Abstract:
The present invention details a sleeve and bushing of an electromechanical automatic planetary transmission. The sleeve and bushing operate to confine the desired flow of transmission lubricant through the components of the planetary gear arrangement. Additionally, the sleeve and bushing assist in maintaining a sufficient pressure level in the cavity of the planetary carrier to enable the lubricant to reach the bearings of the pinion gear. Moreover, the radius or size of the bushing/sleeve arrangement can be adjusted to occupy the radial clearance or cavity between the sun gear and main shaft for an automatic transmission with axially separable splined sun gear and sun gear shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application 60/555,141 filed Mar. 22, 2004. 
    
    
     TECHNICAL FIELD 
     This invention relates to a hybrid electromechanical automatic planetary transmission having a main shaft, sun gear and bushing-sleeve arrangement located between the main shaft and sun gear. 
     BACKGROUND OF THE INVENTION 
     The planetary gear arrangement of an automatic transmission allows the transmission to reduce or enhance the input speed received from the power source. The planetary gear arrangement&#39;s components include a ring gear, planetary carrier with at least one pinion gear, and a sun gear. The gears of the planetary gear arrangement encircle the main shaft of the transmission and through engagement with a series of clutches influence the output speed of the main shaft. 
     Given their essential functionality, planetary gear arrangements are often analyzed for improvements to their manufacturing processes and overall costs. The sun gear, for example, can be separated from its shaft to simplify the manufacturing process for each respective member. Such an alteration can create new demands on neighboring components within the planetary gear arrangement. 
     Optimizing the fuel economy and ensuring proper cooling of all the internal components in the hybrid transmission can also be critical. Planetary components can also assist in directing the flow of a lubricant to transmission components thereby reducing fatigue and increasing the transmission&#39;s lifecycle. 
     An electromechanical transmission is described U.S. Provisional Application Ser. No. 60/531,528, entitled “Two-Mode Compound-Split, Hybrid Electro-Mechanical Transmission Having Four Fixed Ratios,” Schmidt et al., filed Dec. 19, 2003, assigned to General Motors Corporation and hereby incorporated by reference in its entirety. 
     SUMMARY OF THE INVENTION 
     The present invention provides a compact electromechanical transmission with a sleeve and sun gear bushing arrangement which encircles the main shaft of the transmission in a cavity formed between the sun gear and main shaft. Several advantages result from providing the bushing-sleeve arrangement disclosed herein including, (1) enabling a more efficient and cost effective internal spline cutting processes for the sun gear and (2) enabling the desired pressure level inside the planetary carrier compartment by sealing lube oil along the main shaft in order to support lubricant flow. In addition, the invention maintains the desired package space, ease of assembly, and part commonality. 
     In one aspect of the present invention, the bushing and sleeve provide some radial support to the sun gear, which encircles the bushing-sleeve arrangement and the main shaft. 
     In another aspect of the invention, the sun gear contains two axially separable members that are in a drivable relationship (the sun gear member and sun gear shaft member). The size of the bushing-sleeve arrangement is alterable to accommodate the increased radial space required by the axially separable sun gear members and their connecting splines. In this embodiment the bushing-sleeve arrangement also serves to reduce the size of a step located on the main shaft between two areas of the main shaft that are of different radial dimensions and thus reduces the stress concentrations at that point. Reduction in the size of the step on the main shaft significantly enhances the lifecycle of the main shaft. 
     In another aspect of the invention, the sleeve is press-fit into the sun gear to form a bore of predetermined size and diameter to receive the bushing which provides sealing for the cavity between the sun gear and main shaft. 
     More particularly, a radially compact journal oil seal is provided. The seal is in the lube system for the planetary gear arrangement of an automatic transmission and is designed to minimize leakage of lube oil to areas where it is not needed. The planetary gear arrangement includes a relatively rotatable main shaft and sun gear shaft wherein the sun gear member has broachable splines interconnectable with complementary splines on the sun gear member. The two sun gear members are axially separable from one another. The sun gear member has a journal bore formed larger than the root diameter of the internal spline on the sun gear member. The planetary gear arrangement also includes a sleeve press-fit into the journal bore of the sun gear member. The sleeve defines a bushing bore of a predetermined size. A bushing in the bushing bore sufficiently fills the remaining space in the cavity between the journal bore on the sun gear member and the main shaft, thereby acting as a seal for lube oil. 
     Additionally, the invention provides a method for substantially restricting the passage of oil away from a planetary gear arrangement. More specifically, the method includes: providing a main shaft and sun gear; sufficiently encircling the main shaft with the sun gear to form a cavity as a passage for lube oil; and fitting the main shaft with a sleeve and/or bushing sufficiently configured to fill the cavity and substantially prevent the passage of oil away from the planetary carrier. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary cross-sectional view of the planetary gear arrangement and electric motor taken along one side of the centerline of the front portion of an electro-mechanical transmission; 
         FIG. 2  is an exploded perspective view of a sun gear, sleeve and bushing arrangement for use between relatively rotatable shaft components of the transmission shown in  FIG. 1 ; and 
         FIG. 3  is a block diagram of a method for substantially restricting the passage of oil from a planetary gear arrangement. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, there is seen in  FIG. 1 , two of three planetary gear arrangements ( 10 ,  10 ′) in a hybrid electromechanical automatic transmission. Each planetary gear arrangement ( 10 ,  10 ′) consist of three gear sets: the ring gear ( 12 ,  12 ′), the planetary carrier ( 14 ,  14 ′) with at least one pinion gear ( 16 ,  16 ′), and the sun gear ( 18 ,  18 ′). Together, the three gear sets ( 12 ,  14  and  18  as well as  12 ′,  14 ′ and  18 ′) enable the planetary gear arrangements ( 10 ,  10 ′) to alter the output speed of the transmission. 
     Turning our attention to the first planetary gear arrangement  10 , provided is a bushing  20  and steel sleeve  22  as shown exploded in  FIG. 2 . The bushing  20  and steel sleeve  22  are encircled by the sun gear  18  and encircle the main shaft  24  as shown in  FIG. 1 . The bushing-sleeve arrangement ( 20 ,  22 ) provides several technical advantages to the transmission. One technical benefit of the bushing-sleeve arrangement ( 20 ,  22 ) is that it enables the sun gear  18  and sun gear shaft  26  to be axially separable without substantial alteration to the remaining components of the planetary gear arrangement  10 . There are several benefits that accompany separating the sun gear  18  from the sun gear shaft  26  including simplified manufacturing processes and reduced costs. For examples, see Non-Provisional Application entitled, “Splined Sun Gear and Method for Compact Electro-Mechanical Transmission,” Ser. No. 11/013,647, G. Kempf, assigned to General Motors Corporation, and hereby incorporated by reference in its entirety. However, since the sun gear  18  and sun gear shaft  26  must be in a drivable relationship during operation of the transmission, they require a reliable connecting mechanism. 
     In the preferred embodiment, the sun gear  18  and sun gear shaft  24  are connected by a section of complementary splines  28  located between the sun gear  18  and sun gear shaft  26 , as depicted in  FIG. 1 . The sun gear  18  has internal splines  21 , shown in  FIG. 2 , that are connectable to the external splines (as a part of the complementary splines  28  shown in  FIG. 1 ) on the sun gear shaft  26 . These complementary splines  28  increase the radial span of the sun gear  18  and sun gear shaft  26  over the radial span of an integral sun gear and shaft to accommodate for the thickness of the splines. Therefore, the radial distance between the sun gear  18  and main shaft  24  (and thus the cavity  25  defined therebetween) is enlarged. In the preferred embodiment, the bushing-sleeve arrangement ( 20 ,  22 ) accommodates such increase by providing additional radial support to the sun gear  18 . In this arrangement, shown in  FIGS. 1 and 2 , the sun gear  18  requires both a first bore  17  in a first axial portion  19  of the sun gear  18  and internal splines  21  in a second axial portion  15  of the sun gear  18 . To enable the internal splines  21  to be broached, the first bore  17  is sufficiently larger than the root diameter of the internal splines  21  to accommodate the reciprocations of the broaching device  54  (shown in phantom) during the broaching process. 
     Another technical advantage of the present invention is that it does not require the main shaft  24  to have a larger radial span in the area of the main shaft  24  that is adjacent to the first axial portion  19  of the sun gear  18 , as shown in  FIGS. 1 and 2 . A journal portion  27  of the main shaft  24  is narrower or thinner at  30  where the main shaft  24  is adjacent to a thrust bearing  32 . The narrower journal portion  27  of the main shaft  30  provides clearance between the thrust bearing  32  and main shaft  24  during operation of the transmission. The radial variance between the journal portion  27  and the area of the main shaft  24  that is adjacent to the first axial portion  19  of the sun gear  18  creates a radius-formed step  34 . If too steep, the lifecycle of the radius-formed step  34  can be drastically reduced causing the entire transmission to fail prematurely. However, if the size of the radius-formed step  34  is minimized, the lifecycle of the main shaft  24  is preserved. Therefore, the bushing-sleeve arrangement ( 20 ,  22 ) further allows the radius-formed step  34  of the main shaft  24  to maintain the predetermined appropriate size to achieve its desired fatigue life requirements. 
     An additional technical advantage of the present invention is that it enables the transmission lubrication material or oil (not shown) to lube transmission components by sustaining the necessary pressure level throughout the planetary carrier compartment  36 .  FIG. 1  shows the pinion bearings  38  of the pinion gear  16  which are of particular concern because they experience high temperatures while providing support to the pinion gears  16 . The pinion bearings  38  are not easily accessible from the outer surface of the planetary carrier  14 ; therefore, the lubricant must stay pressurized beyond a certain threshold to reach the spindle  40  of the pinion gear  16 , which is adjacent to the pinion bearings  38 . 
     First, as shown in  FIG. 1 , the lubricant (not shown) flows from the main shaft  24  through several apertures like ( 42  and  44 ) to either the electric motor  44  and housing  50  through a housing aperture  52  or the sun gear shaft  26 . The bushing-sleeve arrangement ( 20 , 22 ) substantially prevents the lubricant from flowing between the sun gear  18  and main shaft  24 , thereby helping to maintain the pressure inside the planetary carrier compartment  36 . The oil that travels through the first aperture  42  primarily travels to the electric motor housing  50 , while the oil that travels through the second aperture  44  primary travels to the planetary gear arrangement  10 . The oil that travels through the second aperture  44  is restricted from going elsewhere so that the lubricant caresses the pinion gears  16  of the planetary carrier  14  and is directed towards the spindle  40  of the pinion gear  16  by a first thrust washer  46 . The lubricant then travels along the spindle  40  of the pinion gear  16  to a second thrust washer  48 , which carries the lubricant away from the planetary carrier  14 . Without the bushing-sleeve arrangement ( 20 ,  22 ), the lubricant would flow into unintended areas of the transmission and would not sufficiency reach the pinion bearings  38  of the pinion gear  16 . A similar flow pattern occurs with the second planetary gear arrangement  10 ′ and its components ( 12 ′,  16 ′,  15 ′,  18 ′,  20 ′,  22 ′,  25 ′,  26 ′,  28 ′  30 ′,  32 ′,  34 ′,  36 ′,  38 ′,  46 ′, and  48 ′). A more detailed description of the lubricant flow path is in Non-Provisional Application entitled “Lubrication System for Hybrid Electro-Mechanical Transmission Components,” Ser. No. 11/035,344, G. Kempf, assigned to General Motors Corporation, and hereby incorporated by reference in its entirety. 
     An additional technical advantage of the present invention is that it enables a more simplified assembly sequence for the transmission. The bushing-sleeve arrangement ( 20 ,  22 ) enabled the main shaft  24  journal diameter, shown in  FIG. 1 , to remain small enough so that the sun gear shaft  26 , motor assembly ( 49 , 50 ) and first planetary gear arrangement  10  could be assembled after the main shaft  24  was already in place. The bushing-sleeve arrangement ( 20 , 22 ) fills and seals the cavity  25  between the main shaft  24  and sun gear  18 . Persons of ordinary skill in the art should know; however, that the radial clearance or cavity  25  between the sun gear  18  and main shaft  24  may also be filled by alternative means such as using a larger bushing or sleeve member if available. 
     Lastly, a method for assembling a planetary gear arrangement  10  or  10 ′ with a bushing  20  and sleeve  22  is provided and outlined in  FIG. 3 . The method includes providing a sun gear and main shaft at  110  for the planetary gear arrangement of an automatic planetary transmission, then having the sun gear at  112  encircle the main shaft of the planetary gear arrangement to create a cavity  25  (shown in  FIG. 1 ) between the sun gear  18  and main shaft  24 . The cavity  25  is then filled, at step  116 , by the bushing-sleeve arrangement  20 ,  22 . 
     In one embodiment, the method includes providing a sun gear and sun gear shaft which are axially separable and connectable by complementary splines such as  21 . As previously mentioned, the sun gear involves a first bore  17  of predetermined size to accommodate broaching of the internal splines  21 , which were not needed with an integral sun gear and sun gear shaft. In this instance, the sun gear  18  is broached to form the internal splines  21  and the sun gear  18  thus needs the first bore  17  larger than the root diameter of the sun gear splines  21  to clear for movement of the broaching tool. The sleeve  22  is then press-fit into the first axial portion  19  of the sun gear  18  to form a second bore for receiving the bushing  20 . The inner diameter of the sleeve forms the second bore  23 . The bushing  20  is then inserted into the second bore  23  to sufficiently fill the remainder of the cavity  25  (shown in  FIG. 1 ) to sufficiently prevent the passage of oil from the cavity  25  so that the oil is available for the planetary carrier  14 . 
     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.