GB2536684A

GB2536684A - Planet gear device

Info

Publication number: GB2536684A
Application number: GB1505100.6A
Authority: GB
Inventors: Dorrestijn Igor; Van Ditten Marien
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2015-03-26
Filing date: 2015-03-26
Publication date: 2016-09-28
Also published as: GB201505100D0

Abstract

A planet gear device 1 comprises a central shaft 2 which can be rotated around an axis and has, mounted on an axially stationary inner part 2, an axially moveable outer conical raceway 3 on a sleeve ring 2. Planet rollers 4 roll on the conical raceway 3 and an inner conical raceway 6 of an outer ring 5. The rollers 4 are mounted on a planet carrier (7, fig 2) which can rotate around the axis. Means 8, for axially shifting the sleeve ring 2 in axial direction relative to axially stationary part 2, comprises balls 13 which cooperate with ramp profiles 11, 12 so as to provide the axial movement. The axial stationary inner part 2 has an axial stop 21 and is supported by at least one bearing 9. A spring 18, mounted between the sleeve ring 2 and the bearing 9, urges the sleeve ring 2 in an opposite direction to that of the means 8 which is effectively arranged, via head 18 fixed to inner part 2, between the inner part 2 and the sleeve ring 2.

Description

Planet Gear Device

Technical Field

The invention relates to a planet gear device, comprising a central shaft which can be rotated around an axis, wherein the central shaft has an outer surface which forms a conical raceway, a plurality of rollers, which form planets and roll on the conical raceway, in an outer ring with an inner surface which forms a conical raceway for the rollers, a planet carrier which bears the rollers and which can rotate around the axis and means for axially shifting the conical raceway of the central shaft in axial direction, relative to an axial stationary part of the central shaft.

Background

A planet gear drive of this kind is known from JP 57 140 958 A. Here, in distinc20 tion to a classical planetary gear, rollers are employed which run on the raceways of the central shaft and the outer ring.

Similar and other solutions are known from US 3 433 099, GB 1 341 665 A, JP 59 080 557 A, US 4 537 093 and US 4 617 838.

Planet gear drives of such a kind can be used in electric vehicles.

Current electric vehicles are very susceptible to audible noise. With the trend of using faster motors, the noise especially from the first stage gears in the transmission is getting too loud and requires mitigation. It is known to use noise shields to reduce the emitted noise. Another possibility is to use a planetary gear set with extra noise measures which causes respective costs.

Another aspect is the costs which are quite high for the production of pre-known planet gear drives.

Thus, it is an object of the present invention to further develop a planet gear drive of the generic kind which allows a quiet operation. Furthermore, a design is proposed, which allows the use of components which can be manufactured and as-in a cost-efficient manner. Thus, the costs for the production and assembly of the planet gear drive should be minimized

Summary of the invention

The solution according to the invention is characterized in that the central shaft comprises an axial stationary inner part which is supported by at least one bearing, wherein the conical raceway of the central shaft is formed by a sleeve ring, which is arranged axially movable on the stationary inner part, wherein the means for axially shifting the conical raceway are effectively arranged between the inner part and the sleeve ring.

Preferably, the sleeve ring is arranged on the inner part by means of a sliding scat.

The means for axially shifting the conical raceway are preferably arranged in an axial end region of the central shaft.

Those means for axially shifting the conical raceway can comprise at least one first ramp profile which is arranged effectively in or at the inner part and at least one second ramp profile which is arranged effectively in or at the sleeve ring, wherein the first and second ramp profiles cooperate with each other and cause an axial dis-placement between the inner part and the sleeve ring when the inner part is rotated around the axis relative to the sleeve ring.

Preferably, a plurality of first and second ramp profiles is arranged around the inner part and the sleeve ring. According to a preferred embodiment of the invention between three and five, preferably four, first and second ramp profiles are arranged equidistantly around the inner part and the sleeve ring. Of course, this does not exclude other solutions, for example the use of a design with non-equidistant spaced rolling elements, or even a design with different radii and matching different ramp to angles.

Furthermore, a roller element, preferably a ball, can be arranged between the first and the second ramp profile. Also, tapered or cylindrical rollers can be taken into consideration if the occurring forces become too high. Cylindrical or tapered rollers might be preferred to keep the design compact enough or to use fewer rolling elements (fewer elements allows for shallower angles or more displacement concerning the ramps).

The roller elements are preferably held in position by means of a cage. Of course, also a solution without cage can be realized; in this case the roller elements can be held in position by the ramps (either by having the ramp provide some kind of osculation around the ball -like a Deep Groove Ball Bearing raceway -or by a ridge keeping the ball in place).

The first and second ramp profiles can consist each of two ramp sections, which form a substantially V-shaped surface in the inner part and the sleeve ring -seen in a radial direction (of course a radius can be arranged between the legs of the V-shaped structure). Here, the two ramp sections have preferably different inclinations to the circumferential direction when regarded in a radial direction.

A further embodiment of the invention proposes a shaft head element which is arranged at the axial end of the inner part, wherein the shaft head element comprises the first or second ramp profile. Suitably, a rotational coupling is established between the shaft head element and the inner part; this coupling is preferably a spline connection.

Furthermore, a spring element can be effectively arranged between the inner part and the sleeve ring, wherein the spring element is arranged to create a biasing axial force between the inner part and the sleeve ring. The spring element is preferably at least one Belleville spring washer.

The rollers are preferably taper rollers, wherein the cones of the conical raceway of the central shaft, of the rollers and the conical raceway of the outer ring intersect in one point of the axis.

The proposed planet gear device used as a reduction stage gear element consists thus of an outer ring, preferably three or more planet rollers and a motor shaft acting as the sun gear. The planets have a slight taper (about 1° to 5°, preferably 3°) so that an axial movement of the sun gear changes the preload of the system. The taper an-gles are chosen so as to reduce slip between the planets and the other parts. The axial displacement can be created preferably with a ball ramp pushing the sleeve ring (i.e. a cone ring functioning as the sun in the planetary arrangement) over the motor shaft.

Thus, the proposed planet gear device presents a friction drive which needs no gears as a classical planetary gear. The device is thus based on smooth rollers and friction instead of gear teeth.

A preferred application is the first reduction stage in an electric or hybrid vehicle driveline. Also, all types of electric motors and generators in automotive applica-tions are preferably taken in consideration with respect to the proposed concept.

The proposed friction drive generates less noise than pre-known solutions and is cheaper than a regular planetary gear set. The taper plus ball ramp feature enables the preload to change with the torque requirement, thus optimising system efficien-cy.

Thus, the benefit of the proposed concept is less noise than current helical gear or planetary gear solutions.

in The required parts are cheap in production -compared with classical planetary gears.

Brief description of the drawings

The drawings show an embodiment of the invention.

Fig. 1 shows a perspective view of a planet gear device with dismounted planet carder.

Fig. 2 shows a radial cross sectional view of the planet gear device according to Fig. 1 with dismounted planet carrier, Fig. 3 shows a radial cross sectional view of the planet gear device according to Fig. I with the planet carrier, Fig. 4 shows a perspective view of the sleeve ring of the central shaft of the planet gear device and Fig. 5 shows a view in radial direction onto means for axially shifting the sleeve ring relative to the inner part of the central shaft of the planet gear device.

Detailed description of the invention

In figures 1, 2 and 3 a planet gear device 1 is shown which generally has a central shaft 2 with a conical raceway 3 (which is the outer surface of the central shaft 2), a plurality of rollers 4 which run on the conical raceway 3 and a stationary outer ring in 5 which has a conical raceway 6 (which is the inner surface of the outer ring 5).

That is, the rollers 4 are arranged between the raceway 3 and the raceway 6. The axis of rotation of the different pars is denoted with a, the radial direction with r.

When a torque is applied to the central shaft 2 (from the right sidc in the figures 1 to 3) this rotational movement is transferred to the rollers 4 which in turn roll on the raceway 6 of the stationary outer ring 5.

Thus, according to the principle of a planetary gear, the rollers 4 rotate around the axis a around the central shaft 2 which acts as the sun gear of the planet gear device.

Accordingly, this movement can be taken by a planet carrier 7 (shown only in figure 3) which is connected with an output shaft 19 with a spline 20 for the transfer of the torque (see figure 3).

In figure 3 it can be seen that the planet carrier 7 consists of a first part 7' and a sec-ond part 7" which are connected to encompass the rollers 4 and to securely take their movement and transfer it to the output shaft 19.

According to the proposed design the central shaft 2 comprises a rotatable, but axi-ally stationary inner part 2' which is supported by at least one bearing 9 (see figures 2 and 3). Furthermore, the conical raceway 3 of the central shaft 2 is formed by a sleeve ring 2", which is arranged axially movable on the stationary inner part 2'. The above mentioned means 8 for axially shifting the conical raceway 3 are effectively arranged between the inner part 2' and the sleeve ring 2".

The sleeve ring 2" can axially slide on the inner part 2' of the central shaft 2 by means of a sliding seat 10.

The means 8 for axially shifting the conical raceway 3, i.e. the sleeve ring 2 relatively to the axially stationary inner part 2' of the central shaft 2 have a design in which becomes apparent from figures 2, 3, 4 and 5.

Accordingly, a shaft head element 16 is mounted in one of the axial ends of the inner part 2' of the central shaft 2. The shaft head element 16 is connected with the inner part 2' by means of a central screw 22 (see figure 2). A torque proof cornice-tion with the inner part 2' is established by means of a spline connection 17. The shaft head element 16 has in one of its face sides (which is facing the sleeve ring 2") some first ramp profiles 11, and more specifically four of those first ramp profiles distributed equidistantly around the circumference of the shaft head element 16.

Furthermore, four second ramp profiles 12 are machined in one of the face sides of the sleeve ring 2" (see specifically figure 4).

A ball 13 is arranged between each of the first and the second ramp profiles 11, 12 as can he seen from figures 2, 3 and 5.

As can be seen best from figure 5 each ramp profile 11 and 12 comprises two ramp sections 14 and 15 which have different angles of inclination; those angles are depicted in figure 5 with a I and a,.

Finally, a spring element 18 -which is acting in axial direction -is arranged between the bearing 9 and the sleeve ring 2" which biases the sleeve ring 2" to the left side in figures 1, 2 and 3.

Beneficially, the bearing 9 rests axially against an axial stop 21 (which is a section of the inner part 2' with an enlarged diameter) as becomes apparent from figure 2. The spring element 18 is then located between the bearing 9 and the sleeve ring 2".

The described device works as follows: When torque is applied to the motor shaft, i.e. to the inner part 2' of the central shaft 2, the ball ramp, i.e. the first and the second ramp profiles 11, 12, creates an axial force on the sun ring, i.e. to the sleeve ring 2 The sleeve ring 2 will then move to the right (in figures 1 to 3), increasing the preload in the sun -planet -outer ring system. This ensures that the preload is matched to the torque which is required and thus losses are minimised in the system. Power is taken out from the planet carrier 7.

The angle of the conical raceway 6 of the outer ring 5, the rollers 4 (planets) and sleeve ring 2 (sun ring) all intersect at the shaft centreline, thus eliminating slip in the system.

The spring element 18 (return spring) ensures that the sleeve ring (sun ring) will return to the left (in figures 1 to 3) quickly when the torque reduces.

A cage (ball retainer) for the balls 13 (not depicted) is only required to prevent the balls 13 from falling out. As already mentioned above also a cage can be left out; the ramp can be designed in such a way that the balls 13 are kept in the required position.

Advantageously, the ramp sections 14, 15 (ball ramp) have different angles, i.e. different angles of inclination al, a,. for forward and reverse (see figure 5). This enables a higher safety factor during braking events (i.e. reverse direction). The angles al and an are chosen duly. The steep angle corresponds to a slip safety factor of 1.1 to 1.5, whereas the shallow angle represents a safety factor bigger than 1.5.

The reason behind the asymmetrical ramp sections 14, 15 is the following: For the forward driving direction, the ball ramp angle should apply the axial force In on the sleeve ring (sun) -and thus preload -where the planetary system is on the edge of slipping, plus a safety factor. The axial force from the ball ramp should not be too high as it reduces the system efficiency. Thus, this direction has a steep angle on the ball ramp.

For the reverse direction, the efficiency is not a factor. Therefore a quite shallow angle on the ball ramp can be used to apply a very high preload force on the planetary system in case of negative torque situations like ABS events. This prevents the planetary system from slipping under such conditions.

Reference Numerals: Planet gear device 2 Central shaft 2' Inner part of the central shaft (axially stationary) 2" Sleeve ring 3 Conical raceway (outer surface of the central shaft) 4 Rollers Outer ring (stationary) in 6 Conical raceway (inner surface of the outer ring) 7 Planet carrier 8 Means for axially shifting the conical raceway of the central shaft 9 Bearing Sliding scat 11 First ramp profile 12 Second ramp profile 13 Roller element (hall) 14 Ramp section Ramp section 16 Shaft head element 17 Torque proof connection (spline connection) 18 Spring element 19 Output shaft Spline 21 Axial stop 22 Screw a Axis Radial direction a1 Angle of inclination 0(2 Angle of inclination

Claims

Patent Claims: 1. Planet gear device (1), comprising a central shaft (2) which is rotatable around an axis (a), wherein the central shaft (2) has an outer surface which forms a conical raceway (3), a plurality of rollers (4), which form planets and roll on the conical race-(3), an outer ring (5) with an inner surface which forms a conical raceway (6) for the rollers (4), a planet carrier (7) which bears the rollers (4) and which can rotate around the axis (a), means (8) for axially shifting the conical raceway (3) of the central shaft (2) in axial direction (a) relatively to an axial stationary part of the cen-tral shaft (2), characterized in that the central shaft (2) comprises an axially stationary inner part (2') which is supported by at least one bearing (9), wherein the conical raceway (3) of the central shaft (2) is formed by a sleeve ring (2"), which is arranged axially movable on the stationary inner part (2'), wherein the means (8) for axially shifting the conical raceway (3) are effec-tively arranged between the inner part (2') and the sleeve ring (2").
2. Planet gear device according to claim 1, characterized in that the sleeve ring (2") is arranged on the inner part (2') by means of a sliding scat (10).
3. Planet gear device according to claim 1 or 2, characterized in that the means (8) for axially shifting the conical raceway (3) are arranged in an axial end region of the central shaft (2).
4. Planet gear device according to one of claims 1 to 3, characterized in that the means (8) for axially shifting the conical raceway (3) comprise at least one first ramp profile (11) which is arranged effectively in or at the inner part (2') and at least one second ramp profile (12) which is arranged effectively in or at the sleeve ring (2"), wherein the first and second ramp profiles (11, 12) coop-erate with another and cause an axial displacement between the inner part (2') and the sleeve ring (2") when the inner part (2') is rotated around the axis (a) relatively to the sleeve ring (2").
5. Planet gear device according to claim 4, characterized in that a plurality of first and second ramp profiles (11, 12) is arranged around the inner part (2') and the sleeve ring (2-).
6. Planet gear device according to claim 5, characterized in that between three and five, preferably four, first and second ramp profiles (11, 12) are arranged equidistantly around the inner part (2') and the sleeve ring (2").
7. Planet gear device according to one of claims 4 to 6, characterized in that a roller element (13), preferably a ball, is arranged between the first and the second ramp profiles (i I, 12).
8. Planet gear device according to claim 7, characterized in that the roller ele-ments (13) are held in position by means of a cage.
Planet gear device according to one of claims 4 to 8, characterized in that the first and second ramp profiles (11, 12) consist each of two ramp sections (14, 15), which form a substantially V-shaped surface in the inner part (2') and the sleeve ring (2") seen in a radial (r) direction.
10. Planet gear device according to claim 9, characterized in that the two ramp sections 04, -15) have different inclinations (a1, co) to the circumferential direction when regarded in a radial (r) direction.
11. Planet gear device according to one of claims 4 to 10, characterized in that a shaft head element (16) is arranged at the axial end of the inner part (2'), wherein the shaft head element ( I 6) comprises the first or second ramp profile (11, 12).
12. Planet gear device according to claim 11, characterized in that a rotational coupling (17) is established between the shaft head element 06) and the inner part (2'), especially a spline connection.
13. Planet gear device according to one of claims 1 to 12, characterized in that a spring element (18) is effectively arranged between the inner part (2') and the sleeve ring (2), wherein the spring clement 08) is arranged to create a biasing axial force between the inner part (2') and the sleeve ring (2").
14. Planet gear device according to claim 13, characterized in that the spring element (18) is at least one Belleville spring washer.
15. Planet gear device according to one of claims 1 to 14, characterized in that the rollers (4) are taper rollers, wherein the cones of the conical raceway (3) of the central shaft (2), of the rollers (4) and the conical raceway (6) of the outer ring (5) intersect in one point of the axis (a).