Gearbox arrangement for use in electric drive units

Description

Technical Field

[0001] The invention relates an electric vehicle comprising a gear assembly.Background Art

[0002] Electric drive transmissions in electric vehicles are usually made single speed, with a gear ratio that is a compromise between the maximum torque at start and acceleration and the maximum allowed speed of the electric motor. Using a single stage gear box operating in the low and high speed ranges results in an efficient drive train.

[0003] 2-Speed electric drive trains are provided that result in further efficiency gain and in a longer range. Use of a 2-speed transmission allows downsizing of the electric motor.

[0004] In a known 2-speed electric drive, a planetary gear set is used in a two-speed transaxle having two clutches, one clutch connected to a sun gear and the other to a ring gear. For operation in the low speed range, the first clutch is deactivated so that power is transferred through the planetary gear set via the ring gear. For operation in the high speed range, the first clutch is activated and the second clutch is de-activated so that power is transferred via the sun gear, allowing the ring gear to freely spin without transferring any torque.

[0005] The known system results in losses in the planetary gear stage.

[0006] JP H05 332405 A discloses in its Fig.3 and 6 an electric vehicle comprising a gear assembly, the gear assembly comprising: a planetary gear assembly comprising a first and a second sun gear, a first and a second planetary gear member rotatably supported on a carrier about respective planetary gear axes, whereby the second sun gear is connected to a drive member for rotation of the drive member about the transmission axis, the drive member comprising a differential housing, a brake member that is adapted for fixedly engaging the first sun gear with a locking part of the gear assembly, - the first and second planetary gear members being supported on the carrier at spaced-apart positions along a carrier axis to be jointly rotatable about the carrier axis, the first sun gear being rotatable about the transmission axis, meshing with the first planetary gear member, the second sun gear being rotatable about the transmission axis, fixedly connected to the drive member and meshing with the second planetary gear member, the brake member being connected to the the first sun gear and to the locking part, which is non rotating, for preventing rotation of the first sun gear about the transmission axis when the brake member is engaged, and the electric vehicle further comprising a wheel axle, the axis of which is the transmission axis.

[0007] DE 10 2019 119955 A1 discloses in its Fig.1 a two-speed planetary gear assembly comprising a brake and comprising a block clutch for a direct speed of 1:1.

[0008] DE 10 2013 205013 A1 discloses in its Fig.1 a two-speed planetary gear assembly suitable for connecting an electric motor coaxial with the differential. In its Fig.4 it discloses a two-speed planetary gear assembly suitable for connecting an electric motor parallel to the differential.

[0009] It is an object of the present invention to provide a drivetrain for an electric motor that is of compact and light construction and that has improved efficiency.Summary

[0010] The invention for which protection is sought is defined in claim 1 and concerns an electric vehicle comprising a gear assembly.Brief Descripton of Drawings

[0011] An embodiment of a gear assembly according to the invention as claimed in claim 1 will by way of a non-limiting example, be explained in detail with reference to Fig.2 - 4 of the accompanying drawings. In the drawings: Fig. 1 shows a cross-sectional view through a gear assembly not falling within the wording of claim 1, comprising a single planetary gear with an outer ring, Fig. 2 shows a schematic view of an embodiment of a gear assembly comprising a compound planetary gear and falling within the wording of claim 1, Fig. 3 shows the flow of power through the gear assembly of figure 2 in first gear, Fig. 4 shows the flow of power through the gear assembly of figure 2 in second gear, Fig. 5 shows a schematic view of a further embodiment of a gear assembly, not falling within the wording of claim 1, comprising a compound planetary gear, and Fig. 6 shows a cross-sectional view of the gear assembly of figure 5. Description of Embodiments

[0012] Figure 1 show a gear assembly 1 that is connected to an electric motor 2 having output shaft 3 that is rotatable around an axis 4. The electric motor 2 drives output shafts 5, 6 that are each connected to a wheel (not shown) via a two stage gear assembly 8. The output shafts 5,6 can rotate around a transmission axis 7 that is parallel to the output shaft axis 3, and that is spaced at a distance of, for instance,14 cm.

[0013] The two stage gear assembly 8 comprises a cylindrical gear 9 and a planetary gear assembly 10. The planetary gear assembly 10 comprises a sun gear 11, a carrier 12, planetary gears 13,14 and an outer ring gear 15 that meshes with the planetary gears 13,14. The planetary gears 13, 14 are supported on the carrier 12 to rotate about respective planetary gear axes 18,19. The carrier 12 is part of the housing 20 of a differential 21. The ring gear 15 is connected via a wet clutch 23 to the carrier 12 and to the housing 20 of the differential 21. A brake member 24, such as a mechanical diode, can selectively lock the ring gear 15 to a non-rotating part, for instance to the housing of the gear assembly 8.

[0014] In the low speed range, or first gear, the brake member 24 is engaged and the clutch 23 is released, so that the planetary gear is activated. The ring gear 15 is fixed to the housing and cannot rotate about the axis 7. The cylindrical gear 9 drives the sun gear 11, and power is transmitted by the carrier 12 to the housing 20 via the planetary gears 13, 14 that rotate about their respective axes 18,19 on the carrier 12. From the rotating differential housing 20, the power is transmitted to the differential 21 and to both output shafts 5,6. If the cylindrical gear has a gear ratio of about 4,5:1 and the single stage planetary gear has a minimum ratio of 2,5:1, the total gear ratio of the first gear is 4,5*2,5 = 11,25.

[0015] In the high speed range, or second gear, the brake member 24 is released and the clutch 23 is engaged so that the complete planetary gear assembly 10 is deactivated and locked to the differential housing 20. The second gear can be considered as a single-stage reduction with a gear ratio of for istance 4,5:1. This forms an efficient transmission compared to the the two-stage gear train in the low speed range, and the aim is to drive in second gear as much as possible in the driving cycle.

[0016] Figure 2 schematically shows an embodiment of a gear assembly 30 with a compound planetary gear stage 31 that is suitable for obtaining gear ratios less than 11 in first gear. The rotor shaft 33 of the electric motor 32 and a pinion gear 34 are connected to a gear wheel 36 that is supported on a shaft 41 that is parallel to the rotor shaft 33. The pinion 34 and gear wheel 36 form the first gear reduction stage of the gear assembly 30.

[0017] The shaft of the gear assembly 30 is essentially designed as a planetary carrier 35 for the planetary gear set 31 which is the second gear reduction stage of the gearbox. The planetary gear stage 31 comprises first sun gear 37, planetary gears 38, 39 and second sun gear 40.

[0018] The second sun gear 40 forms the output stage of the planetary stage 31. It is permanently meshed with a number of planetary gears 39 and is fixedly attached to the differential housing 50. The differential housing 50 contains a differential 51 that transmits rotation of the housing 50 to wheel shafts 52,53 of wheels 54, 55.

[0019] A multidisc wet clutch 48 is connecting and disconnecting the planetary carrier 35 with the differential housing 50.

[0020] The first sun gear 37 forms the input of the planetary gear stage 31 and is permanently meshed with a number of planetary gears 38. The first sun gear 37 is also connected to a multidisc brake 42 that is attached to the housing 43 of the gear assembly in a non-rotating manner. When the multidisc brake 42 is locked, the sun gear 37 is held stationary. When the multidisc brake 42 is released, the sun gear 37 is free to rotate on its support bearings 44,45.

[0021] Each of the planetary gears 38,39 is formed as a common compound gear unit that is supported on the planetary carrier 35 via bearings 46,47.

[0022] In gear 1 (high torque, low speed), the power flow goes through both gear reduction stages 34,36 and 31. The brake 42 is locked and the clutch 48 is released. Power is transmitted from the input pinion 34 to the gear wheel 36, to the first sun gear 37, to the planetary gears 38, to the planetary gears 39, to the second sun gear 40, to the differential housing 50, to the differential pin and gears 51, to the drive shafts 52,53 and to the car wheels 54,55.

[0023] In figure 3, the power flow through the gear reduction stages in first gear is indicated by the arrows.

[0024] As shown in figure 2, in gear 2 (low torque, high speed), the power flow goes only through gear reduction stage 1 that is formed by the pinion 34 and gear wheel 36. The brake 42 is released and the clutch 48 is locked so that it connects the planetary carrier 35 with the differential housing 50. The planetary gear stage 31 rotates as a lump mass together with the differential housing 50. Power is transmitted from the input pinion 34 to the gear wheel 36, to the planetary carrier 35, to the clutch 48, to the differential housing 50, to differential pin and gears 51, to the driveshafts 52,53 and the car wheels 54,55.

[0025] In figure 4, the power flow through the gear reduction stages in second gear is indicated by the arrows.

[0026] Figure 5 schematically shows another embodiment of a gear assembly 30 with a compound planetary gear stage 31. The rotor shaft 33 of the electric motor 32 and a pinion gear 34 are connected to a gear wheel 36 that is supported on a shaft 41 which is parallel to the rotor shaft 33. The pinion 34 and gear wheel 36 form the first gear reduction stage of the gear assembly 30.

[0027] The second gear reduction stage 31 of the gearbox, or gear assembly 31, is of the planetary type. The planetary gear set consists of the first sun gear 37, the planetary gears 38, the planetary gears 39 and the second sun gear 40.

[0028] The first sun gear 37 is firmly attached to the gear wheel 36 of the first stage and is concentric with it. The sun gear 37 and the gear wheel 36 form a unit which is supported by bearings 44,45 onto the differential housing 50. The first sun gear 37 is permanently meshed with a number of planetary gears 38.

[0029] The planetary gears 38,39 are formed as a common compound gear unit and the gears are supported via bearings 46, 47 on the planetary carrier 35.

[0030] The second sun gear 40 forms the output of the planetary gear set 31 and it is fixedly attached to the differential housing 50. The second sun gear 40 is permanently meshed with a number of planetary gears 39.

[0031] The multidisc wet clutch 48 connects and disconnects the planetary carrier 35 with the differential housing 50 in a slipping manner.

[0032] Multidisc brake 42 is operated to connect and disconnect the planetary carrier 35 with the gearbox housing 43 (a lock and release planetary carrier).

[0033] In gear 1 (high torque, low speed) the power flow goes through both gear reduction stages 34,36 and 31. The brake 42 is locked and the clutch 48 is released. The power is transmitted from the input pinion 34 to the gear wheel 36, to first sun gear 37, to the planetary gears 38, to the planetary gears 39, to the second sun gear 40, to the differential housing 50, to the differential pin and gears 51 and to the driveshafts 52,53 and the car wheels 54,55.

[0034] As shown in figure 5, in gear 2 (low torque, high speed) the power flow only goes through gear reduction stage 1 that is formed by pinion 34 and gear wheel 36. The brake 42 is released and the clutch 48 is locked. The clutch 48 connects the planetary carrier 35 with the differential housing 50 and the complete planetary gear stage 31 rotates as a lump mass together with differential housing 50. Power flows from the input pinion 34 to the gear wheel 36, to the first sun gear 37, to the planetary gears 38, to the planetary carrier 35, to the clutch 48, to the differential housing 50, to the differential pin and gears 51 and to the driveshafts 52,53 and the car wheels 54,55.

[0035] In figure 6, a cross-sectional view of the gear assembly of figure 5 is shown.

Claims

1. Electric vehicle comprising a gear assembly (30), the gear assembly comprising: - a drive gear (34) connected to an output shaft (33) of an electric motor (32), the drive gear (34) being rotatable around an axis (33) parallel to a transmission axis (52, 53), - a planetary gear assembly (31) comprising a first (37) and a second (40) sun gear (37,40), a first (38) and a second (39) planetary gear member rotatably supported on a carrier (35) about respective planetary gear axes, an input stage that comprises the drive gear (34) and a gear wheel (36), whereby the second sun gear (40) is connected to a drive member (50) for rotation of the drive member about the transmission axis (52, 53), the drive member (50) comprising a differential housing, the first sun gear (37) supported by bearings (44, 45) onto the differential housing, - a clutch member (48) that is adapted for slippingly connecting the carrier (35) with the drive member (50), and - a brake member (42) that is adapted for fixedly engaging the first sun gear (37) with a locking part (43) of the gear assembly (30), wherein the gear assembly is configured such that in a low speed range of the gear assembly, the clutch member (48) and the brake member (42) are operated such that torque is transmitted from the drive gear (34) to the planetary gear assembly (31), and through the second sun gear (40) to the drive member (50), and such that in a high speed range of the gear assembly, the clutch member (48) and the brake member (42) are operated such that the carrier (35) is fixedly connected to the drive member (50) and is rotated about the transmission axis (52, 53) such that torque is transmitted from the drive gear (34) to the drive member (50) via the carrier (35), the planetary gear assembly (31) rotating as a lump mass together with the differential housing, - the first (38) and second (39) planetary gear members being supported on the carrier (35) at spaced-apart positions along a carrier axis to be jointly rotatable about the carrier axis, - the drive gear (34) engaging the gear wheel (36), wherein the latter is firmly attached to the carrier (35) for rotation of the carrier around the transmission axis (52, 53), - the first sun gear (37) being rotatable about the transmission axis (52, 53), meshing with the first planetary gear member (38), - the second sun gear (40) being rotatable about the transmission axis (52, 53), fixedly connected to the drive member (50) and meshing with the second planetary gear member (39), - the brake member being (42) connected to the the first sun gear (37) and to the locking part (43), which is non rotating, for preventing rotation of the first sun gear (37) about the transmission axis (52, 53) when the brake member (42) is engaged, and the electric vehicle further comprising a wheel axle, the axis of which is the transmission axis (52, 53).