Abstract:
A powertrain incorporating an engine, a planetary gear assembly and front and rear final drive assemblies has a plurality of planetary gear sets and torque transmitting mechanisms enclosed within a rotatable housing which transfers power from an output differential mechanism in the planetary gear assembly to a transfer drive mechanism disposed between the transmission input and the transmission gearing. The rotatable housing surrounds a plurality of torque transmitting mechanisms including at least two stationary torque transmitting mechanisms which are secured partially or operatively with a grounding member extending longitudinally within said transmission and being connected with a stationary housing disposed in said transmission housing intermediate said torque transmitting mechanisms and said torque converter.

Description:
TECHNICAL FIELD 
     This invention relates to automatic transmissions for vehicles and, more particularly, to transmissions providing drive to both the front and rear wheels of the vehicle. 
     BACKGROUND OF THE INVENTION 
     All-wheel drives and four-wheel drives are commonly used in many passenger vehicles today. These vehicles generally include sport utility vehicles; however, some passenger type vehicles are also equipped with all-wheel drive powertrains. In the all-wheel drive powertrain, the engine and transmission are generally forward on a vehicle, and a transfer case or drop box is attached to the rear of the transmission and receives input drive from the conventional output shaft of the transmission. The transfer case generally includes a chain or gear drive from one axis to another axis to permit the front-wheel drive or a gear arrangement between the transmission output shaft which is the input to the transfer case and the second axis which contains the front-wheel drive power shaft. 
     The transfer case, as previously mentioned, is secured to the rear of the transmission and therefore extends the longitudinal length of the powertrain, such that additional space under the vehicle is required to accommodate the engine, transmission, and transfer case. This generally means the tunnel hump is extended rearwardly in the vehicle between the driver and passenger seats. The powertrain may also require additional space to accommodate the positioning of the power shaft driving the front wheels. This space may also intrude into the passenger compartment, thereby reducing the amount of room or the volume within the passenger compartment. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an improved powertrain for an all-wheel drive vehicle. 
     In one aspect of the present invention, the transmission includes an input shaft extending longitudinally of the transmission housing and a grounding shaft circumjacent the input shaft also extending longitudinally within the transmission case. 
     In another aspect of the present invention, a plurality of torque transmitting mechanisms, both rotary and stationary, are disposed rearwardly of the torque converter and forwardly of the output shaft. 
     In yet another aspect of the present invention, the stationary torque transmitting mechanisms are selectively connectable with the grounding shaft of the transmission. 
     In still another aspect of the present invention, the transmission includes a ratio gear set disposed rearwardly of the torque transmitting mechanisms and incorporating a differential gear set at the output end of the transmission. 
     In a further aspect of the present invention, the differential gear set incorporates both an output drive to the rear wheels and an output drive to the front wheels. 
     In a yet further aspect of the present invention, the output drive to the front wheels is comprised of a rotatable housing, which extends forwardly outboard of and surrounding the planetary gear set and the torque transmitting mechanism. 
     In a still further aspect of the present invention, the rotatable housing is drivingly connected with a transfer mechanism, which is disposed between the torque converter and the torque transmitting mechanisms of the transmission. 
     A powertrain, incorporating the present invention, includes an engine, a torque converter drivingly connected with the engine, a planetary gear arrangement including a plurality of planetary gear sets and torque transmitting mechanisms, an output differential mechanism drivingly connected with the planetary gear sets, and providing both front and rear wheel output drive mechanisms. 
     The output drive mechanism of the differential gear set, which is directed to the front wheels, includes a rotatable housing, which encloses or is disposed circumferentially of the torque transmitting mechanisms in the planetary gear set. This front wheel drive structure includes a transfer mechanism which transfers the drive from the axis of the transmission to an axis for the front-wheel drive power shaft. 
     The torque transmitting mechanisms, which are disposed interiorly of the rotatable housing, include a plurality of rotating torque transmitting mechanisms or clutches, and a plurality of stationary torque transmitting mechanisms or brakes. The brake mechanisms are disposed forwardly with relation to the powertrain of the rotary torque transmitting mechanisms. 
     A grounding shaft to which the brakes are operatively connectable is disposed circumjacent and coaxial with an input shaft. The input shaft transfers power from the torque converter to the rotating torque transmitting mechanisms and one member of the planetary gear set. The grounding shaft is connectable between the brakes and housings which are surrounding the torque transmitting mechanisms and connectable with various members of the planetary gear set. A portion or some of the rotary torque transmitting mechanisms are connectable with at least one of these housings. 
     The transfer mechanism is comprised of a pair of sprockets, one of which is rotatably mounted on the grounding shaft and the other is rotatably mounted in a housing outboard of the transmission. A chain drive is connected between the sprockets. The outboard sprocket member is drivingly connected with a shaft which transfers power forwardly to the front wheels of the vehicle. Alternatively, a gear drive mechanism may be utilized in place of the chain and sprocket mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are cross-sectional elevational views of a portion of a powertrain incorporating the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A powertrain  10  includes an engine  12 , a transmission  14 , a rear-wheel final drive  16  and a front-wheel final drive  18 . The engine is a conventional internal combustion engine and the final drives  16  and  18  are conventional double-gear type final drive arrangements. 
     The transmission  14  includes a torque converter assembly  20 , a planetary gear arrangement  22 , and a drive transfer mechanism  24 . The transmission  14  also includes a housing or case  26  which encloses the torque converter  20 , the planetary gear arrangement  22  and the transfer mechanism  24 . The torque converter  20  includes an impeller  28 , a turbine  30 , a stator  32  and a torque converter clutch  34 . 
     The impeller  28  has incorporated therewith an input shell  36  which is secured with a flex plate  38  that in turn is secured with a crankshaft  40  of the engine  12 . The turbine  30  has an inner hub  42  which is drivingly connected with a transmission input shaft  44  through a spline connection  46 . The torque converter clutch  34  is disposed between the turbine  30  and the input shell  36  and is adapted to provide a mechanical drive connection between the input shell  36  and the transmission input shaft  44  in a well-known manner. The stator  32  is connected with a grounding shaft  48  that is secured to a pump housing  50  and grounded to the transmission case  26  through said pump housing  50 . The input shaft  44  extends longitudinally from the torque converter  20  into the planetary gear arrangement  22 . 
     The planetary gear arrangement  22  includes three planetary gear sets  52 ,  54  and  56 . The planetary gear set  52  includes a ring gear  58 , a sun gear  60 , and a planet carrier assembly  62 . The planet carrier assembly  62  includes a plurality of pinion gears  64  rotatably mounted on a carrier  66  and disposed in meshing relation with both the sun gear  60  and the ring gear  58 . 
     The planetary gear set  54  includes a sun gear  68 , a ring gear  70  and a planet carrier assembly  72 . The planet carrier assembly  72  is also a portion of the planetary gear set  56 , as is the ring gear  70 . The planet carrier assembly  72  includes a plurality of pinion gears  74  that are rotatably mounted on the carrier  72  and disposed in meshing relation with the sun gear  68  and the ring gear  70 . 
     The planetary gear set  56  also includes a sun gear  76 . The planet carrier assembly  72  also includes a plurality of intermeshing pinion gears  78  and  80  that are rotatably mounted on a carrier portion  82  of the planet carrier assembly  72 . The pinion gear  78  meshes with the ring gear  70  and the pinion gear  80  meshes with the sun gear  76 . 
     The planetary gear arrangement  22  also includes a differential gear set  84  that includes a sun gear  86 , a planet carrier assembly  88 , and a ring gear  90 . The planet carrier assembly  88  includes a carrier member  92  that rotatably supports a plurality of intermeshing pinions  94  and  96  that are disposed in mesh with the sun gear  86  and ring gear  90 , respectively. The ring gear  90  is continuously connected with the ring gear  70  and the sun gear  86  is continuously connected with a rear drive transmission output shaft  98 . 
     The carrier assembly  88  is continuously connected with a rotatable multi-piece housing  100  that extends forwardly in the transmission surrounding the planetary gear arrangement  22  and having a hub  102  that is drivingly connected with a sprocket  104  that is rotatably mounted on the grounding shaft  48 . The sprocket  104  is drivingly connected with a sprocket  106  through a chain drive  108 . The sprocket  106  is drivingly connected with a shaft  110  that is connected to the front-wheel final drive  18 . 
     The transmission input shaft  44  is drivingly connected with the ring gear  58  through a hub  112 . The hub  112  also has formed thereon a clutch housing  114  in which a rotating torque transmitting mechanism or clutch  116  is disposed. The clutch  116  is a member of the planetary gear arrangement  22 . Other members of the planetary gear arrangement  22  include a rotating torque transmitting mechanism  118 , a rotating torque transmitting mechanism  120 , and two stationary torque transmitting mechanisms  122  and  124 . These stationary torque transmitting mechanisms are also commonly termed brakes. A one-way drive mechanism  126  is also a member of the planetary gear arrangement  22 . 
     The clutches  116 ,  118  and  120  and the brakes  122  and  124  are conventional fluid-operated, selectively-engageable type devices which are hydraulically engaged by an electro-hydraulic control mechanism, not shown. The electro-hydraulic control mechanism is a conventional control device used in many transmissions today. 
     The brakes  122  and  124  have friction plates  128  and  130 , respectively, that are splined or otherwise drivingly connected with a housing  132  that is secured to or drivingly connected with the grounding member  48 . The brakes  122  and  124  also include a plurality of friction plates  134  and  136 , respectively, that are drivingly connected with a shell  138  and a shell  140 , respectively. 
     The one-way mechanism  126  includes an outer race  142  that is drivingly connected with a hub  144  that transmits drive to the shell  140 . The one-way mechanism  126  has an inner race  146  that is secured with the grounding member  48 . 
     The clutch  116  includes the outer hub  114  connected to the input shaft  44  and an inner hub  148  that is drivingly connected to a sleeve shaft  150  with the carrier portion  82  of the planetary gear sets  54  and  56 . Thus, when the clutch  116  is engaged, the planet carrier assembly  72  is drivingly connected with the input shaft  44 . 
     The planet carrier assembly  62  includes a hub  152  which is drivingly connected with a hub  154 . The hub  152  is a member of the clutch  120 , and the hub  154  is a member of the clutch  118 . The clutch  118  is operatively connected with the shell  138  which in turn is connected with the sun gear  68 . The hub  152  is connectable with a shell  156  through clutch  120  which in turn is connected with the sun gear  76 . Thus, when the clutch  120  is engaged, the sun gear  76  rotates in unison with the carrier assembly  62  and when the clutch  118  is engaged, the sun gear  68  rotates in unison with the carrier  62 . 
     When the brake  122  is engaged, the sun gear  68  is held stationary through the shell  138 , and when the brake  124  is engaged, the planet carrier assembly  82  is held stationary through the housing  140 . The selective operation of the clutches  116 ,  118  and  120  and the brakes  122  and  124  in various combinations will provide six forward speed ratios and one reverse speed ratio. 
     To establish a reverse drive ratio, the clutch  118  and brake  124  are engaged. To establish the low forward or first forward speed ratio, the clutch  120  and the brake  124  may be engaged. If engine braking is not desired in the first forward speed, the one-way device  126  will automatically engage when the brake  124  is not engaged and the clutch  120  is engaged with no other friction devices engaged. 
     To establish the second forward speed ratio, the clutch  120  and brake  122  are engaged. To establish the third forward speed ratio, the clutch  120  and the clutch  118  are engaged. To establish the fourth forward speed ratio, the clutch  116  and the clutch  120  are engaged. To establish the fifth forward speed ratio, the clutch  118  and clutch  116  are engaged. And, to establish the sixth speed ratio, the clutch  116  and brake  122  are engaged. 
     For a more complete description of the power flow through the planetary gear sets  52 ,  54  and  56 , one may review U.S. Pat. No. 5,106,352 to Lepelletier issued Apr. 21, 1992. This patent provides a more complete description of the power flow within the planetary gear sets. 
     The ring gear  70  is the output member for the planetary gear arrangement  22 . With the present invention, the ring gear  70 , as previously mentioned, is connected continuously with the ring gear  90  of the differential gear set  84 . The sun gear member  86  of the differential gear set  84  is connected to drive the transmission output shaft  98  and the rear-wheel final drive  16  while the planet carrier assembly  88  is connected with the rotatable housing  100  to drive the sprocket  104  and therefore the final drive  18  through the transfer drive  24 . The rotatable housing  100  completely surrounds the planetary gear arrangement  22  in the process of transferring the drive power from the planet carrier assembly  88  to the sprocket  104 . 
     Since the brakes  122  and  124  require ground elements within the planetary gear arrangement  22 , it has been found advantageous to utilize a central longitudinally extending grounding shaft  48  to accomplish this function. With the central grounding shaft  48 , it is possible to transmit the front-wheel drive forces forward from the differential planetary through the rotatable housing  100 , thus making a more compact axial arrangement and radial arrangement also, since a separate transfer shaft from the rear of the transmission forward is no longer necessary. The location of the transfer mechanism  24  is forward in the vehicle and requires less intrusion into the passenger compartment to accomplish this structure. Thus, through the use of a central grounding shaft and an enclosing rotatable drive housing, the overall size of the transmission is reduced considerably, thereby reducing the need for a large intrusion into the passenger compartment.