Transmission device and electric drive unit comprising at least one electric machine and the transmission device

Transmission devices are disclosed having a first planetary drive, a second planetary drive, a hollow shaft, and a shaft which is seated concentrically in the hollow shaft and can be rotated relative to the hollow shaft. In one example, the first planetary drive includes a first sun gear and first planet gears in mesh with the first sun gear, and the second planetary drive has second planet gears in mesh with a second sun gear. The first planet gears and second planet gears may be spaced apart radially from a rotational axis common to the hollow shaft and the shaft, and a shaft section of the shaft may protrude axially from one end of the hollow shaft. In this arrangement, the first sun gear is seated on the shaft section. The second sun gear may be seated on the hollow shaft coaxially with the first sun gear. The first sun gear may carry a seal that rests sealingly on a rotationally symmetrical section of the hollow shaft, which is configured to be rotated relative to the first sun gear about the rotational axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase of PCT Appln. No. PCT/DE2016/200400 filed Aug. 26, 2016, which claims priority to DE 102015216975.8 filed Sep. 4, 2015, the entire disclosures of which are incorporated by reference herein.

TECHNICAL FIELD

A transmission device, which has at least one first planetary drive, a second planetary drive, a hollow shaft, and a shaft which is seated concentrically in the hollow shaft and can be rotated relative to the hollow shaft.

BACKGROUND

A transmission device of this kind is described in JP2002235832A as a component part of an electric drive unit. The electric drive unit has a rotor shaft, which is the input shaft of a transmission device. The transmission device is formed from a differential gear unit and a reduction stage. The reduction stage is a planetary drive, the sun gear of which is seated on the rotor shaft. The differential is a “spur gear differential”, in which the differential gears are planet gears and the output gears are sun gears. Each sun gear is seated on an output shaft of the differential. The torques input via the input shaft/rotor shaft are introduced into the differential via the reduction stage and are distributed by the differential to the output shafts and hence to driven vehicle wheels. The rotor shaft is a hollow shaft, through which one of the output shafts is passed. In this arrangement, an annular gap is formed between the rotor shaft and the output shaft. The output shaft and the respective sun gear are connected to one another for conjoint rotation by splines. Apart from wet-rotor electric motors, the region of the electric machine between the stator and the rotor should be kept free of lubricating oil. However, the transmission device is lubricated with transmission oil. There are drive units in which the annular gap between the output shaft and the rotor shaft is used as an oil duct in order, for example, to feed lubricating oil to a rolling bearing situated axially on the outside. However, there are also drive units in which the rolling bearing situated on the outside is lubricated via other paths or has lifetime lubrication.

SUMMARY

It is an object of the disclosure to provide a transmission device which is adequately sealed.

This object may be achieved by the subject matter disclosed in the description and the drawings.

According to the disclosure, it is envisaged that at least one of the sun gears of the planetary drive carries at least one seal, e.g., also forms the seat for a seal installed in a fixed manner in the sun gear. The seal rests sealingly on a surface segment of the hollow shaft, which can be rotated relative to the first sun gear about the rotational axis. The hollow shaft is a transmission shaft or a rotor shaft or an extension or piece for connection to the rotor shaft, for example.

A seal by which an annular gap between a sun gear of a planetary drive and a transmission shaft in a vehicle transmission is to be sealed off is described in DE 10 2005 012 616A1. The seal is formed by a steel sleeve and a bushing. The steel sleeve is press-fitted in a hole in the sun gear. The bushing is inserted radially between the steel sleeve and the transmission shaft. Since the sun gear and the transmission shaft in DE 10 2005 012 616A1 are rotatable relative to one another, small radial clearances must be formed between the steel sleeve, the bushing and the transmission shaft. These clearances define annular gaps via which leaking oil can pass through the seal. Accordingly, this seal is suitable only for systems in which oil flows are supposed to be selectively distributed but in which the regions on both sides of the seal can or should be wetted by the lubricating oil.

Because the seal is accommodated in the output gear, little or no additional installation space is taken up by the seal since the seal can be integrated into existing projections (e.g. into a hub) of the sun gear. As an alternative, it is envisaged that the seal seat is a ring of hollow-cylindrical design. By way of example, one section of the ring is used to seat it firmly on a hub of the sun gear. By such an embodiment of the disclosure, the sun gear can be made simpler, without a seal seat. The hollow-cylindrical ring is a simple component which can be produced at low cost.

For the sake of simplicity, the sun gears of differentials are generally provided with through holes to enable the internal splines to be produced without hindrance. The output shaft is provided with external splines, which correspond to the internal splines of the sun gear. This known splined joint is very easy to assemble and is therefore readily used. With respect to leaking oil, the splined joint between the sun gears of a differential is a weak point of the differential since this is formed with a clearance. Lubricating oil can escape to the outside through the leakage gaps associated with the clearance. The disclosure contributes to preventing leakage oil from escaping via the splined joint, especially if, as one embodiment of the disclosure envisages, the through hole in the sun gear having the seal is closed by a closure element. With such an arrangement, the transmission device is sealed off by the seal relative to the annular gap between the hollow shaft and the output shaft and by the closure element relative to the splined joint. The closure element can be a plug or cover seated in the through hole. As an alternative, a cover with a rim is placed externally on a hub of the sun gear.

The operation of differentials is sufficiently well known to those skilled in the art. Differentials to which the disclosure relates are gear units in which torques applied to at least one input shaft are distributed uniformly or non-uniformly to at least two output shafts via differential gears and, to this end, they are arranged longitudinally, for example, between two driven axles or alternatively between the driven wheels on one axle. The differential gears are gears of conical design or spur gears. The output gears of the transfer gear unit are sun gears with a conical shape or spur gears.

Embodiments of the disclosure also relate to an electric drive unit which has a transmission device with the features according to the disclosure.

In the electric drive units of the type according to the disclosure, the annular gap between the rotor shaft or hollow shaft and the output shaft should remain dry. If the transmission device is not adequately sealed, lubricating oil, for example, can reach the rotor shaft, which heats up during operation, and can there form a resinous or sooty residue. As a consequence, unwanted deposits can form in the annular gap over the long term. With the aid of the arrangement according to the disclosure, it is possible to prevent oil from getting into the annular gap—especially when the seal is a radial shaft seal (a radial shaft sealing ring), as envisaged by one embodiment of the disclosure.

The radial shaft sealing ring has at least one sealing lip, preferably composed of NBR (Nitrile Butadiene Rubber=Nitrile Rubber) or a polymer such as PTFE (polytetrafluoroethylene), and a hollow-cylindrical seat portion, preferably with a metallic reinforcing ring. It is seated firmly in the sun gear or in a ring on the sun gear. The sealing lip runs on the surface segment of the hollow shaft. The contact pressure of the sealing lip is optionally reinforced by an oil seal spring (garter spring). Lubricating oil forms a relatively firm pressurized film on the surface of a rotating joint. Nevertheless, a radial shaft sealing ring makes it possible to retain the lubricating oil reliably in the transmission device at the joint between the hollow shaft and the transmission device and is advantageously suitable especially for use in an electric drive unit.

DETAILED DESCRIPTION

FIG. 1shows a diagram, not to scale, of an electric drive unit1, which has a transmission device2with an illustrative embodiment of a transfer gear unit3embodied as a differential, in a longitudinal section along the central axis7of the drive unit. An electric machine22is operatively connected to a reduction gear unit24of the transmission device2by a rotor shaft embodied as a hollow shaft23. The reduction gear unit24is a planetary drive8. Double planets25(consisting of two planet gears connected firmly to one another) form a link between the reduction gear unit24and the transfer gear unit3. The transfer gear unit is a planetary drive6.

FIG. 2shows a concrete illustration of a detail of the drive unit1focusing on the connections of the output shafts15and16of the transfer gear unit3, in a longitudinal section along the central axis7of the drive unit1.

The transfer gear unit3has a differential cage9formed by the carrier segments9a,9b,9c, a set of differential gears12, a set of differential gears14, two output gears11and13, and two shafts embodied as output shafts15and16. The transfer gear unit3is embodied in the manner of a planetary drive as a spur gear differential. Accordingly, the differential cage is a planet carrier9. The differential gears are planet gears12and14, and the output gears are sun gears11and13.

The output gears11and13are arranged axially adjacent to one another on a common rotational axis, which is on the central axis7, and can be rotated relative to one another about the rotational axis. The differential gears12and14are supported on planet pins17and18, respectively, in such a way as to be rotatable about pin axes. The planet pins17and18are fixed on the planet carrier9. The differential gears12of the first set of planets are in mesh with output gear11. The differential gears14of the second set of planets mesh with output gear13. One differential gear12in each case is in mesh19with one differential gear14. Moreover, output gears12and14are supported radially on one another at a bearing location26.

The planet carrier9is the input shaft20of the differential and is driven by the double planets25of the reduction gear unit24, which are supported on a ring gear. The planet carrier9is mounted in a housing (not shown) in such a way as to be rotatable about the central axis7, said housing being indicated by housing sections34a-34e. The first output gear11is seated for conjoint rotation on the first output shaft15by a splined joint21, and the second output gear13is seated for conjoint rotation on the second output shaft16by a further splined joint21. The output shafts15and16are situated coaxially with their ends opposite one another, wherein the hollow shaft23forms a shaft duct4for the first output shaft15.

The shaft duct4or rotor shaft4is rotatable about the central axis7relative to the input shaft20and to the output shafts15and18. Seated on the rotor shaft4is a gearwheel33, which is a sun gear33of the reduction gear unit24embodied as a planetary drive. The sun gear33is a component of a geared operative connection between the rotor shaft4, embodied as a hollow shaft, and the input shaft20of the transfer gear unit3and is in mesh with a set of planet gears35of the double planets25.

An annular gap5is formed between the shaft duct4and output shaft15. The first output gear11, that is to say the first sun gear11in this case, is provided with a seal30. The seal30rests sealingly on a rotationally symmetrical surface segment4aof the shaft duct4. Moreover, the gaps27of the respective splined joint21between the output shafts15and16and the respective sun gear11and13are optionally sealed by a closure element28and29, respectively. As illustrated inFIG. 1, the closure elements28and29can be sealing caps. The sealing cap is pushed onto the end of the respective output shaft. The end of the sealing cap is situated opposite the end of the output shafts15and16, respectively. Alternatively, the closure elements28and29are each covers, as illustrated inFIGS. 3 and 4.

FIG. 3shows the first sun gear11as an isolated component in a longitudinal section along the rotational axis thereof.

FIG. 4shows another embodiment of a sun gear11a, which differs from sun gear11in having an alternative seal arrangement and which is also illustrated in a longitudinal section.

The sun gears11and11ahave a through hole32, which is provided with internal splines21a. The seal30is a radial shaft sealing ring, which has a hollow-cylindrical seat section30aand a sealing lip30bconnected thereto by the same material. The seal30is seated by the seat section30ain a hollow-cylindrical projection11b, which is formed integrally with the sun gear11illustrated inFIG. 3. The seal arrangement of the sun gear11aillustrated inFIG. 4has a hollow-cylindrical ring31. The ring31is pressed onto the outside of the hub of the sun gear11abut, as an alternative, can also be press-fitted into a hollow-cylindrical projection of the hub of the sun gear. The seal30is seated in the ring31.

REFERENCE SIGNS

4arotationally symmetrical section of the shaft duct

9acarrier segment of the planet carrier

9bcarrier segment of the planet carrier

9ccarrier segment of the planet carrier

11bprojection of the sun gear

24reduction gear unit

30aseat section of the seal

30bsealing lip of the seal

35planet gears of the double planet