Title
Belt Transmission
Field of the Invention
The invention relates to a belt transmission, and
more particularly, to a belt transmission comprising a
first tensioner and second tensioner engaged about an
intermediate shaft, the first tensioner and second
tensioner each comprising a first arm and second arm and
a torsion spring engaged therebetween, the first arm and
second arm each bearing upon a surface, the first arm and
second arm rotatable by operation of the torsion spring
to exert a force upon the intermediate shaft whereby a
tension is imparted to a first belt and a second belt
engaged with the intermediate shaft.
Background of the Invention
Electric power assist steering systems (EPAS) have
been around since the 1960 's. Hydraulic power assist
steering has traditionally dominated the market.
Hydraulic systems have high parasitic energy loss when
the hydraulic pump is pumping, but power assist is not
required. Early attempts to eliminate this parasitic loss
involved fitting an electric motor to the pump and only
driving the pump when necessary.
Electric hydraulic assisted power steering systems
use an electric motor to drive a hydraulic pump to feed a
hydraulic power steering system. These systems are an
intermediate step by the industry and their use will
likely fade with the increased use of EPAS. EPAS systems
allow realization of reduced noise, reduced energy use,
active safety features, and adjustability to meet driving
conditions. However, the use of these systems has
remained limited until recent C.A.F.E. requirements
became more difficult to meet. This is driving automotive
manufactures to turn to EPAS systems more and more in an
effort to improve vehicle fuel economy. EPAS systems
eliminate the parasitic losses typically found in
hydraulic assist power steering systems.
For example, one difficulty that slowed
implementation of EPAS systems was meeting the power
requirement with a 12 volt electric motor. Recently
systems have been developed that successfully solve this
problem. Further, all EPAS systems require a control
module to sense driver input and control the electric
motor to provide the desired assist. The control module
measures driver input torque and uses this to determine
the amount of assist required. Assist can be tuned to
meet the drivers need depending on driving conditions.
The system can even have a tunable "feel" available to
the driver.
Even though the main driver for automotive EPAS is
fuel economy improvement, EPAS has additional benefits.
The system can make steering assist available even when
the vehicle's engine is not running. It also enables the
use of the automatic parallel parking systems available
today .
There are two main types of EPAS systems; column
assist and rack assist. Rack assist EPAS systems have an
electric motor that is connected to the steering rack.
The electric motor assists the rack movement usually
through driving a lead screw mechanism. Column assist
EPAS systems have an electric motor connected to the
steering column. The electric motor assists the movement
of the column shaft usually through a worm gear type
arrangement. One advantage of these types of systems is
the electric motor can be placed in the passenger
compartment freeing up valuable space under the hood.
This also keeps any sensitive electrical components out
of the harsh under hood environment.
Worm drive column assist systems are usually used in
small cars where the assist power requirements are lower
than what would be needed in a large heavy vehicle. These
systems are limited by the speed of the steering wheel
and the ratio of the worm drive. The steering wheel at
its fastest speed rotates relatively slowly at
approximately 60 rpm. With a 60 rpm speed of the steering
wheel and a worm drive ratio of 15:1, the max speed of
the electric motor would only be 900 rpm. Worm drives are
limited to ratios under 20:1 because ratios higher than
that cannot be back-driven.
The steering system must be able to be operated with
no power. This requires the worm drive be able to operate
with the gear driving the worm (back-driven) . Having a
low motor speed and limited ratio worm drive causes the
need for high torque motor. Even with a high torque
motor, these types of systems have not been made
successful on heavy vehicles. Small vehicles are light
and require less steering effort thus enabling the use of
these systems. Worm drive column assist SPAS systems are
the lowest cost systems and thus also lend themselves to
smaller less expensive vehicles.
Typical steering systems with worm drive assists are
limited in their efficiency. EPAS systems must be
designed to operate when there is no power available. Due
to the nature of worm drive's tendency to lock up during
back driving when ratios exceed approximately 20:1, worm
drive EPAS systems efficiency is not greater than
approximately 85% and nearer to 65% during back-driving
conditions .
Representative of the art is US patent no. 8327972
which discloses a vehicle steering system transmission
comprising a housing, an input shaft journalled to the
housing, an electric motor connected to the housing and
coupled to the input shaft, an output shaft journalled to
the housing, the input shaft and the output shaft coupled
by a first pair of sprockets having a first belt trained
therebetween and having a first ratio, the first belt and
first pair of sprockets comprising a helical tooth
configuration, the input shaft and the output shaft
coupled by a second pair of sprockets having a second
belt trained therebetween and having a second ratio, and
the input shaft and the output shaft coupled by a third
pair of sprockets having a third belt trained
therebetween and having a third ratio.
What is needed is a belt transmission comprising a
first tensioner and second tensioner engaged about an
intermediate shaft, the first tensioner and second
tensioner each comprising a first arm and second arm and
a torsion spring engaged therebetween, the first arm and
second arm each bearing upon a surface, the first arm and
second arm rotatable by operation of the torsion spring
to exert a force upon the intermediate shaft whereby a
tension is imparted to a first belt and a second belt
engaged with the intermediate shaft. The present
invention meets this need.
Summary of the Invention
The primary aspect of the invention is to provide a
belt transmission comprising a first tensioner and second
tensioner engaged about an intermediate shaft, the first
tensioner and second tensioner each comprising a first
arm and second arm and a torsion spring engaged
therebetween, the first arm and second arm each bearing
upon a surface, the first arm and second arm rotatable by
operation of the torsion spring to exert a force upon the
intermediate shaft whereby a tension is imparted to a
first belt and a second belt engaged with the
intermediate shaft.
Other aspects of the invention will be pointed out
or made obvious by the following description of the
invention and the accompanying drawings.
The invention comprises a belt transmission
comprising a housing, a first belt trained between a
first shaft and a first intermediate shaft, a second belt
trained between the first intermediate shaft and a second
intermediate shaft, a third belt trained between the
second intermediate shaft and a second shaft, a first
tensioner and second tensioner each engaged with the
housing and each engaged about the first intermediate
shaft whereby each tensioner exerts a force upon the
first intermediate shaft which thereby imparts a tension
to the first belt and to the second belt, and a third
tensioner and fourth tensioner each engaged with the
housing and each engaged about the second intermediate
shaft whereby each tensioner exerts a force upon the
second intermediate shaft which thereby imparts a tension
to the second belt and to the third belt.
Brief Description of the Drawings
The accompanying drawings, which are incorporated in
and form a part of the specification, illustrate
preferred embodiments of the present invention, and
together with a description, serve to explain the
principles of the invention.
Figure 1 is an exploded view of the device.
Figure 2 is a front perspective view of the device.
Figure 3 is a back perspective view of the device.
Figure 4 is a view of the tensioner assembly.
Figure 5 is an exploded view of a tensioner
assembly .
Figure 6 is a detail of the tensioner assembly in
the device.
Figure 7 is a detail of the input pulley and belt.
Figure 8 is a detail of the compound pulley
sprocket .
Figure 9 is a diagram of the forces on the shaft of
the first compound pulley/ sprocket .
Figure 10 is a diagram of the position of the forces
along the input shaft.
Figure 11 is a diagram of the angular positions of
the forces on the input shaft.
Figure 12 is a detail of the tensioner.
Figure 13 is a detail of the tensioner.
Figure 14 is a detail of the force components in the
tensioner arms.
Figure 15 is a perspective view of housing 9 .
Figure 16 is a perspective view of housing 10.
Figure 17 is a perspective view of the assembled
housing parts.
Figure 18 is a plan view of the assembled housing
parts .
Figure 19 is a detail of a tensioner arm.
Detailed Description of the Preferred Embodiment
Figure 1 is an exploded view of the device. The
inventive device conprises a three stage belt drive
transmission. Drive stage one comprises a multi-ribbed
belt 100 with a drive ratio of 2.4:1. Stage two
comprises a toothed or synchronous belt 101 with a ratio
of 3.8:1. Stage 3 comprises a toothed or synchrounous
belt 102 with a ratio of 3.5:1. The overall drive ratio
of the transmission is 31.9:1. Of course, a desired drive
ratio can be selected by altering the diameter of the
pulleys and sprockets as described herein.
The inventive device comprises input shaft 2 , input
pulley 1 , multi-ribbed belt 100, compound pulley/sprocket
3 , a first intermediate shaft 4 , automatic tensioner
assemblies 5 , 6 , 7 ,and 8 , a compound sprocket 11, a
second intermediate shaft 12, a 3mm pitch toothed or
synchronous belt 101, a 5mm toothed or synchrounous belt
102, an synchronous sprocket 13, housing portion 9 ,
housing portion 10, a plurality of bearings (50, 51, 52,
53, 54, 55, 56), a motor mount 14, and a plurality of
fasteners 15. A synchronous or toothed belt comprises
teeth which extend across a width of the belt.
Input shaft 2 is mounted on bearings 50, 51. Input
pulley 1 is press fit to input shaft 2 . Bearings 51 and
50 are mounted in each housing 9 and housing 10
respectively, thereby supporting input shaft 2 .
Compound pulley/sprocket 3 is mounted on first
intermediate shaft 4 . First intermediate shaft 4 is
mounted on bearings 52, 53. In turn, bearings 53, 52 are
each mounted within an automatic tensioner 5 and
automatic tensioner 6 respectively. Automatic tensioner
5 and automatic tensioner 6 along with bearings 53, 52
are each in contact with housing 9 and housing 10,
respectively. Compound pulley/sprocket 3 comprises
pulley 32 for engaging belt 100 and sprocket 31 for
engaging belt 101.
Second intermediate shaft 12 is mounted on a pair of
bearings 54, 55. Compound sprocket 11 is mounted to
intermediate shaft 12. Bearings 54, 55 are each mounted
in automatic tensioner 7 and automatic tensioner 8
respectively. Automatic tensioner 7 and 8 with bearings
54, 55 respectively are each in contact with housing 9
and housing 10. Compound sprocket 11 comprises sprocket
110 for engaging belt 101 and sprocket 111 for engaging
belt 102.
Output sprocket 13 is mounted on a bearing 56.
Bearing 56 is mounted in housing 10. Housing portion 9
and housing portion 10 are bolted together using
fasteners 15. Motor mount 14 is bolted to housing 10. A
motor or other driver (not shown) can be mounted to motor
mount 14. Sprocket 13 engages belt 102.
Multi-ribbed belt 100 transmits power from input
pulley 1 to pulley 32. A multi-ribbed belt comprises
ribs that extend in the endless of longitudinal direction
of the belt. Belt 101 transmits power from sprocket 31
to sprocket 110. Belt 102 transmits power from sprocket
111 to output sprocket 13.
Output sprocket hub 130 is configured to enable
connection to a vehicle steering shaft (not shown) .
Input shaft 2 is configured to allow connection to an
electric motor or other power source (not shown) . Housing
10 further comprises a bracket 82, see Fig. 18, for
mounting the inventive device to a vehicle (not shown) .
Known tensioners typically comprise a rigidly
mounted base and a moveable arm assembly with an idler
pulley journalled to the moveable arm. The idler pulley
is forceably engaged with a belt by a torsion spring
which tensions a belt. Each automatic tensioner 5 , 6 , 7 ,
and 8 differs from the prior art wherein the prior art
tensioner base is replaced by an arm which acts as a
second tensioner arm in the inventive device, see Fig. 5 .
Automatic tensioner 5 and 6 act cooperatively to
position shaft 4 thereby tensioning belt 100 and belt
101. Automatic tensioner 7 and 8 act cooperatively to
position shaft 12 thereby tensioning belt 101 and belt
102 .
Automatic tensioner 5 and 7 act upon housing 9 .
Automaitc tensioner 6 and 8 act upon housing 10, which in
turn the combination creates a reaction force upon the
movable intermediate shaft 4 . The reaction force
exterted on the moveable intermediate shaft 4 positions
the shaft to a positon of equilibrium based upon the
tension in belt 100 and belt 101. Shaft 4 and pulley 3
move into a position where the belt tension is equal to
the combined force pf tensioners 5 and 6 . The same
operating priniciple is realized by tensioners 7 and 8
acting on intermediate shaft 12 and thereby pulley 11.
In this Figure tensioner 5 and tensioner 7 are shown in
exploded view. Tensioner 6 and tensioner 8 are not shown
in exploded view. Tensioners 5 , 6 , 7 , 8 are of the same
design and description.
Figure 2 is a front perspective view of the device.
Housing 9 is omitted from this drawing.
Figure 3 is a back perspective view of the device.
Shaft 2 engages an electric motor or other suitable
driver (not shown) . Member 82 mounts the device to a
suitable mounting surface (not shown) . Bearing 52
supports tensioner 6 . Bearing 55 supports tensioner 8 .
Figure 4 is a view of the tensioner assembly. The
inventive automatic tensioner comprises an arm 500, a
bushing 502, a torsion spring 504, and an arm 501. Arm
500 is rotatably connected to arm 501 with bushing 502
providing a low friction surface to facilitate movement.
One end 509 of the torsion spring 504 rests against a
face 510 on arm 500. The opposite end 507 of the torsion
spring 504 rests against a face 508 on arm 501. Spring
504 is loaded in the unwinding direction. Arm 500
comprises tangs 503 which hold the tensioner assembly
together. Arm 501 comprises tangs 511 which hold the
tensioner assembly together. Arm 501 comprises arcuate
tensioner surface 506. Surface 506 contacts a bracket
surface 92 on housing 9 , see Figure 15. Arm 500 comprises
arcuate tensioner surface 505. Surface 505 contacts a
bracket surface 91 on housing 9 , see Figure 15. This
description is also applicable to automatic tensioners 6 ,
7 and 8 .
Figure 5 is an exploded view of a tensioner
assembly. Tensioner 5 receives a bearing 52 which in
turn engages shaft 4 . Tensioner arms 500, 501 are cam
like in configuration. The cam like arms rotate around
the center of the bearing 52, namely, the rotation
center, see Figure 19. Arms 500, 501 are each configured
similarly, that is, a circle within a circle having
offset centers and different radii, see Fig. 19.
Arms 500, 501 comprise surfaces 505, 506
respectively which rest on bracket surface 91 and brakect
surface 92, see Figure 15. Torsion spring 504 provides a
moment to each arm in opposing directions. End 507 bears
against tab 508. End 509 bears against tab 510. A spring
force focibly rotates the arm surfaces 505, 506 against
surfaces 91, 92 of the housing 91, 92. Since the arms
are cam like in operation this causes the rotation center
of bearing 52 and thus shaft 4 and pulley 3 to move in a
direction which properly tensions belts 100 and 101. The
movement stops when the belt tension is equal to the
force of tensioners 5 and 6 . This description is also
applicable to operation of automaitc tensioners 6 , 7 and
8 as well.
Figure 6 is a detail of the tensioner assembly in
the device. The tensioners operate in pairs, namely,
tensioners 5 and 6 act cooperatively to support shaft 4 .
Tensioners 7 and 8 act cooperatively to support shaft 12.
Each pair of tensioners forcibly position shaft 4 and
shaft 12 which provides the force necessary to properly
tension the belts.
For the two belts (101, 102) engaged with each
compound pulley/sprocket (3, 11) the tensioning force is
preferably oriented such that the proper force in the
proper direction is applied to create the desired tension
in each belt .
Proper belt tension depends on the diameter of the
pulley and the desired torque in the system. For
example, a torque input to input pulley 1 is 1.88 Nm and
the pulley diameter is 30mm. This yeilds a force of
125. 3N (or DT=125.3 N) applied to belt 100 by pulley 1 .
This is the difference in tension in belt 100 due to
torque regardless of the installed tension in the belt.
Torque = For ce x distance
Torque = 1.88 Nm
Distance = Diameter/2 = 0.030m/2 = 0.015m
Force = Torque/distance
Force = 1.88Nm/ 0.0 15
Force = 125.3N
Figure 7 is a detail of the input pulley and belt.
The difference between the tight side tension and the
slack side tension of belt 100 is 125. 3N. The slack side
tension cannot drop below a certain value without the
drive slipping. This value is determined with the
calculation of the minimum tension as follows:
T 2 W
T l
Where T2 = tight side tension
Tl = slack side tension
m = friction = 1
Q = wrap angle on pulley = 139.7 degrees
Solving for T2 :
T2 = T e
Additionally the torque is equal to the radius of
the pulley times the difference between the tight side
tension and the slack side tension:
Torque = r*AT = r(T2-Tl)
Substituting for T2 and solving for Tl :
Torque
7 1 = R e - l )
T _ 1.88
Tl = 12.0JV
Since DT = 125N we get T2 = 137. 3N
The value calculated above for Tl is the minimum
value so a factor of safety is added to the system, for
example, this value is doubled to 24N which gives a tight
side tension of 149. 3N for belt 100. When there is no
torque in the drive, the tight side and slack side
tensions equalize to become the installed tension. The
magnitude of that is one half the total tension:
1 1 .
Installed tension = Tl = T2 = - total tension = - 149.3 + 24 ; = 86.6N
2 2
The hubload is then the resultant of the sum of
these tension forces applied at the angle of the belt. To
determine the angle of the belt we need to know the wrap
angle of the belt around the pulley. Simple geometry
yields the following formula for wrap angle:
WA = n-2sin (R2-Rl/center distance)
Where :
R2 = radius of opposing pulley = 36mm
Rl = radius of subject pulley = 15mm
Center distance = the distance between the
centers of the pulleys = 61mm
This results in a wrap angle of 139.7 degrees.
The angle of the tension force is:
Tension force angle = TFA = (180-WA)/2
TFA = (180-139.7) /2
The belt tension forces are at angles of +/-20.15
degrees from the line formed between pulley centers.
The hubload (HL) is then:
Hubload = 2 (installed tension*cos (TFA) )
HL = 2* (86 .6*cos (20 .15) )= 162. N
The hubload is applied along a line formed through
the centers of each pully pair at the mid width of the
belt. The force on the output pulley is equal and
opposite the force on the input pulley.
When the pulley is a compound pulley or sprocket,
see Figure 8 , the hubload must be determined for both
belts and applied in the appropriate direction and
location along the shaft. Figure 8 is a detail of the
compound pulley sprocket 3 . Since the forces on each
shaft cancel, it is possible to calculate the forces
necessary from each tensioner to balance the hubloads on
the shaft.
Figure 9 is a diagram of the forces acting on the
shaft 4 of the first compound pulley/sprocket 3 . Figure
10 is a diagram of the position of the forces along the
input shaft 4 . Figure 11 is a diagram of the angular
positions of the forces on the input shaft 4 .
FH1 is the force of hubload from belt 100.
FH2 is the force of hubload from belt 102.
FT1 is the force from tensioner 1 .
FT2 is the force from tensioner 2 .
In order to determine the forces required in each
tensioner, the calculation is simplified by separating
the calculations into the forces from each belt and then
adding them together. The forces are resolved into an x
component and a y component. The x axis is normal to a
line formed between the centers of the pulleys of the
input drive (z-axis) . Considering the x direction from
FH1 we get:
Given :
FH1 = 157. 2N
FH2 = 600N
b = 85 deg
FH1 is in the positive X direction
z1 = 33.5 mm
Z2 = 48.0 mm
Z3 = 13.5 mm
Summing the forces in the X direction (see Figures
7 , 8 , and 9 ) :
0 = FHl-FT2x-FTlx
Where :
FT2x is the force from tensioner 2 in the x
direction .
FTlx is the force from tensioner 1 in the x
direction .
Summing the moments about point A (Figure 10) :
0 = -FHl*zl+FTlx*z2
FTlx = (zl/z2) *FH1
Then:
FTlx = 109. 7N
Substituting :
FT2x = FHl-FHlx
FT2x = 47. 5N
Repeating the calculations for the x direction from
FH2 :
FH2cosP = FT2x'+FTlx'
FT2x'= FH2cosp-FTlx '
Summing moments about A :
0 = -FH2cosP*z3+FTlx' *z2
FTlx'= FH2cosP* (z3/z2)
FTlx'= 14. 7N
Substituting :
FT2x' = FH2cosp-FTlx '
FT2x'= 37. N
Adding the respective forces in the x direction for
the tensioners gives:
FTlx" = FTlx+ FTlx'
FTlx" = 109.7N+14.7N = 124. 4N
And
FT2x" = FT2x+ FT2x'
FT2x" = 47.5N+37.6N = 85. IN
Repeating these calculations for forces in the Y
direction yeilds:
FTly" = 168. IN
FT2y" = 583. ON
Geometry informs the magnetude of FTl and FT2 by:
FTl = 209. IN
FT2 = 589. 2N
From this, simple geometry gives us the angles of
these forces:
Q = asin (FT2y"/FT2) = 81.7 deg
a = asin (FTly"/FTl) = 53.5 deg
Similar determinations of tensioner force can be
made for each tensioner position and then each tensioner
can be configured to create the required force. Table 1
below is a summary of the required tensioner forces. The
values in Table 1 are provided only as examples and are
not intended to limit the scope of the invention.
Table 1
Figure 12 is a detail of the tensioner. Again
turning to tensioner 5 , each arm 500, 510 has a rotation
5 center about the center of shaft 4 , also see Fig. 19.
Torsion spring 504 simultaneously applies a rotational
force to each arm 500, 501. The arms function as an
opposing pair with the same torque being applied to each
arm. Each arm surface 505, 506 rests against a surface
10 of the housing 9 , namely 91, 92 respectively. The torque
applied to the arms by the torsion spring 504 causes them
to rotate. The resulting rotation causes the tensioner
center of rotation, and therby the center of shaft 4 , to
move. The center of rotation moves until an opposing
15 force prevents it, namely belt tension. The opposing
force which equilibrates the system is the desired belt
tension force.
Each arm 500, 501 has a circular profile at the
contact surface 505, 506 respectively. The distance
20 between the tensioner rotation center (shaft 4 center)
and a line perpendicular to the bracket surface 91 at the
point of contact with the arm surface 505, see Figure 12
and Figure 19, is the effective tensioner arm length "E".
The effective arm length E changes with the rotation of
25 the tensioner arms.
Figure 13 is a detail of the tensioner. In Figure 13
line A is perpendicular to the bracket surface 91 and is
perpendicular to line a . Line B is perpendicular to line
b . The effective arm length E is the distance from line
A to the rotation center along line a .
The center of cruvature of the arm surface is offset
a fixed distance from its center of rotation. The
effective arm length is equal to the offset only when
lines A and B are coincident with one another. When
lines A and B are not coincident, the effective arm lenth
is less than the center offset (CO) as a function of the
angle formed between the lines.
E = Effective arm length = CO*cos (w)
Given :
CO = 6mm
w = 8deg
Effective arm length = 6 cos (8) = 5.94mm
The force from each tensioner arm is equal to the
torque on the arm divided by the effective arm length.
Knowing the force required of the tensioner acts
against the angular surfaces of the housing, for exmaple,
91, 92, at the point of contact of the tensioner arm and
the surface, one can determine the force required at
these surfaces and from that, the torque required in the
tensioner arm.
Given :
SA = Surface 91 angle = 30 deg
TF = Tensioner force = 635N
Then :
Arm force = (TF/2 )*cos (SA)
AF = (635/2) *cos (30)
AF = 275N
The torque required in the arm is simply the arm
force (AF) times the effective arm length (EAL) .
Torque = AF*EAL
T = 275N*0 .00594m = 1.63Nm
Tensioners 5 , 6 , 7 , 8 are designed such that as the
arms rotate, the effective arm length is reduced. Each
respective torsion spring (504, 604, 704, 804) also
provides less torque as the tensioner arms rotate. If
the torsion spring has a spring rate of O.OlNm/deg and
the arms rotate 20 degrees, then the torque from the
spring drops by 0.2Nm. The effective arm length changes
from the above 5.94mm to 5.30mm. The resulting tensioner
arm force remains nearly constant at 270N.
The included angle of the faces of the housing
surfaces 91, 92 can range between 180deg to 90deg giving
a surface angle of Odeg to 45deg as described above, see
Figure 14, Figure 15 and Figure 19.
If the angle between surfaces 91, 92 is 0 degrees,
there is no horizontal force component from the tensioner
arms. Surface angles greater than zero causes the
tensioner to self center due to the horizontal component
of the force being equal and opposite from each tensioner
arm. If the surface angle exceeds 45 degrees, these
horizontal components exceed the tensioning force. This
creates a condition of "diminishing returns" on the
spring torque. As the spring torque is increased, the
horizontal component of tensioner force grows more than
the tensioning force.
Figure 14 is a detail of the force components in the
tensioner arms. Vector "A" indicates the force on
surface 505 exerted by surface "TS" at the point of
contact between 505 and TS . Vector "B" indicates the
force on surface 506 exerted by surface "TS" at the point
of contact between 506 and TS . Surface TS is analogous to
surface 91 and surface 92. Surface TS depicts the 180
degree condition between surfaces 91, 92. Given the
offset of each tensioner arm 500, 501, see Figure 5 and
Figure 19, vectors A and B are not co-axial.
Figure 15 is a perspective view of housing 9 .
Housing 9 comprises bracket surface 91 and bracket
surface 92. Tensioner surface 505 and tensioner surface
506 engage surfaces 91 and 92 respectively.
Figure 16 is a perspective view of housing 10.
Bearing 50 engages receiving portion 80. Bearing 56
engages receiving portion 81. Tensioner surface 805
engages surface 91c. Tensioner surface 806 engages
surface 92c. Tensioner surface 605 engages surface 91a.
Tensioner surface 606 engages surface 92a.
Figure 17 is a perspective view of the assembled
housing parts. Bracket 82 on housing 10 provides means
to attach the device to a mounting surface (not shown) .
Tensioner 5 engages surfaces 91 and 92. For tensioner 6 ,
arcuate surfaces 605 and 606 engage surfaces 91a and 92a
respectively. For tensioner 7 , arcuate surfaces 705 and
706 engage surfaces 91b and 92b respectively. For
tensioner 8 , arcuate surfaces 805 and 806 engage surfaces
91c and 92c respectively.
Figure 18 is a plan view of the assembled housing
parts .
Figure 19 is a detail of a tensioner arm. Rotation
center (RC) is the point about which the arm 500 rotates
during operation. RC also coincides with the axis of
rotation of shaft 4 . The arm profile center (PC) is the
center of curvature of surface 505, see Figure 13. The
distance between the two points is the offset. The
rotation center radius (Rl) is less than the radius of
curvature (R2) of surface 505. This description is also
applicable to arm 501. This description for Figure 19
also applies to each of the arms for tensioners 6 , 7 and
8 .
Although a form of the invention has been described
herein, it will be obvious to those skilled in the art
that variations may be made in the construction and
relation of parts and method without departing from the
spirit and scope of the invention described herein.

Claims
We claim:
1 . A belt transmission comprising:
a first belt trained between a first shaft and a
first intermediate shaft;
a second belt trained between the first intermediate
shaft and a second intermediate shaft;
a third belt trained between the second intermediate
shaft and a second shaft;
a first tensioner and second tensioner engaged about
the first intermediate shaft, the first tensioner and
second tensioner each comprising a first arm and second
arm and a first spring engaged therebetween, the first
arm and second arm each bearing upon a housing surface,
the first arm and second arm rotatable by operation of
the first spring to thereby exert a force upon the first
intermediate shaft to impart a tension to the first belt
and second belt; and
a third tensioner and fourth tensioner engaged about
the second intermediate shaft, the third tensioner and
fourth tensioner each comprising a first arm and second
arm and a second spring engaged therebetween, the first
arm and second arm each bearing upon a housing surface,
the first arm and second arm rotatable by operation of
the second spring to thereby exert a force upon the
second intermediate shaft to impart a tension to the
second belt and third belt.
2 . The belt transmission as in claim 1 , wherein the
first belt comprises a multi-ribbed profile, the second
belt comprises a toothed profile and the third belt
comprises a toothed profile.
3 . The belt transmission as in claim 1 , wherein the
first spring is a torsion spring.
4 . The belt transmission as in claim 1 , wherein the
second spring is a torsion spring.
5 . The belt transmission as in claim 1 , wherein the
first shaft is an input shaft.
6 . The belt transmission as in claim 1 , wherein the
second shaft is an output shaft.
7 . A belt transmission comprising:
a housing comprising a mount for receiving a driver;
a first belt trained between a first shaft and a
first intermediate shaft;
the first shaft connectable to the driver;
a second belt trained between the first intermediate
shaft and a second intermediate shaft;
a third belt trained between the second intermediate
shaft and a second shaft, the second shaft connectable to
a load;
a first tensioner engaged about the first
intermediate shaft, the first tensioner comprising a
first arm and second arm and a first spring engaged
therebetween, the first arm and second arm each bearing
upon a first housing surface, the first arm and second
arm rotatable b y operation o f the first spring to exert a
force upon the first intermediate shaft whereby a tension
is imparted to the first belt and second belt; and
a second tensioner engaged about the second
intermediate shaft, the second tensioner comprising a
first arm and second arm and a second spring engaged
therebetween, the first arm and second arm each bearing
upon a second housing surface, the first arm and second
arm rotatable by operation of the second spring to exert
a force upon the second intermediate shaft whereby a
tension is imparted to the second belt and third belt.
8 . The belt transmission as in claim 7 , wherein the
first belt comprises a multi-ribbed profile, the second
belt comprises a toothed profile and the third belt
comprises a toothed profile.
9 . The belt transmission as in claim 7 , wherein the
first spring is a torsion spring.
10. The belt transmission as in claim 7 , wherein the
second spring is a torsion spring.
11. A belt transmission comprising:
a housing comprising a mount for receiving a driver;
a first belt trained between a first shaft and a
first intermediate shaft;
the first shaft connectable to the driver;
a second belt trained between the first intermediate
shaft and a second intermediate shaft;
a third belt trained between the second intermediate
shaft and a second shaft, the second shaft connectable to
a load;
a first tensioner and a second tensioner engaged
about the first intermediate shaft, the first tensioner
and second tensioner each comprising a first arm and
second arm and a torsion spring engaged therebetween, the
first arm and second arm each bearing upon a housing
surface, the first arm and second arm rotatable about the
first intermediate shaft by operation of the torsion
spring to exert a force upon the first intermediate shaft
whereby a tension is imparted to each of the first belt
and second belt; and
a third tensioner and a fourth tensioner engaged
about the second intermediate shaft, the third tensioner
and fourth tensioner each comprising a first arm and
second arm and a torsion spring engaged therebetween, the
first arm and second arm each bearing upon a second
housing surface, the first arm and second arm rotatable
about the second intermediate shaft by operation of the
torsion spring to exert a force upon the second
intermediate shaft whereby a tension is imparted to each
of the second belt and third belt.
12. The belt transmission as in claim 11, wherein the
first belt comprises a multi-ribbed profile, the second
belt comprises a toothed profile and the third belt
comprises a toothed profile.
13. A belt transmission comprising:
a housing;
a first belt trained between a first shaft and a
first intermediate shaft;
a second belt trained between the first intermediate
shaft and a second intermediate shaft;
a third belt trained between the second intermediate
shaft and a second shaft;
a first tensioner and second tensioner each engaged
with the housing and each engaged about the first
intermediate shaft whereby each tensioner exerts a force
upon the first intermediate shaft which thereby imparts a
tension to the first belt and to the second belt; and
a third tensioner and fourth tensioner each engaged
with the housing and each engaged about the second
intermediate shaft whereby each tensioner exerts a force
upon the second intermediate shaft which thereby imparts
a tension to the second belt and to the third belt.
14. The belt transmission as in claim 13, wherein the
first tensioner and second tensioner each comprise a
first arm and second arm and a first spring engaged
therebetween, the first arm and second arm each bearing
upon a housing surface, the first arm and second arm
moveable by operation of the first spring.
15. The belt transmission as in claim 13, wherein the
third tensioner and fourth tensioner each comprising a
first arm and second arm and a second spring engaged
therebetween, the first arm and second arm each bearing
upon a housing surface, the first arm and second arm
moveable by operation of the second spring.
16. The belt transmission as in claim 13, wherein the
first belt comprises a multi-ribbed profile, the second
belt comprises a toothed profile and the third belt
comprises a toothed profile.
17. The belt transmission as in claim 14, wherein the
first spring comprises a torsion spring.
18. The belt transmission as in claim 15, wherein the
second spring comprises a torsion spring.
19. A belt transmission comprising:
a housing;
a first belt trained between a first shaft and a
first intermediate shaft;
a second belt trained between the first intermediate
shaft and a second intermediate shaft;
a third belt trained between the second intermediate
shaft and a second shaft;
a first tensioner and second tensioner each engaged
with the housing and each engaged about the first
intermediate shaft whereby each tensioner exerts a force
upon the first intermediate shaft which thereby imparts a
tension to the first belt and to the second belt; and
a third tensioner and fourth tensioner each engaged
with the housing and each engaged about the second
intermediate shaft whereby each tensioner exerts a force
upon the second intermediate shaft which thereby imparts
a tension to the second belt and to the third belt.
20. The belt transmission as in claim 19, wherein the
first tensioner comprises a first tensioner first arm and
a first tensioner second arm and a first tensioner spring
engaged therebetween, an arcuate first tensioner first
arm surface and an arcuate first tensioner second arm
surface each bearing upon a housing surface, the first
tensioner first arm and first tensioner second arm
moveable by operation of the first tensioner spring.
21. The belt transmission as in claim 19, wherein the
second tensioner comprises a second tensioner first arm
and a second tensioner second arm and a second tensioner
spring engaged therebetween, an arcuate second tensioner
first arm surface and an arcuate second tensioner second
arm surface each bearing upon a housing surface, the
second tensioner first arm and second tensioner second
arm moveable by operation of the second tensioner spring.
22. The belt transmission as in claim 19, wherein the
third tensioner comprises a third tensioner first arm and
a third tensioner second arm and a third tensioner spring
engaged therebetween, an arcuate third tensioner first
arm surface and an arcuate third tensioner second arm
surface each bearing upon a housing surface, the third
tensioner first arm and third tensioner second arm
moveable by operation of the third tensioner spring.
23. The belt transmission as in claim 19, wherein the
fourth tensioner comprises a fourth tensioner first arm
and a fourth tensioner second arm and a fourth tensioner
spring engaged therebetween, an arcuate fourth tensioner
first arm surface and an arcuate fourth tensioner second
arm surface each bearing upon a housing surface, the
fourth tensioner first arm and fourth tensioner second
arm moveable by operation of the fourth tensioner spring.
24. The belt transmission as in claim 19, wherein the
first belt comprises a multi-ribbed profile, the second
belt comprises a toothed profile and the third belt
comprises a toothed profile.
25. A belt transmission comprising:
a housing;
a first multi-ribbed belt trained between an input
shaft and a first intermediate shaft;
a second belt having teeth trained between the first
intermediate shaft and a second intermediate shaft;
a third belt having teeth trained between the second
intermediate shaft and an output shaft;
a first tensioner and second tensioner each engaged
with the housing and each engaged about the first
intermediate shaft whereby each tensioner exerts a force
upon the first intermediate shaft which thereby imparts a
tension to the first belt and to the second belt; and
a third tensioner and fourth tensioner each engaged
with the housing and each engaged about the second
intermediate shaft whereby each tensioner exerts a force
upon the second intermediate shaft which thereby imparts
a tension to the second belt and to the third belt.
26. A belt transmission comprising:
an input shaft;
a belt trained between the input shaft and a first
intermediate shaft;
a second belt trained between the first intermediate
shaft and a second intermediate shaft;
a third belt trained between the second intermediate
shaft and an output shaft;
the position of the first intermediate shaft being
moveable during operation of the belt transmission to
thereby apply a tension to the first belt and second
belt; and
the position of the second intermediate shaft being
moveable during operation of the belt transmission to
thereby apply a tension of the second belt and the third
belt.
27. The belt transmission as in claim 26, wherein the
first intermediate shaft is supported by a first
tensioner and a second tensioner .
28. The belt transmission as in claim 26, wherein the
second intermediate shaft is supported by a third
tensioner and a fourth tensioner.
29. The belt transmission as in claim 26, wherein the
first belt has a multi-ribbed profile.
30. The belt transmission as in claim 27, wherein:
the first tensioner comprises a first arcuate
surface bearing upon the housing and a second arcuate
surface bearing upon the housing.