Engine torque transmission system

Abstract

The invention relates to a motor torque transmission system comprising a rotor (1) driven in rotation relative to a stator (2) housed in a casing (3), said rotor being mounted in rotation in the casing (3) by means of a rear bearing (4) and a front bearing (5) which are axially spaced between said rotor and said casing, said rotor being equipped with a torque transmission mechanism (6) which is disposed in front of the front bearing (5), each of said bearings having an inner element (4i, 5i) fixed around the rotor (1), an outer element (4e, 5e) and rolling elements disposed between said elements to allow the rotation of said inner element relative to said outer element around the axis (A) of the rotor (1), the outer element (4e) of the rear bearing (4) being axially immobilized in the casing (3), the outer element (5e) of the front bearing (5) being axially sliding mounted in said casing. Figure 1b

Description

Title of the invention: Engine torque transmission system

[0001] The invention relates to an engine torque transmission system comprising a rotor driven in rotation relative to a stator housed in a casing.

[0002] The invention relates in particular to an electrical machine of the motor and / or generator type in which the casing integrates means of electromagnetic coupling with the rotor so as to transform electrical energy into mechanical energy transmitted by said rotor and / or such mechanical energy into electrical energy.

[0003] It applies in particular to such machines for the propulsion of a motor vehicle with an electric motor, in which the rotor comprises a mechanism for transmitting a motor torque to the wheels, said mechanism also making it possible to transmit a motor torque from said wheels to generate an electric current for recharging a battery.

[0004] Conventionally, the rotor is rotatably mounted in the casing by means of a rear bearing and a front bearing which are axially spaced between said rotor and said casing, each of said bearings having an inner member fixed around the rotor, an outer member and rolling bodies arranged between the members to allow rotation of said inner member relative to said outer member around the axis of the rotor.

[0005] In addition to their function of guiding the rotation of the rotor, the bearings must hold said rotor axially and radially in the casing in order to guarantee optimal transmission of the engine torque, as well as the reliability of the cooperation between said rotor and the stator.

[0006] In particular, the bearings are subjected to significant mechanical forces during operation of the system, in particular generated by the transmission mechanism, the mass of said system and the mechanical and magnetic unbalances, these forces being all the more restrictive in a high speed, high load, high temperature and long service life application, such as in the automotive field.

[0007] More precisely, the front bearing which is arranged close to the torque transmission mechanism is highly stressed radially and axially, in proportions such that the Hertz pressure reached in said bearing can, unless its size is increased unacceptably, significantly exceed its capacity to maintain its operation over time, and without maintenance.

[0008] The invention aims to improve the prior art by proposing in particular a system for transmitting an engine torque in which the bearings ensure an optimal compromise between their functions of guiding and holding the rotor in the casing, and this in particular in a high speed, high load, high temperature application. temperature and long service life which requires reduced axial movement of the rotor while remaining within an acceptable footprint to allow integration into a compact assembly.

[0009] To this end, the invention proposes a system for transmitting an engine torque comprising a rotor driven in rotation relative to a stator housed in a casing, said rotor being mounted in rotation in the casing by means of a rear bearing and a front bearing which are axially spaced between said rotor and said casing, said rotor being equipped with a torque transmission mechanism which is arranged in front of the front bearing, each of said bearings having an inner member fixed around the rotor, an outer member and rolling bodies arranged between the members to allow rotation of said inner member relative to said outer member around the axis of the rotor, the outer member of the rear bearing being axially immobilized in the casing, the outer member of the front bearing being mounted to slide axially in said casing.

[0010] Other objects and advantages of the invention will appear in the following description, given with reference to the appended figures, in which:

[0011] [Fig. la],

[0012] [Fig.lb],

[0013] [Fig. le] and

[0014] [Fig.1d] schematically represent a transmission system according to an embodiment of the invention, respectively in perspective view from the rear ([Fig.1a]), in longitudinal section ([Fig.1b]), in enlargement of [Fig.1b] at the level of the front bearing ([Fig.1c]) and in enlargement of [Fig.1b] at the level of the rear bearing ([Fig.1d]);

[0015] [Fig.2] is a view similar to [Fig.ld] showing an alternative embodiment;

[0016] [Fig.3],

[0017] [Fig.4] and

[0018] [Fig.5] are views similar to [Fig.ld] showing respectively another mode of realization of the rear bearing according to the invention.

[0019] In relation to these figures, a system for transmitting an engine torque is described below, for example in the form of an electric machine of the motor and / or generator type which can be used for the propulsion of a motor vehicle with an electric motor.

[0020] The transmission system comprises a rotor 1 driven in rotation about an axis A relative to a stator 2 housed in a casing 3 integrating electromagnetic coupling means with said rotor so as to transform electrical energy into mechanical energy transmitted by said rotor and / or such mechanical energy into electrical energy.

[0021] The rotor 1 is rotatably mounted in the casing 3 by means of a rear bearing 4 and a front bearing 5 which are axially spaced between said rotor and said casing, in particular by each being arranged in an interface formed between a rear wall - respectively front - of the casing 3 and a rear portion - respectively front - of the rotor 1.

[0022] In the description, the terms "front" and "rear" are defined in relation to the direction of use of the system for a location respectively on the left and on the right, in particular in [Fig.lb]. The terms "outside" and "inside" are defined in relation to the axis A of rotation of the rotor 1, respectively for a location far and close to said axis.

[0023] The rotor 1 has a torque transmission mechanism 6 which is arranged in front of the front bearing 5. In relation to [Fig.1a], the torque transmission mechanism 6 comprises at least one gear which is mounted around the rotor 1 in front of the front bearing 5.

[0024] In particular, the gear may be of the helical type to mesh with a complementary gear of the driven element, the cooperation of said gears inducing variations in force on the rotor 1 during the transmission of the engine torque.

[0025] Each of the bearings 4, 5 has an inner member 4i, 5i fixed around the rotor 1, an outer member 4e, 5e and rolling bodies arranged between said members to allow the rotation of said inner member relative to said outer member around the axis A of the rotor 1.

[0026] In an electric motor, the modulation of the supply current necessary for the speed variation is ensured by the switching of transistors integrated into the power electronics. These switchings generate high-frequency harmonics which electrically charge the rotor 1 relative to the stator 2 up to a breakdown voltage.

[0027] Bearings 4, 5 being one of the shortest electrical paths between rotor 1 and stator 2, it is common for breakdown to occur within them, generating local damage which can lead to serious failures (noise, flaking, bearing failure).

[0028] To avoid these risks, the rolling bodies of at least one bearing 4, 5 are advantageously made from an electrically non-conductive ceramic material, in particular from Si3N4, a grade chosen for its good mechanical performance. However, the higher Young's modulus (300 GPa for Si3N4 compared to 210 GPa for 100Cr6 steel) generates an increase in Hertz pressure which can reach +10% and limits the capacity of the bearing 4, 5 and its service life.

[0029] The internal members 4i, 5i each have a bore, the rotor 1 having a front bearing surface 7a - respectively rear bearing surface 7b - on which a complementary bearing surface said bore is fixed in particular by hooping.

[0030] In the figures, the front bearing surfaces 7a - respectively rear 7b - extend axially and have a rear shoulder 8a - respectively front 8b - on which the internal member 5i, 4i respectively comes into axial abutment at the end of shrinking.

[0031] The internal members 4i, 5i are held in axial abutment on the shoulders 8b, 8a by a retaining means. In the embodiments shown, the retaining means comprises a ring 9 arranged in a groove 10 formed opposite the shoulder 8a, 8b, said ring being in axial interference with the internal member 4i, 5i to retain it axially on said shoulder.

[0032] The outer member 4e of the rear bearing 4 is axially immobilized in the casing 3. In particular, the casing 3 has a rear bearing surface 3a on which the outer member 4e of the rear bearing 4 is fixed, in particular by shrink fitting, said rear bearing surface being bordered by a shoulder 3b on which said outer member is held in axial abutment by a retaining means.

[0033] In relation to figures 1d, 3 and 4, the retaining means comprises a plate 11 which is axially clamped on the casing 3 opposite a rear shoulder 3b, said plate being in axial interference with the external member 4e to retain it axially in abutment on said shoulder. In particular, the clamping is carried out by a screw 12 engaged in the casing 3 and the plate 11.

[0034] [Fig.2] shows another embodiment in which the retaining means comprises a ring 13 arranged in a groove 14 formed opposite a front shoulder 3b, said ring being in axial interference with the external member 4e to retain it axially in abutment on said shoulder.

[0035] The outer member 5e of the front bearing 5 is mounted to slide axially in the casing 3. Thus, by axially releasing the front bearing 5, it is possible to optimize it to support the significant radial loads induced by the transmission mechanism 6, and this without constraint on its axial behavior insofar as the axial forces are taken up by the rear bearing 4, which can be optimized to limit the axial movement of the rotor 1.

[0036] The transmission system may comprise a means of axial elastic constraint 16 of the sliding of the outer member 5e of the front bearing 5, in particular in the direction of the rear bearing 4. The objective of this elastic constraint means being to limit the axial movement of the outer member 5e of the bearing, during torque inversions of the system (transition from traction to regeneration). These frequent inversions during use of the system at low load (typically in urban driving for an automobile application) may result in the generation of "clacking" type noise.

[0037] According to one embodiment, the limitation of the maximum axial movement of the rotor 1, consequently of the external member 5e, can make the use of the means of elastic stress 16.

[0038] In the embodiments shown, the casing 3 has a front bearing surface 3c on which the outer member 5e of the front bearing 5 is mounted to slide axially, said front bearing surface being bordered by a wall 15 extending radially at the front of said front bearing, the elastic constraint means 16 being compressed axially between said wall and said outer member.

[0039] In particular, the elastic constraint means comprises an axially corrugated washer 16 to induce an axial preload on the external member 5e.

[0040] In relation to [Fig. 1e], the members 5i, 5e of the front bearing 5 each have a rolling track 17i, 17e forming between said members a rolling path in which is arranged a row 18 of spherical rolling bodies which are mounted in radial contact in said rolling path.

[0041] In particular, the rolling bodies are spherical, since this configuration generates fewer friction or rubbing losses than a solution with conical or cylindrical rolling bodies.

[0042] Advantageously with respect to the absorption of radial forces, the oscillation rate (i.e. the ratio of the radius of the rolling path to the diameter of the spherical rolling body) of the inner member 5i is less than 0.51, the oscillation rate of the outer member 5e being less than 0.52, so as to limit the Hertz pressure in the front bearing 5.

[0043] These low oscillation rates can be envisaged to the extent that the rear bearing 4 axially maintains the rotor 1, and therefore the cohesion of the members 5i, 5e of the front bearing 5, in particular without risking an overflow of the Hertz pressure ellipse (i.e. a stress zone which leaves the path).

[0044] In particular, without axial load to be taken up, the oscillations of the front bearing 5 can be reduced to 0.508 for the inner member 5i and to 0.518 for the outer member 5e, see 0.506 / 0.516, and even 0.504 / 0.512, knowing that a change from 0.51 to 0.505 reduces the maximum pressure in the front bearing 5 by 12%, which increases the service life by more than 30%.

[0045] The rotor 1 in operation has an axial clearance which is preferably less than 200 qm, in particular less than 150 qm and ideally less than 100 qm to guarantee optimal transmission of the engine torque, as well as the reliability of the cooperation between said rotor and the stator 2. To do this, the axial clearance between the members 4i, 4e of the rear bearing 4 is less than 100 qm, preferably less than 30 qm, in particular of the order of 60 qm.

[0046] However, in a high-speed application, axial clearance between the members 4i, 4e of the rear bearing 4 is necessary to avoid heating and energy consumption due to excessive friction.

[0047] In particular, this axial clearance between the members 4i, 4e of the rear bearing 4 conditions the axial travel of the rotor 1, that is to say the distance traveled axially by the rotor 1 subjected successively to two extreme load cases (a traction case followed by a regeneration case in the case of a motor), which must be as small as possible.

[0048] This deflection, in particular induced by the use of helical teeth for the mechanism 6, misaligns the teeth of the driving and driven shafts, the rotor 1 of the stator 2 and the possible motor angle measurement system with respect to its target. Too much axial deflection can generate several failures (noise of the teeth, wear of the teeth, loss of efficiency, loss of signal from the motor angle measurement system).

[0049] In relation to figures 1 to 4, a small axial clearance can be obtained with a rear bearing 4 whose members 4i, 4e each have two rolling tracks 18i, 19i; 18e, 19e which are axially spaced so as to form between said members two rolling paths in which is arranged respectively a row 20, 21 of spherical rolling bodies, said rows of rolling bodies being in oblique contact in said rolling paths.

[0050] According to another embodiment shown in [Fig. 5], the rear bearing 4 may be of the four-point contact type, that is to say that the members 4i, 4e of the rear bearing 4 each have a rolling track 18i, 18e forming between said members a rolling path in which is arranged a row 20 of spherical rolling bodies, said row of rolling bodies being in oblique contact in the rolling path. In particular, the inner member 4i may be formed of two axially joined rings, one side of the rolling track 18i being formed on each of said rings.

[0051] In particular, the oblique contact angle, for example of the order of 35°, makes it possible to increase the filling of the raceway, by the use of additional rolling bodies, and therefore to reduce the forces on each rolling body, which makes it possible to reduce the forces on the rolling bodies, and therefore to envisage a significant limitation of their size to limit the bulk and, in particular in relation to the use of a ceramic material, the induced cost.

[0052] In particular, compared to a bearing with a single row of radial contact rolling bodies, the second row 20, 21 of rolling bodies may not significantly increase the width of the bearing 4 while making it possible to reduce the external diameter.

[0053] In Figures 1 to 4, the rows 20, 21 of rolling bodies are in oblique contact in the raceways according to an O-shaped arrangement, that is to say that the load lines which connect the contact surfaces between the rolling bodies of a row and the tracks 18i, 19i; 18e, 19e cross according to an O. As a variant, an X-shaped arrangement can be envisaged.

[0054] In the embodiments shown, the outer member 4e of the rear bearing 4 is formed from a single piece on which the two rolling tracks 18th, 19th are formed, said rolling tracks being connected by a central zone 22 formed on the piece.

[0055] In relation to figures 1 to 3, the internal member 4i of the rear bearing 4 is formed from a single piece on which the two rolling tracks 18i, 19i are formed, said rolling tracks being connected by a central zone 23 formed on the piece, one of the zones 22, 23 being able to form a collar projecting radially on the corresponding piece.

[0056] In particular, the production of a rear bearing 4 with two single-piece members 4e, 4i makes it possible to control the axial play of said bearing as best as possible, without applying axial preload which would be detrimental to friction losses.

[0057] In relation to [Fig.4], the inner member 4i of the rear bearing 4 is formed of two axially joined rings, a rolling track 18i, 19i being formed on each of said rings.

[0058] In relation to figures 1 and 2, the rolling paths have substantially the same diameter, the same number of rolling bodies being provided for each row 20, 21, in particular by maintaining said rolling bodies in their row 20, 21 by means of a retention cage.

[0059] In Figures 3 and 4, each of the rows 20, 21 of rolling bodies has a pitch diameter, a contact angle on the corresponding path, a number of rolling bodies and a diameter of rolling bodies, at least one of these geometric parameters being different between said rows.

[0060] Thus, to the extent that the rows 20, 21 of rolling bodies ensure the axial stopping of the rotor 1 depending on whether the force experienced drives said rotor respectively to the left or to the right, the geometric parameters of each of said rows can be optimized independently depending on the needs of the direction of the force experienced, in particular in order to reduce the size and cost of the ceramic rolling bodies.

[0061] In particular, the dimensioning is done in such a way as to reduce the number and size of the rolling bodies used, in order to reduce the cost of the assembly and to obtain an ideal balance of the Hertz pressures seen by each row 20, 21.

[0062] In relation to [Fig. 3], the front row 20 has geometric parameters which are optimized to take up traction forces which are greater than the regeneration forces taken up by the rear row 21.

Claims

Claims

1. A system for transmitting an engine torque comprising a rotor (1) driven in rotation relative to a stator (2) housed in a casing (3), said rotor being mounted in rotation in the casing (3) by means of a rear bearing (4) and a front bearing (5) which are axially spaced between said rotor and said casing, said rotor being equipped with a torque transmission mechanism (6) which is arranged in front of the front bearing (5), each of said bearings having an inner member (4i, 5i) fixed around the rotor (1), an outer member (4e, 5e) and rolling bodies arranged between said members to allow rotation of said inner member relative to said outer member around the axis (A) of the rotor (1), said system being characterized in that the outer member (4e) of the rear bearing (4) is axially immobilized in the casing (3), the outer member (5e) of the front bearing (5) being mounted to slide axially in said casing.

2. Transmission system according to claim 1, characterized in that the rotor (1) has a front bearing surface (7a) on which the inner member (5i) of the front bearing (5) is fixed, said front bearing surface being bordered by a rear shoulder (8a) on which said inner member is held in axial abutment by a retaining means.

3. Transmission system according to one of claims 1 or 2, characterized in that the rotor (1) has a rear bearing surface (7b) on which the inner member (4i) of the rear bearing (4) is fixed, said rear bearing surface being bordered by a front shoulder (8b) on which said inner member is held in axial abutment by a retaining means.

4. Transmission system according to any one of claims 1 to 3, characterized in that the casing (3) has a rear bearing surface (3a) on which the external member (4e) of the rear bearing (4) is fixed, said rear bearing surface being bordered by a shoulder (3b) on which said external member is held in axial abutment by a retaining means.

5. Transmission system according to any one of claims 1 to 4, characterized in that it comprises a means of axial elastic constraint (16) of the sliding of the external member (5e) of the front bearing (5).

6. Transmission system according to claim 5, characterized in that the casing (3) has a front bearing surface (3c) on which the outer member (5e) of the front bearing (5) is mounted to slide axially, said front bearing surface being bordered by a wall (15) extending radially to the front of said front bearing, the elastic constraint means (16) being axially compressed between said wall and said external member.

7. Transmission system according to any one of claims 1 to 6, characterized in that the members (4i, 4e) of the rear bearing (4) each have two rolling tracks (18i, 19i; 18e, 19e) which are axially spaced so as to form between said members two rolling paths in which is respectively arranged a row (20, 21) of spherical rolling bodies, said rows of rolling bodies being in oblique contact in the rolling paths.

8. Transmission system according to claim 7, characterized in that the outer member (4e) of the rear bearing (4) is formed from a single piece on which the two rolling tracks (18e, 19e) are formed.

9. Transmission system according to one of claims 7 or 8, characterized in that the inner member (4i) of the rear bearing (4) is formed from a single piece on which the two rolling tracks (18i, 19i) are formed.

10. Transmission system according to any one of claims 7 to 9, characterized in that each of the rows (20, 21) of rolling bodies has a pitch diameter, a contact angle on the corresponding path, a number of rolling bodies and a diameter of rolling bodies, at least one of these geometric parameters being different between said rows.

11. Transmission system according to any one of claims 1 to 6, characterized in that the members (4i, 4e) of the rear bearing (4) each have a rolling track (18i, 18e) forming between said members a rolling path in which is arranged a row (20) of spherical rolling bodies, said row of rolling bodies being in oblique contact in the rolling path.

12. Transmission system according to any one of claims 1 to 11, characterized in that the axial play between the members (4i, 4e) of the rear bearing (4) is less than 100 qm.

13. Transmission system according to any one of claims 1 to 12, characterized in that the members (5i, 5e) of the front bearing (5) each have a rolling track (17i, 17e) forming between said members a rolling path in which is arranged a row (18) of spherical rolling bodies which are mounted in radial contact in said rolling path.

14. Transmission system according to claim 13, characterized in that the oscillation rate of the inner organ (5i) is less than 0.51, the oscillation rate of the outer organ (5e) being less than 0.

52.

15. Transmission system according to any one of claims 1 to 14, characterized in that the rolling bodies of at least one bearing (4, 5) are made from an electrically non-conductive ceramic material.

16. Transmission system according to any one of claims 1 to 15, characterized in that the torque transmission mechanism (6) comprises at least one gear which is mounted around the rotor (1) in front of the front bearing (5), in particular a helical gear.

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