CN1964864A - Epicyclic differential transmission - Google Patents

Abstract

A single-speed planetary differential transmission allows an input shaft (12) to be connected to two output shafts (16, 23) with substantially equal torque distribution. The transmission includes two planetary gear trains sharing a common ring/sun gear (17, 18) that acts as a differential gear to accommodate speed variations in the output shafts (16, 23).

Description

planetary differential transmission

technical field

The invention relates to a planetary differential gearing suitable in particular for vehicles, in particular electric vehicles with two drive wheels.

Background technique

Vehicles with two drive wheels and a single power source require the splitting of a single drive shaft into two half shafts associated with the respective drive wheels. A differential gear is also required to accommodate relative motion between the two drive wheels, for example when cornering. There is also a need to distribute drive torque equally between the two drive wheels so as to avoid torque modulation, especially in front wheel drive vehicles.

Typically, a final drive reduction gear, possibly a bevel gear, is combined with a conventional bevel differential gear. This setup is not very compact.

Electric vehicles typically require only a single speed reduction gear because the torque characteristics of an electric motor allow road speed to be directly proportional to motor speed. For compact assembly, a coaxial arrangement is desired in which one half shaft passes axially through the rotor of the electric motor to the associated drive wheel.

Contents of the invention

According to the present invention, there is provided a single-speed planetary differential transmission comprising a housing, an annular rotatable input member, two opposing rotatable output members, and a planetary gear train, The annular rotatable input member has an axis of rotation in the housing, two rotatable output members are opposite on said axis, one of which is adapted to be driven through the input member, the planetary gear train is arranged around the The input member, wherein the input member includes a sun gear, internal planet gears meshing with the sun gear are provided, and an internal planet gear carrier is rotatably provided, the carrier is connected to the output member associated with the input member fixed together to provide an internal ring gear meshing on the inside with said internal planetary gears and externally with external planetary gears rotatable on the axis of said housing, and providing an internal ring gear meshing with said external planetary gears and An external ring gear connected to the other of the outputs.

This arrangement provides a single-speed transmission with a short axial length and in which the elements of the planetary gear train act as a differential gear to accommodate the relative rotation of the corresponding output members while simultaneously giving a substantially equal distribution of torque.

Preferably, the sun gear, inner planet gears and inner ring gear are arranged in a substantially common plane. Preferably, the inner ring gear, outer planet gears and outer ring gear are arranged in a substantially common plane. In a preferred embodiment, the sun gears, planet gears and ring gears are all arranged in a substantially common plane. A particular advantage of this arrangement is that the inner ends of the output members can be arranged very close together, allowing the half shaft length to be maximized and the half shaft connection to be minimized during stationary movement of the vehicle.

In a preferred embodiment four inner planetary gears and four outer planetary gears are provided.

The arrangement may also include a locking pawl engageable to retain a member of the planetary gear train relative to the housing, thereby locking the transmission and providing a lockout function. The pawl may, for example, engage an external ring gear.

In a preferred embodiment, the sun gear has 33 teeth, the inner planet gear has 26 teeth, the inner ring gear has 87 teeth on the inside and 103 teeth on the outside, the outer planet gear has 19 teeth, and The outer ring gear has 141 teeth. This arrangement provides an overall gear ratio of 7.24:1.

It should be appreciated that the inner ring gear includes a ring gear of an inner planetary gear train and a sun gear of an outer planetary gear train. This inner ring gear floats between the other elements of the inner and outer planetary gear trains, giving the effect of a differential gear.

It will be appreciated that the gear ratios need to be chosen carefully so as to ensure a substantially equal distribution of torque, but it is within the ability of an experienced transmission engineer to calculate which gear ratios are appropriate, bearing in mind the required final drive reduction ratios and This is a problem with the constraints imposed by the size of the successive planetary gear elements.

In a preferred embodiment, the axial length of a transmission according to the present invention is approximately 50% that of a conventional final drive/differential unit, and the number of parts is reduced by approximately 30%. In a small vehicle, a shorter axial length is advantageous because it maximizes space for ride and suspension components.

The invention also allows the incorporation of a locking or limited slip differential, eg by fixing or controlling the speed ratio between the output shafts. This can be done relatively simply, since the output members are immediately adjacent and on the same axis of rotation.

Description of drawings

Features of the invention will become apparent from the following description of a preferred embodiment, shown by way of example only in the accompanying drawings, in which:

Figure 1 shows a schematic arrangement of a transmission according to the invention; and

Figure 2 shows a practical embodiment of the design of Figure 1 in axial section.

Detailed ways

Referring to Fig. 1, a transmission has a main axis of rotation 10 on which an electric motor 11 having a hollow rotor (not shown) is provided. The rotor is directly connected to a hollow input shaft 12 of the transmission which, as shown, includes the sun gear 13 of a two-stage planetary transmission in which all the main gear components are located in a substantially common plane.

A series of internal planet gears 14 (typically four) meshingly rotate around the sun gear and are journaled on a generally planet carrier 15 . The bracket 15 is coupled to a drive shaft 16 via the input shaft 12 and the electric motor 11 for connection to a drive wheel of a vehicle.

Surrounding the planet gears 14 is an inner ring gear (ring gear) 17 having gear teeth on the inner diameter that mesh with the inner planet gears 14 . Furthermore, the inner ring gear has gear teeth on the outer diameter which form a sun gear 18 of an outer planetary gear train.

A series of outer planetary gears 19 (typically four) meshingly rotate around sun gear 18 and are journaled on relatively stationary bushings 20 of a gearbox 21 .

An external ring gear (ring gear) 22 meshes with the external planetary gears 19 and is connected to a further drive shaft 23 for connection to a second drive wheel of the vehicle.

In use, drive torque from the electric motor 11 is transmitted through the input shaft 12 to the sun gear 13 . The reactive torque provided by the internal ring gear 17 causes the internal planetary gears to rotate and drive the carrier 15 and drive shaft 16 .

The outer sun gear 18 also turns (along with the inner ring gear 17 ) and transmits torque to the outer ring gear 22 via the outer planet gears 19 . The external planetary gears are effectively provided with a fixed carrier formed by the gearbox 21 . The outer ring gear thus rotates and drives the drive shaft 23 .

It should be understood that the speed balance between the two drive axles is controlled by the road wheels in contact with the road. The inner ring gear 17/outer sun gear 18 is a differential gear that allows relative rotation of the respective drive shafts, eg during vehicle cornering.

Drive torque from the electric motor is split between the two planetary gear trains, and the torque balance is dictated by the selected speed ratio. An equal torque split is desirable for vehicles driving the wheels on a substantially common axis, but other torque splits may be selected, for example, for driving axles connected to different axes of an all-wheel drive vehicle, or for Special non-automotive applications.

FIG. 1 shows a detent pawl 24 that engages on demand to lock the outer ring gear 22 to the transmission case 21 . It will be appreciated that by preventing the outer ring gear from turning, the transmission will be locked and thus a vehicle can be provided with wheel brakes.

This arrangement is also suitable for modifying the external control of the differential gear 17/18. It will be appreciated that by externally controlling this gear 17/18, the torque distribution between the two drive shafts 16, 23 can be adjusted. A suitable means of braking the differential gear 17/18 may be a brake band, clutch or viscous coupling.

By arranging the inner ends of the drive shafts 16, 23 in close proximity, the transmission provides for minimal drive shaft connection during stationary vehicle movement as compared to a conventional arrangement of differential gears between the inner drive shaft ends . This setup is of particular value for small front-wheel drive vehicles where the vehicle has a relatively narrow track. Furthermore, the proximity of the drive shaft ends provides a relatively simple form of coupling which locks the drive shafts together or restricts relative rotation therebetween. Thus, this arrangement may provide a locked differential or a limited slip differential, which may be valuable for certain types of vehicles.

In the exemplary embodiment of Figure 1, the gears are provided with the following number of teeth to give a substantial torque distribution without external control of the differential gear 17/18.

Internal sun gear 13 — 33 teeth

Internal planetary gear 14 — 26 teeth

Internal ring gear 17 — 87 teeth

External sun gear 18 - 103 teeth

External planetary gear 19 — 19 teeth

External ring gear 22 — 141 teeth

The total reduction ratio of these individual ratios is 7.24:1.

An actual transmission setup for a front wheel drive vehicle is shown in Figure 2, showing the transmission case 11, bearings, shaft seals and other conventional components in detail. Where appropriate, parts have been given reference numerals corresponding to Figure 1; a lockout arrangement is not shown.

It will be appreciated that the transmission case 21 is bolted directly to the motor case 30 as shown.

Claims (8)

1. epicyclic differential transmission, comprise a shell (21), the rotatable input component (12) of one annular, two relative rotatable output (16,23), an and planet train of gears, this annular turns input component (12) and have a pivot center (10) in described shell, two rotatable output (16,23) on described axis (10), be relative, one of them is suitable for being driven passes described input component (12), this planetary gear train is arranged to around described input component (12), wherein, described input component (12) comprises a sun gear (13), the internal planetary gear that is meshed with described sun gear (13) (14) is provided, one internal planetary gear carriage (15) is provided rotationally, this carriage (15) is fixed together with the output (16) relevant with described input component (12), be provided at inboard and described internal planetary gear (14), and the outside with can go up the internal ring gear (17) that the outer planet gears (19) of rotating is meshed at the axis (20) of described shell, and provide and be meshed with described outer planet gears (19) and be connected to another an external rings generating gear (22) in the described output (23).

2. driving device as claimed in claim 1 is characterized in that, described sun gear (13), internal planetary gear (14) and internal ring gear (17) are arranged in the common substantially plane.

3. driving device as claimed in claim 1 or 2 is characterized in that, described internal ring gear (17), outer planet gears (19) and external rings generating gear (22) are arranged in the common substantially plane.

4. as claim 2 or 3 described drivings device, it is characterized in that described sun gear (17), planetary wheel (14,19) and Ring gear (17,22) all are arranged in the common substantially plane.

5. any described driving device in the claim as described above is characterized in that, four internal planetary gears (14) and four outer planet gears (19) are provided.

6. any described driving device in the claim as described above, it is characterized in that, also comprise a lock pawl (24), this lock pawl (24) can engage and keep an element of described planetary gear train with respect to described shell (21), thereby pins described driving device and provide one to stop lock function.

7. driving device as claimed in claim 6 is characterized in that, described pawl (24) engages described external rings generating gear (22).

8. any described driving device in the claim as described above, it is characterized in that, described sun gear (13) has 33 teeth, described internal planetary gear (14) has 26 teeth, described internal ring gear (17) has 87 teeth and has 103 teeth in the outside in the inboard, described outer planet gears (19) has 19 teeth, and described external rings generating gear (22) has 141 teeth.

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