Planetary gear transmission systems or components – Nonplanetary variable speed or direction transmission... – Interrelated control of in series transmissions
Reexamination Certificate
1999-09-16
2001-02-20
Wright, Dirk (Department: 3682)
Planetary gear transmission systems or components
Nonplanetary variable speed or direction transmission...
Interrelated control of in series transmissions
C475S218000
Reexamination Certificate
active
06190280
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a multispeed mechanical transmission with an optional hydrostatic attachment, useful in, but not limited to agricultural tractors.
BACKGROUND OF THE INVENTION
The prior art is replete with various transmissions for agricultural tractors and the like. Multispeed transmissions having countershafts are widely used in the power train of tractor arrangements because a plurality of rotating clutch assemblies and associated gears can be positioned on parallel shafts to allow considerable flexibility in adapting them to different space requirements and “gear spacing”.
“Gear spacing” is the ratio change between gears which produces the change in vehicle speed when the operator shifts to a different gear. The smaller this gear spacing the better the optimum engine speed can be matched to the optimum ground speed. The more gear selections that are available, the finer the gear spacing can be designed. However, the number of clutches and gears increases with added gear selections, increasing the cost, etc.
“Shift quality” is the operator's perception of how smoothly a transmission reacts when making a shift. Many factors affect shift quality, such as rapid changes in speed of elements with large inertia within the transmission, poor timing of the pressure control, large torque interruptions at heavy loads, large gear spacing, and most of all, the number of clutch “swaps” required from one gear selection to the next. (A single clutch swap is defined as the disengagement of one clutch and the engagement of another clutch to complete a shift.) All currently manufactured powershift transmission have multiclutch swaps during some shifts in the operating range. It is difficult, if not impossible, to make multiclutch swaps smooth because during a shift, one or more of the engaging clutches opposes the direction of the shift. For example, in one typical transmission, during a triple clutch swap upshift from 6
th
to 7
th
gear, one of the clutches shifts up while the other two clutches shift down.
Any sequence of clutch engagements will cause torque reversals. This effect is inherent in all multiswap shifts of current designs. Only single clutch swaps can be shifted smoothly by overlapping the engagement of oncoming clutch with the disengagement of the outgoing clutch.
There are special applications for the type of vehicle using the transmission described herein where exact speed control is important, such as trenching or certain planting and harvesting operations, among others. In many of these applications, most of the engine power is used to drive the mechanism of the towed attachment through the power take off (PTO) with only part of the power used for the forward motion of the vehicle. Here, transmission efficiency is of secondary importance, with the primary importance being the ability to vary the ground speed at small increments independently of the engine. In such cases, an continuously variable transmission is desirable. Continuous variability can be achieved, for example, through the use of hydrostatic units, in which case, transmission efficiency is sacrificed. Other continuously variable transmissions include electrical generator-motor sets or variable friction drives.
Two types of the continuously variable transmission are of interest:
1. Continuous variability from a certain minimum vehicle speed to the maximum vehicle speed with full power transmission capability in one mode of operation, and continuous variability from zero to a certain low vehicle speed with maximum traction capability in another mode of operation. In the full power mode a means (such as a clutch) must be available to start the vehicle in motion at full load. As pertains to the present invention, this type will be called a partial continuously variable transmission (PCVT).
2. Continuous variability from zero to maximum vehicle speed with full power and maximum traction capability within a single mode of operation. As pertains to the present invention, this type will be called a full continuously variable transmission (FCVT).
SUMMARY OF THE INVENTION
It is the object of the present invention to provide the largest known number of gear selections with a given number of clutches. For example, current transmissions with 9 clutches provide between 16 and 18 speeds forward with 4 to 6 reverse speeds. A typical arrangement of the present invention provides 23 forward and 8 reverse speeds using 9 clutches. These five extra speeds allow a closer gear spacing.
It is a further object of this invention to provide a variety of transmission systems from which to choose for specific applications.
It is a further object of the present invention to provide single clutch swaps for all single step and double step shifts throughout the normal operating range. Single step means sequential shifts and double step means skipping a gear selection.
It is a further object of the present invention to maximize the efficiency by keeping the number of gear meshes low. Also, the clutch sizes and speeds can be minimized for low losses.
It is a further object of the present invention to provide continuous variability of the type PCVT via an optional attachment. In this case, the present invention proposes the use of modulated clutches for starting the vehicle motion, thus allowing for the use of relatively small hydrostatic units.
It is a further object of the present invention to provide an alternate transmission system with continuous variability of the type FCVT. A continuously variable transmission from zero to maximum vehicle speed is realized by making the hydrostatic units large enough for sufficient torque to start the vehicle motion.
It is a further object of this invention to provide a compact transmission package using a unique gear, shaft, clutch and bearing arrangement.
General Description of the Basic Powershift Transmission
“Transmission” as used in this document is an arrangement of gears, shafts, clutches and bearings located in a housing for the purpose of transmitting rotational power, “input” meaning power absorbing, “output” meaning power delivering. The transmission system consists of an input transmission, a compound planetary system and an output transmission.
A compound planetary system is a planetary system consisting of at least two simple planetaries.(
FIGS. 16
,
17
and
18
) There are two kinds of simple planetaries, the single and the double planetary. These are defined as follows.
A single planetary is comprised of a internal ring gear, a sun gear and a set of planets (usually three) which are rotatably mounted on sets of shafts anchored in a planet carrier. Each planet gear is in mesh with the ring gear and with the sun gear thus acting as an idler gear between the ring and the sun gear.
A double planetary is comprised of an internal ring gear, a sun gear and two sets of planet gears which are rotatably mounted on two sets of shafts each set of shafts being anchored in a planet carrier. One set of planets is in mesh with the ring gear and with the other set of planets which in turn is in mesh with the sun gear.
Another type of compound planetary system uses cluster planet gears. (as schematically represented in
FIGS. 19
,
20
and
21
) Usually an equivalent planetary system of the first type described above can be constructed. The input transmission has one input member connected to the engine or motor and two output members each of which is selectively connectable to the input member by clutches through various gear ratios in forward and reverse. The output members are connected to the two input members of the compound planetary system.
The compound planetary system has two input members connected to the input transmission (as stated in the previous paragraph) and two output members connected to the output transmission.
The output transmission has two input members connected to two output members of the planetary system (as stated in the previous paragraph) and one output member connected to the rear and/or to the front wheel drive of the tractor. The
Harbst John W.
Wright Dirk
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