Hydromechanical transmission with two planetary assemblies that are clutchable to both the input and output shafts

A power transmission having two planetary assemblies, each having its own carrier and its own planet, sun, and ring gears. A speed-varying module is connected in driving relation to the input shaft and in driving relationship to the two sun gears, which are connected together. The speed-varying means may comprise a pair of hydraulic units hydraulically interconnected so that one serves as a pump while the other serves as a motor and vice versa, one of the units having a variable stroke and being connected in driving relation to the input shaft, the other unit, which may have a fixed stroke, being connected in driving relation to the sun gears. A brake grounds the first carrier in the first range and in reverse and causes drive to be delivered to the output shaft through the first ring gear in a hydrostatic mode, the first ring gear being rigidly connected to the output shaft. The input shaft also is clutchable to either the carrier or the ring gear of the second planetary assembly. The output shaft is also clutchable to the carrier of the second planetary assembly when the input is clutched to the ring gear of the second planetary assembly, and is clutchable to the ring gear of the second planetary assembly when the input is clutched to the carrier thereof.

BACKGROUND OF THE INVENTION 
This invention relates to an improved transmission. It may be considered an 
improvement on the hydromechanical transmission described in U.S. Pat. No. 
3,888,139 which issued June 10, 1975, to Elias Orshansky, Jr. 
The transmission of U.S. Pat. No. 3,888,139, and the transmission of the 
present invention each provide a hydromechanical infinitely variable 
transmission. Each provides for improved utilization of vehicle engine 
power by enabling the engine to operate within a narrow speed range which 
has been optimized for minimum emissions, maximum fuel economy and maximum 
power, regardless of vehicle operating conditions. 
In U.S. Pat. No. 3,888,139 the hydraulic units used as a speed-varying 
means were driven by gears from either the input or the reaction or both. 
The present invention eliminates those gears, four gears altogether, and 
their bearings reduce the size and weight of the transmission and reduce 
the cost of the transmission. 
It is also an object to provide a transmission which can weigh less than 
conventional transmissions. 
The transmission of this invention has a concentric or coaxial construction 
and an entirely different hydrostatic start from the transmission of U.S. 
Pat. No. 3,888,139, in order to provide reduction in the number of parts, 
the size, the weight, and also the cost of the transmission. 
In order to avoid having to use the extra gears which connected the 
planetary assemblies to the hydraulic units in U.S. Pat. No. 3,888,139, 
the hydraulic units in the present invention are especially designed to be 
installed in line with the planetary assemblies without a separate gear 
drive. This considerably reduces power losses, size, weight, and cost. 
A conventional torque converter or manual transmission requires the 
imposition of many compromises upon the engine, because it must provide 
adequate performance over a wide range of torque and speed. The practice 
of most vehicle manufacturers of providing a selection of optional axle 
ratios for the vehicle is only one of the many attempts which have been 
made to reduce the compromise for any given application. 
The infinitely variable transmission of this invention enables the engine 
to be operated at all times in a speed range in which it is capable of 
producing rated power. Therefore, vehicle performance in any given 
application can be maintained or even improved while utilizing a smaller 
engine. In contrast, infinitely variable transmissions of the pure 
hydrostatic type are limited to applications where significant power 
losses can be tolerated in return for the benefits of improved 
transmission ratio control. 
Hydromechanical transmissions offer the control benefits of hydrostatic 
transmission, and, since only a portion of the engine power is transmitted 
by the hydraulic units, they provide a means for removing the performance 
barrier of excessive power losses. The extent to which any hydromechanical 
transmission can accomplish this is a function of the percentage of power 
which must be transmitted hydraulically. 
The new transmission hereof can transmit high horsepower over a wide range 
of output speed variation at a constant input speed and horsepower. It 
differs from the previous transmissions in its ability to transmit power 
over a wide range with a minimum of transmitted hydraulic horsepower, and 
a minimum of installed hydraulic horsepower. It also provides full engine 
braking over its entire range of operation. 
The invention avoids the pitfalls of excessive complexity, speeds, or loads 
in the gear train. Maximum reliability and minimum cost have been obtained 
by utilizing standard commercial hydraulic unit design practice to provide 
units which are operated totally within their long-life rated conditions 
of speed and power. In addition, the clutches can utilize the same 
low-cost paper elements presently employed in high production automobile 
torque converter transmissions. For a comparable power rating, a smaller 
number of elements than in a torque converter power shift transmission can 
be utilized, because at all shift points the clutch elements are virtually 
synchronous. The number of elements is, therefore, a function not of their 
thermal capacity, but of their steady-state torque capacity. 
This new transmission is valuable for use in passenger and competition 
cars, highway and off-highway trucks, buses, agricultural and construction 
equipment, military vehicles, and industrial drives and machine tools. 
With this invention it is possible to design transmissions having an 
extremely wide range of speed and torque variation at full power. This is 
required in construction and off-highway equipment, for example, where 
torque multiplication of the order of 18:1 and 24:1 may be encountered. 
Machine tool drives may require even wider ranges, and they are possible. 
The use of this transmission in a piston-engine vehicle enables reduction 
of exhaust emissions and improvement in the specific fuel consumption by 
programming the engine to operate within its optimum range under all road 
conditions without regard to transmission torque output requirements. Both 
hydrocarbon and nitrogen oxide emissions can be minimized by optimizing 
the engine for operation in a specific narrow range. In addition, a 
smaller engine may be utilized for any application, as the transmission 
enables full engine power to be developed at any vehicle speed except for 
the lower speeds where the vehicle is traction limited. It is particularly 
desirable to operate turbocharged diesel engines in a narrow range of 
speed. 
Rotary combustion engines can use this new transmission with the same 
advantages as for piston engines. The benefit in reduction of hydrocarbon 
emissions is there of a much greater magnitude, however, due to the high 
rate of change in emission characteristics for rotary combustion engines 
with respect to engine speed. 
Gas turbines would also be benefited significantly by this invention. 
Manufacturing cost is a major drawback in producing a turbine today. This, 
to a large degree, is a function of the complexity required in the design 
of a turbine for use under the varying torque and speed conditions of a 
road vehicle. With the hydromechanical transmission of this invention, the 
turbine can be programmed to operate only under those conditions during 
which it is most efficient. Therefore, a single-shaft turbine becomes 
feasible, as it is more economical to manufacture than the two-shaft 
design normally proposed for vehicle application. Since constant-speed 
operation is feasible, the problems in connection with the throttle 
response time of a turbine do not arise. Because there is an infinite 
variation in speed and torque in the transmission, and no interruption of 
power flow occurs at any time, the turbine is never unloaded. 
SUMMARY OF THE INVENTION 
The power transmission of the invention includes, in combination with input 
means and output means, two planetary assemblies, each having its own 
carrier and its own planet, sun, and ring gears. Both of the sun gears are 
connected together on a common shaft, and a speed-varying module connected 
to the input drives the sun gears. The speed-varying module may comprise a 
pair of hydraulic units hydraulically interconnected so that one serves as 
a pump while the other serves as a motor and vice versa, one of the 
hydraulic units being connected in driving relation to the input, and the 
other being connected in driving relation to the sun gears. 
A brake may be used for grounding the first carrier and causing the drive 
from the speed-varying module through the first set of planetary gears to 
be delivered to the output means through the first ring gear, which is 
rigidly connected to the output means. A first clutching arrangement can 
connect the second carrier to the input means while the second ring gear 
is connected with the output means. A second clutching arrangement can 
connect the second ring gear to the input means while the second carrier 
is connected to drive the output means. 
The brake is a low-range clutching means used for both reverse and for 
starting in a hydrostatic Range I; the speed-varying module can be run in 
reverse, forward, or zero drive, and at varying speeds in forward or 
reverse, such as by respective strokings of a controlling wobble-plate. 
The speed of the ring gear of the second planetary assembly increases 
during forward transmission drive in Range I and at the end of that range 
becomes equal to the speed of the input shaft. At that point, this second 
ring gear is clutched to the input shaft and the second carrier is 
clutched to the output shaft, and then the brake is released. The 
transmission is now hydromechanical and is in Range II. 
During Range II, the speed of every element of the two planetary assemblies 
is either at or approaching the speed of the input shaft, and at the end 
of Range II, when every element reaches that speed, a shift is made into 
Range III by clutching the output shaft to the second ring gear and the 
input shaft to the second carrier. Then the clutches for Range II are 
disengaged. 
In Range III, the second carrier stays at the speed of the input shaft, 
while the two ring gears, rotating at the output speed, continue to 
increase in speed. 
The range shifts in this new transmission occur at synchronized speeds, 
without interruption of power flow on either the upshift or the downshift. 
The starting and reverse ranges are hydrostatic and are not considered 
part of the working ranges. In most cases, the starting and reverse ranges 
operate at less than maximum power and may approach a maximum constant 
torque, since maximum output torque may be limited by either maximum 
pressure or traction. The working ranges are considered to be Ranges II 
and III, which may operate at full and constant horsepower. 
The present invention enables extending the ratio range while employing 
only two planetary assemblies, both simple planetary assemblies. One of 
these planetary assemblies serves as the drive in both of the 
hydromechanical ranges, the ring gear and the carrier of that assembly 
alternating in function, so that one of them serves as the output member 
while the other is the input member, and vice versa. The sun gear of this 
same planetary assembly is the reaction member in both of the 
hydromechanical ranges. By minimizing the gearing, manufacturing cost is 
minimized.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A transmission 10 of this invention has two planetary assemblies 11 and 12, 
having respective sun gears 13 and 14; respective ring gears 15 and 16; 
and respective carriers 17 and 18 with respective planet sets 19 and 20. 
An input shaft 21 drives a speed-varying hydraulic module 22, the other end 
of which is suitably connected to a hollow shaft 23 that carries the two 
sun gears 13 and 14. The module 22 comprises a variable-displacement 
hydraulic unit 24 in driving relationship with a fixed-displacement 
hydraulic unit 25, with hydraulic fluid transmitted between them through a 
stationary port plate block 26. A wobble plate 27 is provided for the 
hydraulic unit 24. 
A brake 28, when engaged, holds the first carrier 17 stationary, i.e., 
relative to a main frame 35. The first ring gear 15 is rigidly connected 
to or directly mounted on a drum 29 which is secured to an output shaft 
30. 
There are four clutches, which work in pairs: a clutch 31 for connecting 
the input shaft 21 to the second carrier 18, a clutch 32 for connecting 
the input shaft 21 to the second ring gear 16, a clutch 33 for connecting 
the second ring gear 16 to the output shaft 30, and a clutch 34 for 
connecting the second carrier 18 to the output shaft 30. The clutches 32 
and 34 are engaged in Range II, and the clutches 31 and 33 are engaged in 
Range III. 
The input shaft 21, output shaft 30, hydraulic units 24 and 25, and 
planetary assemblies 11 and 12, are all co-axial. 
When the brake 28 is engaged, the first planetary gears 19 rotate but are 
arrested in their planetary motion. This makes a reversing drive between 
the first sun gear 13 and the first ring gear 15, causing a rotation of 
the third ring gear 15 which is reversed in rotation to that of the first 
sun gear 13. 
The low-range brake 28 is engaged for starting (and also for reverse), 
causing the driving connection between the sun gear 13 and the drum 29 
through the planetary gears 19 and the ring gear 15, causing the first 
ring gear 15 to run in a reverse direction and at a reduced speed with 
respect to the sun gear 13. The sun gear 13 itself is driven by the 
speed-varying module 22 during starting and reverse. In this region the 
drive is purely hydrostatic, and when the variable-displacement hydraulic 
unit 24 is on zero stroke, the vehicle is at a standstill, since no drive 
is then coming through the speed-varying module 22 and since the brake 28 
is engaged. 
If the wobble plate 27 of the variable-displacement unit 24 is stroked in 
one direction, the transmission 10 is in reverse, and if the wobble plate 
27 is stroked in the opposite direction, the transmission 10 is in 
forward. When the wobble plate 27 is stroked in forward, the sun gear 13 
traverses in speed from zero to a negative speed, as shown in Range I in 
FIG. 3, and with the carrier 17 of the first planetary assembly 11 
grounded by the brake 28, the first ring gear 15 increases from zero 
output speed, as shown in Range I in FIG. 3. 
During Range I, the second planetary assembly 12 transmits no power, the 
transmission 10 being in its hydrostatic mode. The second sun gear 14, 
decreases in speed exactly with the first sun gear 13, the second carrier 
18 gains speed by virtue of having the clutch 34 engaged, and the second 
ring gear 16 gains speed even faster. Alternately, the clutch 32 may be 
engaged in Range I. 
When the forward speed of the second ring gear 16 becomes equal to the 
forward speed of the input shaft 21, the clutches 32 and 34 are engaged, 
and the transmission 10 goes into Range II, the brake 28 then being 
released. The transmission 10 is then in its hydromechanical mode. 
The drive is then from the input shaft 21 through the second ring gear 16 
and the second carrier 18 to the output shaft 30. The first ring gear 15 
from then on has no driving function, and the low-range brake 28 may 
simply slip, producing some loss, but such losses are usually very low. 
When the end of Range II is reached, the speeds of all the planetary 
elements are identical--exactly the speed of the input shaft 21 (as is the 
output shaft 30), and it is thus possible to engage the high-range second 
clutch arrangement--clutches 31 and 33 to put the transmission into the 
high Range III, immediately thereafter releasing the clutches 32 and 34. 
To those skilled in the art to which this invention relates, many changes 
in construction and widely differing embodiments and applications of the 
invention will suggest themselves without departing from the spirit and 
scope of the invention. The disclosures and the description herein are 
purely illustrative and are not intended to be in any sense limiting.