Planetary gear transmission systems or components – With means to vary drive ratio or disconnect drive – Plural elements selectively braked
Reexamination Certificate
1998-06-23
2001-06-19
Estremsky, Sherry L. (Department: 3681)
Planetary gear transmission systems or components
With means to vary drive ratio or disconnect drive
Plural elements selectively braked
C475S299000, C475S303000
Reexamination Certificate
active
06248038
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a transmission gear, particularly one built into heavy-duty vehicles as an auxiliary gear between a main gear and the driveline leading to the drive wheels in order to double the number of gears available in the main gear. All gear steps of the main gear can thus be further transmitted to the driveline either with a lower transmission or with a higher transmission. Transmission gears of this kind usually comprise a planetary gear whose ratio of transmission will come into effect when the transmission gear is to transmit the gear steps of the main gear with a lower transmission to the driveline.
Although known transmission gears can change the overall transmission of the driveline, the drive shaft and the driven shaft of known transmission gears will always rotate in the same direction.
SUMMARY OF THE INVENTION
The invention therefore has the object of providing a transmission gear which in a simple manner allows its driven shaft to also rotate opposite the direction of rotation of its drive shaft.
This object is achieved according to the present invention by a transmission gear comprising a fixed gear case, a drive shaft and a driven shaft supported for independent rotation in the gear case and a planetary gear arranged between the drive and driven shafts. The planetary gear comprises a sun wheel that is nonrotatably connected with the drive shaft, a planetary wheel carrier around the sun wheel which is rotated with respect to the sun wheel, at least one planet wheel supported on the planet wheel carrier around the sun wheel and each planet wheel mates with the sun wheel to be rotated thereby. A gear rim rotates with respect to and mates with the planet wheels. An axially displaceable clutch element has a first axial position at which the clutch element couples the planet wheel carrier with the gear case in a torsionally rigid manner and has a second axial position at which the clutch element couples the planet wheel carrier with a driven shaft in a torsionally rigid manner. The clutch element comprises separated but joined together clutch wheels. The gear rim encompasses the planet wheels and is also axially moveable between third and fourth positions. The gear rim mates with the planet wheel. In the third position, the gear rim is torsionally rigidly connected with the gear case. In the fourth position, the gear rim is torsionally rigidly connected with the driven shaft.
Whereas the planet wheel carrier of the planetary gear contained in the transmission gear is conventionally fixedly connected with the driven shaft, it is possible according to the present invention to detach the connection between the planet wheel carrier and the driven shaft in order to couple the planet wheel carrier in a torsionally rigid manner with a fixed gear case of the transmission gear. In the transmission gear according to the present invention it is therefore possible to couple the planet wheel carrier with the driven shaft on the one hand or with the gear case or also any other fixed component on the other hand. In the transmission gear according to the present invention, if the planet wheel carrier is torsionally rigidly connected with the gear case (or any other fixed component), the driven shaft of the transmission gear rotates in the opposite direction of its drive shaft. The main gear connected upstream therefore no longer needs to be provided with a reverse gear, because the transmission gear according to the present invention enables every gear of the main gear to also be used as a reverse gear. This allows saving of three toothed wheels and one shaft in the main gear. The overall length of the main gear can thus be kept shorter, which benefits the stability of the main gear, and in particular its resistance against introduced high forces and torques. Moreover, the main gear is lighter and is cheaper to produce owing to omission of the reverse gear. Although the layout of a transmission gear according to the present invention is slightly more complicated and also slightly heavier in comparison with conventional transmission gears, the combination of a transmission gear according to the present invention and a main gear without a separate reverse gear is still considerably lighter and also cheaper than the combination of a conventional transmission gear with a conventional main gear.
The clutch element is axially displaceable between two positions. According to the present invention, the clutch element allows coupling the planet wheel carrier either with the gear case or with the driven shafts. In the preferred embodiment of the transmission gear, the clutch element comprises two axially spaced, annular clutch wheels which are mutually connected in a torsionally rigid way. Each clutch wheel concentrically encompasses an axial extension of the planet wheel carrier with a reduced diameter. The two axial extensions of the planet wheel carrier extend from mutually opposite faces thereof. Such an arrangement leads to a particularly compact design of the transmission gear according to the present invention.
According to a modified embodiment a first one of the two annular clutch wheels is internally and externally toothed and couples the planet wheel carrier torsionally rigidly with the gear case in the first position of the clutch element by a respective mating of teeth. The planet wheel carrier is provided with a toothing which mates with the inner toothing of the first clutch wheel, whereas the casing (or any other fixed component) is provided with a toothing which mates with the outside toothing of the first clutch wheel. The second of the two annular clutch wheels is internally toothed in this embodiment and couples the planet wheel carrier in a torsionally rigid way with the driven shaft in the second position of the clutch wheel by a respective mating of teeth. For this purpose, the associated axial extension of the planet wheel carrier is provided with a toothing which can mate with the inner toothing of the second clutch wheel, and the driven shaft is also provided with such a toothing.
The torsionally and axially rigid connection of the two clutch wheels of the clutch element is preferably achieved according to the present invention by one or several components which extend(s) through at least one of the planet wheels, in particular through its shaft. Such an arrangement benefits the compact design of the transmission gear according to the present invention.
The displacement of the clutch element between its two positions, i.e. the changeover between rotation of the drive and driven shaft in the same and opposite directions, is advantageously achieved by an axially movable actuating member which projects radially into the gear case and engages one of the clutch wheels with its radially inner end. As a result of the torsionally and axially rigid connection between the two clutch wheels, the other clutch wheel is also axially displaced when the first clutch wheel is axially displaced by the actuating member.
According to a preferred embodiment, the radially outer end of the actuating member is rigidly connected with an actuating rod which extends in the axial direction radially outside of the gear rim of the transmission gear. This actuating rod can be coupled with a switch or servo cylinder to be controlled by the driver, so that it is easy to change over between forward and reverse run of the transmission gear.
For the purpose of changing over between its lower and its higher transmission, the transmission gear according to the present invention is preferably provided with a first toothing which is torsionally rigidly connected with the gear case and a second toothing which is axially spaced from the first one and is torsionally rigidly connected with the driven shaft. An axially displaceable gear rim is arranged between the two toothings. The gear rim is provided in this embodiment with mating teeth at its axial ends in continuation of its inner teeth. By means of these teeth, and depending on its axial position, the gear rim can
Nilsson Dag
Strandås Lars-Olov
Estremsky Sherry L.
Ostrolenk Faber Gerb & Soffen, LLP
Scania CV AB
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