Electrically variable transmission

This invention relates to transmissions that include at least one electric motor, a housing, and a member that at least partially circumscribes the motor and cooperates with the housing to form an annular flowpath.

Electrically variable transmissions, such as those described in U.S. Pat. No. 5,931,757, employ two electric motors mounted inside a transmission housing. The electric motors are coaxially oriented with an input shaft, an output shaft, and two planetary gearsets. Each motor is operatively connected to a member of one of the planetary gearsets to provide a range or mode of transmission operation characterized by a continuously variable speed ratio between the input shaft and the output shaft.

The electric motors in electrically variable transmissions must have very precise location, low sensitivity of location to thermal events, and very uniform coolant flow. Thus, manufacturing tolerances for components, such as the housing, that interface with the motors are typically small and, accordingly, limit the manufacturing processes that may be employed.

An electrically variable transmission is provided. The transmission includes a transmission housing defining a generally cylindrical cavity. The transmission also includes an electric motor located within the cavity. The electric motor includes a generally ring-shaped stator and a rotor. The transmission also includes a member having a generally cylindrical portion that circumscribes at least a portion of the stator. The member and the housing define an annular coolant flowpath therebetween, and the member includes a plurality of holes formed therein so that coolant in the annular flowpath flows radially inward toward the stator windings to provide a concentric radial spray feature. Concentric radial spray of coolant provides superior cooling of the stator windings compared to other methods available in the prior art, and therefore enables the motor to be smaller compared to the prior art.

In a preferred embodiment, the stator is mounted to the member rather than the housing, thus enabling larger manufacturing tolerances for the housing. The member thus enables the housing to be formed using manufacturing processes, such as die casting, suitable for high-volume production.

In a preferred embodiment, the transmission includes two motors mounted to the member to form a preassembled module for simplified assembly. The module enables insertion of the motors into the housing from one direction, and allows both of the stators, speed sensors, and wiring to be subassembled and tested prior to insertion into the housing. The module also provides ease of replacement during transmission servicing. The preassembled module enables a reduced transmission diameter compared to the prior art because the module, including both motors, may be fastened to the housing at the forward end and not at the rearward end, thus eliminating the rearward split-line.

The member is preferably steel to prevent thermal clearance changes, to allow standard clearance bearings, and to provide electromagnetic shielding for speed sensors, i.e., speed resolvers, that monitor rotor speed and the wires of speed sensors.

The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

FIG. 1 is a schematic cross-sectional side view of a portion of an electrically variable transmission;

FIG. 2 is a schematic perspective view of the transmission portion of FIG. 1 ;

FIG. 3 is a schematic cross-sectional side view of an alternative transmission configuration according to the claimed invention;

FIG. 4 is a schematic cross-sectional side view of a portion of another alternative transmission configuration, including a transmission housing and a motor module operatively connected thereto; and

FIG. 5 is a schematic cross-sectional side view of a portion of the transmission of FIG. 4 .

Referring to FIG. 1 , a portion of an electrically variable transmission 10 is schematically depicted. Exemplary electrically variable transmissions are described in U.S. Pat. No. 5,558,595, issued Sep. 24, 1996 to Schmidt et al; U.S. Pat. No. 5,931,757, issued Aug. 3, 1999 to Schmidt; U.S. Pat. No. 6,478,705, issued Nov. 12, 2002 to Holmes et al; and U.S. Pat. No. 6,527,658, issued Mar. 4, 2003 to Holmes et al, each of which is hereby incorporated by reference in its entirety. The transmission 10 includes a housing 14 that defines the exterior surface 18 of the transmission. The housing 14 includes an inner surface 22 that defines a generally cylindrical cavity 26 .

The transmission 10 also includes a first electric motor/generator 30 A and a second electric motor/generator 30 B. Each electric motor generator 30 A, 30 B includes a generally ring-shaped stator 34 A, 34 B fixed with respect to the housing 14 , and a rotor 38 A, 38 B. The motors 30 A, 30 B are coaxially aligned with an input shaft (not shown) and a plurality of planetary gearsets 42 A, 42 B. The motors 30 A, 30 B are operatively connected to the gearsets 42 A, 42 B in a manner similar to that described in the aforereferenced patents.

The transmission housing 14 includes a wall 46 extending radially-inwardly toward the transmission centerline 50 from the inner surface 22 . The wall 46 separates the stator 34 A of the first motor 30 A from the stator 34 B of the second motor 30 B, and includes a formation 54 for receiving threaded fasteners 58 . A member 62 A is affixed to the wall 46 at the formation 54 by threaded fastener 58 . The member 62 A includes a generally cylindrical portion 66 A that circumscribes at least part of stator 34 A, and cooperates with the housing 14 to form an annular coolant flowpath 70 A therebetween. The annular coolant flowpath 70 A is in fluid communication with a source of pressurized fluid coolant. The member 62 A defines a plurality of holes 74 sufficiently positioned to direct coolant from the annular coolant flowpath 70 A radially inward toward the stator 34 A. O-rings or other seals 78 are employed between the member 62 A and the housing 14 to seal the annular flowpath 70 A.

A similar member 62 B is mounted to the wall 46 at the formation 54 by a threaded fastener 58 to circumscribe at least a portion of stator 34 B with a generally cylindrical portion 66 B. Member 62 B also cooperates with the housing 14 to form an annular flowpath 70 B, and includes holes 74 formed therein to direct coolant from the flowpath 70 B radially inward toward the stator 34 B. Support members 82 are affixed to the wall 46 by fasteners 58 to rotatably support rotors 38 A, 38 B at bearings 86 . The stators 34 A, 34 B are preferably staked to the members 62 A, 62 B. The members 62 A, 62 B are preferably sized to maintain a light press on the stators.

FIG. 2 , wherein like reference numbers refer to like components from FIG. 1 , is a schematic perspective illustration of a portion of housing 14 and member 62 A. Only a portion of the rotor 38 A of motor 30 A is depicted in FIG. 2 .

Referring to FIG. 3 , wherein like reference numbers refer to like components from FIGS. 1 and 2 , an alternative transmission 10 ′ and member configuration is schematically depicted. Members 62 A′, 62 B′ are each attached to opposite sides of housing wall 46 ′, such as by threaded fastener, rivet, physical part interference caused by the stators 34 A′, 34 B′, etc.

Members 62 A′, 62 B′ each include respective outer walls 90 A, 90 B that cooperate with the housing 14 ′ to form annular flowpaths 70 A′, 70 B′. The members 62 A′, 62 B′ also include respective inner walls 94 A, 94 B. Inner wall 94 A is positioned with respect to the outer wall 90 A such that an open space 98 A is formed therebetween that contains a portion of stator 34 A′. Similarly, inner wall 94 B is positioned with respect to outer wall 90 B such that an open space 98 B is formed therebetween that contains a portion of stator 34 B′. Inner walls 94 A, 94 B each have a bearing 86 mounted thereto to rotatably support rotors 38 A′, 38 B′. Inner walls 94 A, 94 B also support speed resolvers 102 for monitoring the speed of the rotors.

Referring to FIG. 4 , wherein like reference numbers refer to like components from FIGS. 1-3 , another alternative transmission 10 ″ configuration is schematically depicted. The transmission 10 ″ includes a preassembled module 106 that includes member 110 and two motors 30 A″, 30 B″, of which only the respective stators 34 A″, 34 B″ are depicted in FIG. 3 . The member 110 includes an outer wall 114 , the outer surface 118 of which cooperates with the housing 14 ″ to define annular flowpaths 70 A″, 70 B″. Inner surface 122 of outer wall 114 defines a generally cylindrical space 126 in which the stators 34 A″, 34 B″ of motors 30 A″, 30 B″ are located. Member 110 also includes wall 130 that extends radially inward from inner surface 122 . Inner wall 134 extends axially from wall 130 , and is spaced a distance from outer wall 114 . A portion of stator 34 A″ is between the outer wall 114 and inner wall 134 . A portion of stator 34 B″ is between the outer wall 114 and inner wall 134 . Bearings 86 are attached to inner wall 134 to rotatably support the rotors of motors 30 A″, 30 B″. Speed resolvers 102 are also affixed to the inner wall 134 . Hole 138 is formed in wall 130 through which wiring 142 for speed resolvers extend. Member 110 is preferably steel to prevent thermal clearance changes, to allow standard clearance bearings, and to provide electromagnetic shielding for the resolvers and wires.

Referring to FIG. 5 , wherein like reference numbers refer to like components from FIGS. 1-4 , the member 110 of module 106 preferably includes a flange 146 . The member 110 is mountable to the housing 14 ″ at the flange 146 using the same bolt 58 that is used to connect the transmission front transmission support assembly 150 .

Commonly-assigned U.S. Patent Application Ser. Nos. 60/555,141, filed Mar. 22, 2004, and 60/555,270, filed Mar. 22, 2004, are hereby incorporated by reference in their entireties.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.