Note: Descriptions are shown in the official language in which they were submitted.
7'~05
'rilIS INVENTION relates to variable speed transmissions.
In Canadian Application Serial No. 284,971 filed August
18, 1977, the transmission disclosed featured a traction drive
assembly through which a small fraction of the total torque
transmitted by the transmission is utilised to vary and
establish the overall transmission drive ratio in a practical
and efficient manner by providing a favourable relationship
between the drive ratio and the contact pressure in the traction
drive assembly. The traction drive assembly is positioned in
laterally spaced relationship to the transmission gearing and
includes a driven traction roller axially shiftable along a
fixed path parallel to the common rotational axis for the
transmission input and output shafts. The other traction roller
of variable diameter is mounted on a pivotally displaceablè
bracket for limited corrective displacement during axial shift
of the driven roller engaged therewith to vary the drive ratio.
~ According to the present invention, there is provided a
: change speed transmission, comprising input and output members,
a power transmitting gear arrangement drivingly interconnecting
said input and output members for establishing a relatively
high torque power path therebetween, a low torque biasing gear
- arrangement drivingly connected between the input member and
the power transmitting gear arrangement for establishing a
drive ratio between the input and output members, and a
variable traction drive driven by the input
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member for controlling, by means of the torque biasing gear
arrangement, said drive ratio, said traction drive including
a traction roller rotatable about a fixed axis common to
the input and output members~
In the preferred embodiment the traction drive includes
a roller, whose diameter varies along its length driven by
an input shaft about the rotational axis common to the input
and an output shaft. A driven traction roller is mounted on a
pivotal bracket and is axially shiftable along its spLlne shaft
to change the transmission drive ratio. Contact pre~sure
between the rollers is changed as a function of the driven
roller position and the pitch line curvatures of the roller~
at the contact zone. The contact pressure is thereby varied
in an optimum manner characterised by a minimum pressure in
the neutral position of the driven roller as predetermined
by the drive relation~hips in the gearing which is axially
aligned with the variable diameter tr~ction rollerO As an
alternative, the axially shiftable roller could be rotatable
about a fixed axis common with the input and output shafts
; 20 while the variable diameter roller i~ mounted at an angle
thereto on the bracket. In the latter arrangement, a
plurality of variable diameter rollers could be mounted by
a plurality of brackets for drive engagement with the
axially shiftable roller in order to distribute the torque
load and thereby increase the load capacity of the transmission.
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Power transmis~ion through the gearing may be interrupted by
release of a hydrosta-tic brake holding a floating carrier for
a gear train interconnecting orbit gears in the high torque
transmitting gear assembly of the transmission~
The invention will be further described with reference
to the accompanying drawings, in which:-
Figure 1 is a somewhat simplified and partially
schematic side elevational view of an embodiment of
transmission in accordance with the present inven-tion,
Figures 2, 3 and 4 are enlarged partial sectional
views of the gearing taken substantially on planes indicated
by section lines 2-2, 3-3 and 4-4 in Figure l;
: Figure 5 is an ~nlarged partial sectional view of the
. traction drive assembly taken substantially through a plane
`~ 15 indicated by section line 5-5 in Figure 1:
Figure 6 is a graph showing various operational
relationships associated with the transmission of Figure 1.
Referring now to Figure 1 in particular, the
transmission 12 includes an input shaft 16 and an axially
aligned output shaft 18. The input shaft i5 directly
connected to an infinitely variable traction drive assembly
generally referred to by réference numeral 42 through which
selection of the over-all transmission drive ratio is
effected. A power transmitting gear assembly 40 drivingly
interconnects the input`and output shafts while torque bias
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control means 44 drivingly interconnects the variable traction
drive assembly 42 with the powcr transmitting gear assembly 40.
The torque bias control means 44 is arranged to reduce the
ordinarily expected load and power requirements imposed on
the variable traction drive assembly in performing its drive
ratio changing function for the over-all tran~mission.
As more clearly seen in Figures 1, 3 and 4, the power
transmitting gear assembly 40 includes a differential planetary
gear set 46 formed by a sun gear 48 fixed to the inner end of
the input shaft 16. The sun gear 48 is in constant mesh with
planet gears 50 rotatably mounted on a carrier 52. The planet
gears 50 also mesh with an internal orbit gear 54 having
train
external gear teeth 56 enmeshed with a floating gear/comprising
intermeshing gears 58, 60 drivingly connecting the orbit gear
54 to orbit gear 64 associated with a power path combining
planetary gear set 66. The gear train includes intermeshing
gears 58 and 60. The parallel axes of the gears in this year
. train are rotatable on a carrier. 62 adapted to be retarded
against rotation by a hydrostatic braking device 74 of any
well-known type connected to a cloced fluid control circuit 22.
The gear set 66 includes planet gears 68 in constant mesh with
.~ the orbit gear 64 and rotatably mounted on a carrier 70 fixedto th~ output shaft 18. The planet gears 68 are also in mesh
with a sun ~ear 72 that is fixed to the carrier 52 of the
: 25 differential gear set 460
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It will be apparent that the :input ~haft 16 will
transmit torque through the gear set 46 at a drive ratio
dependent on the rotational ~peed of the carrier 52 relative
: to the sun gear 48. The carrier 52 is, therefore, rokated
at a lower speed than the input sha~t to enable transmission
of high torque through gear set 4~ to the orbit gear 54 under
control of a relativ~ly low torque drive throu~h the variable
traction drive assembly 42. The power path through which low
torque is transmitted to the carriex 52 ~or drive rat:Lo control
purposes terminates at the sun gear 72 of gear set 66 to
~ which high torque is transmitted from orbit gear 54 through
: the gear train formed by gears 58, 60 and 61 ~hen the floating
gear carrier 62 is held stationary by the hydrostatic
: brake 74. Manual or override control over the transmission: 15 may be exercised through the hydrostatic brake by means of
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its fluid control circuit 22. A neutral and drive control
valve assembly 24 may accordingly be a~sociated with the fluid
circuit to selectively restrict 10w therein. A spring or
automatically biased torque control valve 26 may also be
connected in parallel with the control valve assembly 24.
. Shock protection is provided by an accumulator 28.
A pressure sensor 29 connected to the fluid circuit will be
~ effective to monitor the torque transmitted through the
; gearing and thereby supply a signal to an automatic control
30 for ~hanging the spring tension of the device 152 in order
. to compens~te for abrupt increa~es in torque loading on the
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transmission. Other control arrangements may, of course,
be utilised for the brake device 74. A parking brake element
80 i5 al~o provided on the c)utput shaft 18.
It will be apparent that a suitable housiny will be
provided for the transmission hereinbefore described,
constituting the sta~ionary frame for the gearing. The
housing frame supports a fixed pivot 92 about which a slide
bracket 120 is pivotally displaceable in a pivotal plane
intersecting the common rotational axis of the input and
output shafts. The slide bracket 120 rotatably mounts an
; elongated position control screw 124 by means of spaced
bearings carried by the bracket 120. The screw 124 is
threadedly engaged with a carriage 112 as shown in Figures
; 1 and 5 for displacement of a traction roller element 110
axially along a shaft 118 to which it is splined. The shaft
118 is rotatably mounted on the bracket 120 by a bearing 90
for rotation about an axis parallel to that of the screw
shaft 124. A suitable coupling joint 100 connects the spline
shaft 118 to a gear 132 ~or transmitting a low control torque
to the torque bias control means 40. Gear 132 and gear 134
with which it is enmeshed are fixed axes gears for
transmitting the low torque to an orbit gear 136 associated
with the torque bias control means 44. The orbit gear 136
is in constant mesh with planet gears 138 as shown in Figures
2~ 1 ahd 2, said planet gears being rotata~ly mounted on the same
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carrier 52 associated with the power transmitting gear
assembly 40. A sun gear 140 fixed to the input shaft 16
meshes with the planet gear 13~.
The traction roller element 110 which is of substan-
tially constant drive diameter is held in frictional drive
en~agement with a variable cliameter traction drive element 94
fixed to thP input shaft for rotation therewith about ~he
central rotational axis of the transmission. An adju~table
tension device 152, such as that disclosed in my prior copending
Application aforementioned, bears against the pivotal slide
bracket 120 so as to establish the drive engaging pressure
between the traction roller elements 110 and 94 at their zone
of contact. The zone of co~tact is, of course, shifted by
; rotation of the screw shaft 124 so as to change the transmission
- 15 drive ratio and will at the same time change the leverage ratio
throuyh which the tension device 152 exerts its force at the
zone of contact. Therefore, the contact force will vary for
each position of the roller element 110 in accordance with
some non-linear function as depicted by curve 168 in
Figure 6. The geometry of the arrangement described is such
; that the minimum point 170 on the curve 168 coincides with
the neutral condition of the transmission corresponding to a
zero drive ratio, the drive ratio being reflected on the
ordinate 162. The drive ratio is proportional to the
displacement of the roller element 110 as depicted by the
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straigh~ line curve 158 plotted again~t the roller e1.ement
position on the absci3~a 160.
The roller element 110 i~ sh.ifted along shaft 118
between one limit position clS shown in Figure 1 at which the
roller elements are of equal diameter as shown by way of
example to an opposite limit: po~ition at which the di~neter
of roller element 94 is sub~tantially greater than that of
roller element 110 in order to vary the dri~e ratio in the
drive a~sembly 42 and thereby vary the over-all transmi~ion
drive ratio as aforementioned. Ordinarily the roller elements
engage each othex along a straight or constant coniaal pitch
line corresponding to the pitch angle between the rotational
axes of the input shaft 16 and the roller spline ~haft 118.
In order to meet varying torque requirements, the pitch line
along which the r~ller elements engage each other iq varied by
providing the roller element 94 with a variable pitch
curvature 154. The curvature 154 may be de~igned to effect
a change in contact pressure as a.function of the transmis~ion
drive ratio. A crown curvature 1.56 al~o deviating from the
basic pitch angle i~ provided for the roller element 110.
A ~mall amount of pivotal displacement ~f the roller element
110 ~bo~t pivot 92 occur~ during movement of the roller element
~ etween it~ limit position3 for corrective variation in
the basi~ pitch ~ngle from-which.the roller curvature~ 154 and
156 ~viate,The curvature~ 154 and 156 are theoretically
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tangent to each other at the contact zone between the roller
surfaces for all positions of the roller 110 to minimise
slippage. Some corrective modification of the curvature 156
may also be necessary to maintain the intersection between
the rotational axis of roller 94 and the pitch line at a
constant distance from the pivot point of pivot 92 in order
to minimise normal spin moment of traction. Such error
compensation will result in some variation in the contact
zone area between the engaging roller elements to affect
the contact pressure for any given contact force exerted by
the ten~ion device 152 at the variable leverage aforementioned.
The resultant contact pressure, dependent-on such variables
as the contact force, the contact zone area, the roller
curvatures and the leverage ratio will vary as a function of
the displacement of the roller 110 as depicted by curve 174
in Figure 6. As shown, this resultant pressure curve 174
also has a minimum peak at the neutral position of the
; roller 110.
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