Axle differential with two radially arranged planetary gears

Abstract

Axle drive comprising a drive shaft (1'), a first output shaft (2) and a second output shaft (3), a first planetary gear and a second planetary gear, wherein a drive torque of the drive shaft (1') can be transmitted to the first and second output shafts (2, 3) by means of the first planetary gear and the second planetary gear, wherein the second planetary gear is formed radially outside coaxially around the first planetary gear, wherein the ring gear (4) of the first planetary gear forms the sun gear of the second planetary gear, characterized in that the ring gear (4) of the first planetary gear has helical teeth on its outside and on its inside, so that the axial forces on the ring gear (4) of the first planetary gear are compensated overall, wherein the ring gear (4) of the first planetary gear is guided axially only by two sliding guides (5) and is guided radially by the helical teeth.

Description

Field of the InventionThe present invention relates to a final drive comprising an input shaft, a first output shaft and a second output shaft.Prior ArtSuch final drive units are used in motor vehicles to transmit a drive torque from a drive motor, for example an electric motor, to two output shafts, in particular to a left and a right axle of the motor vehicle and ultimately to driven wheels.In this case, a transmission ratio or reduction of the input rotational speed to a desired rotational speed of the outputs can take place at the final drive.It is also known that final drive units can have a differential in order to allow a rotational speed difference between the first and second output shafts.It is known that such final drive transmissions may use a planetary gear for distributing the driving torque to the output shafts. There are also already solutions which use a plurality of planetary gearings and in the process usually require a larger axial installation space. Such transmissions are known, for example, from DE 10 2014 201 245 A1 or DE 10 2011 102 749 A1.DE 10 2011 005 615 A1 discloses a drive device for driving a driven vehicle axle, comprising a drive motor, an electric machine and a transmission, wherein the transmission has two identically constructed minus planetary gear sets which are arranged coaxially with one another, wherein the sun gears of the first planetary gear set and of the second planetary gear set are connected to one another in a rotationally fixed manner by means of a shaft, wherein the ring gear of the first planetary gear set and the ring gear of the second planetary gear set have, in addition to a continuous internal toothing for realizing the ring gear function, an external toothing which is designed as a crown or bevel gear toothing and with which a cone or crown gear of a crown shaft connected in a rotationally fixed manner to the output of the electric machine meshes, wherein an output of the drive motor is connected to the shaft by means of a transmission stage, which connects the sun gear of the first planetary gear set to the sun gear of the second planetary gear set to one another and wherein the output of the drive device takes place via the carrier of the first planetary gear set and the carrier of the second planetary gear set, which are each connected to a wheel of the driven vehicle axle.WO 2005 / 120 877 A1 discloses a planetary gear with differential gearing, comprising a housing, an annular rotatable input element with a rotational axis in the housing, opposite rotatable output elements on the axle, one of which is configured for driving by the input element, and a planetary gear arranged around the input element, wherein the input element has a sun wheel and inner planetary gears are in engagement with the sun wheel, an inner planetary gear carrier is connected in a rotationally fixed manner to the output element, which is connected to the input element, wherein an inner toothed ring is provided in engagement on the inner side with the inner planetary gears and on the outer side with outer planetary gears rotatable on the axles of the housing, and an outer toothed ring is in engagement with the outer planetary gears and is connected to the other of the output elements.From US 2018 / 0 112 740 A1 a transmission device is known, comprising a first gear; a second gear, which meshes with the first gear; and a third gear, which meshes with the second gear, wherein the first gear comprises a first tooth row and a second tooth row, which are aligned along an axial direction of an axis of rotation of the second gear and have mutually different inclined directions of a tooth flank; the third gear comprises a third tooth row and a fourth tooth row, which are aligned along the axial direction of the axis of rotation of the second gear and have mutually different inclined directions of a tooth flank; the second gear comprises first engagement teeth, second engagement teeth, third engagement teeth and fourth engagement teeth; the first engagement teeth mesh with teeth of the first tooth row of the first gear; the second engagement teeth mesh with teeth of the second tooth row of the first gear; the third engagement teeth are provided in a tooth row different from a tooth row of the first engagement teeth; the third engagement teeth mesh with teeth of the third tooth row of the third gear; the fourth engagement teeth are provided in a tooth row different from a tooth row of the second engagement teeth; the fourth engagement teeth mesh with teeth of the fourth tooth row of the third gear; a helical direction of the first engagement teeth and a helical direction of the third engagement teeth are the same direction; and a helical direction of the second engagement teeth and a helical direction of the fourth engagement teeth are the same direction.Document DE 10 2004 003 632 A1 teaches a portal drive for a portal axle of a vehicle, wherein a spur gear transmission produces an axle offset between a drive wheel and an output wheel of the spur gear transmission, wherein the drive wheel of the spur gear transmission is an internally and externally toothed ring gear, wherein at least one toothing is designed as helical toothing, in which the axial forces are supported via pressure combs.US 5 484 348 A discloses a differential unit comprising input means for receiving power; a first arrangement of gears for transmitting power to first output means; a second arrangement of gears for transmitting power to second and third output means; wherein the first arrangement of gears transmits power from the input means for receiving power to both the first output means and input means of the second arrangement of gears and operates as a differential connected between the first output means and the input means of the second arrangement of gears, the second arrangement of gears transmits power from their input means to both the second and third output means and operates as a differential connected between the second and third output means; the first gear arrangement is a planetary arrangement having a first ring gear providing the input device for the differential, a first plurality of planet gears, a first planet carrier, and first and second gears; the second gear arrangement is a planetary arrangement having a second ring gear providing the input device for the second gear arrangement, a second plurality of planet gears, a second planet carrier, and a third sun gear; and a gear serves as both the first sun gear of the first arrangement and the ring gear of the second arrangement, the second sun gear providing the first output device, the second planet carrier providing the second output device, and the third sun gear providing the third output device.SUMMARY OF THE INVENTIONIt is an object of the invention to specify a final drive which enables a rotational speed ratio and a differential function and in the process requires a small axial installation space.The object is achieved by a device according to claim 1.According to the invention, a final drive comprises a drive shaft, a first output shaft and a second output shaft, a first planetary gear and a second planetary gear, wherein a drive torque of the drive shaft can be transmitted to the first and second output shaft by means of the first planetary gear and the second planetary gear, wherein the second planetary gear is formed coaxially around the first planetary gear radially on the outside, wherein the ring gear of the first planetary gear forms the sun gear of the second planetary gear, wherein the ring gear of the first planetary gear has a helical toothing on its outside and on its inside, so that overall the axial forces on the ring gear of the first planetary gear are compensated, wherein the ring gear of the first planetary gear is guided axially only by two sliding guides and is guided radially by the helical toothings.According to the invention, two planetary gears are used which are arranged coaxially with one another at at least approximately the same axial position, so that the axial length of the final gear can be small.For this purpose, the ring gear of the first planetary gearing is used twice. In addition to its internal toothing, it also has an external toothing and, by means of this external toothing, simultaneously forms the sun wheel of the surrounding second planetary gearing.By using two planetary gears, the two output shafts can be connected to the input shaft in such a way that they are normally subjected to the same torque. Depending on the load on the wheels or output shafts, it is possible to set a different rotational speed on the output shafts and thus to provide a differential effect.According to the invention, the ring gear of the first planetary gear set has a helical toothing on its outer side and on its inner side, so that overall the axial forces on the ring gear of the first planetary gear set are compensated. "Compensating" also comprises according to the invention a partial compensation, i.e. partial mutual lifting of the forces. Preferably, however, a complete or approximately complete compensation of the forces takes place.The ring gear of the first planetary gear can then preferably be guided axially by only two sliding guides and radially by the helical tooth arrangements.The ring gear of the first planetary gear preferably forms a ring which has a helical toothing on its outer side and on its inner side. This ring is only axially supported by lateral sliding guides.The drive shaft of the final drive preferably drives the sun gear of the first planetary drive or forms the sun gear.Preferably, the output to the first output shaft is from the planet carrier of the first planetary gearing.Preferably, the output to the second output shaft is from the ring gear of the second planetary gearing.The ring gear of the first planetary gear preferably rotates counter to the direction of rotation of the first and second output shafts.The planets of the second planetary gear are preferably mounted fixed to the housing.The drive shaft can preferably be designed as a hollow shaft and the first output shaft can be arranged radially on the inside in the drive shaft.Needle bearings are preferably arranged between the first and the second output shaft and / or friction elements are arranged. Such friction elements can be acted upon in particular by an oblique toothing of the ring gear of the first planetary gearing with an axial force under tensile load in order to achieve a locking effect of the differential.Brief Description of the DrawingsThe invention is described below by way of example with reference to the drawings. FIG. 1 is a sectional view of an axle transmission according to the invention. FIG. 2 schematically shows the kinematics of an axle transmission according to the invention according to FIG. 1.DETAILED DESCRIPTION OF THE INVENTIONFIG. 1 shows an axle transmission according to the invention, which comprises an input shaft 1', a first output shaft 2 which leads to the right in FIG. 1, and a second output shaft 3 which leads to the left in FIG. 1. The drive shaft 1' can be driven by an electric motor.The final drive comprises a first planetary gear and a second planetary gear. The second planetary gear is formed radially outside coaxially around the first planetary gear. By means of the first planetary gearing and the second planetary gearing, a drive torque of the drive shaft 1' can be transmitted to the first and second output shafts 2, 3.The first planetary gear comprises a sun gear 6, wherein the sun gear 6 of the first planetary gear is driven by the drive shaft 1' or is formed on the drive shaft 1'.The sun gear 6 meshes with planets 11 which are mounted on a planet carrier 7.The transmission of the torque from the planet carrier 7 of the first planetary gear mechanism takes place to the first output shaft 2, or the planet carrier 7 can be formed integrally with the first output shaft 2.The planets 11 mesh with the internal toothing, designed as helical toothing, of the ring gear 4 of the first planetary gearing.The ring gear 4 of the first planetary gear set simultaneously forms the sun gear of the second planetary gear set. The outside of the ring gear 4 likewise has a helical toothing. The ring gear 4 can be designed as a ring which is supported laterally by two slide bearings 5.The ring gear 4 and thus the sun gear of the second planetary gear set meshes with planet gears 9 of the second planetary gear set. The planets 9 of the second planetary gear are mounted fixed to the housing. The planet carrier of the second planetary gear is thus formed by the housing or rotationally fixedly with the housing of the final drive.The planets 9 mesh with an internal toothing of the ring gear 8 of the second planetary gearing. The torque is transmitted from the ring gear 8 of the second planetary gear mechanism to the second output shaft 3, or the ring gear 8 can be formed integrally with the second output shaft 3.The ring gear 4 of the first planetary gear set rotates in this configuration counter to the direction of rotation of the first and second output shafts 2, 3.The drive shaft 1' is designed as a hollow shaft and the first output shaft 2 is arranged radially on the inside in the drive shaft 1'.The input shaft 1' and the second output shaft 3 are mounted on the housing of the final drive via bearings 12.Between the first and the second output shaft 2, 3 needle bearings 10 are arranged. Instead or additionally, friction elements can also be arranged between the first and the second output shafts 2, 3 in order to achieve a higher self-locking effect of the differential by increasing the friction between the output shafts 2 and 3 by means of the axial force caused by the helical gearing. A controllable differential lock can also be arranged between the output shafts 2 and 3.FIG. 2 shows the circumferential speeds of the individual components of the final drive of FIG. 1, wherein the circumferential speed v is shown in each case on the x-axis and the height on the y-axis of FIG. 2 corresponds to the radial spacing of the component or of the respective circumference according to FIG. 1.The solid line 13 represents an operation of the final drive with the same rotational speeds at the first output shaft 2 and the second output shaft 3 and therefore the same speeds-based on the same radius-of the planetary carrier 7 of the first planetary gear and the ring gear 8 of the second planetary gear. The line of circumferential speed of the planet carrier 7 shown therefore coincides, at the same speeds of the output shafts 2 and 3, with the line of circumferential speed of the ring gear 8.The planet gears 11 and the ring gear 4 of the first planetary gear set rotate in the opposite direction as compared with the input shaft 1' and the output shafts 2 and 3.The dotted line 14 represents the corresponding speeds in an operation in which the first output shaft 2 and therefore the planet carrier 7 rotates more rapidly than the second output shaft 3 and therefore the ring gear 8, which allows a different speed of a left and a right wheel of a motor vehicle.The stationary transmission ratio (sun to ring gear with stationary planet carrier) of the transmission shown is, for example, 3.8, and therefore 4.8 times the input torque is transmitted to the planet carrier 7 of the first planetary transmission and is thus conducted to the right-hand, first output shaft 2. The stationary transmission ratio of the outer planetary gearing is 1.263, namely 4.8 / 3.8, and thus the input torque on the ring gear 8 of the second planetary gearing or on the left, second output shaft 3 is also 4.8 times. The torque distribution is thus 50:50, the axle ratio is 9.6, and this axle ratio can also be read from FIG. 2, since the circumferential speed v at the drive shaft 1' is 9.6 when the circumferential speed v of the first and second output shafts 2, 3 is 1 with approximately the same circumference. With such an axle transmission, transmission ratios in the range of approximately 5 to 10 can be realized in a simple manner, and higher transmission ratios can be realized, for example, by connecting a further planetary transmission in front of it.List of reference characters1' Input shaft 2 First output shaft 3 Second output shaft 4 Ring gear of the first planetary gear set 5 Sliding guide 6 Sun gear of the first planetary gear set 7 Planet carrier of the first planetary gear set 8 Ring gear of the second planetary gear set 9 Planet of the second planetary gear set 10 Needle bearing 11 Planet of the first planetary gear set 12 Bearing 13 Equal rotational speeds of the first and second output shafts 14 First output shaft faster than the second output shaft v Peripheral speed

Claims

Final drive comprising an input shaft (1'), a first output shaft (2) and a second output shaft (3), a first planetary gear and a second planetary gear, wherein a drive torque of the input shaft (1') can be transmitted to the first and second output shaft (2, 3) by means of the first planetary gear and the second planetary gear, wherein the second planetary gear is formed coaxially around the first planetary gear radially on the outside, wherein the ring gear (4) of the first planetary gear forms the sun gear of the second planetary gear, characterized in that the ring gear (4) of the first planetary gear has a helical toothing on its outside and on its inside, so that overall the axial forces on the ring gear (4) of the first planetary gear are compensated, wherein the ring gear (4) of the first planetary gear is guided axially only by two sliding guides (5) and is guided radially by the helical toothings.Final drive according to Claim 1, characterized in that the ring gear (4) of the first planetary drive rotates counter to the direction of rotation of the first and second output shafts (2, 3).Axle transmission according to at least one of the preceding claims, characterized in that the drive shaft (1') drives or forms the sun wheel (6) of the first planetary transmission.Axle transmission according to at least one of the preceding claims, characterized in that the output to the first output shaft (2) is effected by the planet carrier (7) of the first planetary transmission.Final drive according to at least one of the preceding claims, characterized in that the output to the second output shaft (3) is effected by the ring gear (8) of the second planetary drive.Axle transmission according to at least one of the preceding claims, characterized in that the planets (9) of the second planetary transmission are mounted fixed to the housing.Axle transmission according to at least one of the preceding claims, characterized in that the drive shaft (1') is designed as a hollow shaft and the first output shaft (2) is arranged radially on the inside in the drive shaft (1').Final drive according to at least one of the preceding claims, characterized in that needle bearings (10) are arranged between the first and the second output shaft (2, 3) and / or friction elements are arranged.

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