METHOD FOR COOLING AN ELECTRIC MOTOR IN A HYBRID TRANSMISSION AND A CORRESPONDINGLY DESIGNED HYBRID TRANSMISSION

Abstract

Hybrid transmission (10), with: a gearbox housing with a surface (76B) that defines an engine cavity (78B); a motor module (16) arranged in the motor cavity (78B) of the transmission (10), the motor module (16) comprising: a cylindrical module housing (54B) defining an outer surface (62B) and an inner surface (64B), wherein the module housing (54B) has an open end (58B) and a closed end (66B) opposite the open end (58B) and includes several coolant openings (90) formed therein; a motor assembly (46B) arranged within the module housing (54B), the motor assembly (46B) comprising: a stator (50B); a rotor (48B) surrounded by the stator (50B); wherein the outer surface (62B) of the module housing (54B) and the surface (76B) of the gearbox housing (72B) define an annular cavity (74B) between them, which is in fluid communication with the multiple coolant openings (90); and wherein the coolant in the annular cavity (74B) is distributed through the multiple coolant openings (90) onto the stator (50B) to cool the motor assembly (46B).

Description

TECHNICAL FIELD

[0001] This invention relates to a method for cooling an electric motor of a hybrid transmission and a correspondingly designed hybrid transmission. BACKGROUND OF THE INVENTION

[0002] The electric motors in an electromechanical hybrid transmission generate heat during operation. If this heat is not adequately dissipated, the motors' performance and reliability can be compromised.

[0003] For example, DE 197 39 906 A1 describes a hybrid transmission in whose housing a motor module is fitted, wherein a thread is cut into the outside of the module housing as a fluid channel, via which the motor module can be cooled by means of a fluid flowing through the thread.

[0004] Furthermore, US 5 718 302 A describes an electric motor with a housing in which there is an oil passage which has spray openings through which oil can be sprayed onto the winding ends of the stator of the motor. SUMMARY OF THE INVENTION

[0005] The present invention is directed to a method having the features of claim 9 for cooling an electric motor of a hybrid transmission, as well as to a hybrid transmission having the features of claim 1. A substantially cylindrical motor housing is provided having first and second engagement surfaces. During assembly, the first and second engagement surfaces of the motor housing engage the transmission housing, forming an annular chamber therebetween. Pressurized coolant is directed through an access opening in the transmission housing into the annular chamber and is then applied to the stator windings of the electric motor through a plurality of coolant openings in the motor housing. The pressurized coolant is preferably a transmission fluid, obviating the need for an additional reservoir for the coolant.

[0006] According to a preferred embodiment, the first and second engagement surfaces each comprise an O-ring configured to seal the annular cavity. A drain is provided in the motor housing to prevent excessive accumulation of coolant. The drain may be at a height adapted to maintain a steady-state level of accumulated coolant within the motor housing, such that the electric motor is cooled both by the initial application of pressurized coolant and by the accumulated coolant within the housing. A housing cover is preferably attached to the motor housing to enclose the electric motor and retain the accumulated coolant.

[0007] The above features and advantages and other features and advantages of the present invention will be readily apparent from the following detailed description of the best modes for carrying out the invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic fragmentary cross-sectional view of an electromechanical hybrid transmission; Fig. 2 is a schematic fragmentary cross-sectional view of a front portion of the transmission of Fig. 1; Fig. 3 is a schematic fragmentary cross-sectional view of a rear portion of the transmission of Fig. 1; Fig. Figure 4 is a schematic perspective view of a housing and attached cover for a motor module used in the transmission of Fig. 1 is used; and Fig. 5 is a schematic cross-sectional view of a front part of the transmission of Fig. 1. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Referring to the drawings, wherein like reference numerals refer to like components, Fig. 1 the upper half of a transmission 10 in cross-section. The lower half of the transmission (not shown) is arranged on the opposite side of the central axis 12. A first and second electric motor module 14 and 16, respectively, are arranged about the central axis 12 within the transmission 10. A main shaft 20 is arranged longitudinally for rotation about the central axis 12. A plurality of inner shafts, such as an inner shaft 22, are arranged concentrically about the main shaft 20 and are also rotatable about the central axis. An input shaft 24 is arranged forward of the main shaft 20 and serves to transmit power from a prime mover or motor (not shown) to the transmission 10. Engagement of one or more of a plurality of clutches included in the transmission 10 (first, second, third, and fourth clutches 26, 28, 30, and 32, respectively, being shown) connects one or more of a first, second, and third planetary gear set 34, 36, respectively.38 to transmit power at different ratios to an output member (not shown). As will be readily understood by those skilled in the art, each of the planetary gear sets includes a sun gear member, a member of a planetary carrier assembly, and a ring gear member. A fifth clutch, referred to as a lockout clutch 42, serves to decouple a torsional isolator 44 (also referred to as damper springs) from surrounding component elements and to provide a direct connection between the engine and the transmission.

[0009] As in Fig. 2 and Fig. 3, the first and second motor modules 14, 16 are enclosed assemblies. The motor modules 14, 16 each include a motor 46A, 46B, respectively. The motors 46A, 46B each include a rotor 48A, 48B, respectively, and a stator 50A, 50B, respectively. The stator 50A includes stator windings 79A and 81A, and similarly, the stator 50B includes stator windings 79B and 81B. Those skilled in the art should appreciate that the stator windings 79A, 81A, 79B, and 81B generate heat during operation and therefore must be cooled to ensure optimal performance and reliability of the motors 46A, 46B.

[0010] The motors 46A, 46B are preferably enclosed within a drum 52A, 52B consisting of a substantially cylindrical module housing 54A, 54B and a module housing cover 56A, 56B. Each module housing 54A, 54B has an open end 58A, 58B adapted to facilitate motor insertion and a closed end 60A, 60B. The module housing covers 56A, 56B are respectively attached to the open end 58A, 58B of the module housing 54A, 54B after the motors 46A, 46B have been inserted therein, respectively, as described in detail later. According to a preferred embodiment, the housing 54A, 54B is formed steel, and the cover 56A, 56B is stamped steel; However, it should be understood that the housing and cover may be made of other materials and / or manufactured according to other known manufacturing processes.

[0011] After Fig. 3, the housing 54B defines an outer surface 62B and an inner surface 64B. The outer surface 62B is substantially linear with a raised portion 66B near the open end 58B of the housing 54B. A first engagement surface 68B, adapted to engage the gear housing 72B, is located near the closed end 60B of the housing 54B, and a second engagement surface 70B, adapted to engage the gear housing 72B, is located on the raised portion 66B of the outer surface 62B. The portion of the outer surface 62B between the first and second engagement surfaces does not contact the gear housing 72B and, as described in detail below, partially defines the annular cavity 74.To manufacture the housing 54B utilizing the preferred molding process, it may be necessary to machine the engagement surfaces 68B, 70B to meet desired tolerances necessary to properly fit the module housing 54B within the transmission 10. Advantageously, this embodiment provides a precision fit between the housing 54B and the transmission 10 without the effort required to machine the entire outer surface 62B.

[0012] The transmission housing 72B has a surface 76B defining a motor cavity 78B configured to receive the module housing 54B. The cavity surface 76B preferably has a draft angle of approximately 3 degrees to facilitate installation of the module housing 54B. During installation, the first and second engagement surfaces 68B, 70B of the module housing 54B engage the cavity surface 76B such that the surface defined axially between the first and second engagement surfaces 68B, 70B and radially between the outer surface 62B of the module housing 54B and the cavity surface 76B of the transmission housing 72B forms the annular cavity 74B. A (in Fig. Coolant 100 (shown in Figure 5) is introduced into the annular cavity 74B through an access port 80B in the transmission housing 72B. The coolant 100 is preferably pressurized to facilitate its application to the motor 76B; however, the coolant 100 may alternatively be applied using its own weight. The coolant 100 is preferably a fluid from the transmission cooling system (not shown) that is used to cool other transmission components; however, it should be recognized that other fluids are contemplated for this purpose. The application of a fluid from the transmission cooling system is particularly advantageous because it does not require additional parts for storing, pressurizing, and transferring a separate fluid source.

[0013] The first and second engagement surfaces 68B, 70B of the module housing 54B each define an O-ring groove 82 with an O-ring 84 disposed therein. The O-rings 84 are adapted to seal the annular cavity 74B and prevent leakage of the coolant 100 (shown in Fig. 5). The O-rings 84 also help guide and center the module 16 in the gear housing 72B prior to fastening. The module housing 14 of the Fig. 1 and Fig. 2 has structural characteristics similar to those described above for the motor module 16.

[0014] After Fig. 2 and Fig. 4, a plurality of coolant openings 90 are arranged around the periphery of the module housing 54A in fluid communication with the annular cavity. The (in Fig. 5) in the annular cavity will spray from the coolant openings 90 at a rate determined by the amount of pressure in the annular cavity as well as the size, shape, and number of the coolant openings 90. According to a preferred embodiment, a first plurality of coolant openings 90 are arranged around the periphery of the module housing 54A in alignment with the stator windings 79A, and a second plurality of coolant openings 90 are arranged around the periphery of the module housing 54A in alignment with the stator windings 81A, such that the pressurized coolant 100 is applied directly to the stator windings 79A, 81A to cool the motor 46A. However, it should be recognized that other configurations of the coolant openings are conceivable. A similar cooling structure is shown on the motor module 16 of Fig. 3 is provided.

[0015] After Fig. 4 and Fig. 5, the coolant 100 introduced into the housing 54A through the coolant opening 90 accumulates until its level reaches a drain 102A. The steady-state level of the coolant 100 in the module housing is therefore controllable by the location of the drain 102A. It should be appreciated that in addition to cooling the stator windings 79A, 81A by the application of the coolant 100 from the openings 90, the stator windings 79A, 81A are also cooled by the accumulated coolant 100 stored in the housing 54A.

[0016] The housing cover 56A is preferably guided onto the open end 58A of the module housing 54A and screwed in place with screws 106 so that the cover 56A is removable if, for example, it becomes necessary to repair the motor 46A. However, it should be recognized that the cover 56A may alternatively be attached to the module housing 54A in a conventional manner.

[0017] The housing cover 56A preferably includes a plurality of mounting tabs 104 radially spaced around the cover, which allow the module housing 14 to be bolted to the main housing of the transmission. The mounting tabs 104 provide an easily accessible attachment and facilitate the absorption of stator torque by the transmission housing 72A. The second motor module 16 of the Fig. 1 and Fig. 3 has similar structural properties.

Claims

[1] Hybrid transmission (10), with: a transmission housing having a surface (76B) defining a motor cavity (78B); a motor module (16) disposed in the motor cavity (78B) of the transmission (10), the motor module (16) comprising: a cylindrical module housing (54B) defining an outer surface (62B) and an inner surface (64B), the module housing (54B) having an open end (58B) and a closed end (66B) opposite the open end (58B) and including a plurality of coolant openings (90) formed therein; a motor assembly (46B) disposed within the module housing (54B), the motor assembly (46B) comprising: a stator (50B); a rotor (48B) surrounded by the stator (50B); wherein the outer surface (62B) of the module housing (54B) and the surface (76B) of the transmission housing (72B) define therebetween an annular cavity (74B) in fluid communication with the plurality of coolant openings (90); and wherein the coolant in the annular cavity (74B) is distributed through the plurality of coolant openings (90) to the stator (50B) to cool the motor assembly (46B). [2] The hybrid transmission of claim 1, wherein the outer surface (62B) of the module housing (54B) has a first engagement surface and a second engagement surface. [3] The hybrid transmission of claim 1, wherein the outer surface (62B) of the module housing (54B) includes a plurality of O-rings (84) configured to seal the annular cavity (74B). [4] The hybrid transmission of claim 1, wherein the module housing (54B) includes a drain (102A) configured to drain the coolant that collects within the module housing (54B). [5] The hybrid transmission of claim 1, wherein the motor module (16) includes a housing cover (56B) attached to the open end (58B) of the module housing (54B). [6] The hybrid transmission of claim 1, wherein the transmission housing (72B) has an access opening (80B) through which the coolant is introduced into the annular cavity (74B). [7] The hybrid transmission of claim 1, wherein the coolant comprises a transmission fluid. [8] The hybrid transmission of claim 1, wherein the stator (50B) includes a plurality of stator windings (79B, 81B) in alignment with at least one of the plurality of coolant openings (90); and wherein the pressurized coolant in the annular cavity (74B) is distributed through the plurality of coolant openings (90) to the stator winding (79B, 81B) to cool the motor assembly (46B). [9] A method for cooling an electric motor (46B) in a hybrid transmission (10), the method comprising the steps of: Providing a motor module (16) which contains: a cylindrical module housing (54B) defining an outer surface (62B) and an inner surface (64B), the module housing (54B) having an open end (58) and a closed end (60B) opposite the open end (58) and containing a plurality of coolant openings (90); a motor assembly (46B) disposed within the module housing (54B), the motor assembly (46B) comprising: a stator (50B) having a plurality of stator windings (79B, 81B) in alignment with at least one of the plurality of coolant openings (90); and a rotor (48B) surrounded by the stator (50B); and a housing cover (56B) attached to the open end (58B) of the module housing (54B); Installing the motor module (16) into a motor cavity (78B) of a transmission housing (72B) such that an annular cavity (74B) is defined between the outer surface (62B) of the module housing (54B) and the transmission housing (72B); and Introducing a coolant into the annular cavity (74B) such that the coolant is distributed through the plurality of coolant openings (90) onto the stator (50B) to cool the motor assembly (46B). [10] The method of claim 9, further comprising: Sealing the annular cavity (74B). [11] The method of claim 9, further comprising: Pressurizing the coolant before it is introduced into the annular cavity (74B). [12] The method of claim 9, further comprising: Draining excess coolant that collects within the module housing (54B).

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