ACTUATOR FOR A MOTOR VEHICLE TRANSMISSION

Description

[0001] The invention relates to an actuator for a transmission system of a motor vehicle.

[0002] The invention relates more particularly to an electromagnetic actuator which is intended to be housed inside a transmission casing of the transmission chain by being linked to a coupling device.

[0003] Document US 20170159726 A1 discloses an electromagnetic actuator for actuating a coupling device fitted to a differential system. The coupling device has an uncoupled state in which the differential is free to distribute torque from a motor to two axle shafts of an axle of the vehicle and a coupled state which deactivates the "differential" function so that the two axle shafts cannot rotate at different speeds. The electromagnetic actuator comprises a housing which is intended to be fixed in a transmission casing in which the differential system is also housed. Furthermore, the electromagnetic actuator comprises a housing having an annular space in which are housed an overmolded coil and a piston mounted movably between a retracted position and a deployed position.The various movements of the piston between its retracted position, its extended position and vice versa cause noise or shocks in contact with metal parts. The noises are particularly undesirable for the comfort of the vehicle's passengers and the shocks can cause vibrations of the actuator and ultimately prevent proper operation or even destroy the actuator.

[0004] Document US 2020094676 A1 discloses an actuator for a transmission system according to the preamble of claim 1.

[0005] The present invention aims to improve current solutions, in particular by proposing an actuator with a simple architecture and making it possible to reduce noise and shocks linked to the movements of the piston between its retracted position, its deployed position and vice versa.

[0006] More particularly, the invention relates to an actuator for a transmission system comprising a housing defining an annular space of axis X in which an annular piston is housed intended to transmit an actuating force to a coupling device, the piston being arranged coaxially with the axis X and being mounted axially movable along the axis X between a retracted position and a deployed position, the housing comprises a radially internal skirt, a bottom surface and a radially external skirt, an annular coil comprising a winding of conductive wire, the coil being encapsulated by a coating, the coating forms an annular radial extension defining an end-of-travel stop for the piston, the piston is mounted movable in a housing defined between the coil and the internal skirt or the external skirt of the housing, the radial extension of the coil extending inside this housing.

[0007] Thus, the actuator according to the invention will be able to absorb all or part of the noise and shocks of the piston during its movements thanks to the radial extension of the coil.

[0008] According to the invention, the coating of the annular coil is made of polymer material, for example epoxy resin, polyurethane or polyamide. In other words, the coil is overmolded.

[0009] According to a feature of the invention, the piston is located radially inside the coil. Alternatively, the piston may be located radially outside the coil.

[0010] Advantageously, the radial extension defines an end-of-stroke stop for the piston when it is in the retracted position. Alternatively, the radial extension defines an end-of-stroke stop for the piston when it is in the extended position.

[0011] According to the invention, the housing, seen in section, is U-shaped and is made of a single material, preferably a magnetic material, for example steel. A single material is understood to mean that the housing is a single piece. The use of a housing made of a single material simplifies the design and manufacture of the actuator.

[0012] Alternatively, the housing, seen in section, is U-shaped consisting of two assembled L-shaped parts, the two parts preferably being made of a magnetic material, for example steel. The two L-shaped parts are for example assembled by a crimping, roller rolling or press-fitting operation.

[0013] According to a feature of the invention, if the piston is located radially inside the spool then the piston guide surface is the radially inner skirt. If the piston is located radially outside the spool then the piston guide surface is the radially outer skirt.

[0014] The piston guide surface may be coated with a thermochemical treatment in order to surface harden the part in sliding contact with the piston and thus facilitate sliding.

[0015] Preferably, the surfaces of the case may be machined to obtain a good surface finish and may also be combined with a surface treatment, for example of the “DLC” type, which stands for “diamond-like carbon” in English, “TiN” which stands for titanium nitride, or “MOS2” which stands for molybdenum disulfide or nitride. These treatments make it possible to optimize the tribological performance of the surfaces of the case.

[0016] According to another feature of the invention, the housing is made of a material whose carbon content is less than 0.2%, for example steel. This steel is thus called low carbon steel. This feature makes it possible to reduce the mass of the actuator.

[0017] According to the invention, the radial extension of the coil comprises at least one axial slot. This axial slot allows indexing of the coil on a tool in order to facilitate the operation of winding the conductive wire.

[0018] According to an additional characteristic of the invention, the radial extension of the coil comprises at least two sections angularly spaced by at least two axial slots.

[0019] According to the invention, the annular space of the housing is closed by a magnetic cover, the magnetic cover defining an end-of-travel stop for the piston when it is in the deployed position.

[0020] The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given solely for illustrative and non-limiting purposes, with reference to the appended drawings: there [ Figure 1 ] illustrates an actuator according to the invention in front view; the [ Figure 2 ] illustrates the actuator of the figure 1 in section along the AA axis; the [ Figure 3a ] illustrates an annular coil of the actuator according to a first embodiment; the [ Figure 3b ] illustrates an annular coil of the actuator according to a second embodiment; the [ Figure 4 ] illustrates the annular coil of the actuator in rear face view; the [ Figure 5 ] illustrates an alternative embodiment of the actuator; the [ Figure 6 ] illustrates a perspective view of the actuator housing according to the variant of the figure 5 .

[0021] In relation to the figure 1 , an actuator 1 is described according to an embodiment of the invention which is capable of being housed in a transmission casing. The transmission casing can be constituted by any casing of the transmission chain of a vehicle, in particular a differential casing. The actuator 1 is here an electromagnetic actuator capable of being linked to a coupling device (not shown) of a motor vehicle transmission. It comprises a housing 2 which is intended to be fixed to a transmission casing (not shown). In this housing 2 are arranged an annular coil 5 as well as an annular piston 3 which will be described in relation to the following figures.

[0022] The actuator 1 comprises an electrical connector 10 which is intended for connecting the coil 5 to a control device which is positioned outside the casing. The electrical connector 10 is connected to the coil 5 by at least one flexible cable and makes it possible to electrically power this coil 5.

[0023] There figure 2 allows for a better visualization of the constituent elements of the actuator 1. The actuator 1 thus comprises a housing 2 defining an annular space of axis X in which the annular piston 3 intended to transmit an actuating force to a coupling device and the annular coil 5 are housed. The piston 3 is arranged coaxially with the axis X and is mounted axially movable along the axis X between a retracted position R and a deployed position D. The piston 3 is located radially inside the coil 5.

[0024] In the embodiment of this figure 2 , the housing 2 is U-shaped and is made of a single material, preferably magnetic steel. This steel has a carbon content of less than 0.2%. The housing 2 comprises a radially internal skirt 21 serving as a guide surface for the piston 3, a bottom surface 22 and a radially external skirt 23. On the bottom surface 22 on the external side of the housing 2 there are protrusions 26 distributed angularly around the axis X and allowing contact with an element of the transmission, for example a bearing. In the present embodiment, four protrusions 26 are present.

[0025] The annular coil 5 consists of a winding of conductive wire and is sealed by a coating 6 made of polymer material, for example epoxy resin, polyurethane or polyamide. The coating 6 forms an annular radial extension 7 defining an end-of-travel stop for the piston 3 when it is in the retracted position R. The radial extension 7 is located axially along the axis X on the side of the bottom surface 22 of the housing 2. In other words, the radial extension 7 is in contact with the bottom surface 22 of the housing 2.

[0026] The piston 3 is mounted movably in a housing 11 defined between the coil 5 and the internal skirt 21 of the housing 2. The radial extension 7 of the coil 5 extends inside this housing 11. The radial extension 7 extends radially in the direction of the axis X.

[0027] The annular space of the housing 2 is closed by a magnetic cover 8, the magnetic cover 8 defines an end-of-travel stop for the piston 3 when the piston 3 is in the deployed position D. The magnetic cover 8 is fixed to the housing 2 by means of tabs 9 belonging to the external skirt 23 of the housing 2. These tabs 9 are folded towards the magnetic cover 8 during assembly. The piston 3 has a shoulder intended to come into abutment against a shoulder of the magnetic cover 8 when the piston 3 is in the deployed position D.

[0028] The piston 3 is made of ferromagnetic material, such as iron or steel for example. The piston 3 further comprises a non-magnetic end piece 4, also of annular shape, which is fixed to the piston 3 and by which the actuating force is transmitted to the coupling device. Non-magnetic means a material having an absence of magnetic properties. The non-magnetic end piece 4 of the piston 3 thus makes it possible to avoid unwanted leakage of magnetic flux to the other components of the coupling device. The non-magnetic end piece 4 is for example made of bronze or aluminum.

[0029] When the actuator 1 is located in a differential housing, as in the present invention, this actuator 1 is partially immersed in a hydraulic fluid, such as oil. This oil makes it possible to lubricate the elements in contact in the differential housing but also to limit heating. In the case of the present invention, it is particularly useful to take advantage of this humid environment in order to lubricate and cool the constituent elements of the actuator 1. For this purpose, the housing 2 comprises an opening 25 located in the radially external skirt 23, this opening 25 allows the passage of the fluid from the outside to the inside of the housing 2. This opening also allows the passage of the electrical connector 10 of the coil 5. In order to conduct the fluid inside the housing 2, there is at least one means for guiding a fluid 12a, 12b, 14a, 14b, 24 provided between the housing 2 and the covering 6 of the coil 5.

[0030] There figure 3a shows a first means of guiding this fluid. Indeed, the internal surface 51 of the coating 6 of the coil 5 is provided with grooves 12a allowing the guidance of a fluid between the coating 6 of the coil 5 and the piston 3. These grooves 12a are distributed angularly and at regular intervals over the entire periphery of the internal surface 51 of the coil 5. These grooves 12a extend axially along the axis X. The surface 71 of the radial extension 7 facing the piston 3 is also provided with grooves 12b allowing the guidance of the fluid. These grooves 12b are distributed angularly and at regular intervals over the entire periphery of the radial extension 7 of the coil 5 facing the piston 3. These grooves 12b extend perpendicular to the grooves 12a. The grooves 12a and 12b thus form a continuous groove. The grooves 12b have a direction which converges towards a point located on the X axis.

[0031] The radial extension 7 of the coil 5 comprises at least one axial slot 11. This axial slot 11 separates two sections 13. According to the embodiment visible in figure 4 , there are three sections 13 separated by three axial slots 11. This axial slot 11 allows indexing of the coil 5 on a tool in order to facilitate the operation of winding the conductive wire.

[0032] The embodiment of coil 5 visible on the figure 3b is an alternative embodiment of the embodiment visible on the figure 3a . The characteristics that are identical between the two modes have the same numerical references. Unlike the figure 3a , there figure 3b shows the external surface 52 of the covering 6 of the coil 5 provided with grooves 14a. These grooves 14a are opposite the radially external skirt 23 of the housing 2 and allow the flow of fluid between the housing 2 and the coil 5. These grooves 14a are distributed angularly and at regular intervals around the entire periphery of the external surface 52 of the coil 5. These grooves 14a extend axially along the axis X.

[0033] Of course, it is also possible, while remaining within the scope of the present invention, to propose a coil 5 having only grooves on the external surface 52 of the covering of the coil 5 without having grooves on the internal surface 51 or on the radial extension 7.

[0034] The grooves 12a, 12b, 14a, 14b also have the function of participating in reinforcing the mechanical strength of the overmolding of the coil 5.

[0035] There figure 4 shows the surface 53 of the coating 6 of the coil 5 facing the bottom surface 22 of the housing 2. This surface 53 has grooves 14b allowing the fluid to be guided between the coating 6 of the coil 5 and the bottom surface 22 of the housing 2. These grooves 14b extend parallel to an axis Y orthogonal to the axis X.

[0036] There figure 5 represents an alternative embodiment of the housing 2. In this embodiment, the bottom surface 22 of the housing 2 comprises an annular groove 24 facing the surface 53 of the coating 6 of the coil 5. Only one groove 24 is shown but it is entirely possible to produce several concentric grooves 24.

[0037] There figure 6allows to visualize by a perspective view this groove 24 arranged on the bottom surface 22 of the housing 2. This groove 24 is concentric to the axis X and is radially close to the radially internal skirt 21 of the housing 2. At least one opening 27 is provided in this groove 24 in order to allow the fluid to circulate between the outside and the inside of the housing 2 and vice versa. In the present case, three openings 27 are provided in the groove 24. More generally, the opening 27 is provided on the bottom surface 22 of the housing 2.

[0038] The operation of the actuator 1 will now be described. When the coil 5 is energized with an intensity greater than a threshold intensity, this makes it possible to move the piston 3 from the retracted position R to the deployed position D. When the piston 3 is in the deployed position D, the magnetic cover 8 exerts an attraction on the piston 3, which makes it possible to maintain it in the deployed position D. The supply intensity of the coil 5 can then be reduced as long as it remains greater than said threshold intensity. When the coil 5 is de-energized or is supplied with an intensity lower than the threshold intensity, an elastic return means (not shown) returns the coupling device to the uncoupled position, which makes it possible to counter the attractive force between the magnetic cover 8 and the piston 3 and returns the piston 3 from the deployed position D to the retracted position R.

[0039] The path of the fluid inside the actuator 1 will now be described. The fluid enters inside the actuator 1 through the opening 25 and is guided by the external surface 52 of the coil 5 (via the grooves 14a when they are present) towards the bottom surface of the housing 2. Then, the grooves 14b guide the fluid along the bottom surface of the housing 2. When the groove 24 exists, this groove 24 participates in guiding the fluid between the coil 5 and the housing 2. The fluid then passes into the passage located between the radial extension 7 and the radially internal skirt 21 of the housing 2. The fluid is then in the housing 11 in which the piston 3 is located. The fluid is then guided in this housing 11 by the grooves 12a which are located on the internal surface 51 of the coil. When the fluid is in housing 11, it participates in the lubrication of the contact surfaces between the piston 3 and the radially internal skirt 21 of the housing 2.The fluid also participates in hydraulic damping when the piston 3 is at the end of its stroke, whether in the deployed position D or in the retracted position R. The fluid is then evacuated from the actuator 1 through the passage located between the magnetic cover 8 and the radially internal skirt 21 of the housing 2 or through the opening 27.

[0040] Generally, the width of the grooves 12a, 12b, 14a, 14b, 24 is between 1mm and 5mm, preferably 2mm. The depth of the grooves 12a, 12b, 14a, 14b, 24 is between 1mm and 3mm.

[0041] Generally speaking, the grooves 12a, 12b, 14a, 14b, 24 also have the function of participating in the filtration of the fluid as it travels inside the actuator 1.

[0042] Although the invention has been described in connection with several particular embodiments, it is quite obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these fall within the scope of the invention, defined by the claims.

[0043] In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

Claims

1. Actuator (1) for a transmission system comprising a housing (2) defining an annular space of axis X in which there are housed an annular piston (3) intended to transmit an actuating force to a coupling device, the piston (3) being disposed coaxially with the axis X and being mounted so as to be axially movable along the axis X between a retracted position (R) and a deployed position (D), the housing (2) comprising a radially inner skirt (21), a bottom surface (22) and a radially outer skirt (23), an annular coil (5) comprising a winding of conductive wire, the coil (5) being encapsulated by a coating (6), the coating (6) forming an annular radial extension (7) defining an end-of-travel stop for the piston (3), characterized in that the piston (3) is mounted movably in a receptacle (11) defined between the coil (5) and the inner skirt (21) or the outer skirt (23) of the housing (2), the radial extension (7) of the coil (5) extending inside this receptacle (11).

2. Actuator (1) according to Claim 1, characterized in that, seen in section, the housing (2) is in the shape of a "U" and is produced from a single material, preferably a magnetic material.

3. Actuator (1) according to Claim 1, characterized in that, seen in section, the housing (2) is in the shape of a "U" constituted by two assembled "L"-shaped parts, the two parts preferably being produced from a magnetic material.

4. Actuator (1) according to one of the preceding claims, characterized in that the housing (2) is produced from material whose carbon content is less than 0.2%.

5. Actuator (1) according to one of the preceding claims, characterized in that the radial extension (7) of the coil (5) comprises at least one axial slot (11).

6. Actuator (1) according to one of the preceding claims, characterized in that the radial extension (7) of the coil (5) comprises at least two portions (13) that are angularly spaced apart by at least two axial slots (11).

7. Actuator (1) according to one of the preceding claims, characterized in that the annular space of the housing (2) is closed by a magnetic cap (8), the magnetic cap (8) defining an end-of-travel stop for the piston (3) when it is in the deployed position (D).