Planetary gear transmission systems or components – Nonplanetary variable speed or direction transmission... – Nonplanetary transmission is belt or chain gearing
Reexamination Certificate
1999-12-08
2001-04-03
Marmor, Charles A (Department: 3681)
Planetary gear transmission systems or components
Nonplanetary variable speed or direction transmission...
Nonplanetary transmission is belt or chain gearing
Reexamination Certificate
active
06210298
ABSTRACT:
BACKGROUND OF THE INVENTION
A continuously variable transmission has been described in U.S. Pat. No. 3,340,749. This continuously variable transmission is a power split transmission with three driving modes, a belt drive variator transmission and two mechanical power branches. A mechanical power branch can optionally be drivingly connected by clutches with the input shaft. The engaged mechanical branch and the power branch with continuously variable rotational speed of the belt drive transmission are combined to form a planetary transmission acting as compound gear. In another driving mode, both mechanical power branches are drivingly uncoupled by the input shaft and, by one other clutch, the shaft of the secondary bevelled pulley pair of the belt drive transmission is directly connected with the output shaft. The total power is thus transmitted, via the belt drive transmission, to the output shaft.
In transmissions of this kind, when the vehicle is parked, the variator, as a rule, is adjusted in a manner such that in the driving mode of the slowest speeds with limited transmission input rotational speed, the transmission output rotational speed is zero. To start, the clutch of the slowest driving mode is engaged when still inactive. The starting operation occurs by adjusting the variator. Thus the transmission output rotational speed increases in the compound gear. A slight adjustment of the variator results in a clear change of the total gear ratio. Thereby a regulated start becomes extremely difficult. In particular, a careful shunting is hard to control according to automatic control technology. In this range of very low output rotational speeds of the transmission with limited input rotational speeds, the torque on the variator is stronger than the torque on the transmission output. The variator is thus loaded with a very high torque with a stronger torque than in a direct drive, via the variator, without power split.
This difficult adjustability of the transmission when starting and the strong torque load of the variator constitute a considerable disadvantage.
The problem on which the invention is based is to provide a continuously variable transmission in which starting and reversing are easy to regulate and strong torques on the variator are prevented.
This problem is solved with a continuously variable transmission.
SUMMARY OF THE INVENTION
The continuously variable transmission, according to the invention, is a power split transmission having one power branch with continuously variable rotational speed in the form of a variator and one mechanical power branch. It has two driving modes. In the first driving mode, the mechanical power branch is drivingly connected, via a clutch K
1
, with a planetary transmission acting as compound gear. The secondary side of the variator is firmly connected with the compound gear. In the second driving mode, when the clutch K
1
is opened, i.e. when the mechanical power branch is opened, a clutch K
2
connects the output of the variator with the output of the planetary transmission. The two driving modes, shiftable by the clutches K
1
and K
2
, can optionally be shifted by a clutch Kv for forward drive and by a clutch Kr for reverse drive in the driving train for forward and reverse drive. The clutches Kv and Kr are designed as twin clutches. The twin clutches are disposed in the power train after the variator and the mechanical power branch serves as start clutch and as reverse unit. This transmission arrangement offers the advantage that the variator rotates even when the twin clutches are uncoupled and thus are easy to adjust. A twin clutch is comparatively economical. It offers the added advantage that the draft torque, which mainly appear in case of viscous clutch oil due to low temperatures, mutually cancel each other. Such drag torques can lead to unintentionally moving the vehicle, especially when a creep speed group is engaged in the transmission. As starting elements, clutches are easy to control or regulate. To control or regulate clutches, it is possible to refer to a vast treasure of experience. Controls for reverses have also been well tried. A protected shunting with the time-tried draft of regulated or controlled start and reverse clutches is not problematic, according to the regulating technology or control technology. Thus have been overcome the technical problems of regulation or control of the starting of these power split transmission from the parked position by changing the adjustment of the variator.
The twin clutch is preferably given a robust design in a manner such that for any arbitrarily adjusted ratios in the first driving mode, it is exclusively possible to start or reverse by an actuation of the twin clutch without the ratio having to be adjusted therefor. The control and reversing operation, e.g. can thus take effect only by a control of the twin clutch without the variator adjustment having to be changed.
A speed increasing ratio is preferably disposed between the transmission input shaft and the variator, thereby the torque is reduced on the variator and its service life prolonged.
The variator is advantageously designed as a belt drive transmission. In another advantageous development of the invention, the variator is designed as a toroidal drive. This transmission is advantageously used in commercial vehicles for agriculture and forestry.
A creep speed group in countershaft design is preferably disposed on the output side of the twin clutch. Very low speeds, such as needed in a tractor when used in planting without very high requirements having to be set on the regulating precision of the variator, can be very accurately adjusted.
The ratio is laid out in a manner such that the total efficiency of the transmission is optimal in the most frequently used speed and traction ranges. The transmission spreading action in the driving mode with power split is greater than the variator spreading action. By virtue of the strong transmission spreading action, two driving modes of the continuously variable transmission are absolutely sufficient. The transmission thus can be very simply built. Compared to transmissions with more driving modes, many parts can be spared for teeth, clutches, etc. At the same time, the transmission ratio is laid out so as to limit the maximum torque acting on the variator by the slip limit between tire and ground or road. An overload of the variator is thus prevented.
The switching point at which the clutch K
1
is closed and the clutch K
2
opened or vice versa is advantageously selected so that sun gear, ring gear and planet carrier of the compound gear rotate synchronously, thereby a traction downfall or an interruption of the traction is prevented.
In order to overcome the problem of the difficult controllability and of the great torque increase, the ratio of output rotational speed of the transmission to the input rotational speed of the countershaft with limited input rotational speed is selected in an advantageous method above a preset minimum value.
Starting and reversing are a frequent operational state, e.g. in agricultural commercial vehicle in activities like loading or stacking. A rough, jerky start and reverse with imprecisely presettable end positions of the movement of the vehicle as can occur in the case of starting controls by upward regulation of the output rotational speed of the transmission beginning from zero by adjusting the variator can load to dangerous situations and is thus intolerable. Therefore, the starting advantageously takes effect by controlled or regulated closing of the clutch Kv or Kr, the reversing by controlled or regulated switching of the clutches Kv and Kr.
In an advantageous development of the invention, all rotating parts are placed over the oil sump. Thus churning losses are prevented and the efficiency favorably developed.
The hydraulic oil for the adjustment of the variator and the retaining pressure of the clutches are preferably made available by a suction-throttled radial piston pump. Thereby the power loss of the transmission is
Baur Erwin
Konrad Helmut
Muller Franz
Davis & Bujold P.L.L.C.
Marmor Charles A
Pang Roger
ZF Friedrichshafen AG
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