Gearbox

Details Gearbox Gearbox

2000-06-16

2002-05-14

Estremsky, Sherry (Department: 3681)

Planetary gear transmission systems or components

Nonplanetary variable speed or direction transmission...

Reexamination Certificate

active

06387006

ABSTRACT:

BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a variable speed transmission especially a variable speed transmission for motor vehicles.
Various types of variable speed or variable ratio transmissions are known. Transmissions of this kind are used for example in a motor vehicle for changing the rotational speed of an engine with a certain transmission ratio or torque conversion. In addition, a transmission of this kind can ensure the idling of an engine when a vehicle is at rest. Finally, it is possible to reverse the direction of rotation of the drive shaft by means of a transmission.
A simple variable speed transmission can be created by a manual gearbox with an input (drive) shaft, an output shaft, and a countershaft. The drive shaft is connected with the engine by a clutch so that it can be decoupled forcewise from the engine when shifting. A drive gear sits on the drive shaft that drives the countershaft which in turn is nonrotatably connected with other gears. Gears mounted on the countershaft can be meshed with the gears of the drive shaft. Depending on the choice of a speed and hence of one such gear pair, a desired transmission ratio can be created.
The manual gearbox mentioned above has high efficiency, low weight, and is relatively inexpensive because of its simple design. However, no automatic mode can be achieved with a manual gearbox of this kind. In addition, the load between the engine and the input wheels is interrupted with every shift so that the force of the engine cannot be utilized constantly during a continuous acceleration process. In general, the manual gearbox has a relatively low level of comfort. In addition, a separate starting clutch must be provided to decouple the transmission with the input engine.
An automatic transmission is known as a conventional transmission with an automatic mode as the name itself suggests. A conventional automatic transmission usually has a flow converter on the input shaft side that serves as a starting clutch and produces increases in torque in the conversion range. Usually combinations of several planetary transmissions are connected downstream of the converter, said transmissions depending on the positions of individual gears or groups of gears, and perform a torque and rpm conversion as well as a possible reversal of the direction of rotation for a reverse gear. The shifting processes are usually performed by an electrohydraulic control that produces automatic upshifts and downshifts of the individual gears at the correct point in time.
The automatic transmission suffers from relatively high losses and requires a complex design. A transmission of this kind is generally cost-intensive, has a high weight, and requires complex control.
The same disadvantages affect an automatic transmission with an integrated starting clutch. In a transmission of this kind, only the losses can be reduced slightly.
Another alternative for a variable speed transmission is offered by a manual gearbox with automated shifting. In such a transmission, which resembles the manual transmission described above, all of the clutching and shifting processes are performed fully automatically in accordance with the driver's wishes. In this way, an automatic mode can in fact be achieved but even with this transmission subject to load interruption when shifting cannot be reduced. Otherwise, in the course of an automated shift, a high control effort, especially in engine control, is required. It also requires a starting clutch with similarly automated control.
Another possibility for a variable speed transmission is provided by a stepless automatic transmission with transfer belts or steel thrust belts, or in a transmission of this kind, a planetary transmission with a forward gear and a reverse gear as well as a multiplate clutch and a continuously adjustable primary v-pulley are provided in such a transmission on the drive shaft. The force transfer to a secondary v-pulley on the drive shaft is accomplished for example through a steel thrust belt. By axial displacement of one diagonally opposite disk half of the v-pulley, the effective lever arms become larger or smaller and the transmission ratio can be chosen, depending on the choice of the ratio of the lever arms r
1
to r
2
.
With such a transmission, however, only lower power levels can be transmitted. Such a transmission is not suitable for transmitting high torques.
Finally, a double clutch transmission is known in which two clutches act on a two-part drive shaft with fixed gears. One half shaft is hollow and surrounds approximately half the second half shaft. Loose gears fit on the drive shaft and are connected with the latter by mechanical selector sleeves. In order to shift gears, one clutch must be released and the other engaged at the same time while the mechanical shifting process is completed within the final closing phase of both clutches. The double clutch also acts as a starting clutch.
The disadvantage of such a double clutch transmission is the use of two clutches which must be so designed that they can transmit even the maximum torque that develops.
The goal of the invention is to provide an economical variable-speed gearbox with an automatic mode, which can transmit high torques and avoids complete load interruption when shifting or changing gear.
This goal is achieved by the variable transmission especially for motor vehicles with an input shaft and a output shaft, as well as a first device located between the input shaft and the output shaft, delivering torque and permitting variable rpm transmission ratios, said device in one operating mode ensuring a complete power flow decoupling of the input shaft and the output shaft, and with a second device provided in parallel with the first device for force transmission between the input shaft and output shaft, with which in contrast to the first device, a continuously selectable torque in the range from zero to the maximum applied torque can be transmitted characterized in that the second device comprises a planetary transmission.
Accordingly, in parallel (especially with regard to a power flow) to a first device, therefore essentially to a first transmission, between the input shaft and the output shaft, a second torque-transmitting device is interposed as well with which a continuously selectable torque in the range from zero to the maximum applied torque can be transmitted between these two shafts. The value of the torque can be controlled or regulated.
Since it is possible to have an interruption in the power flow between the input and output shafts in both the first and second devices, it is not necessary to provide a separate clutch any longer between an input motor and the transmission itself. The clutch is already integrated into the gearbox with a corresponding design, and it is not necessary to perform any maintenance. This “integrated clutch” is economical, requires less space for the transmission-engine unit, and reduces the cost of construction as well as maintenance and repair expenses.
An important point regarding the invention consists in the fact that by a suitable control of the second device, such a torque transmission from the input to the output shaft or vice versa can be performed, that no further torque is transmitted through the first unit, and the transmission ratio in this first unit can be easily changed; for example a shiftable spur gear to be brought into or out of engagement with a shaft or another gear can be shifted in a force-free manner. Since a positive connection or torque connection through the second torque-transmitting device can be maintained between the input and output shafts even when shifting the first device, a complete interruption of the load, for example between a drive motor and drive wheels, is effectively prevented. With suitable control of the second device, a load decrease can be kept very small. The driver then gains the impression, even while shifting, that the vehicle is being continuously accelerated or decelerated. A “jerk effect” caused by different acc

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