Electric drive with combined differential and reduction gearbox

Abstract

Electric vehicle drive system (10, 110, 210, 310), comprising: an electric motor (12) with an output shaft (14); a differential planetary gear (18) with a first sun gear (16) connected to the output shaft (14) of the electric motor (12), wherein a plurality of first planet gears (20) are supported by a first planet carrier (22) and mesh with the first sun gear (16) and a first ring gear (24); a reversing planetary gear (26) with a second sun gear (28) non-rotatably connected to the first ring gear (24), wherein a plurality of second planet gears (30A, 30B) are supported by a second planet carrier (32) and mesh with the second sun gear (28) and a second ring gear (34); a first axle shaft (40) non-rotatably connected to the first planet carrier (22). is;and a second axle shaft (42) which is non-rotatably connected to the second planet carrier (32), characterized by a separating brake (36) on the second ring gear (34).

Description

The present disclosure relates to electric vehicles and in particular to an electric vehicle drive with a combined differential and reduction gear. BACKGROUND Most currently used motor vehicles are powered by combustion engines, which have high mechanical losses and low energy efficiency, resulting in significant energy consumption and environmental pollution. Electric vehicles use stored electrical energy to power an electric motor. As battery technology has improved, the popularity of hybrid and electric vehicles has increased over the past few years. However, the packaging requirements for conventional electric motor drive systems have impacted vehicle designs and efficiency. Therefore, it is desirable to provide an electric drive with a more compact layout and improved efficiency. From US Patent 5,845,732 A, an electric vehicle drive system with the features according to the respective preamble of claims 1 and 2 is known. DE 10 2014 119 168 A1 describes a similar electric vehicle drive system that includes a primary and a secondary electric motor. US patent 2015 / 0283918A1 describes a drive system for a vehicle which has a first axle coupling on a first axle shaft and a second axle coupling on a second axle shaft to individually adjust drive forces for a right and a left wheel of the vehicle. WO 2005 / 120 877 A1 describes an epicyclic differential gear designed to compensate for a speed difference between two output shafts. One object of the invention is to create an electric vehicle drive system that has a high efficiency due to low rotational losses and a compact arrangement. SUMMARY This problem is solved by an electric vehicle drive system having the features of claim 1 or 2. The electric vehicle drive system includes an electric motor with an output shaft. A differential planetary gear set includes a first sun gear connected to the output shaft of the electric motor, with a plurality of first planet gears supported by a first planet carrier and meshing with the first sun gear and a first ring gear. A reverse planetary gear set includes a second sun gear non-rotatably connected to the first ring gear, with a plurality of second planet gears supported by a second planet carrier and meshing with the second sun gear and a second ring gear. A first axle shaft is non-rotatably connected to the first planet carrier. A second axle shaft is non-rotatably connected to the second planet carrier. An optional first coupling can non-rotatably connect the first and second planet carriers.Second and third optional couplings can each limit the torque transmitted by the first and second axle shafts. An optional torque transmission device can be rotationally fixed to either the first support, the first ring gear, or the second support. DRAWINGS Fig. 1A is a schematic representation of the electric vehicle drive system according to the principles of the present disclosure; Fig. 1B is a schematic representation of the same, also including optional second and third clutches; Fig. 1C is a schematic representation of the electric vehicle drive system according to the principles of the present disclosure, also including optional torque transmission devices; Fig. 1D is a schematic representation of the electric vehicle drive system according to the principles of the present disclosure, also including a hydraulic torque transmission device for providing torque vectoring; Fig. 2 is a cross-section of the differential planetary gear and reverse planetary gear according to the principles of the present disclosure; and Fig.Figure 3 is a schematic representation of an alternative stacked planetary gear for use in the electric vehicle drive system according to the principles of the present disclosure. The same reference symbols in the different views of the drawings refer to the same parts. DETAILED DESCRIPTION Exemplary embodiments will now be described in more detail with reference to the accompanying drawings. With reference to Fig. 1A, an electric vehicle drive system 10 will now be described. The electric vehicle drive system 10 comprises an electric motor 12 with an output shaft 14, which is driven by a sun gear 16 of a differential planetary gear set 18. The differential planetary gear set 18 comprises a plurality of planet gears 20, which are supported by a planet carrier 22 and are in mesh with the sun gear 16 and a ring gear 24. A reversing planetary gear set 26 is provided with a sun gear 28, which is driven by the ring gear 24 of the differential planetary gear set 18. The reversing planetary gear set 26 comprises a plurality of inner planet gears 30A and outer planet gears 30B, which are supported by a planet carrier 32 and are each in mesh with the sun gear 28 and a ring gear 34.This means that each of the inner planet gears 30A is in mesh with the sun gear 28 and one of the outer planet gears 30B, and each of the outer planet gears 30B is in mesh with one of the inner planet gears 30A and the ring gear 34. The ring gear 34 can be connected to a controllable disconnect brake 36, which can prevent the ring gear 34 from rotating. A first axle shaft 40 is connected to the planet carrier 22 of the differential planetary gear 18, and a second axle shaft 42 is connected to the planet carrier 32 of the reverse planetary gear 26. Each of the axle shafts 40 and 42 is accordingly connected to a pair of drive gears 44, 46, and can include a CV joint 48 in conjunction with each of the drive gears. The differential planetary gear 18, the reversing planetary gear 26, the electric motor 12 and each of the axle shafts 40, 42 are concentric, so that they rotate around a common axis.Additionally, the first axle shaft 40 passes through a central opening in the electric motor 12. An optional first clutch 50A can also be provided in connection between the first and second axle shafts 40, 42 to limit the relative rotation between them and thus serve as a slip-limiting differential clutch. Referring to Fig. 1B, an alternative electric vehicle drive system 110 includes a first axle-to-axle coupling 50A, second and third axle couplings 50B, 50C along the first and second axle shafts 40, 42. The drive system 110 further includes a controller 120 that can receive inputs from wheel speed sensors 122A, B assigned to each wheel 44, 46, a motor speed sensor 124, a steering wheel position sensor 126, and an acceleration sensor (such as a yaw rate sensor) 128. The controller 120 provides output signals for controlling the electric motor 12 and the couplings 50A, 50B, and 50C for torque vectoring to improve cornering performance. In particular, the controlled engagement of the clutches 50A, 50B and 50C enables a better distribution of torque to the drive wheels 44, 46 while they rotate at different speeds. With reference to Fig. 1C, an alternative electric vehicle drive system 210 includes an optional torque transmission device 50D, such as a hydraulic motor or a secondary electric motor. As shown in Fig. 1C, the torque transmission device 50D is a secondary electric motor that is driven by the ring gear 24 of the differential planetary gear 18 via an intermediate gear 202. Alternatively, the torque transmission device 50D can be rotationally fixed to one of the following: the first axle shaft 40 and thus the planet carrier 22 of the differential planetary gear 18, or the second axle shaft and thus the planet carrier 32 of the reverse planetary gear 26. The secondary electric motor 50D can be controlled by a controller 120 to add drive torque or drive resistance to provide torque vectoring to the drive wheels for improved cornering performance.In particular, the controlled engagement of the torque transmission device 50D enables better torque distribution to the drive wheels 44, 46 while they rotate at different speeds. With reference to Fig. 1D, an alternative electric vehicle drive system 310 includes an optional torque transmission device 50E, such as a hydraulic motor. As shown in Fig. 1D, the torque transmission device 50E is driven by the planetary carrier of the differential planetary gear 18. A first hydraulic pump 312 comprises a fixed housing and an internal rotor, which is mounted on the first axle shaft 40, while a second hydraulic pump 314 comprises a fixed housing and an internal rotor, which is mounted on the second axle shaft 42. First and second oil channels 316, 318 are provided within the first and second axle shafts 40, 42 and are connected to the hydraulic motor 50E. A third oil channel 320 between the first hydraulic pump 312 and the second hydraulic pump 314 is provided to complete the hydraulic circuit.A speed difference between the first and second hydraulic pumps 312, 314 causes the hydraulic motor 50E to add drive torque for faster wheel rotation and to provide torque vectoring for the drive wheels for improved cornering performance. In particular, the hydraulic motor 50E enables better torque distribution to the drive wheels 44, 46 while they are rotating at different speeds. With reference to Fig. 2, a detailed cross-sectional view of the electric motor 12, the differential planetary gear 18, and the reversing planetary gear 26 is now described, using the same reference numbers as in Fig. 1. As shown in Fig. 2, the electric motor 12 includes an output shaft 14, which is driven by a sun gear 16 of a differential planetary gear 18. The differential planetary gear 18 includes a plurality of planet gears 20, which are supported by a planet carrier 22 and mesh with the sun gear 16 and a ring gear 24. A reversing planetary gear 26 is provided with a sun gear 28, which is driven by the ring gear 24 of the differential planetary gear 18.The reversing planetary gear 26 comprises a plurality of inner planet gears 30A and outer planet gears 30B, which are supported by a planet carrier 32 and are each in mesh with the sun gear 28 and a ring gear 34. The ring gear 34 is supported by a housing part 54 and prevented from rotating. A first axle shaft 40 is connected to the planet carrier 22 of the differential planetary gear 18, and a second axle shaft 42 is connected to the planet carrier 32 of the reversing planetary gear 26. The electric motor 12, the differential planetary gear 18, and the reversing planetary gear 26 are all arranged in a common housing 51, including the housing parts 52 and 54 bolted together. The housing part 52 surrounds the electric motor 12, while the housing part 54 contains the differential planetary gear 18 and the reversing planetary gear 26.The housing part 52 contains a bearing support element 56 for supporting a bearing 58, which rotatably carries the motor output shaft 14. An intermediate plate 60 is arranged inside the housing 51 and contains a bearing support element 62 for supporting a bearing 64 for carrying a second end of the motor output shaft 14. A needle bearing 66 is carried by the motor shaft 14 near one end of the axle shaft 40 to rotatably support the planet carrier 22 of the differential planetary gear 18. The housing part 54 carries a needle bearing 68 for supporting the planet carrier 32 of the reversing planetary gear 26. The electric vehicle drive system according to the principles of this disclosure can provide a 6:1 to 10:1 speed reduction from an electric motor to the wheels by combining speed reduction with differential action using a simple planetary gear as the differential and a reversing gear at one of the two outputs of the simple planetary gear. The reversing gear provides reaction torque to the speed-reducing planetary gear at negative speed instead of zero speed, thus increasing the effective ratio of the speed-reducing planetary gear. The speed reduction and differential action are integrated into a single stage instead of separate stages. The system reduces rotational losses and further reduces the vehicle-wide axial distance for the coaxial electric motor drive axle compared to a two-stage planetary gear and a differential. The electric vehicle drive system according to the principles of the present disclosure can provide the same function as the well-known limited-slip differential by using a coupling that rotatably connects both wheels, with a fixed axial preload on the coupling or a variably controllable load on the coupling. Up to the slip limit of this coupling, additional couplings can distribute different amounts of torque to the two outputs, for example, a small amount of torque to the wheel on the inside of a turn and a larger amount of torque to the wheel on the outside of a turn. An alternative to additional couplings is to add torque to or subtract torque from one of the outputs using a secondary motor. With reference to Fig. 3, an alternatively stacked planetary gear system 70 is shown, comprising a sun gear 72 connected to the output shaft 14 of the electric motor 12. A plurality of first planet gears 74 are supported by a first planet carrier 76 and mesh with the sun gear 72 and a ring gear 78. The ring gear 78 has internal teeth 80 and external teeth 82, which mesh with a plurality of secondary planet gears 84 supported by a second planet carrier 86. The plurality of secondary planet gears 84 also mesh with the internal teeth of a second ring gear 88. The second planet carrier 86 can be fixedly mounted and / or connected to a braking device, thus preventing its rotation.The first planet carrier 76 is rotationally fixed to the first axle shaft 40, while the second ring gear 88 is connected to the second axle shaft 42. The stacked planetary gear set 70 has a compact axial profile to provide a drive connection between an electric motor and a pair of axle shafts. The sun gear 72, the multiple first planet gears 74, the first planet carrier 76, and the ring gear 78 form a differential planetary gear set and divide a forward input from the electric motor 12 into a forward output to the first axle 40 and a reverse output to a reversing gear set. The ring gear 78 and its external teeth 82 form a sun gear for the reversing planetary gear set.The ring gear 78 and its external teeth 82, the multitude of second planet gears 84, the second planet carrier 86 and the ring gear 88 form the reversing planetary gear, which reverses one of the outputs of the differential planetary gear for the second axle 42 and makes the ratio between the electric motor 12 and the second axle 42 equal to the ratio between the electric motor 12 and the first axle 40.

Claims

Electric vehicle drive system (10, 110, 210, 310), comprising: an electric motor (12) with an output shaft (14); a differential planetary gear (18) with a first sun gear (16) connected to the output shaft (14) of the electric motor (12), wherein a plurality of first planet gears (20) are supported by a first planet carrier (22) and mesh with the first sun gear (16) and a first ring gear (24); a reversing planetary gear (26) with a second sun gear (28) non-rotatably connected to the first ring gear (24), wherein a plurality of second planet gears (30A, 30B) are supported by a second planet carrier (32) and mesh with the second sun gear (28) and a second ring gear (34); a first axle shaft (40) non-rotatably connected to the first planet carrier (22). is;and a second axle shaft (42) which is non-rotatably connected to the second planet carrier (32), characterized by a separating brake (36) on the second ring gear (34). Electric vehicle drive system (10, 110, 210, 310), comprising: an electric motor (12) with an output shaft (14); a differential planetary gear (18) with a first sun gear (16) connected to the output shaft (14) of the electric motor (12), wherein a plurality of first planet gears (20) are supported by a first planet carrier (22) and mesh with the first sun gear (16) and a first ring gear (24); a reversing planetary gear (26) with a second sun gear (28) non-rotatably connected to the first ring gear (24), wherein a plurality of second planet gears (30A, 30B) are supported by a second planet carrier (32) and mesh with the second sun gear (28) and a second ring gear (34); a first axle shaft (40) non-rotatably connected to the first planet carrier (22). is;and a second axle shaft (42) which is rotationally fixed to the second planet carrier (32), characterized by a first pump (312) on the first axle shaft (40), a second pump (314) on the second axle shaft (42) and a hydraulic motor (50E) which is connected to the first and the second pump (312, 314) and is driven by a component of the differential planetary gear (18) or the reversing planetary gear (26). Electric vehicle drive system (10, 110, 210, 310) according to claim 1 or 2, wherein the first axle shaft (40) extends through an opening in the electric motor (12). Electric vehicle drive system (10, 110, 210, 310) according to claim 1, 2 or 3, wherein the electric motor (12), the differential planetary gear (18) and the reverse planetary gear (26) are all coaxial with the first and second axle shafts (40, 42).

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