Electric powertrain system with planetary drive

[0001] The subject invention relates to an electric drive unit for a vehicle wheel that utilizes an in-line, two-stage planetary drive to provide a radially and axially compact configuration.

[0002] Electric drive vehicles utilize a combination of electric motors and gear sets to drive vehicle wheels. An electric motor and associated gear drive must provide a power dense package, i.e. a high gear reduction, which can fit within a limited space to drive a vehicle wheel. The required gear reduction is typically achieved by using multiple gear sets.

[0003] One disadvantage with using multiple gear sets is that significant areas of axial and radial packaging space are consumed by the gear sets to the expense of other wheel end components. For example, an electric motor and gear box configuration oriented at a right angle relative to the wheel shaft can adversely affect packaging of brake and suspension components.

[0004] Thus, there is a need for an electric powertrain configuration that provides both a radially and axially compact design, and which also provides a high gear reduction.

[0005] An electric drive unit for a vehicle wheel includes an electric motor having a motor output shaft coupled to a planetary gear drive. The planetary gear drive includes a first stage gear set and a second stage gear set that are both driven by the motor output shaft. The second stage gear set is coupled to a wheel shaft to drive the vehicle wheel.

[0006] In one example, the motor output shaft, the planetary gear drive, and the wheel shaft are coaxial to provide an axially and radially compact configuration. The first stage gear set includes a first sun gear and a first plurality of planet gears and the second stage gear set includes a second sun gear and a second plurality of planet gears. The first and second sun gears are both driven by the motor output shaft. A common ring gear is in meshing engagement with the first and second pluralities of planet gears.

[0007] In one disclosed configuration, each of the first plurality of planet gears is supported on a pin that is fixed to a non-rotating motor housing structure. The first sun gear rotates each associated planet gear about a respective individual axis, however, these planet gears do not rotate as a unit about the sun gear. These planet gears then rotate the common ring gear. The second stage gear set includes a planet carrier that supports the second plurality of planet gears via a pin connection. The planet carrier is a rotating component such that the planet gears of the second stage gear set rotate as a unit about the second sun gear. The planet carrier comprises a driving output that is coupled to the wheel shaft.

[0008] The planetary gear drive and the electric motor are axially aligned with a wheel axis, which results in a simplified packaging configuration with the additional benefit of being radially compact. Also, the planetary gear drive allows for a large reduction ratio in a very compressed axial design. The common ring gear, along with the possibility of using similar planet gears for the first and second stage gear sets allow for reduced manufacturing costs. Additionally, the gears could be easily varied to provide a wide range of gear reductions.

[0009] These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

[0013] An electric drive unit 10 for a vehicle wheel 12 is shown in FIG. 1. The electric drive unit 10 includes an electric motor 14 with a stator and rotor as known, and a planetary gear drive, shown generally at 16. The electric motor 14 includes a motor output shaft 18 that is rotatable about a motor axis 20. The planetary gear drive 16 is driven by the motor output shaft 18 and is coupled to drive a wheel shaft 22, which extends in a lateral direction across a vehicle width. The wheel shaft 22 rotates about a wheel axis 24 and is coupled to drive the vehicle wheel 12. In the example shown, motor axis 20 and the wheel axis 24 are co-axial, which provides an axially compact design.

[0014] The electric motor 14 includes a motor housing 26 that is mounted to a non-rotating structure 48. The non-rotating structure 48 could be a vehicle frame member, suspension component, or other vehicle structure, for example. The motor housing 26 includes a main portion 28 that encloses the rotor and stator and an extension portion 30 that extends outwardly from the main portion 28 toward the vehicle wheel 12. The extension portion 30 defines an inner cavity 32 that receives and substantially encloses the planetary gear drive 16.

[0015] The motor output shaft 18 is supported on bearings 34 that are mounted to the motor housing 26. The motor output shaft 18 includes a first portion 36 positioned within the main portion 28 of the motor housing 26 and a second portion 38 that extends into the extension portion 30. The first portion 36 is defined by a first diameter D1 and the second portion 38 is defined by a second diameter D2 that is less than the first diameter D1 in the example shown. It should be understood that D2 can also be larger than D1. The second portion 38, in this example, also includes a reduced diameter portion defined by a third diameter D3 that is less than the second diameter D2.

[0016] The planetary gear drive 16 includes a first stage gear set 40 and a second stage gear set 42 that cooperate to provide driving output to the wheel shaft 22. The first stage gear set 42 includes a first sun gear 44 mounted directly to the second portion 38 of the motor output shaft 18 at the second diameter D2, and a plurality of first planet gears 46 that are in direct meshing engagement with the first sun gear 44. In the disclosed embodiment there are four first planet gears 46 (see FIG. 2) to provide increased stability; however, the number of first planet gears 46 could be varied as needed.

[0017] The second stage gear set 42 includes a second sun gear 50 mounted directly to the second portion 38 of the motor output shaft 18 at the third diameter D3, and a plurality of second planet gears 52 that are in direct meshing engagement with the second sun gear 50. In the disclosed embodiment there are four second planet gears 52 (see FIG. 3) to provide increased stability; however, the number of second planet gears 52 could be varied as needed. The first planet gears 46 and the second planet gears 52 are both in direct meshing engagement with a common ring gear 54. In other words, the first 40 and second 42 stage gear sets share a single ring gear 54. The ring gear 54 is a floating ring gear that is rotated by the first 46 and second 52 planet gears about the motor axis 20 relative to the extension portion 30 of the motor housing 26. Thrust washers (not shown) may be utilized within the planetary gear drive 16 to assist with holding the floating ring gear 54 in a desired axial position.

[0018] The first planet gears 46 are each supported on a first planet pin 58. The first planet pins 58 are fixed to the motor housing 26, such that the first planet gears 46 each rotate about their own axis 60. Thus, the first planet gears 46 as a unit are held fixed relative to the first sun gear 44, i.e. the first planet gears 46 do not rotate as a unit about the first sun gear 44 but only rotate about their own respective axes 60. The motor output shaft 18 directly drives the first sun gear 44, which in turn rotates the first planet gears 46 about their axes 60. The first planet gears 46 rotate the ring gear 54.

[0019] The second stage gear set 42 includes a planet carrier 62 that rotates relative to the motor housing 26 about the motor axis 20. The second planet gears 52 are each supported on a second planet pin 64 that is mounted to the planet carrier 62. Thus, the planet gears 52 can each rotate about their own axis 66 in addition to being able to rotate as a unit about the second sun gear 50. The motor output shaft 18 directly drives the second sun gear 50, which in turn rotates the second planet gears 52 whose mesh with the ring gear 54 provide a net orbital planet rotation reduction that is output to the wheel shaft 22 through the planet carrier 62.

[0020] The planet carrier 62 includes first 68 and second 70 mounting portions that are positioned on opposing sides of the second planet gears 52. In other words, the second planet gears 52 are positioned axially between the first 68 and second 70 mounting portions. The planet carrier 62 also includes a collar portion 72 that extends outwardly from the second mounting portion 70. The collar portion 72 is coupled to the wheel shaft 22.

[0021] The motor output shaft 18, the first sun gear 44, the ring gear 54, the second sun gear 50, and the planet carrier 62 all rotate about the motor axis 20. The planet carrier 62 rotates the wheel shaft 22 about the wheel axis 24, which as described above is coaxial with the motor axis 20. This provides a very axially and radially compact electric drive unit because all of above-mentioned components are laterally in-line with the wheel shaft 22. This frees up packing space for other wheel end components such as brake and suspension components, for example.

[0022] FIG. 2 shows a cross-sectional view of the first stage gear set 40. The first sun gear 44 is defined by a first sun diameter SI and the first planet gears 46 are defined by a first planet diameter P1.

[0023] FIG. 3 shows a cross-sectional view of the second stage gear set 42. The second sun gear 50 is defined by a second sun diameter S2 and the second planet gears 52 are defined by a second planet diameter P2.

[0024] In the example shown, the first sun diameter S1 is greater than the second sun diameter S2 and the first planet diameter P1 is less than the second planet diameter P2. By varying the sizes of the sun and planet gears in the first 40 and second 42 stage gear sets, a desired gear reduction can be achieved at the output to the planet carrier 62. The example shown in FIGS. 1-3 is just one example, and it should be understood that the diameters of any of the sun and planet gears can be increased or decreased in various combinations as needed to provide a desired reduction.

[0025] The subject invention provides a fixed-differential star-planetary gear set that is integrated within an electric motor to provide an axially and radially compact electric drive unit for a vehicle wheel. The planetary gear drive and electric motor are in-line, i.e. axially aligned with each other, which allows for a very small radial package. Further, using a two-stage planetary configuration allows for large reduction ratios in a very compressed axial space. In the example configuration shown, the electric motor housing has a maximum diameter of nine inches or less, while still providing a significant gear reduction of at least 6:1.

[0026] Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.