Note: Descriptions are shown in the official language in which they were submitted.
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Disclosure
Technical Field
This invention relates to general types of transmissions for, but not
restricted to,
vehicular use. It may be described as a reversible, split power continuously
variable
transmission.
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Background
The most common type of CVT is the belt driven type. This type of transmission
operates through the use of a pair of variable diameter pulleys. To change the
transmission ratio, one pulley decreases in diameter as the other one
increases in
diameter. This process reverses to produce the opposite effect. While useful,
this
transmission requires that all of the force that is to be transferred from the
source to the
application must be transferred through the belt, which operates by friction.
A
transmission that is based on friction is severely limited in the amount of
power that can
be transferred to the output shaft. If there is too much power being
transferred, the belt
will slip. Another problem with this type of transmission is that it does not
continuously
vary to the transmission ratio of zero, or below, into the negative ratios.
This creates the
need to disengage the transmission from the engine to stop the output shaft.
This also
brings forth the need for a reversing gear set to reverse the output shaft.
It was discovered that through coupling a regular belt type CVT to a
differential it
is possible to extend the range of the transmission to the ratio of zero, and
below, into the
negative ratios. Coupling a belt type CVT to a differential also splits the
power transfer
between the belt and a gear set. This considerably reduces the load that the
belt must
carry, in turn increasing the total load the transmission as a whole can
handle.
In the patent search process, there were no CVTs found that contained a
differential coupled to a belt type CVT in the manner utilized in this design.
Canadian
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patents number 1,130,112 and 1,200,988 and 1,289,387 are described to contain
differentials and continuously variable belt and pulley arrangements. These
patents,
however, utilize the differential for the standard purpose of preventing
binding in the
output shafts between the transmission output and the tires. These
transmissions utilize
the differential with one input (the ring gear) and two outputs (the side
gears). In
addition, the inclusions of the differentials in these designs do not extend
or alter the
usable variable range of the variable belt and pulley arrangements. The Split
Power,
Differential Aided CVT for which this application is written, on the other
hand, combines
the differential to the variable pulley and belt arrangement in a manner that
significantly
alters the achievable final transmission ratio, that is from positive to zero
and negative
transmission ratios without disengaging any part of the transmission (i.e., by
clutch or
torque converter). The differential in this design instead has two inputs and
one output.
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Summary
As will be described in further in the following detailed preferred
embodiment,
the split power, differential aided continuously variable transmission extends
the range of
a standard belt type C VT in addition to reducing the torque that is
transmitted through it.
The split power, differential aided CVT includes a belt type CVT, consisting
of a pair of
variable diameter pulleys and a wide V-belt. The final transmission ratio
varies as a
function of the variable belt ratio due to the inclusion of a differential
gear set and an
additional simple gear set. Utilized in this application, the differential has
two inputs and
one output. The additional gear set connects the transmission input shaft, on
which the
first gear is mounted, through mesh with an intermediate gear to the
differential's ring
gear, causing the ring gear to turn in the same rotational direction as the
input shaft. The
aforementioned continuously variable belt and pulley arrangement connects the
transmission input shaft to the differential's second input, a shaft inserted
into one of the
differential side gears, on which the second variable pulley is mounted. The
other
differential side gear and the shaft extending from it serve as the
transmission output
shaft. It is the combination of the variable belt ratio with the differential
and the fixed
gear ratio in the aforementioned manner that achieves a variable final
transmission ratio
range that a standard variable belt arrangement cannot achieve, namely from
positive
ratios to negative ratios, including a zero ratio. As the belt ratio
increases, the differential
input side gear will begin to rotate faster than the differential housing,
causing the output
shaft to rotate slower than the differential housing, eventually coming to a
stop.
Continuing the belt ratio increase will reverse the output shaft's rotational
direction.
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Brief Description of the Drawing
Figure 1 shows the basic configuration of the parts of the split power,
differential
aided continuously variable transmission. The transmission's operation and
advantages
will be fully understood by reading the following detailed preferred
embodiment,
together with the drawing, in which:
Items 1 and 2 are the variable diameter pulleys and item 3 is the V-belt
comprising the continuously variable belt mechanism.
Items 4 and 5 are gears, allowing the various shafts to be connected,
providing a
means to share the torque transmitted through the transmission as a whole with
the
continuously variable belt. The gears transmit their portion of the shared
torque from one
variable diameter pulley to item 6, the differential ring gear.
Item 7 is the differential gear set consisting of side gears 7a and 7c and
spider
gears 7b. Differential 7 serves as the confluence for the shared torque,
transmitting it to
the output shaft. Item 6, the differential ring gear, is bolted to item 7d,
the differential
housing.
Items 8, 9 and 10 are shafts, which serve to connect pulleys to gears, or to
allow
free rotation of gears. Each of items 8, 9 or 10 can serve as the input shaft.
Shaft 8 is
affixed to gear 4 such that they rotate together. Shaft 9 is affixed to gear 5
such that they
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rotate together. Shaft 10 is affixed to item 7a, a differential side gear such
that they rotate
together. Shaft 10 is allowed to rotate freely within items 6 and 7d, the
differential ring
gear and housing assembly. Variable diameter pulley 1 is affixed to shaft 8 in
a manner
such that they rotate together, but the halves of the pulley are allowed to
slide axially
along the shaft to vary the pulley diameter. Variable diameter pulley 2 is
affixed to shaft
in a manner such that they rotate together, but the halves of the pulley are
allowed to
slide axially along the shaft to vary the pulley diameter. All shafts rotate
freely in the
support structure, as shown on the drawing.
Item 11 is the output shaft. Shaft 11 is affixed to item 7c, a differential
side gear
such that they rotate together. Shaft 11 is allowed to rotate freely within
item 7d, the
differential housing. Shaft 11 also rotates freely in the support structure,
shown on the
drawing.
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Detailed Description of the Preferred Embodiment
Referring to the drawings, the preferred embodiment of the Split Power,
Differential Aided Continuously Variable Transmission as shown in Figure 1 is
as such:
Item 8 is the preferred input shaft where the input torque is to be applied.
Item 1 is
the first of variable diameter pulley, also referred to as the input pulley,
which is mounted
to shaft 8. Item 4 is the first gear in the gear set, referred to as the input
gear, also
mounted to shaft 8. These three components all rotate in unison, in the same
rotational
direction.
Item 2 is the second variable diameter pulley, also called the output pulley.
Item 3
is a wide V belt. It provides one torque path, referred to as the belt torque,
for the input
torque to be transmitted to the output shaft. Belt 3 interfaces with pulley 1
and pulley 2
transmitting the belt torque from input pulley 1 to output pulley 2. Moving
the halves of
each pulley together or apart varies its diameter. As the pulley halves move
apart, belt 3
is allowed to slip further into the pulley groove, decreasing the pulley's
effective
diameter. As the pulley halves move together, belt 3 is forced outwards,
increasing the
pulley's diameter. The belt ratio varies by varying the diameters of pulley 1
and pulley 2
in opposite direction. That is, as the diameter of pulley 1 increases, the
diameter of pulley
2 decreases, and as the diameter of pulley 1 decreases, the diameter of pulley
2 increases.
Because the pulleys can be set to any diameter between their maximum diameter
and
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minimum diameter, the belt ratio can vary infinitely between it's maximum and
minimum. Items 1, 2 and 3 together comprise the continuously variable belt
mechanism.
Item 5 is a gear that meshes with input gear 4 and item 6, the differential
ring
gear. Gear 5 is mounted on item 9, an independent shaft, which is allowed to
freely rotate
inside the transmission assembly. Shaft 9 also serves as an alternate
transmission input
shaft. The inclusion of gear 5 in this transmission ensures that input gear 4
and
differential ring gear 6 rotate in the same rotational direction. Items 4, 5
and 6 together
comprise the gear set, which provides the second path for torque, referred to
as the gear
torque. The ratio of the rotational speed of input gear 4 and differential
ring gear 6 is
referred to as the gear ratio.
Item 7 is the differential. As used in other normal applications differential
ring
gear 6 would be the differential's input, and the two shafts that come out of
the
differential would serve as the output shafts, on which wheels would most
commonly be
placed. In any application of this invention, one of these output shafts must
serve as an
input shaft. Item 10 is this shaft, on which output pulley 2 is mounted. Shaft
10 transmits
the belt torque from output pulley 2 to the differential side gear 7a.
Differential side gear
7a meshes with the differential spider gears 7b, which in turn mesh with
differential side
gear 7c. Differential side gear 7c is connected to item 11, the output shaft
of the
transmission assembly. Item 7d is the differential housing. Differential ring
gear 6 is
externally fixed to differential housing 7d and is coupled such that torque
from ring gear
6 is transmitted directly to the housing 7d. The differential spider gears 7b
are mounted
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internally to differential housing 7d and are allowed to freely rotate in the
previously
described mesh with side gears 7a and 7c.
Differential 7 achieves the recombination of the split torque at the
differential
spider gears 7b. While freely rotating in mesh with the side gears 7a and 7c
the spider
gears 7b rotate with the differential housing 7d and the differential ring
gear 6. This
allows the belt torque in differential side gear 7a to be applied through the
mesh with
spider gears 7b, simultaneously with the gear torque from differential housing
7d, applied
through the spider gear 7b internal mounting. The belt torque from the mesh
and the gear
torque from the mounting are both transmitted to the differential side gear
7c.
Output shaft 11, extending from side gear 7c, is then connected to the desired
application of the transmission's output torque. The ratio of the rotational
speed of input
shaft 8 and output shaft 11 is referred to as the transmission ratio.
To better understand the benefits of coupling a belt type CVT and a
differential,
and to describe the belt ratio and transmission ratio relationship of the
split power,
differential aided CVT formulae were derived to mathematically model the
behavior.
Through these mathematical formulae graphs can be drawn to show the
transmission's
final output ratio as a function of the variable belt ratio and how force
transmitted
through the belt is reduced.
CA 02269350 2008-04-09
This transmission was originally invented utilizing shaft 10 as the input
shaft.
Formulae using shaft 10 as the input shaft are described by the words
"original
configuration". It was discovered that utilizing shaft 8 as the input shaft
would simplify
adoption of this transmission in preferred applications, and would allow the
overall
transmission ratio to extend further into the negative range.
Formula la describes the differential behavior for the original configuration.
Q)i COo
COd= 2+ 2 (la)
Formula 1 b describes the differential behavior for the preferred embodiment.
cm ClJb
COd = 2 2 (lb)
Formula 2 describes the overall transmission ratio.
RT = coo
(2)
CV i
Formula 3 describes the continuously variable belt ratio.
RB = (3)
COi
Formula 4a describes the fixed gear ratio of the original configuration.
a1d
Ru = (4a)
Coi
Formula 4b describes the fixed gear ratio of the preferred embodiment.
Rc = COd (4b)
COi
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Where:
w; is the angular Speed of Input Shaft 10 (original configuration) or 8
(preferred),
co,) is the angular Speed of Output Shaft 11
wd is the angular Speed of Differential Gear 6
cot is the angular Speed of Shaft 8 (original configuration) or 10 (preferred)
RT is the Transmission Ratio
RB is the Belt Ratio
RG is the Gear Ratio
Substituting and solving the final transmission ratio formulae are obtained.
The final
transmission ratio relationship for the original configuration is shown in
equation 5a.
RT=2*RB*RG-1 (5a)
The transmission ratio relationship for the preferred embodiment is shown in
equation 5b.
RT = 2 *.RG -RB (5b)
These final relationships can then be plotted to graphically show their
behavior. The
plots are performed between the belt ratios of 1:4 to 4:1, or.25 < RB < 4.
Graph 1 shows
the relationship between transmission ratio and belt ratio of the original
configuration.
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Transmission Ratio vs. Belt Ratio
8
6
ca
c 4
0
IA
(A 2
E
0250.50.75 1 1.25 1.51.75 2 2.252.52.75 3 3.25 3.5 3.75
-2
Belt Ratio
Graph 1: Transmission Ratio as a Function of Belt Ratio
Graph 2 shows this same relationship for the preferred embodiment.
Transmission Ratio vs. Belt Ratio
2
1.5
1
0
0 0.5
0 0
0 25 0.5 0.75 1 1.25 1.5 1.75 2 2.5 2.75 3 3.25 3.5 3.75
~ -1
-2.5-
Belt Ratio
Graph 2: Preferred Embodiment Relationship
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It should be noted that the above graphs are plotted with the fixed gear ratio
of 1. The
gear ratio is chosen on a per application basis, such that a more desirable
overall
transmission ratio range can be obtained. Graph 3 is a plot of the preferred
embodiment
ratio range with a fixed gear ratio of 1.5.
Transmission Ratio vs. Belt Ratio
3
2.5
2
0
c 1.5
o 1
E 05-
0
-0 50 25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 -,"3N7%5 3.75
-1
-1.5
Belt Ratio
Graph 3: Preferred Embodiment Relationship
In the preferred embodiment, it can be seen that altering the gear ratio
simply moves the
ratio line up or down. This simplicity is beneficial in fitting this
transmission to perform
a specific task in a specific application.
Gears 4 and 5 and differential ring gear 6 used shares the torque that is to
be
transmitted from the source to the destination with the belt, thereby reducing
the load on
the belt. This effectively increases the total load that the transmission as a
whole can
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handle. The force analysis is done for the regular CVT, and then the
differential aided
CVT for comparison. The calculations and plotting were done between the belt
ratios of
1:4 and 4: 1, or .25 to 4.
rl Ti,
FT
Figure 3.1: Standard CVT Force Relationship
From figure 3.1, we can obtain the mathematical relationship:
Ti. Fr=- (6a)
ri
Where:
FT is the tension force in belt
Ti, is the input torque from engine
For the split power, differential aided version of the CVT, the force is
transmitted
differently.
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1 /2 Tul 1 /2 Tin
r Tin
i
CVT Belt RGear Set
FT
Figure 3.2: Split Power, Differential Aided CVT Force Relationship
From figure 3.2, the belt force can be calculated by:
in
FT = - (6b)
2*r-i
As shown in figure 3.2, for the differential aided variation of the CVT, the
torque is
shared between the belt and the gear set. To create formulae to display the
reduction in
belt force the following formula is needed:
RB = ri (7)
r2
Where RB is the belt ratio, rl is input pulley 1 radius and r2 is output
pulley 2 radius. For
a unit ri and r2, r2 can be obtained as a function of rl:
r2 = 2 - ri (8)
Substituting equation 7, 8 and RB = RT into equation 6a, the belt force as a
function of
transmission ratio for a regular CVT can be obtained.
Fr = Till + Ti, (9)
2 *Rr 2
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Substituting equations 7, 8 and 5b into equation 6b we obtain the belt force
as a
function of transmission ratio for the differential aided CVT.
Ti. T
.
Fr=8*RG-2*RT+ 4 (10)
These results can then be plotted for a unit-input torque, or Tin = 1. Graph 4
is a
comparison of the belt force in a regular CVT to the belt force in the
differential aided
CVT. The regular CVT is plotted in a dotted line, while the differential aided
(DA) CVT
is plotted with a gear ratio of 1, in a thin single line, and 1.5, shown in a
thick single line.
Belt Force in CVTs (Unit Input Torque)
3
2.5
2
m
o
`o
"-1.5
1
0.5
0
-2 -1.7 -1.4 -1.1 -0.8 -0.5 -0.2 0.1 0.4 0.7 1 1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4
3.7 4
Transmission Ratio - = - - = - = Regular CVT DA CVT Rg=1 DA CVT Rg=1.5
Graph 4: Belt Force With a Unit Input Torque
We can see that by increasing the gear ratio, the force transferred through
the belt
is further reduced.
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For a vehicle to accelerate at a constant rate, a constant output torque is
required.
For all transmissions, the output torque varies inversely to the transmission
ratio for a
constant input torque, as seen in the following formula.
RT = 1 - = Tin
- (11)
RTQ Tout
or:
Ttn = RT * Tout (12)
Where:
TQõG is the output torque applied to the application
RTQ is the torque ratio
Applying equation 12 to equation 9, we can obtain the relationship between the
force in
the belt and the transmission ratio for a constant output torque in a regular
CVT.
T = Tout + Rr *Tont 2 2 (13)
Also, applying equation 12 to equation 10, we can obtain the relationship
between the
force in the belt and the transmission ratio for a constant output torque in
the differential
aided CVT.
FT _ RT *Tout + RT *T w 8*Ro-2*RT 4 (14)
We again plot these relationships between the belt ratio range of 1:4 to 4:1,
this time with
a unit output torque. Again, the standard CVT is in a dotted line, while the
differential
aided (DA) CVT is plotted with a gear ratio of 1 in a thin line and the gear
ratio of 1.5 in
a thick line.
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Belt Force in CVTs (Unit Output Torque)
3
2.5
2
d 1.5
U
0
LL 1
0.5
0
2 -1.7 -1.4 -1. . --- 5 -0.2 0.1 0.4 0.7 1 1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4 3.7
-0.5
-1
Transmission Ratio - - . - - - RegularCVT DA CVT Rg=1 DA CVT Rg=1.5
Graph 5: Belt Force with a Unit Output Torque
It is clear in graphs 4 and 5 that the split power, differential aided CVT
transmission has
less force in the belt as compared to a regular CVT.
