intended purpose~ ~lowelr~r" the use o~
sprin~ for ~ffeçtlng ~he entire ~cens:loning forc~ on a drive
b~lt or ch~in, cith~r fo~ applying or retracting ~ tensioning
m~mber ~here~om, presents problems. The operating charac~
teri~tics o~ these springs will change oYer the t~e of the
20 spring and ~von in r~ponse to ch~ s in ~bient temperatur~.
Also, ~s the driY~ ~elt s~retçn~s, the spring ' s bi~sing 0f:f~ct
~hanges, making i~ difficult ~o m~ln~ain a constant ~nsioning
force on the dr~e bclt. Likewise, ~he springs may beco~
ruseed and corroded and brcalc durlng the li~ o~ ~he Yehicl~,
presen~ing mechanical main~nanc~ problems for the v~hicle
~wner.
~ y of ~che~e probl~ms are 13~1ie~retl to ~e sl1~ina~ed
by ~he ilnproY~d hyd~aulic b~l~ t~nsioner collstruç~iolls sho~m in
United States Patent numbers 4,283,181 and 4,276,038, issued
3~ August 11, 1981 and June 30, 1981, respectively, both of which
are assigned to -the same assignee as is the~present applica-~ion.
These improved belt tensioners
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7~t;9
are operated by hydraulic pressure exerted b~ fluid from
the vehicle engine, such as the relatively low fluid
pressure of the engine's ~il lubricatiny system or the
high fluid pressure developed by the power steering pump
of the vehicle.
However, some vehicle manufac-turexs prefer
not to use -the hydraulic fluid which is used for other
purposes in the engine, such as lubricating or power
st~ering, for the operation of the belt tensioner. This
presents a possible problem situation in that if a serious
leak occurs, it could affect the other operations of the
vehicle and possibly damage or ruin an engine i~ no-t
detected soon enough.
Accordingly, it is desirable to provide a belt
tensioning device and arrangement which ellminates the use
of springs for controlling the entire belt tensioning
force, which device will maintain a nearly constant pre-
determined tension on the belt throughout the belt life
and regardless of whe-ther the engine is on or off or
being driven at high or low speeds, and which device uses
a source of hydraulic fluid completely independent of the
vehicle hydraulic system for operation ~hereof.
There is no known belt tensioning device or
arrangement of which I am aware which imparts and main-
tains a nearly constant predetermined tensioning force on
an endless accessory drive belt by a hydraulic piston
which is actuated by hydraulic fluid from a self-contained
fluid supply reservoir completely independent of the
vehicle hydraulic fluid sys-tem, and which maintains this
constant pressure on the belt whether the engine is on or
off or operating at various speeds, and which prevents
belt whip and achieves a highly efficient damping effect.
~-~ mab/ J 1
6~
The hydraulic belt tensioner of the presen-t
inven-tion is construc-ted for automatically tensioning an
endless belt of the drive system Eor the vehicle acces-
sories, in which one of the vehicle accessories is pivot-
ally mounted with respect to the vehicle engine and oper-
atively engaged with and driven by the endless belt,
wherein the general nature of the belt tensioner may be
stated as including self-contained hydraulic fluid supply
and pump means adapted to be mounted in a fixed position
with respect to the vehicle engine; an idler pully
drivingly engaged with the fluid supply and pump means for
actuation of said pump means upon rotation of said pulley,
said pulley being adapted to be operatively engaged with
and driven by the endless drive belt; and piston means
operatively con~ected to the fluid supply and pump means
~o~ hydraulic actuation of said piston means, said piston
means being.adap~ed to be operatively engaged with the vehicle
accessory.for pivotally moYin~ ~aid accessory to tension thé arive belt
engaged therewith upon actuation of the pump ~eans by the idler pulley.
Objectives of the invention include providing
a hydraulic belt tensioner construction which is actuated
from a source of hydraulic fluid completely separate and
independen-t o:E the vehicle accessory drive system and at
a predetermined pressure regardless of the operating con-
dition of the yehicle's engine; providing such a belt
tensioner using a hydraulic piston for pivotally moving
one of the vehicle accessories to tension the dri~e belt
which is engaged therewith. In a specific embodiment of
the invention, check valve system prevents the escape of
hydraulic fluid from the piston cylinder to maintain con-
stant pressure on the piston, thereby providing a damping
effect and elimina-ting belt whip upon starting and stop-
ping of the vehicle engine or upon rapid engine acceler-
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~7~69
ation or deceleration; and there is providecl a belt
-tensioner in which a coil spring is mounted within the
cylinder of -the hydraulic pis-ton and biases the piston
rod outwardly from the cylinder, and wherein the tension-
ing force exerted by the pis-ton on -the pivotally mounted
accessory is provided partially by the mechanical force of
the spring with the major portion of this tensioning force
being exerted hydraulically,-the spring ensuring a
sufficient tensioning force on the belt to provide a
driving engagement with the various accessories even upon
the loss of hydraullc pressure in the cylinder, while
overcoming the disadvantages of t.he use of springs for
exerting the entire force, as in prio~ tensioner construc-
tions. The belt tensioner has a self-contained supply of
hydraulic fluid which is separate from the engine lub-
ricating fluid or power steering fluid, and in which this
fluid is pumped in-to the cylinder of the tensioning pis-
ton by a relatively inexpensive year pump mechanism driven
by the endless drive belt of the accessory drive system.
The hydraulic cylinder and piston rod may be relatively
simple and inexpensive componen-ts formed from sheet metal
tubing, which are extremely lightweight! and which form
a piston having a minimum number oE parts. The belt
tensioner is of a relatively simple construction, which
eliminates maintenance and repair problems, and achieves
the stated objectives in a simple, effective and xelatively
inexpensive manner, and which solves problems and satisfies
needs existing in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred emxx~D~nt of the invention - illustrative
of the best mode in which Applicant has contemplated applying the
principles - is set forth in the following description and shown in
the accompanying drawings and is particularly and
mab/~
7~
1 distinctly pointed out and set forth in the appended claims.
Fig. 1 is a diagrammatic view looking toward the front
of an engine illustrating an endless drive belt operatively
engaged in a driving relationship with the vehicle accessories
with the improved ~elt tensioner construction incorporated
therein;
Fig. 2 is a fragmentary left-hand end view of the
engine and drive belt system, looking in the direction of
arrows 2-2 9 Fig. l;
Fig. 3 is an enlarged view of the hydraulic cylinder
and associated piston rod of the improved belt tensioner con-
struction of Fig. 1, with portions broken away and in section;
Fig. 4 is an enlarged sectional view taken on line
4-4, Fig. 3;
Fig. 5 is an enlarged sectional view taken on line
5-5, Fig. 3;
Fig. 6 is a side elevational view of the self-con-
tained hydraulic fluid supply and pump assembly with the idler
pulley mounted thereon, looking in the general direction of
arrows 6-6, Fig. l;
Fig. 7 is an enlarged sectional view of the improved
fluid supply and pump assembly and idler pulley combination,
taken on line 7-7, Fig. 6;
Fig. 8 is a vertical sectional view taken on line
8-8, Fig. 7; and
Fig. ~ i5 a schematic diagram of the hydraulic system
of the fluid supply and pump assembly and actuator piston o-f
Fig. 1.
Similar numerals refer -to similar parts throughout the
drawings.
~ 6 ~
l DESCRIPTION OF THE PR~FERRED EMBODIMENT
Referring to Fig. 1 of the drawings, the improved belt
~ensioner construction is indicated generally at 1, and is shown
tensioning an endless drive belt 2 of a power transmission belt
drive system or the vehicle accessories. The drive system
consists of a plurality of belt pulleys or sheaves having con-
figurations and diameters determined by their associated engine
accessories and locations relative to each other. The various
pulleys are supported on their respective engine components
which are mounted on an engine 2a in a usual manner known in
the art. Pre~erably, belt 2 operates in a single vertical plane,
which eliminates binding and skewing of drive belt 2, as shown
in Fig. 2.
The engine accessories drive system consists of a main
driving pulley 3 which is operatively connected to the main
shaft of the engine, a pulley 4 which is operatively connected
to the air conditioning motor, a pulley 5 which is operatively
connected to an alternator 6 which provides the electrical
power for the engine, a pulley 7 which is operatively connected
to the engine air pump, a pulley ~ which is operatively connec-
ted to the vehicle's power steering unit, and a pulley 9 which
is operatively connected to the engine water pump. Alternator
6 is pivotally mounted by a bottom bolt 10 and is moved in a
counterclockwise direction by improved belt tensioner 1 for
applying a tensioning ~orce on belt 2 through its engagement
with pulley 5 of alternator 6.
Tensioner 1 includes as main components a hydraulic
piston and a self-contained fluid supply and pump assembly~
indicated generally at 13 and 14~ respectively. These components
are hydraulically connected by a section of flexible conduit 15.
Hydraulic piston 13~ shown particularly in Figs. 3-5,
7~
1 includes a tubular-shaped cylinder 16 which is adap~ed to be
pivotally mounted on engine 2a by a bracket 17. Bracket 17
includes a U-shaped base 18 having a pair of pivot pin-receiving
holes 19 formed therein and an annularly curved top portion 20
which is clamped about cylinder 16. Conduit 15 is connected to
one end of cylinder 16 by a rigid coupling 21 which is threadably
engaged in an end plug 22 which seals the outer open end of
cylinder 16 (Fig. 3). An opening 23 is formed axially through
end plug 22 and provides a fluid passage with a hydraulic -fluid
chamber 24 formed within cylinder 16.
A piston rod 26 is slidably mounted within the open
front end of cylinder 16, and in accordance with one of the
features of the invention is for~ed of an inexpensive cylindri-
cal hollow tube. Outer end 27 of the tube is crimped to form a
closed L-shaped cross-sectional configuration, as shown in Figs.
3 and 4. A hold 28 is formed in piston rod end 27 for receiving
a pivot bolt 29. Bolt 29 connects piston rod 26 to the upper
end of the alternator bracket for pivotally moving alternator 6
about its lower pivot bolt 10 ~Fig. 1) in a counterclockwise
direction to tension belt 2. A cup 31 is welded or brazed
within the forward end of piston rod 26 adjacent the start of
the crimped end 27 to provide a fluid seal for the outer end of
the hollow rod interior. A sealing ring 32 is mounted within
an annular recess 33 formed in the outer open end of cylinder
16 to provide a seal between cylinder 16 and piston rod 26.
A coil spring 35 is located within the hollow interior
of piston rod 26 and cylinder 16J with one end being seated with-
in sealing cup 31 and the opposite being seated within an annu-
lar recess 36 formed in the inner end cf end plug 22 and con-
centric with end opening 23. Spring 35 is selected so that itexerts a predetermined biasing force on piston rod 26 to bias
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1 the same outwardly from within cylinder 16. Pisto~ rod 26,
through the biasing effect of spring 35, exerts a predetermined
mechanical tensioning force on belt 2 by the pivotal movement
of alternator 6, in a manner as shown in Fig. 1, prior to any
hydraulic fluid being supplied to chamber 24.
In accordance wi~h another of the main features
of the invention, the self-contained hydraulic fluid supply and
pump assembly 14 is mounted in a fixed position on engine 2a and
has an idler pulley 37 rotatably mounted thereon which is
engaged with and driven by belt 2. Assembly 1~ is shown partic-
ularly in Figs. 7 and 8, and is mounted on engine 2 by a bracket
arm 38 (Fig. 6) which is attached by bolt 39 to assembly 14.
Assembly 14 includes a generally cylindrically shaped
bearing housing 41 having a central bore 42. A bearing 43 is
mounted within bore 42 by a front retaining ring 44 which clamps
bearing 43 against a rear annular shoulder 45 Idler pulley 37
includes a usual, preferably sheet metal, belt-engaging pulley
member 47 which is mounted in a fixed relationship on the outer
end of a shaft 48 for rotation therewith. The inner end of
shaft 48 is rotatably mounted within bearing 43 and secured
therein by an inner retaining ring 49 and an outwardly spaced
collar 50 which abuts against bearing 43.
A gear pump assembly 52 is mounted on the inner wall
surface of bearing housing 41 by a plurality of circumferentially
spaced bolts 53. Pump assembly 52 includes a generaily disc-
shaped gear-mounting block 54 and a pair of pump gears 55 and 56
rotatably mounted within a central recess 51 formed in block 54
by stub shafts 57 and 58, respectively. Gears 55 and 56 are
enclosed within recess 51 by an end sealing plate 59.
Gear 55 is the driving gear of the gear pump pair and
is attached to stub shaft 57 for rotation therewith. Sha-ft 57
~.~4~
1 has a reduced end 60 whi.ch is splined in a complementary hole
ormed in the inner end of pulley shaft 48, whereby rotation of
pulley shaft ~8 will drive gear pump shaft 57 and correspond-
ingly gear 55. Shaft 48 is rotated by the engagement of endless
drive belt 2 with pulley member 47. Gear stub shaft 58 is
freely rotatably mounted within an opening 61 formed in gear
mounting block 54~ enabling pump gear 56 to be driven by and in
unison with driving gear 55. Gear pump assembly 14 may have
other configurations than the two-shaft, externally meshing
gear arrangement described above without affecting the concept
of the invention. Pump assembly 14 is a readily available and
known structure which provides a source of fluid pressure from
a fluid supply reservoir.
A check valve assembly 62 is mounted on gear mounting
block 54 by a plurality of spaced bolts 64 which clamp assembly
62 against end sealing plate 59 of gear pump assembly 52. Check
valve assembly 62 preferably is formed from a rigid block of
material 63, such as metal or plastic. A pair of ball check
valves 65 and 66 are formed in valve block 63 to control the flow
of hydraulic fluid into piston 13, and correspondingly to regu-
late the amount of hydraulic pressure exer~ed on piston rod 26
for tensioning of belt 2. Check valves 65-66 include cavities
67 and 68 containing valve balls 69 and 70 which are biased
toward seated position by springs 71 and 71a, respectively.
Check valves 65-66 may be of another type or arrangement, if
desired, without affecting the concept of the invention.
In accordance with another feature of the invention~
assembly 14 includes its own hydraulic fluid system for supplying
the hydraulic pressure and fluid to cylinder 13, completely
eliminating the need for using hydraulic fluid from any part or
component of the vehicle. A cylindrical-shaped fluid reservoir
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1 housing 72, preferably ormed of plastic or sheet metal, is
mounted on bearing housing 41 by various types of attachment
means~ such as the use of rolled outer end edges 73 seated with-
in an annular groove 74 formed in the outer surface o~ bearing
housing 41. An annular seal 75 then is mounted within a corre-
sponding annular groove 77 to provide a fluid seal between the
cylindrical wall of housing 72 and the outer surface of bearing
housing 41.
A supply of hydraulic fluid, such as oil 76 ~Fig. 7),
is contained within fluid housing 72. Housing 72 preferably
will contain sufficient fluid, due to the closed loop arrangement
of assembly 14, to eliminate replenishing or refilling housing 72
at any time throughout the life of belt tensioner 1. ~ousing 72
also may be attached to valve block 63 ~Fig. 8) by a threaded
coupling 78 of fluid conduit 15. ~oupling 78 is threadably
engaged with a boss 79 formed on the outer surface of fluid
housing 72 and in a corresponding threaded opening 80 formed in
check valve block 63 to clamp fluid housing 72 and block 63
tightly together.
A hydraulic fluid inlet opening 82 is formed in the
lower portion of end sealing plate 59 and communicates with pump
gear 56 The incoming low-pressure hydraulic fluid from oil
supply 76 enters gear pump assembly 52 through opening 82 and is
discharged with a higher pressure through a high-pressure open-
ing 83 and into a fluid passage 84 formed in valve block 63.
This high-pressure oil easily unseats check valve ball 69 of
check valve 65 and flows through an outlet passage 85 and into
a tube 86 of threaded coupling 78. This high-pressure oil then
enters chamber 24 of piston 13 to force piston rod 26 outwardly
in a belt-tensioning direction. High-pressure discharge passage
85 is connected to check valve 66 by a fluid bypass passage 87
.
- 13 -
~ 7 ~ ~9
1 (~igs. 7 and 8). Check valve spring 71a has a predetermined
biasing force on valve ball 70 so that as long as the predeter-
mined hydraulic pressure is exerted on piston rod 26 within
cylinder 13, the high-pressure oil produced by gear pump assembly
52 will lift ball 70 rom its closed seated position, enabling
this oil to flow through relief passage 87 and into cavity 68.
This oil then flows through a bypass return passage 88 and into
oil supply 76 for recycling ~hrough gear pump assembly 32.
This closed loop system thereby ensures continuous source of
high-pressure hydraulic fluid provided by pump assembly 52,
which is applied to piston rod 26 and subsequently to alternator
6 for tensioning belt 2.
Fig. 9 is a schematic drawing of the check valve and
hydraulic fluid system discussed above, with the various numerals
used in Fig. 9 corresponding to the numerals of the components
described above and shown particularly in Figs. 7 and 8. Low-
pressure oil is drawn :Erom fluid supply 76 (Arrow A) and is
expelled by pump assembly 52 as high-pressure fluid ~Arrow B)
which flows through passage 84 and through check valve 65. This
flow of high-pressure fluid (Arrow B) will thenflow either into
piston 13 through conduit 15 (Arrow C) or if no additional
hydraulic fluid is required will flow through relie-F passage 87
and through check valve 66 (Arrow D) and through bypass return
passage 88 back into fluid supply 76.
The operation of improved belt tensioner construction
1 is as follows. The amount of tensioning force which is
necessary for proper tensioning of belt 2 by movement of alter-
nator 6 is determined by various standard calcula~ions and past
experience. This force then is used to determine the correspond-
ing outward force required to be exerted by piston rod 26. Coilspring 35 then is selected so that approximately one-third of
l the total force ~o be exerted by piston rod 26 will be the
result of the biclsing action of spring 35, with the remaining
two-thirds of this force being exerted hydraulically on rod 26.
For example, assume that a 300 pound force is desired
to be exerted by piston rod 26. Spring 35 will be chosen so as
to exert a force of approximately 100 pounds. Check valve spring
71a then is chosen or adjusted in valve block 63 due to its
threaded engagement therewith, so as to become unseated and move
upwardly to an open position when the pressure exceeds the prede-
termined fluid pressure necessary to produce a 200 pound hydrau-
lic force on pis~on rod 26, which when combined with the spring
force, provides the required 300 pound force on alternator 6.
Opening of check valve 66 enables high pressure fluid from pump
assembly 52 to return to fluid supply 76 through passage 88.
Thus, high-pressure fluid discharged by pump assembly 52 will
continue to Elow into piston chamber 24 through check valve 65
and conduit 15 until the desired pressure is reached, whereupon
any additional high-pressure fluid discharged from pump assembly
52 will unseat valve ball 70 with the excess oil returning to
supply 76.
Should any oil leak from piston 13, it will immediately
be made up during operation of the vehicle engine. During engine
operation, pulley 37 is rotated by belt 2 which rotates gear
shaft 57 through its splined engagement with pulley shaft ~8 to
pump additional make-up hydraulic fluid into ~ylinder'chamber
24 until the predetermined pressure is achieved~ whereupon by-
pass check valve 66 will open as described above.
Spring 35 ensures that sufficient tensioning pressure
is always exerted on belt 2 through pivotal movement of alterna-
tor 6 for operation of the vehicle accessories even upon com-
plete loss of hydraulic fluîd from piston 13. Therefore~ if a
- 15 -
1 serious leak occurs for any reason in the sel:E-contained hydrau-
lic fluid system, the vehicle accessories would still operate
when the engine is running. Any make-up :Eluid required will be
applied to chamber 2~ immediately upon actuation of pump assem-
bly 52 until the predetermined pressure is reached.
Improved hydraulic belt tensioner 1 and its arrange-
ment and operation with the vehicle accessories and drive belt
has a numberof advantages. The self-contained hydraulic fluid
supply and pump assembly l~ completely eliminates the use of
the engine lubricating fluid or the power steering fluid for
operation of the tensioning piston as heretofore required in
prior constructions. Assembly 14 provides a relatively inex-
pensive and compact unit which is mounted on the engine at a
convenient location in combination with the mounting of piston
13. Another advantage is that spring 35 ensures that sufficient
tensioning force is always exerted on belt 2 for operation of
the vehicle accessories even upon loss of hydraulic pressure.
Also, due to the location of spring 35 within the hydraulic
cylinder, it is protected from corrosion or damage as in prior
belt tensioners using springs. Furthermore, piston 13 is an
extremely ine~pensively formed component consisting only of a
pair of tubular sleeves which can be fabricated easily from
available metal conduits or plastic materials.
The particular check valve arrangement also ensures
that the desired amount of hydraulic fluid and pressure is always
available at piston 13 since pump assembly 52 continuously
creates a supply of high-pressure fluid in chamber 24 during
engine operation. This fluid will only be supplied to piston 13
when necessary and usually will flow through check valve 66 back
into the fluid supply reservoir. The check valve system also
traps the hydraulic fluid in piston 13 and connecting conduit lS
- 16 -
1 when the engine is shut of. Therefore, piston 13 will continue
to exert the full amount of pressure on alternator 6 (both
spring and hydraulic force) even when the engine is off and the
fluid will not drain from the piston during engine shutoff, as
in prior art tensioner constructions. The maintaining of this
tensioning force which is produced by the hydraulic pressure on
the belt, even when the engine is not running, is desirable to
prevent a whipping action from occurring upon engine start up.
Also, this trapped hydraulic fluid provides a damping effect at
all times to the piston to prevent whipping of the belt during
sudden engine acceleration or deceleration.
Improved tensioner construction 1 also enables main-
tenance to be performed easily on belt 2 or on any of the acces-
sories operated thereby. The hydraulic fluid is drained from
piston 13 enabling the spring-biasing tensioning to be easily
overcome manually for removal and/or installation of belt 2.
This hydraulic fluid will be replaced in piston 13 immediately
when the engine is started. Reservoir housing 72 also will con-
tain suf-ficient oil or other hydraulic fluid to compensate for
any minor leakage which could occur in piston 13 or connections
therewith, eliminating refilling housing 72 with additional fluid
throughout the life of belt tensioner deviçe 1. Also, fluid
supply and pump assembly 14 may be mass produced at a suficiently
low cost so as to provide a disposable assembly. There-fore, if
replacement is required, the existing assembly would be replaced
by a new assembly with a minimum amount of service time and cost
and without the need of repairing the existing assembly.
Accordingly, the improved belt tensioner and its
arrangement provides a construction which is simplified, effec-
tive, safe and inexpensive, which achieves all o~ the enumeratedobjectives, provides for eliminating difficulties encountered
- 17 -
1 with prior tensioning devices, 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 unnecessary
limitations are to be implied therefrom beyond the requirements
of the prior art, because such terms are used for descriptive
purposes and are intended to be broadly construed.
Moreover, the description and illustration of the
invention is by way of example, and the scope of the invention
is not limited to the e~act details of the construction shown
or described.
Having now described the features, discoveries and
principles of the invention, the manner in which the improved
hydraulic belt tensioner construction is constructed, assembled
and operated, the characteristics of the new construction, 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.
