Patent Application
20150080169
This application claims priority from German patent application serial no. 10 2013 218 615.0 filed Sep. 17, 2013.
The invention concerns a powershift transmission.
Automatic variable-speed transmissions, particularly for commercial vehicles, as a rule comprise a starting element in the form of a torque converter which, in particular, brings about an increase of the torque delivered by the internal combustion engine. The disadvantages of such a torque converter are, on the one hand, the hydraulic losses caused by the slip between the pump and turbine wheel, and, on the other hand, the relatively large weight of the converter.
In DE 10 2008 041 887 A1 by the present applicant, in the case of hybrid drives for motor vehicles it has been proposed to replace the hydrodynamic torque converter with a transmission input stage having a high transmission ratio, wherein the transmission input stage is in the form of a planetary gearset with a sun gear, a planetary carrier and a ring gear. In this case the ring gear can be coupled to the internal combustion engine and/or the electric machine, the planetary carrier is connected to the transmission input shaft and the sun gear is fixed permanently relative to the transmission housing. This produces a fixed transmission ratio for the planetary transmission. By virtue of the transmission input stage, the torque of the electric machine is increased by around 70%.
The purpose of the present invention is, in an automatic powershift transmission of the type mentioned to begin with, to reduce the losses occurring in the starting element.
This objective is achieved by the characteristics of the automatic powershift transmission described below. Advantageous design features emerge from the subordinate claims.
According to the invention, the torque converter previously usually present in an automatic powershift transmission is replaced by a planetary gearset wherein the ring gear and the planetary carrier of the planetary gearset can be coupled to one another and the sun gear can be fixed. During starting, this results in a transmission ratio between the drive input shaft and the transmission input shaft in the slow range, i.e. the torque delivered by the internal combustion engine is increased—similarly to the way it is by the hydrodynamic converter. This enables quick and easy starting. In particular, however, losses are low since there are no hydraulic losses and only geartooth frictional losses occur. Furthermore, the weight of an automatic transmission with a starting element according to the invention is lower compared with one having a conventional converter.
In a preferred embodiment at least one shifting element of the variable-speed transmission serves as the starting element, i.e. the shifting elements in any case present in the transmission additionally adopt a starting function, namely the bridging of the rotational speed difference between the driveshaft or transmission input shaft and the transmission output shaft when starting.
In another preferred embodiment, the planetary carrier can be coupled by means of a shifting clutch to the driveshaft, i.e. the two transmission elements, the ring gear and the planetary carrier, can be “locked” to one another so that they run synchronously. The clutch is engaged as soon as the starting process has ended; this eliminates the need for the starting transmission ratio.
In a further preferred embodiment, during the starting process the sun gear or the sun gear shaft is supported, i.e. held fixed relative to the housing, by means of a freewheel. Thus, during the starting process the planetary gearset operates with a fixed transmission ratio between the ring gear and the planetary carrier. As already mentioned, a transmission ratio is obtained in the slow range and the torque on the transmission input shaft is thereby increased.
According to another preferred embodiment, the ring gear is connected directly to the drive input shaft, i.e. the internal combustion engine drives the ring gear of the planetary gearset directly.
In a further preferred embodiment, the ring gear can be coupled to an electric machine, so that the electric machine preferably adopts the function of a starter-generator. Thus the internal combustion engine can be started by means of the electric machine (starter function), or the electric machine is driven by the internal combustion engine (generator function).
Example embodiments of the invention are illustrated in the drawing and are described in more detail below, so that further characteristics and/or advantages can emerge from the description and/or the drawings, which show:
The automatic transmission 1 with the starting element 3 according to the invention works as follows:
When starting, the clutch 7 is opened and the sun gear 12 is held fast by the freewheel 8. This produces for the planetary transmission 6 a fixed transmission ratio from the ring gear 9 to the spider shaft 10, i.e. a step-down transmission ratio (as viewed from the drive input side AN to the drive output side AB). The torque from the internal combustion engine transmitted by the driveshaft 13 is thus increased. The starting process takes place by way of a starting clutch, whose function is performed by the shifting element A (clutch) and by the shifting element F (brake) of the variable-speed transmission 2. At the beginning of the starting process the clutch A is closed, so that the torque is transmitted via the sun gear to the gearset RS3. By closing the brake F in a controlled manner the ring gear of the gearset RS3 is braked, so that the drive output can take place via the spider shaft of the gearset RS3 to the transmission output shaft 5.
As soon as the starting process has ended, the clutch 7 is closed so that the spider shaft 10 and the ring gear 9 are connected with one another in a fixed manner, i.e. “locked”. The ring gear 9 and the spider shaft 10 then rotate synchronously. The freewheel 8 is unlocked, so that the sun gear 12 can rotate freely. The torque delivered by the internal combustion engine is now transmitted one-to-one to the transmission input shaft 4. The starting transmission ratio stage is omitted.
In addition, in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 218 615.0 | Sep 2013 | DE | national |
