U.S. patent application number 11/178739 was filed with the patent office on 2006-01-05 for continuously variable hydro-mechanical transmission.
Invention is credited to Cecil A. Weeramantry.
Application Number | 20060003861 11/178739 |
Document ID | / |
Family ID | 24976649 |
Filed Date | 2006-01-05 |
United States Patent
Application |
20060003861 |
Kind Code |
A1 |
Weeramantry; Cecil A. |
January 5, 2006 |
Continuously variable hydro-mechanical transmission
Abstract
A transmission for use with a power source and a load includes a
primary sun gear adapted to be coupled to the power source, a
hydrostatic power unit including a pump coupled to a motor, a ring
gear driven by the motor, a secondary sun gear coupled to a first
output shaft, a compound planetary gear carrier coupled to a second
output shaft and a compound planetary gear carried by the compound
planetary gear carrier and in engagement with the ring gear and the
secondary sun gear. The first output shaft and the second output
shaft are adapted to be selectively coupled to the load.
Inventors: |
Weeramantry; Cecil A.;
(Darien, IL) |
Correspondence
Address: |
CNH AMERICA LLC
INTELLECTUAL PROPERTY LAW DEPARTMENT
700 STATE STREET
RACINE
WI
53404
US
|
Family ID: |
24976649 |
Appl. No.: |
11/178739 |
Filed: |
July 11, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10960740 |
Oct 7, 2004 |
|
|
|
11178739 |
Jul 11, 2005 |
|
|
|
10345578 |
Jan 16, 2003 |
6852056 |
|
|
10960740 |
Oct 7, 2004 |
|
|
|
09740469 |
Dec 19, 2000 |
6565471 |
|
|
10345578 |
Jan 16, 2003 |
|
|
|
Current U.S.
Class: |
475/72 |
Current CPC
Class: |
F16H 47/04 20130101;
F16H 2037/0886 20130101; F16H 2037/088 20130101 |
Class at
Publication: |
475/072 |
International
Class: |
F16H 47/04 20060101
F16H047/04 |
Claims
1-21. (canceled)
22. A transmission for use with a power source and a load, the
transmission comprising: a primary sun gear adapted to be
selectively coupled to the power source; a hydrostatic power unit
including a pump coupled to a motor, the pump being adapted to be
driven by the power source; a ring gear adapted to be selectively
driven by the motor; a secondary sun gear coupled to a first output
shaft; a compound planetary gear carrier coupled to a second output
shaft; and a compound planetary gear carried by the compound
planetary gear carrier and in engagement with the ring gear and the
secondary sun gear, wherein the first output shaft and the second
output shaft are adapted to be selectively coupled to the load.
23. The transmission of claim 22 including: a load shaft adapted to
be coupled to the load; and a plurality of range gear sets
selectively coupled between the load shaft and one of the first or
second output shafts.
24. The transmission of claim 22 including: a load shaft adapted to
be coupled to the load; an intermediate shaft; and a plurality of
range gear sets coupled to the intermediate shaft and selectively
coupled between the load shaft and at least one of the first output
shaft and the second output shaft.
25-26. (canceled)
27. The transmission of claim 24, wherein at least two of the range
gear sets are engaged for a selected speed.
28. A work vehicle representing a load in the form of motive and
output power, the vehicle comprising: a power source; and a
transmission including a primary sun gear selectively coupled to
the power source; a hydrostatic power unit including a pump coupled
to a motor, the pump being adapted to be driven by the power
source; a ring gear adapted to be selectively driven by the motor;
a secondary sun gear coupled to a first output shaft; a compound
planetary gear carrier coupled to a second output shaft; and a
compound planetary gear carried by the compound planetary gear
carrier and in engagement with the ring gear and the secondary sun
gear, wherein the first output shaft and the second output shaft
are selectively coupled to the load.
29. The work vehicle of claim 28 including a selectively actuatable
reverse power train.
30. The work vehicle of claim 29, wherein the reverse power train
includes at least one clutch for selectively actuating the reverse
power train.
31-32. (canceled)
33. The work vehicle of claim 28 including a load shaft adapted to
be coupled to the load; an intermediate shaft; and a plurality of
range gear sets coupled to the intermediate shaft and selectively
coupled between the load shaft and at least one of the first output
shaft and the second output shaft.
34-36. (canceled)
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/345,578 filed on Jan. 16, 2003, which is a
divisional application of U.S. patent application Ser. No.
09/740,469 filed on Dec. 19, 2000, now U.S. Pat. No. 6,565,471.
FIELD OF THE INVENTION
[0002] The present invention relates to an improved transmission of
the type including a combination of hydrostatic (fluid) and
mechanical devices.
BACKGROUND OF THE INVENTION
[0003] Both hydrostatic transmissions and geared transmissions are
used in agricultural and construction equipment to transmit power
from power sources, such as internal combustion engines to
equipment for accomplishing a desired task. For example,
transmissions are used to properly transmit power to the wheels of
a vehicle, or to a vehicle implement. Two important considerations
in selecting transmissions are their efficiency and range of input
and output speed variability. In general, hydrostatic transmissions
provide extremely high-speed variability between the input and
output, but are less efficient than geared transmissions. Unlike
construction equipment applications, the agricultural applications
require prolonged operation at full power in the "tillage" or
"working" speed range. Under these conditions, optimum efficiency
is required. Further, "on road" haulage performance requirements
similar to that of a truck is desired for operating the work
vehicle on the highway. In certain instances, it is required that
the work vehicle has the capability of maintaining a road speed of
50 km per hour.
[0004] In an agricultural equipment application, such as on a
tractor, power to drive an implement is typically obtained from a
power take-off (PTO) device that is coupled to the tractor's
primary power source or engine. When the tractor is using the PTO,
the engine speed must be held constant to maximize the efficient
use of the implement. With a conventional transmission, such
situation cannot be maintained if the tractor speed changes since
that will affect the PTO's rpm and therefore affect the implement's
efficiency.
[0005] Thus there is a need for a transmission for use with
agricultural equipment that will provide a constant horsepower with
the ability to change speed and torque in a seamless manner, in
other words, "continuously variable". There is also a need for a
continuously variable hydro-mechanical transmission that provides a
"working range" for tillage and heavy draw bar applications and a
"roading range" for haulage and transport on the highway.
SUMMARY OF THE INVENTION
[0006] According to one aspect of the present invention, a
transmission for use with a power source and a load includes a
primary sun gear adapted to be coupled to the power source, a
hydrostatic power unit including a pump coupled to a motor, a ring
gear driven by the motor, a secondary sun gear coupled to a first
output shaft, a compound planetary gear carrier coupled to a second
output shaft and a compound planetary gear carried by the compound
planetary gear carrier and in engagement with the ring gear and the
secondary sun gear. The first output shaft and the second output
shaft are adapted to be selectively coupled to the load.
[0007] According to another aspect of the present invention, a work
vehicle includes a power source and a transmission. The
transmission includes a primary sun gear coupled to the power
source, a hydrostatic power unit including a pump coupled to a
motor, a ring gear driven by the motor, a secondary sun gear
coupled to a first output shaft, a compound planetary gear carrier
coupled to a second output shaft and a compound planetary gear
carried by the compound planetary gear carrier and in engagement
with the ring gear and the secondary sun gear. The first output
shaft and the second output shaft are selectively coupled to the
load.
[0008] According to another aspect of the present invention, a
transmission includes a hydrostatic power unit including a pump
coupled to a motor, a primary sun gear adapted to be coupled to a
power source, a secondary sun gear selectively coupled to the
motor, a ring gear selectively coupled to the motor in
synchronization with the secondary sun gear, a compound planetary
gear carrier coupled to an output shaft and a compound planetary
gear cluster carried by the compound planetary gear carrier and in
engagement with the ring gear and the secondary sun gear.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is an exemplary embodiment of a work vehicle with the
present continuously variable hydro-mechanical transmission
configured with four input shafts and one output shaft and further
providing for two different hydrostatic inputs, whereby the
hydro-mechanical transmission can provide a pure mechanical power
flow or a combined hydro-mechanical power flow from the vehicle
power source.
[0010] FIG. 2 is a partial sectional view of an exemplary
embodiment of a compound planetary gear unit illustrated in FIG.
1.
[0011] FIG. 3 is an exemplary embodiment of a work vehicle with the
present continuously variable hydro-mechanical transmission
configured with three input shafts and two output shafts, whereby
the hydro-mechanical transmission can provide a pure hydrostatic
power flow or a combined hydro-mechanical power flow from the
vehicle power source.
[0012] FIG. 4 is a partial sectional view of an exemplary
embodiment of a compound planetary gear unit illustrated in FIG.
3.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0013] FIG. 1 is a schematic diagram of a work vehicle, such as an
agricultural tractor designated by the reference numeral 2. Vehicle
2 includes a power source for such as an internal combustion engine
mechanically coupled to a continuously variable hydro-mechanical
transmission 10. A hydro-mechanical transmission 10 drives the
hydrostatic power unit 12 and a compound planetary gear unit 30
which are coupled to a range gear set 58 mounted within the
transmission housing 11 and coupled to a load L which can be the
wheels of the vehicle. It should be understood that the vehicle can
also be operated with tracks supported by the wheels and that the
work vehicle may be articulated with appropriate coupling and power
transmission equipment between the articulated parts.
[0014] Continuously variable hydro-mechanical transmission 10 is
supported in the work vehicle 2 by a housing or support frame 11.
The hydro-mechanical transmission 10 comprises a transmission
housing 11 with a hydrostatic power unit 12 associated with the
housing 11 and including a pump 16 coupled to a motor 18 with the
hydrostatic power unit 12 coupled to a first input shaft 14 and a
first output shaft 20. The hydrostatic power unit 12 is coupled to
a synchronous lockup clutch 24 by the first output shaft 20.
Depending upon the desired speed of work vehicle 2 or the desired
rpm of the load L, an electronic controller actuates clutch 24 to
couple drive gears 26, 28 to input shafts 36 and 40, respectively,
to select an appropriate hydrostatic input gear range. At the same
time, the electronic controller also adjusts the angle of a swash
plate of motor 18. The motor 18 of the hydrostatic power unit 12 is
connected to the pump 16 by appropriate hydraulic conduits 17 and
appropriate fluid filters and storage tanks (not shown) as
required. The pump 16 and motor 18 are operated in a closed
circuit. An exemplary embodiment of the hydrostatic power unit 12
is provided with a variable displacement hydraulic pump and a fixed
displacement hydraulic motor, preferably with an electronically
controlled variable displacement hydraulic pump. A hydrostatic
power unit driving gear 7 coupled to the input shaft 6 from the
power source 4 with the hydrostatic power unit driving gear 7
engaging a hydrostatic power unit driven gear 8 that is coupled to
the first input shaft 14 drives the hydrostatic power unit 12.
[0015] The hydro-mechanical transmission 10 also includes a
compound planetary gear unit 30 mounted in the housing and coupled
to the power source 4 with a second input shaft 32 and the input
shaft 6 from the power source. The compound planetary gear unit 30
also includes a third input shaft 36, a fourth input shaft 40 and a
second output shaft 44. The second input shaft 32, the third input
shaft 36, the fourth input shaft 40 and the second output shaft 44
are all coaxial with the second input shaft 32 inside the hollow
third input shaft 36 which in turn is within the fourth input shaft
40 as shown in FIGS. 1 and 2. The compound planetary gear unit 30
is selectively coupled to the load L selectively coupled to the
hydrostatic power unit 12 and coupled to the power source 4
utilizing various clutches as will be described below. The
hydro-mechanical transmission 10 also includes a load shaft 60
which is coupled to the load L and mounted for rotation in the
housing 11. An intermediate shaft 56 rotatably mounted in the
housing 11 supports a range gear set 58 mounted for rotation in the
housing 11 and selectively coupled to the compound planetary gear
unit 30 and the load shaft 60.
[0016] The compound planetary gear unit 30 comprises a primary sun
gear 34 coupled to the second input shaft 32, which is directly
coupled to the power source via input shaft 6 from the power source
4. A secondary sun gear 38 is coupled to the third input shaft 36
with the third input shaft 36 selectively coupled to the first
output shaft 20 by a synchronous lockup clutch 24. A ring gear 42
is coupled to the fourth input shaft 40, which is selectively
coupled to the first output shaft 20 also with the synchronous
lockup clutch 24. A compound planetary gear cluster 46 mounted on a
compound planetary gear carrier 48 engages with the primary sun
gear 34, the secondary sun gear 38 and the ring gear 42. The
compound planetary gear carrier 48 is coupled to the second output
shaft 32 of the compound planetary gear unit 30. A compound
planetary gear carrier 48 supports three compound planetary gears
47 which make up the compound planetary gear cluster 46.
[0017] The synchronous lockup clutch 24 selectively engages driving
gears 26 and 28 which engage a third input shaft 36 and fourth
input shaft 40, respectively. When driving gear 26 is driven by the
hydrostatic power unit 12, it drives the secondary sun gear 38.
When driving gear 28 is driven by the hydrostatic power unit 12, it
drives the fourth input shaft 40, which in turn drives the ring
gear 42 within the compound planetary gear unit 30. The above
described power transmissions occur in the upstream side of the
compound planetary gear unit 30 of the hydro-mechanical
transmission 10. On the down stream side of the compound planetary
gear unit 30 a single output shaft, designated as the second output
shaft 44 is coupled within the compound planetary gear unit 30 with
the compound planetary gear carrier 48. The second output shaft 44
is coupled to the directional clutch 50, which has a forward
component 54 and a reverse component 52 which respectively drive
gears 55 and 53 to control the forward or reverse directions of the
work vehicle 2.
[0018] An intermediate shaft 56 is rotatably mounted in the housing
11 and supports a road range input gear 62, which in turn engages a
road range output gear 64 mounted on the load shaft 60. A work
range input gear 66 coupled to the intermediate shaft 56 engages a
work range output gear 68 also mounted on the load shaft 60. A
reverse gear 70 is coupled to the intermediate shaft 56 and engages
an idler reverse gear 72 mounted on the load shaft 60. A range
selector 74 is coupled to the load shaft and is used by the
operator of the vehicle 2 to select either the road range speeds or
the work range speeds. In an exemplary embodiment of the
hydro-mechanical transmission, the range selector 74 is a sliding
collar or synchronizer 76.
[0019] The hydro-mechanical transmission described above can be
operated in a pure mechanical configuration in which the compound
planetary gear unit 30 is driven only by the power source 4 via
input shaft 6 and second input shaft 32. In the pure mechanical
configuration, the hydrostatic power unit 12 is disconnected by
hydrostatic disconnect clutch 22 coupled to the first output shaft
20. In the pure mechanical configuration, synchronous lockup clutch
24 is actuated into engagement with both driving gears 26 and 28.
The hydro-mechanical transmission 10 can also be configured to
operate with both the mechanical input directly from the power
source 4 via the second input shaft 32 and input from the
hydrostatic power unit 12 via driving gears 26 and 28 engaging,
selectively, the third input shaft 36 and the fourth input shaft 40
of the compound planetary gear unit 30.
[0020] Once the operator selects between the working range and road
range speeds by manipulating the range selector 74, controlling the
pump swash plate angle in the hydrostatic power unit 12 and the
selection of one of the drive gears 26 or 28 coupled to the first
output shaft 20 achieve speed control. In low speeds, the
hydrostatic drive is driven through ring gear 42, which is coupled
to the fourth input shaft 40 and is driven by driving gear 28. The
gear ratios in the compound planetary gear unit 30 are designed so
that a synchronous condition occurs at the most desirable speed
within a given working range. With the vehicle 2 starting from
rest, the swash plate angle of the hydraulic motor 18 is increased
in order to increase vehicle or rpm speed until a synchronous speed
is reached (i.e., the two sun gears, 34 and 38, the ring gear 42
and the planet carrier 48, supporting the compound planetary gear
cluster 46 all rotate at the same speed). At that same speed, the
synchronous lockup clutch 24 can disengage driving gear 28 and
engage driving gear 26 to drive the secondary sun gear 38. With
such change occurring at a synchronous speed it is "seamless" with
little or no energy dissipation. With the hydrostatic drive being
delivered through the secondary sun gear 38, the swash plate angle
is reduced to increase speed of the compound planetary gear carrier
48 until a maximum speed of the vehicle 2 is reached. It is also
possible for the operator to engage both drive gears 26 and 28 with
the synchronous lockup clutch 24 and with disconnect clutch 22
disconnecting output shaft 20 in which all gears of the compound
planetary gear unit 30 will be transmitting power and thereby
providing a very high efficiency through the hydro-mechanical
transmission 10. It has been determined that the optimal speed
range for such operation is between 7 and 9 km per hour. As stated
above, it is also possible to completely disengage the hydrostatic
power unit 12 from the compound planetary gear unit 30 through the
hydrostatic disconnect clutch 22. In such instance, only direct
mechanical power from the power source 4 is provided to the
compound planetary gear unit driving only the primary sun gear 34
which in turn drives the compound planetary gear cluster 46 and the
second output shaft 44.
[0021] It is also possible for a full shuttle reverse in either the
work range or road range by means of the directional clutch 50.
Since the directional change occurs downstream of the compound
planetary gear unit 30, it is not necessary to change the swash
plate position of the pump 16 in the hydrostatic power unit 12 if
the same forward to reverse ratio is retained.
[0022] The configuration of the hydro-mechanical transmission,
described above provides that the synchronized ratio change gear
speeds takes place on the input side (upstream side) of the
compound planetary gear unit 30 in the hydrostatic power unit 12
with only one output shaft 44 from the compound planetary gear unit
30. It is contemplated, that the control of the various clutches
and the swash plate angle of the pump 16 in the hydrostatic power
unit 12 can be controlled by an electronic control circuit operated
from the cab of work vehicle 2 and utilizing appropriate sensors
located at appropriate locations in the work vehicle 2.
[0023] In another embodiment, a hydro-mechanical transmission 10
there is no operator preselected work range or road range of speeds
per se. However, seamless speed changes from zero to a maximum
speed, such as 50 km per hour can be obtained through four gear
ranges defined as range "A", "B", "C", and "D" with synchronized
shift points between each range to obtain the seamless speed
changing. In this embodiment, the synchronized ratio changing takes
place on the output side (downstream side) of the compound
planetary gear unit 30 which has two coaxial output shafts 44 and
45 and will be discussed more fully below.
[0024] FIG. 3 is a schematic diagram of a work vehicle 2 such as an
agricultural tractor. Work vehicle 2 includes a power source 4
mechanically coupled to a continuously variable hydro-mechanical
transmission 10. The hydro-mechanical transmission 10 selectively
drives a hydrostatic power unit 12 and a compound planetary gear
unit 30, which in turn drives a plurality of range gear sets 58
which are coupled to a load L. The load can be the wheels of the
work vehicle 2.
[0025] The hydro-mechanical transmission 10 is supported in the
work vehicle by housing or support frame 11. The hydro-mechanical
transmission 10 comprises the transmission housing 11, which
supports the hydrostatic power unit 12, which is associated with
the housing 11. The hydrostatic power unit 12 as shown in FIG. 3 is
contained within the hydro-mechanical transmission housing 11 but
it may also be external to the housing 11 and accessed with
appropriate couplings. The hydrostatic power unit 12 includes a
pump 16 coupled to a motor 18 with the hydrostatic power unit 12
coupled to a first input shaft 14 and a first output shaft 20. The
power to the hydrostatic power unit 12 is provided by a driven gear
8 mounted on the first input shaft 14 and engaged with a
hydrostatic power unit driving gear 7 mounted on the input shaft 6
of the power shaft 4. The pump 16 is in fluid communication with
the motor 18 by appropriate conduits 17. The first output shaft 20
rotably supports a gear for engaging a third input shaft of the
compound planetary gear unit 30 as described below.
[0026] A hydro-mechanical transmission 10 also includes a compound
planetary gear unit 30 mounted in the housing. The compound
planetary gear unit 30 includes a second input shaft 32, a third
input shaft 36, a second output shaft 44 and a third output shaft
45. (See FIG. 4) The compound planetary gear unit 30 is selectively
coupled to the load L, coupled to the hydrostatic power unit 12 and
selectively coupled to the power source 4. The compound planetary
gear unit 30 can be connected to a plurality of range gear sets 58
as will be described below. The second input shaft 32, the third
input shaft 36, the second output shaft 44, and the third output
shaft 45 are coaxial with the third input shaft being hollow and
the second input shaft, 32 being supported within the third input
shaft 36. The second output shaft 44 is hollow and third output
shaft 44 is supported within the hollow second output shaft 44 as
shown in FIG. 3. The hydro-mechanical transmission 10 also includes
a load shaft 60 coupled to the load L and mounted for rotation in
the housing. An intermediate shaft 56 supporting a plurality of
range gear sets 58 is mounted for rotation in the housing and
selectively coupled to the compound planetary gear unit 30 and the
load shaft 60.
[0027] The compound planetary gear unit 30 of the hydro-mechanical
transmission 10 comprises a primary sun gear 34, which is coupled
to the second input shaft 32. A ring gear 42 is coupled to the
third input shaft 36 and coupled to the first output shaft 20 with
the hydrostatic power unit with the gear 26 engaging the third
input shaft 36. A compound planetary gear cluster 46 mounted on a
compound planetary gear carrier 48 and engaged with the secondary
sun gear 30 and the ring gear 42 is mounted within the compound
planetary gear unit 30. A compound planetary gear carrier 48 is
coupled to the second output shaft 44. The compound planetary gear
cluster 46 includes three compound planetary gears 47.
[0028] In operation, the continuously variable hydro-mechanical
transmission 10 can be configured to have a combined hydrostatic
and mechanical power flow by engaging the reverse clutch 52 or
forward clutch 54 which respectively drive a reverse drive gear 53
and a forward drive gear 55 which in turn drives the first input
shaft 20 and the second input shaft 32. It is also possible to
configure the hydrostatic mechanical transmission for a pure
hydrostatic power flow by disengaging both clutches 52 and 54 in
which case the second input shaft 32 is not directly driven by the
power source 4. In the pure hydrostatic configuration, one range
gear is coupled to carrier 48 and another range gear 58 is
connected to the secondary sun gear 38 simultaneously.
[0029] As described above, a preferred exemplary embodiment of the
hydro-mechanical transmission 10 provides a variable displacement
hydraulic pump 16 and a fixed displacement hydraulic motor 18. It
is contemplated that the operator from the cab of the work vehicle
can control the swash plate angle of the pump 16 preferably by
electronic controls. The plurality of arranged gear sets 58
comprise an A-range output gear 80 coupled to the intermediate
shaft 56 and engaged with an A-range input gear 82 mounted on the
second output shaft 44. A B-range output gear 84 is coupled to the
intermediate shaft 56 and engaged with a B-range input gear 86
mounted on the third output shaft 45. A C-range output gear 88
coupled to the intermediate shaft 56 and engaged with a C-range
input gear 90 is mounted on the second output shaft 44. A D-range
output gear 92 is coupled to the intermediate shaft 56 and engaged
with D-range input gear 94 mounted on the third output shaft 45. A
plurality of range selectors 74 is coupled to the intermediate
shaft to provide the selection of range gear sets. A typical range
selector 74 in this exemplary embodiment is a clutch 77 associated
with the respective range gear sets. A main input drive gear 96 is
coupled to the intermediate shaft 56 and engaged with a main output
drive gear 98, which is mounted on the load shaft 60.
[0030] As stated above in this embodiment, there is no selection
for a work range or road range per se. However, the four ranges
(A-D) provide a seamless transition between ranges similar to the
work/road configuration previously described. Speed change from
zero to maximum speed is achieved in a smooth and continuous manner
by changing the swash plate angle of the pump 16, preferably by
appropriate electronic controls. For high efficiency, the first
stall point of the motor 18 in the hydrostatic power unit 12 (i.e.,
ring gear 42 is a relative zero speed point) is selected in the 7-9
km per hour optimum speed range in order to transmit 100% of the
power from the power source 4. A full shuttle reverse is also
available through the clutches 52 and 54 since the directional
change occurs on the input side (upstream side) of the compound
planetary gear unit 30. Since directional changes occur on the
input side of compound planetary unit gear 30, it may be necessary
to adjust the position of the swash plate in motor 18 depending
upon the desired forward to reverse speed change ratio. In the low
speed pure hydrostatic power flow regenerative heat is kept under
control during prolonged creep operation of the work vehicle 2.
Also, in the pure hydrostatic power flow mode, different creep
speed ranges can be achieved by engaging different combinations of
the range clutches. For example, range gear set A, 80, 82 and B
range set 84, 86 can be simultaneously engaged through their
respective range selectors 74. Similarly, range set 80 can be
combined with C or D to obtain a different creep speed range as
selected by the operator of the work vehicle 2. With this
embodiment, it is also possible to shuttle between forward and
reverse in either the combined hydro-mechanical mode or the pure
hydrostatic mode. Further, in this embodiment, the vehicle speed
can be controlled independent of engine speed enabling constant
output speed from the PTO during implement operation.
[0031] Thus, there is provided a continuously variable
hydro-mechanical transmission which provides seamless speed changes
within ranges selected by the operator. One embodiment of the
continuously variable hydro-mechanical transmission provides for a
synchronized change in speed ranges in the hydrostatic power unit
on the input side of the compound planetary gear unit. This enables
the continuously variable hydro-mechanical transmission to run at
an optimum speed with the compound planetary gear unit locked up
and all power being transmitted mechanically by the power source.
Such arrangement facilitates a peak efficiency point and low speed
creeper ranges which reduces regenetative heat in the transmission.
A single output shaft from the compound planetary gear unit assists
in achieving a full forward to reverse capability without changing
the hydraulic pump swashplate angle in the hydrostatic power unit.
In another embodiment, the compound planetary gear unit is
configured to have two input shafts and two output shafts which
facilitate a pure hydrostatic operation feature in this embodiment
of the continuously variable hydro-mechanical transmission. In the
pure hydrostatic mode of operation, three different creep speed
ranges can be achieved by engaging different combinations of the
four range gear sets located downstream of the compound planetary
gear unit within the transmission housing. This embodiment of the
continuously variable hydro-mechanical transmission allows a work
vehicle speed to be controlled independent of the engine speed of
the work vehicle and enabling a constant output speed from the
power unit 12 coupled to the present transmission.
[0032] It will be understood that the foregoing descriptions are
for preferred embodiments of this invention and that the invention
is not limited to the specific forms shown. Other modifications may
be made in the design and arrangement of other elements without
departing from the scope of the invention as expressed in the
appended claims.
* * * * *