Two-stage planetary gearbox for electric machine

Abstract

The coaxial single-ratio 2-speed reducer for electric machines comprises a first planetary gear train 30, where the ratio of the number of teeth on the ring gear 40 to that on the planet gear 31 is R1, and a second planetary gear train 50, where the ratio of the number of teeth on the ring gear 62 to that on the planet gear 51 is R2. The two trains are arranged in two different axial spaces. These two planetary gear trains, mounted in series, perform both reduction and differential functions because the ring gear 40 of the first train 30 is connected to the planet gear 51 of the second train 50, the electric machine is connected to the planet gear 31 of the first train 30, one of the wheels is connected to the main body 34 of the planet carrier of the first train 30, and the other wheel is connected to the hub 64 of the ring gear 62 of the second train 50. The relationship between the reduction ratios is: R2 = 1 + 1 / R1. Figure for the abridged version: [Fig.1]

Description

Title of the invention: Two-planetary gear reducer for an electric machine TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a single-ratio coaxial-type reducer for an electric powertrain.

[0002] This reducer is made up of two simple epicyclic gear trains (called planetary) whose arrangement makes it possible to ensure, on the one hand, the transmission of the engine torque to the wheels according to a single multiplication ratio and, on the other hand, a function, called differential, of equal sharing of the engine torque to the wheels, the latter rotating or not at the same speed. STATE OF THE ART

[0003] Such a device is known in particular from publication WO 2005 / 120877.

[0004] In this publication the two planetary gear trains are arranged in the same axial space, in other words a first gear fits radially into a second.

[0005] The first train comprises a hollow central planetary pinion 13 connected to the electric machine. The planet carrier 15 is connected to a shaft 16 passing through the sun gear, then the electric machine 11 and provides the left wheel with torque and movement. The crown 17 of this first train and the sun gear 18 of the second train are connected and form a single ring carrying an internal toothing (crown) and an external toothing (planet). Each satellite 19 of this second train is carried by an axis 20 planted in an intermediate fixed plate between the motor casing 30 and the closing casing 21 of the reducer. The crown 22 of the second train is guided and held axially by a ball bearing carried by the casing 21 of the reducer. This crown transmits movement and torque to the shaft 23 connected to the right wheel.

[0006] In this publication, an exemplary embodiment (number of teeth for each element) is claimed. The corresponding reduction ratio is given in the description: 7.24. It is too low to be suitable for vehicles currently on the market, except by equipping them with a very high torque motor, which greatly reduces the interest of this particularly axially compact reducer. Increasing the reduction ratio is of course possible, but the radial size then becomes a handicap.

[0007] In the concept presented, the common crown 17 and planetary 18 ring is self-centered on the inner 14 and outer 19 satellites. The axial forces not being balanced, an axial stop is achieved on both sides by fixed plates (not numbered) positioned and held by the axes of the satellites. We will therefore have friction under stress between the ring 17,18 and the plates, which can be detrimental to the acoustics and durability of the reducer. PRESENTATION OF THE INVENTION

[0008] the object of this invention is a single-ratio reducer for an electrical machine of coaxial type and comprising two planetary gears ensuring the two functions of reduction and differential.

[0009] According to a first characteristic, the two planetary gears are arranged in two different axial spaces, to gain radial space.

[0010] To the crown of the first train and to the sun gear of the second train, linked together, is attached a flange, not radially centered and positioned axially by two needle stops.

[0011] the main supporting element of the planet carrier of the second train is a ring, not radially centered, stopped axially with a very small clearance by a flat support on each of the two casings containing the planetary trains and blocked in rotation by at least one pin planted in the two casings.

[0012] the electric machine is connected to the sun gear of the first train, and the wheels to the planet carrier of the first train and to the crown wheel of the second train.

[0013] An adjusting washer, arranged between the hub of the crown of the second train and one of the needle thrust bearings for axially holding the flange attached to the crown of the first train - planetary of the second train assembly, makes it possible to cancel the axial clearances and to apply a possible preload to the elements of the stack having rolling bodies and which are the bearing carrying the planetary of the first train, the bearing carrying the hub of the crown of the second train, the needle thrust bearing for supporting the satellite carrier of the first train on its planetary and the two needle thrust bearings for axially holding the crown of the first train - planetary of the second train assembly.

[0014] The planet carrier of the first train, linked to one wheel, is centered on the hub of the crown of the second train, linked to the other wheel, using a smooth ring because the differential speeds are, except in very rare exceptions (slipping), equal or very little different (turns).

[0015] The planetary gear of the first gear carries a parking wheel. DETAILED DESCRIPTION OF THE INVENTION

[0016] These characteristics, aims and advantages of the present invention will appear on reading the detailed description which follows and with regard to the appended drawings given as non-limiting examples and in which:

[0017] [Fig-1] is a sectional view of the entire powertrain comprising the reducer which is the subject of this invention and a conventional radial magnetic flux electric motor.

[0018] [Fig.2]is a sectional view of the reducer describing the housings and bearings

[0019] [Fig.3]is a sectional view of the reducer describing the first planetary gear set

[0020] [Fig.4]is a sectional view of the reducer describing the second planetary gear set.

[0021] [Fig.5a] is the Ravigneaux diagram under normal operating conditions straight-line operation without slippage.

[0022] [Fig.5b] is the Ravigneaux diagram when the right wheel is in complete slippage.

[0023] [Fig.5c] is the Ravigneaux diagram when the left wheel is in complete slippage.

[0024] [Fig.5d] is the Ravigneaux diagram when the parking wheel is blocked.

[0025] the powertrain 1 shown in section in [Fig.l] comprises a reducer 2 coupled to a conventional radial flux electric machine 3.

[0026] the rotational movement and the torque are transmitted by the motor 3 to the input shaft 31 provided with the splines 31a, of the reducer 2.

[0027] the rotational movement and the torque is transmitted from the reducer 2 to the right wheel (not shown) by the sleeve 64 provided with grooves 64a.

[0028] the rotational movement and the torque is transmitted from the reducer 2 to the left wheel (not shown) by means of a relay shaft 4 provided with splines 4b at its left end, splines 4a at its right end and held axially and guided by the bearing 5. The splines 4a of the sleeve 4 cooperate with the splines 34a of the sleeve 34.

[0029] The machine being cooled with the oil common to the reducer, the sealing of the power unit 1 is ensured on the right by the dynamic seal 26 and on the left by the dynamic seal 16.

[0030] In [Fig.2], the reducer 2 has two planetary gears 30,50 contained in a casing 10 and a cover 20.

[0031] The first train 30 located on the left is supported by the casing 10 by means of the bearing 11. The latter is axially blocked on the casing by means of a plate 12, and screws 14. The passage through the canvas of the casing 10 by the screws holding the plate 12 is sealed by the washers 13. The inner ring of the bearing is axially blocked on the sun gear of the train by the stop ring 15.

[0032] The second train 50 located on the right in [Fig.2] is supported by the cover 20 by means of the bearing 21. The latter is axially locked on the casing by a plate 22, and screws 24. The crossing of the fabric of the cover 20 by the screws 24 holding the plate 22 is sealed by the washers 23. The inner ring of the bearing is axially locked on the sleeve of the crown of the train by the stop ring 25. Finally a dynamic seal 26 ensures the local sealing of the reducer.

[0033] [Fig.3] is the description of the first planetary gear 30. It consists of a hollow planetary 31 since the transmission shaft 4 shown in [Fig.l] passes through it. It is driven by the electric machine via the splines 31a, and transmits the power to the satellites via the teeth 31b.

[0034] The satellites 32, here 3 in number, are carried by an axis 33 supported at each end by the main body 34 of the satellite carrier and at the opposite end, by the reinforcing plate 35. Each satellite is mounted on a needle bushing 36 and rests axially on the washers 37.

[0035] the sleeve part of the satellite carrier drives the transmission shaft 4 shown in [Fig.l] by the splines 34a. It is obstructed by the cover 38. A needle thrust bearing 39 is interposed between the flange 34 and the sun gear 31. The first train is completed by a crown 40.

[0036] [Fig.4] is the description of the second planetary gear 50. It consists of a sun gear 51 secured to the crown 40 of the first gear by the intermediate element 52.

[0037] A flange 51a is attached to the sun gear 51. This flange, not centered on the sleeve part of the planet carrier 34, takes up the differential of the axial forces and ensures the axial positioning of the assembly 40, 51 by resting on the needle stops 53 and 54.

[0038] The satellites 55, here 4 in number, are carried by an axis 56 supported at each end by the main body 57 of the satellite carrier and at the opposite end by the reinforcing plate 58. Each satellite is mounted on a needle bushing 59 and rests axially on the washers 60.

[0039] The main body 57, in the form of a ring, not radially centered, is stopped axially with a very small clearance by a flat support 10a on the casing 10 and a second flat support 20a on the cover 20 and is blocked in rotation by at least one pin 61 mounted in the casing 10 and the cover 20.

[0040] The second train is completed with a crown 62.

[0041] The intermediate element 63 attaches the crown 62 to the hub 64 carried by the bearing 21. Thus the crown 62 is centered and held axially.

[0042] At the end of the hub 64, there is arranged an adjustment washer 65, bearing on the needle thrust bearing 54, which makes it possible to cancel the axial clearances and to possibly apply a preload to the elements of the stack having rolling bodies and which are the bearing 11 carrying the sun gear 31 of the first train, the bearing 21 carrying the hub 64 of the crown wheel 62 of the second train, the needle thrust bearing 39 supporting the satellite carrier 34 of the first train on its sun gear 31 and the two needle thrust bearings 53, 54 for axial locking of the crown wheel 40 assembly of the first train - planetary wheel 51 of the second train.

[0043] A smooth ring 66 shrunk into the sleeve 64 provides consistent centering additional to the planet carrier 34. The differential speeds between the planet carrier 34, linked to one wheel and the sleeve 64, linked to the other wheel being, except in very rare exceptions (slipping), equal or very little different, a smooth ring is more suitable than a needle roller bushing.

[0044] The sleeve 64 has internal grooves 64a for driving a transmission shaft (not shown). It is obstructed by the cover 67.

[0045] [Fig.5a] is the representation of the reducer according to the Ravigneaux diagram. In this diagram, the speeds are on the ordinate and the numbers of teeth of the sun gear and the crown on the abscissa. The representation of the reducer is from left to right the sun gear 31, the satellite carrier PSI 34, the crown 40 grouped with the sun gear 51 of the second train, the planet carrier PS2 57 and the crown of the second train 62.

[0046] By designating the numbers of teeth and the ratios of the trains in the following manner, for the first train: • Number of planetary teeth 31: NPi • Number of crown teeth 40: NCi • The train ratio: Nci / Npi = RI And for the second train: • Number of planetary teeth 51: NP2 • Number of crown teeth 62: NC2 • The train ratio: Nc2 / Np2= R2

[0047] We can express the relationship giving an exact differential function, that is to say having both an equal distribution of torques and equality of speeds in the case of perfect grip when driving in a straight line, and a double rotation speed for the wheel in total loss of grip while the other is stationary. This relationship is as follows: R2 = 1+1 / R1

[0048] This condition being respected, the reduction ratio Rd for the two wheels, in a situation of good grip and in a straight line is then: Rd = 2 x (Rl+1)

[0049] Fig.5a shows the Ravigneaux diagram in a straight line driving situation with perfect grip.

[0050] [Fig.5b] shows the Ravigneaux diagram in a situation where the left wheel has no grip and the right wheel is then stationary.

[0051] [Fig.5c] shows the Ravigneaux diagram in a situation where the right wheel has no grip and the left wheel is then stationary.

[0052] The reducer is equipped with a park wheel 70, carried by the planetary 31 of the first gear. Placed in this location, the planetary gears are not locked. But as the Ravigneaux diagram in [Fig.5d] shows, if one of the wheels rotates, the other is forced to rotate in the other direction. Due to adhesion, this is not actually possible and the vehicle is effectively immobilized.

Claims

Claims

1. Single-ratio reducer (2), of coaxial type for an electric machine, composed of a first planetary gear train (30), consisting of a sun gear (31) connected to the electric machine (3), a main body (34) of the planet carrier connected to a first transmission shaft (4), and a crown wheel (40) secured by the intermediate element (52) in the form of a ring to the sun gear (51) of a second gear train (50) further consisting of a planet carrier whose main body (57), not radially centered, is locked in rotation by at least one pin (61) mounted in the casing (10) and the cover (20), is stopped axially with a very small clearance by a flat support (10a) on the casing (10) and a second flat support (20a) on the cover (20),and a crown (62) linked to the hub (64) driving a second transmission shaft (not shown) characterized in that this series assembly of the two trains (30) and (50) thus makes it possible to ensure the dual function of reducer and differential.,

2. Single-ratio reducer (2) according to claim 1 characterized in that the two planetary gears (30) and (50) are arranged in two different axial spaces.

3. Reducer (2) for an electric machine according to claim 1 characterized in that the assembly constituted by the sun gear (51) of the second train (50), secured to the crown (40) of the first train (30) and the intermediate element (52) is attached to a flange (51a), not radially centered and held axially by two needle roller bearings (53), (54).

4. Reducer (2) for an electrical machine according to claims 1 and 3, characterized in that an adjusting washer (65), arranged between the hub (64) of the crown (62) of the second train (50) and the needle thrust bearing (54) for axially stopping the flange (51a) attached to the crown (40) and sun gear (51) assembly, makes it possible to cancel out the clearances and to apply a possible preload to the elements of the stack having rolling bodies and which are the bearing (11) carrying the sun gear (31) of the first train, the bearing (21) carrying the hub (64) of the crown (62) of the second train, the needle thrust bearing (39) for supporting the main body (34) of the planet carrier of the first train (30) on its sun gear (31) and the two needle thrust bearings (53, 54) for axially locking the flange (51a).

5. Reducer 2 for an electric machine according to claim 1 characterized in that the main body (34) of the planet carrier of the first train (30), is centered on the hub (64) of the crown (62) of the second train (50), using a smooth ring (66).

6. Reducer (2) for an electric machine according to claim 1, characterized in that by designating the numbers of teeth and the ratios of the trains thus: for the first train (30): • Number of teeth of the sun gear (31): NPi • Number of teeth of the crown (40): NCi • The ratio of the train: Nci / Npi = RI And for the second train (50): • Number of teeth of the sun gear (51): NP2 • Number of teeth of the crown (62): NC2 • The ratio of the train: Nc2 / Np2 = R2 the relationship to be respected to obtain a rigorous differential function is this: R2 = 1+1 / R1

7. Reducer (2) for an electric machine according to claim 6, characterized in that the reduction ratio Rd has the expression: Rd = 2 x (Rl+1)

8. Reducer (2) for an electric machine according to claim 1, characterized in that it is equipped with a park wheel (70), carried by the sun gear (31) of the first train (30).

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