Abstract:
A system for venting a sealed, enclosed volume in the powertrain of an automotive vehicle includes a first housing, a second housing mechanically connected to the first housing, the first and second housings enclosing a volume, a seal located at an interface between the first and second housings for sealing said volume against passage of fluid; and a hollow vent tube having a length and including a first end communicating with the volume, and a second end spaced along the length from the first end, the second end permitting pneumatic fluid to enter and leave the vent tube.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the invention 
         [0002]    This invention relates generally to an apparatus for venting air from a sealed housing containing components of a hybrid electric vehicle powertrain. 
         [0003]    2. Description of the Prior Art 
         [0004]    In a motor vehicle powertrain, various housings are interconnected at bolted connections, such as where a transmission housing, which contains hydraulic controls and actuation components, gearing, shafts, servos, clutches and brakes, is mechanically connected to an engine block. Transmission housings, for example, may be vented to the atmosphere to prevent differential air pressure across the seals located the housing interface connections. Such venting of the transmission housing is typically located in the main part of the transmission case on the opposite side of the pump body from the location of the bell housing, which contains a torque converter. 
         [0005]    Hybrid electric vehicle powertrains include motor/generator assemblies, which can be located in the bell housing. These assemblies include the rotor and stator of the electric machine that drives the vehicle wheels in combination with an internal combustion engine (ICE). Cooling and lubricating the stator, rotor, bearings, and related components in a vehicle powertrain that includes an ICE, an integrated starter generator (ISG), and transmission, especially one that requires the powertrain to be partially or fully submersible, requires good sealing and preferably both an independent lubrication system and an elevated air vent to accommodate thermal expansion and contraction of hydraulic lubricant and air within the housing. 
         [0006]    When the temperature of air in an enclosed, sealed container rises relative to the ambient temperature of the external environment, its expansion creates a differential pressure, which can cause failure of the seals located at metal-to-metal interfaces between adjoined portions of the container. Depending on the temperature and pressure differentials and the pressure resistance capacity of the seals, air pressure alone can cause the seals to become dislodged or have local breaks in their continuity, thereby permitting fluids located in the housing to flow past the sealed interfaces. When increasing temperature of hydraulic lubricant in the sealed container occurs concurrently with its effect on air in the container, their combined expansion increases the risk of seal failure. 
         [0007]    There is a need, therefore, for a fluid tight, hermetically sealed, vented assembly of housings in a hybrid electric vehicle powertrain that will perform satisfactorily when submerged in a hydraulic fluid, such as automatic transmission fluid (ATF), water or another fluid. 
       SUMMARY OF THE INVENTION 
       [0008]    A system for venting a sealed, enclosed volume in the powertrain of an automotive vehicle includes a first housing, a second housing mechanically connected to the first housing, the first and second housings enclosing a volume, a seal located at an interface between the first and second housings for sealing said volume against passage of fluid; and a hollow vent tube having a length and including a first end communicating with the volume, and a second end spaced along the length from the first end, the second end permitting pneumatic fluid to enter and leave the vent tube. 
         [0009]    The system permits a vehicle powertrain to be submersed in hydraulic fluid to a depth that will not compromise safety and operation of the powertrain. The system permits the submersion function to be realized in low volume applications using add-on components in a powertrain that is in production instead of requiring a redesign of existing transmissions, transfer cases, differential mechanisms, etc. 
         [0010]    A hermetically sealed and vented housing or multiple housings around a motor/generator and the interfacing powertrain components is used with lubrication. To avoid damage to the seals at the interface between housing components caused by pressure in the sealed volume within the housing, a hollow vent tube having one end open to the atmosphere and the opposite end communicating with the interior volume of the housing may be used. 
         [0011]    A sealed air bladder may be used if venting to the atmosphere is not desired. An accumulator in the form of a flexible bladder can be located below the submersion depth specification of the motor vehicle, provided the bladder is sealed. 
         [0012]    The bladder can have a small volume, whose size is matched in respect of its elastic expansion and contraction to the anticipated pressure changes in the sealed volume bounded by the housing. 
         [0013]    Preferably the seal used at the housing interface is tolerant of high temperatures and corrosive liquids, such as salt water. The seal should accommodate hydraulic and electric connections that cross the boundaries of the housing to the external environment. 
         [0014]    The venting system may be utilized with units anywhere in the powertrain, such as around motor/generators, between an engine and transmission, in a transfer case, or in a driveline or axle unit. 
         [0015]    The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0016]    These and other advantages will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
           [0017]      FIG. 1  is a cross section illustrating a first embodiment of a drive system apparatus; 
           [0018]      FIG. 2  is schematic diagram showing a vent tube connecting a sealed volume in  FIG. 1  to atmosphere; 
           [0019]      FIG. 3  is a schematic diagram showing a vent tube connecting the sealed volume to an accumulator; and 
           [0020]      FIG. 4  is a top view of a motor vehicle driveline that includes a transmission, transfer case, and rear differential or axle housing; and 
           [0021]      FIG. 5  is side view of a jiggle cap. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    Referring first to  FIG. 1 , a first power source, such as an internal combustion engine, includes an engine crankshaft  10 , which is connected by bolts  12  and a flex plate  14  to a torsion damper  16 , whose output  18  is driveably connected through a spline  20  to a shaft  22 . 
         [0023]    A second power source, an electric machine  24 , includes a stator  26  secured to a housing  28 , which is secured by a series of bolts  30  to the engine rear face of an engine block, and by a series of bolts  32  to a transmission housing  34 . Fitted in aligned recesses at the interface between housing  28  and the engine block is a fluid-tight, hermetic seal  31 , located on the parting plane between adjacent housings and which is compressed by torque applied to bolts  30 . Also fitted in aligned recesses at the interface between housing  28  and transmission housing  34  is a fluid-tight, hermetic seal  33  located on the parting plane between adjacent housings and which is compressed by torque applied to bolts  32 . Housing  28 ,  34  and the engine block provide an assembly of sealed and mechanically interconnected housings, which contain an electric machine  24 , a torque converter  48  and other components of the powertrain. 
         [0024]    The electric machine  24  includes a rotor  36 , which is supported on a disc member  38  such that the radial outer surface of the rotor stator is spaced a short distance  39  from the radial inner surface of a stator  26 , which is secured to and supported on housing  28 . The rotor and other rotating components of the drive system rotate about an axis  41 . The disc member  38  includes a hub  40 , which is supported on and secured to shaft  22 . The housing  28  of the electric machine  24  includes a stationary disc member  42 , which is secured at its radial outer end by bolt  30  to the engine and is formed at its radial inner end with a pilot surface  43 . The hub  40  of disc member  38  is also formed with a pilot surface  44 . A first bearing  46 , located at the axial forward side of torque converter  48 , engages the pilot surfaces  43 ,  44  and supports shaft  22  and rotor  36  as they rotate about axis  41  on the transmission housing  34 . 
         [0025]    A torque converter  48  includes a bladed impeller wheel  50 , a bladed turbine wheel  52 , and a bladed stator wheel  54 , which is supported on a one-way clutch  56 . The torque converter  48  includes a casing  58 , which encloses the impeller  50 , turbine  52 , and stator  54  and extends axially toward the disc member  38 . A bolt  59  can be used to connect mutually the casing  58  and member  38 , or they can be mutually secured at  60 . The radial inner end of cover  58  is secured at  62  to shaft  22 . 
         [0026]    A bypass clutch  64  and torsion damper  66  are located within the torque converter case  58 . The bypass clutch  64 , which includes an input secured to the case  58  and an output secured to the turbine wheel  52  and damper  66 , alternately opens and closes a drive connection between the case  58  and turbine wheel  52 . When bypass clutch  64  is engaged, a direct mechanical connection between shaft  22  and a transmission input shaft  70  is produced, thereby bypassing the hydrokinetic connection produced by the torque converter  48  when clutch  64  is disengaged. The torsion damper  66  includes an output secured to a turbine wheel hub  68 , which is splined to input shaft  70 . 
         [0027]    A pump body  72 , secured to the transmission case  34 , is formed with a third pilot surface  73 . The hub  76  of the impeller case  58  is formed with a fourth pilot surface  75 . A second bearing  74 , located at the axial rearward side of torque converter  48 , engages pilot surfaces  73 ,  75  and supports converter case  58  on the transmission housing  34  as it rotates about axis  41 . 
         [0028]    The kinematic assembly, hydraulic actuation system and electronic controls of an automatic transmission are located at the right-hand side, i.e., rearward, of the oil pump body  72 . 
         [0029]    The electric machine  24  and torque converter  48  require fluid for cooling and lubrication. Therefore, a system  78  for supplying, recovering and recirculating hydraulic fluid for the powertrain equipment and for preventing leakage of fluids across the housing interfaces is required.  FIG. 3  illustrates a hydraulic pump  80 , a fluid supply line  82  connected to the pump outlet  84  and then leading to the electric machine  24 , and a fluid return line  86  carrying fluid collected at the base of the electric machine to a sump  88  from which fluid enters the pump inlet  90 . Fluid exiting supply line  82  can be sprayed onto the surfaces of the stator  26  and rotor  36  or the fluid can be allowed to collect in a pool at the lowest elevation of the electric machine  24 , where rotation of the rotor draws fluid from the pool and splashes it against the stator. Fluid from the stator and rotor returns to the pool and reenters the fluid return line  86  for recirculation to the sump  88  and pump  80 . Alternately, the rotor  36  and stator  26  can be enclosed in an oil jacket, which is continually supplied with fluid lubricant or coolant from the pump outlet  84  To prevent differential pressure across the hermetic seals  31 ,  33 , a snorkel tube or vent tube  92  has one end  94 , located in the sealed housings  28 ,  34 , and another end  96 , located at an elevation  98  above, or at least at the elevation specified in the submersion or fording specification of the vehicle in which the system  76  is employed. End  96  communicates with the atmosphere. The submersion or fording specification of the vehicle indicates the maximum depth above the elevation where the wheels contact the road surface, to which the vehicle can be driven without incurring harm to its electrical system or other systems, such as would stall the engine, wet the electric drive and control system, or otherwise jeopardize the function or structure of the vehicle due to entry of hydraulic fluid into the vehicle. 
         [0030]    The vent tube end  96  is covered, by not sealed by a jiggle cap  89 , which allows pneumatic fluid to enter and leave tube  92 , but prevents hydraulic fluid from entering and leaving the tube, as illustrated in  FIG. 5 . The preferred cap  89  is also know by the following and other terms “crimped vent cap”, “vent” “loose, retained vent”, “breather”, “breather cap”, “right angle vent”, “transmission vent assembly”, or other names can be, and are, used. Alternately the cap  89  can be replaced by waterproof, air-venting artificial fiber cloths and other semi-permeable materials, such as GORE-TEX®. Suitable materials of this kind prevent passage of non-pressurized liquid and fine dust, but they permit pressurized air to pass through. 
         [0031]      FIG. 3  illustrates an alternate embodiment of the system  78 , in which a sealed air bladder or another accumulator  100  may also be used, if venting of the housings  28 ,  34  to the atmosphere is not desired. In  FIG. 3 , differential pressure across the hermetic seals  31 ,  33 , is prevented by extending the vent tube  92  from its first end  94 , located in the sealed housings  28 ,  34 , to a second end  102 , which communicates with the pneumatic accumulator  100 . Preferably pressure in accumulator  100  is substantially equal to atmospheric pressure at the location of the vehicle. 
         [0032]    If the accumulator  100  is a flexible bladder, its internal pressure will change in response to ambient atmospheric pressure and temperature because its volume will expand and contract. The elastic expansion and contraction of the bladder accumulator  100  is preferably matched to the anticipated pressure change of the sealed volume within the housings  28 ,  34  due to temperature changes in the volume of pneumatic fluid and hydraulic fluid enclosed by and sealed in the housings. 
         [0033]    If the accumulator  100  is a canister with inflexible walls, a pressure regulation valve  104  may be provided to maintain its internal pressure equal to or within an acceptable range of atmospheric pressure. 
         [0034]    Accumulator  100  can be located below the submersion depth specified for the vehicle, provided the accumulator is sealed. 
         [0035]      FIG. 4  illustrates the powertrain of a motor vehicle that includes various sealed, interconnected housings to which the present invention can be applied. The powertrain includes front and rear wheels  110 ,  112 , a power transmission housing having its components located in transmission housing  34  and bell housing  28 , produces multiple forward and reverse speed ratios driven by an engine (not shown). A transfer assembly having its components located in a transfer case  116  continuously driveably connects the transmission output to a rear drive shaft  118 . The transfer assembly  116  selectively connects the transmission output to both the front drive shaft  120  and rear drive shaft  118  when a four-wheel drive mode of operation is selected. Shaft  118  transmits power to a rear wheel differential mechanism located in a housing  138 , from which power is transmitted differentially to the rear wheels  112  through axle shafts  124 ,  126 , which are contained within the differential housing  138 . The front wheels are driveably connected to right-hand and left-hand halfshafts  132 ,  134 , to which power is transmitted from the front drive shaft  120  through a front differential mechanism located in a housing  136 . 
         [0036]    The transfer assembly continually transmits rotating power to the rear driveshaft  118  and rear wheels  112 , which is the primary power path. The transfer assembly intermittently transmits rotating power to the front driveshaft  120  and the front wheels  110 , which is the secondary power path, when a clutch, located in the transfer case  116  is actuated. 
         [0037]    In addition to the sealed housing interfaces shown in  FIG. 1  between the engine block and bell housing  28  and between bell housing  28  and transmission housing  34 , other sealed housing interfaces, such as those between the transmission housing  34  and transfer case  116 , between the rear differential housing  138  and its rear cover, and between portions of the front differential mechanism housing  136 , can be vented by the technique described here. 
         [0038]    In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.