Abstract:
A transaxle for transmitting power to output at multiple speed ratios includes halfshafts having a portion located in a transaxle case and a second portion extending toward a wheel. A differential mechanism located in the case transmits power between the output and differentially to the halfshafts. A clutch driveably secured to the output and connectable to one of the halfshafts for controlling the magnitude of a speed differential between a speed of the output and a speed of the halfshaft includes a cylinder and a piston moveable in the cylinder. A hydraulic system includes a passage located adjacent a halfshaft and hydraulically communicating an inlet and the cylinder, the inlet being sealed at axially opposite sides against passage of fluid by a seal rings located in a wall that surrounds the passage.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation-in-part of the co-pending U.S. patent application Ser. No. 11/255,793, filed Oct. 12, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to a transaxle for transmitting power continually to the front wheels of a motor vehicle. More particularly, the invention pertains to a transaxle that contains an inter-wheel differential and an actively controlled, on-demand clutch.  
         [0003]     In the powertrain of an all-wheel drive motor vehicle, whose engine and transaxle are transversely mounted in an engine compartment at the front of the vehicle, it is conventional for the transaxle case to contain a bevel-pinion differential mechanism, which is driven from the transmission&#39;s output and is driveably connected to the front halfshafts. The space that is enclosed by the transaxle case is relatively small. But an open, bevel gear differential mechanism requires a relatively large volume in the transaxle case. To overcome this difficulty, an additional component, a rear drive unit (RDU) such as a transfer case, is located in the driveline between the transaxle and a rear differential. The RDU contains an on-demand transfer clutch assembly, which transmits a portion of the torque to the rear axles depending on the degree to which the clutch is slipping or fully engaged.  
         [0004]     The on-demand clutch couples a rear drive shaft to the transaxle output. These coupler assemblies require a pump, hydraulic control bodies, electronic controllers and lubrication systems, which are located in the transaxle, to control and actuate the on-demand clutch in the RDU. If, however, the components that produce the function of the RDU or transfer case could be integrating with the transaxle case, the powertrain would have fewer components, lower cost and improved operating reliability.  
         [0005]     Current front-wheel drive vehicles that have no all-wheel drive capability use an open differential mechanism in the transaxle to transmit power differentially to the front wheels. When one front wheel is on a low friction surface, that wheel will tend to spin freely reducing vehicle traction on the road surface. Integrating a clutch between the differential&#39;s outputs to the right-hand side and left-hand side halfshafts provides a component that can be controlled to reduce wheel slip, thereby improving vehicle traction.  
         [0006]     The clutch could be configured so that it controls the magnitude of torque transmitted between the differential&#39;s input and one of the side outputs or both outputs.  
         [0007]     The differential mechanism could be a bevel gear differential or a compound planetary gearset. The on-demand clutch could be controlled hydraulically from the same controls used to operate the automatic transaxle.  
       SUMMARY OF THE INVENTION  
       [0008]     A transaxle for transmitting power to output at multiple speed ratios includes halfshafts having a portion located in a transaxle case and a second portion extending toward a wheel. A differential mechanism located in the case transmits power between the output and differentially to the halfshafts. A clutch driveably secured to the output and connectable to one of the halfshafts for controlling the magnitude of a speed differential between a speed of the output and a speed of the halfshaft includes a cylinder and a piston moveable in the cylinder. A hydraulic system includes a passage located adjacent a halfshaft and hydraulically communicating an inlet and the cylinder, the inlet being sealed at axially opposite sides against passage of fluid by seal rings located in a wall that surrounds the passage.  
         [0009]     The differential mechanism according to this invention may replace the open, front differential in a transaxle case with an assembly that includes an open differential and a hydraulically controlled on-demand transfer clutch. The differential transmits torque to the right and left wheels subject to the variable torque-transmitting capacity of an on-demand clutch. The differential may include a compound planetary gearset or a bevel gear mechanism.  
         [0010]     In front wheel drive and rear wheel drive applications, the on-demand clutch is preferably controlled hydraulically using the same control and actuation system that is used to operate an automatic transaxle or transmission, respectively, thereby eliminating redundant components, minimizing the required space, and reducing manufacturing and assembly cost.  
         [0011]     The transfer clutch can be controlled with dual gain using one on/off solenoid, one variable force solenoid, one pressure regulator valve, and one gain control valve. The hydraulic circuit is supplied with line pressure and a controlled solenoid feed pressure. If solenoid feed is unavailable, a regulator valve is used to produce regulated solenoid feed pressure. A simpler circuit can be used for a single gain clutch.  
         [0012]     The scope of applicability of the present invention 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, since various changes and modifications to the described embodiments and examples within the spirit and scope of the invention will become apparent to those skilled in the art. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0013]     These and other advantages of the present invention 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:  
         [0014]      FIG. 1  is a top view of a motor vehicle driveline for transmitting power between a transaxle and the vehicle wheels;  
         [0015]      FIG. 2  is a partial cross section through the transaxle case showing details of the front inter-wheel differential mechanism and a transfer clutch;  
         [0016]      FIG. 3  is schematic diagram of a hydraulic system for controlling the transfer clutch;  
         [0017]      FIG. 4-7  are cross sections through the transaxle case showing details of a bevel gear differential mechanism and a clutch for controlling the differential; and  
         [0018]      FIG. 8  is a cross section through the transaxle case showing details of a compound planetary differential mechanism and a clutch for controlling the differential. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]      FIG. 1  illustrates a motor vehicle powertrain  10  to which the present invention can be applied. The powertrain shown there is for an all-wheel drive vehicle whose engine and transaxle  12  are transversely mounted in an engine compartment at the front of the vehicle. The transaxle  12  produces multiple forward and reverse ratios of the speed of its output  14 , which is continuously driveably connected to front wheels  16 ,  17 , to the speed of its input, which is driveably connected to an engine crankshaft.  
         [0020]     An inter-wheel differential mechanism  18 , located in the transaxle case, transmits power differentially to a right-side halfshaft  20  and to a left-side halfshaft  21 , which are connected to the wheels  16 ,  17 , respectively. An on-demand transfer clutch  22 , also located in the transaxle case, transmits power selectively between the transaxle output  14  and driveshaft  24  through a bevel pinion  26  and a mating bevel gear  27  secured to the driveshaft. The degree to which clutch  22  is engaged, slipping or disengaged determines the torque capacity of the clutch and the magnitude of torque transmitted to the driveshaft  24 . Drive shaft  24  transmits power to a rear inter-wheel differential mechanism  28 , from which power is transmitted differentially to the rear wheels  30 ,  31  through axle shafts or halfshafts  32 ,  33 , respectively.  
         [0021]     Referring now to  FIG. 2 , the transaxle  12  is located in a transaxle case  40 , which is preferably a machined casting of aluminum or magnesium formed in several case sections secured mutually at hydraulically sealed, bolted connections. A torque converter case section  42  contains a torque converter, which produces a hydrokinetic connection between the crankshaft  44  of an engine, or the shaft of another power source, such as a motor shaft, and the transaxle input shaft  46 . A valve body  48 , located in a valve body case  50 , which is secured to the torque converter case  42 , contains hydraulic valves, solenoids that control the valves, a connection to the outlet of a hydraulic pump, hydraulic passages that carry fluid to the clutch and brakes from the valves, and other elements of a hydraulic system. A transaxle case segment  52 , which is secured to the valve body case section  50 , contains several planetary gear units, hydraulically actuated clutches and brakes for controlling the gear units, shafts, and mechanical components interconnecting these components. The transaxle case section  52  containing a front inter-wheel differential, the on-demand transfer clutch  22 , and the front halfshafts  20 ,  21 , is secured to the torque converter case section  42  and the gear case segment  52 . The front differential may be a bevel gear differential  18 , such as that shown in  FIG. 1 , or a planetary differential mechanism  70 , such as that shown in  FIG. 2 .  
         [0022]     Torque at the output  56  of the planetary gear units is transmitted to a wheel  58  supported on and secured to an intermediate shaft  60 . Bearings  61 ,  62  support the intermediate shaft  60  as it rotates on the torque converter casing  42  and casing  52 . A wheel  64 , driveably connected to intermediate shaft  60 , is formed at its inner radial surface with a ring gear  66 , concentric about the axis  68  of the halfshafts  20 ,  21 .  
         [0023]     The front inter-wheel differential illustrated in  FIG. 2  is a planetary differential mechanism  70 , which includes a sun gear  72 , driveably connected through a spine  74  to the left-side halfshaft  21 ; a planet pinion carrier  76 , driveably secured by a spline  78  to the right-side halfshaft  20 ; and two sets of planet pinions  80 ,  81 . The members of pinion set  80  are in continuous meshing engagement with ring gear  66  and the members of pinion set  81 , and are rotatably supported on the carrier  76 . The members of pinion set  88  are in continuous meshing engagement with sun gear  72  and the members of pinion set  80 , and are rotatably supported on the carrier  76 .  
         [0024]     Preferably the ratio of the pitch diameter of ring gear  66  to the pitch diameter of sun gear  72  is 2.0, i.e., the number of ring gear teeth to the number of sun gear teeth is 2.0. With this preferred ratio, one-half of the magnitude of torque transmitted through the differential mechanism  70  is transmitted to the right-side halfshaft  20  and one-half of that torque is transmitted to the left-side halfshaft  21 .  
         [0025]     The on-demand clutch  22  includes plates  86 , splined to the inner surface of a drum  88 , which is secured to output member  64 , and friction discs  90 , interleaved with the plates  86  and splined at  92  to a rear drive output sleeve shaft  94 . The ring  64 , sun gear  72 , both halfshafts  20 ,  21 , and rear output shaft  94  are rotatably supported on the cases  42 ,  54  by bearings  82 ,  84 . Bevel pinion  26  is secured to the rear output shaft  94 , and the bevel pinion  27  is in continuous meshing engagement with bevel gear  26 , which transmits power to the rear wheels  30 ,  31  through driveshaft  24  and the rear differential mechanism  28 .  
         [0026]     The transfer clutch  22  includes a hydraulically actuated piston  96 , which moves leftward forcing the friction discs  90  and plates  86  into mutual frictional engagement when the hydraulic cylinder  98  is pressurized. The clutch cylinder  98  is pressurized and vented through a passage  100  formed of the hydraulic system that controls operation of the transaxle. When cylinder  98  is vented, piston  96  moves rightward allowing the transfer clutch  22  to disengage. In operation, the transfer clutch  22  may slip or fully engage, but the degree to which it is partially or fully engaged determines the magnitude of torque transmitted to the rear wheels  30 ,  31 , and to the front wheels. But the magnitude of torque transmitted to each of the front halfshafts  20 ,  21  and front wheels  16 ,  17  is equal.  
         [0027]     A hydraulic system that controls actuation of the on-demand clutch  22  is illustrated in  FIG. 3 . The hydraulic system is located in the transaxle case  52 , particularly in the valve body  48  housed in the valve body case segment  50 . Hydraulic pressure at the pump outlet  110  is communicated to a solenoid feed pressure regulator valve  112  and to a transfer clutch pressure regulator valve  114 . Regulated solenoid feed pressure produced at the output  124  of the regulator valve  112  is applied to an on-off solenoid valve  116 , whose output is either at the regulated pressure or is zero, and to a variable force solenoid valve  118 , whose output varies with the magnitude of current supplied to the solenoid that actuates valve  118 . Transfer clutch  22  is further controlled by a gain control valve  120 .  
         [0028]     Pressure at the pump outlet is carried through line  122  to the pressure regulator valve  112 . Regulated outlet pressure in line  124  is fed back through line  126  tending to close the valve and to balance the force of a compression spring  128  operating on the spool  130  and tending to open the valve. In this way, valve  112  regulates the magnitude of outlet pressure in line  124  that is communicated to valves  116 ,  118 .  
         [0029]     Gain control valve  120  has a high gain state and a low gain state. When valve  116  opens line  124  to line  128  thereby communicating regulated pressure to the SS 1  port of valve  120 , the low gain state is produced, in which spool  129  is forced rightward against its compression spring and opens a connection between the outlet of valve  118  through line  130  and line  136 . The low gain state produces a variable force in line  136 .  
         [0030]     When valve  116  closes line  124  to line  128  thereby preventing communicating of regulated pressure to the SS 1  port of valve  120 , the high gain state is produced, in which spool  129  is forced leftward by the compression spring, closing a connection between the outlet of valve  118  and line  136  and opening a connection between the VFSX port  134  and exhaust port  132 . The high gain state produces zero pressure in line  136 .  
         [0031]     Clutch pressure regulator valve  114  includes a VFS port connected by line  140  to valve  118 , a VFSF port  144  connected by line  136  to valve  120 , an exhaust port  146 , an outlet port  142  connected by line  100  to the cylinder  98  of transfer clutch  22 , a feedback port connected by line  138  to the clutch pressure outlet  142 , and a pump port connected by line  122  to the pump outlet. When gain control valve  120  is in the high gain state, pressure at port  144  is zero, VFS pressure forces the spool  147  rightward against the force applied by the compression spring, causing the valve to modulate outlet port  142  between connections to exhaust port  146  and the pump port depending on the magnitude of VFS pressure and the outlet pressure.  
         [0032]     When gain control valve  120  is in the low gain state, pressure at port  144  is present on the differential area of the spool  147 , thereby reducing the net effect of the VFS pressure force tending to move the spool rightward against the force applied by the compression spring. This causes a lower magnitude of clutch pressure as valve  114  modulates outlet port  142  between connections to exhaust port  146  and the pump port.  
         [0033]     Referring now to the inter-wheel differential shown in  FIG. 4 , the transaxle output wheel  65 , which is driveably connected to intermediate shaft  60 , is formed with splines  150  at its radial inner surface. The splines  150  driveably connect a hydraulic cylinder  152  to output wheel  65  and provide a surface onto which friction discs of clutch  154  are secured. The friction discs  156  are interleaved with the spacer plates  157 , which are splined at their radial inner surface to the flange of a disk  158 , which is secured, preferably by welding, to the left-hand bevel gear  160  of a differential mechanism  162 .  
         [0034]     A connecting member  164  is also driveably connected by the spline  150  and extends to the pin  166  of the differential mechanism  162 , to which it is secured for rotation as a unit. Pin  166  passes through center bevel pinions  168  located at opposite lateral sides of the central axis  68 , and in continuous meshing engagement with the left side bevel pinion  160  and the right side bevel pinion  170 . The right side bevel pinion  170  is splined at  172  to the right side half-shaft  20 , and the left side bevel pinion  160  is splined at  174  to the left side half-shaft  21 .  
         [0035]     A piston  176 , located within cylinder  152 , actuates clutch  154  toward engagement. The piston  176  moves rightward when a space between the piston and cylinder is pressurized, and, when that space is vented, it moves leftward in response to the force produced by a return spring  178 . Piston  176  carries a dynamic seal  180 , which moves on the leg of a channel  182  as the piston moves in the cylinder  152 . A second seal  181  also hydraulically seals the space between the cylinder and piston. Channel  182  is supported by bushings  183  for rotation on the outer surface of half-shaft  21 .  
         [0036]     Hydraulic passage  184  formed in casing  52  supplies lubricant to bearing  84 . Passages  186  and  188 , communicate pressurized fluid to a passage  190 , which extends axially and radially outward to the space in cylinder  152  behind piston  176 . When pressure within passages  186 ,  188 ,  192  is high due to a connection to a fluid pressure source, piston  76  moves rightward forcing the clutch discs  156  into frictional contact with spacer plates  157 , thereby producing a drive connection between output wheel  65  and side bevel gear  160 . The torque transmission capacity of clutch  154  varies with magnitude of pressure applied to cylinder  152 . Return spring  178  acts continually in opposition to the pressure force developed on the face of piston  176  and returns the piston to the disengaged position shown in  FIG. 4  when the cylinder  152  is vented. Seals  192 ,  194 , located at opposite axial sides of radial passage  190  and adjacent halfshaft  21 , prevent hydraulic fluid leaking past the seals.  
         [0037]     In operation, power is transmitted from output wheel  65  to the differential mechanism  162 . Speed across clutch  154 , called slip, varies with torque capacity of the clutch  154  and the magnitude of its actuating pressure. The speed difference across differential  154  between the half-shafts  20 ,  21  is controlled by varying the torque capacity of the clutch.  
         [0038]     In the embodiment of  FIG. 5 , hydraulic cylinder  152 , spacer plates  156  of clutch  154 , and the connecting member of  164  engage the spline  150  formed on the inner radial surface of output wheel  65 . The left side bevel gear  200  is in continuous meshing engagement with the center bevel pinion  168 , is splined at  202  to the left half-shaft  204 , and is secured to disc  158 , to which the spacer plates  157  of clutch  154  are splined. Piston  176 , located within cylinder  152 , moves rightward when actuated by hydraulic pressure, thereby engaging clutch  154  by forcing its friction discs  156  into frictional contact with the spacer plates  157 , thereby producing a drive connection between output wheel  65  and the left side bevel gear  204 . The source of hydraulic control pressure communicates through passage  186  and radial passage  188 ′ with the hydraulic cylinder  152 .  
         [0039]     In the embodiment of  FIG. 6 , the left side bevel gear  220  is in continuous meshing engagement with the center bevel gears  168 , is splined at  224  to left half-shaft  204 , and is splined at  225  to the friction discs  226  of the clutch  228 . The clutch blocker plates  230 , interleaved with the spacer plates  226 , are splined to the inner radial surface of output wheel  65 . Piston  232  contacts a blocker plate  240  that when actuated forces the friction discs  226  into engagement with the spacer plates  230  to produce a drive connection between bevel gear  220  and the output wheel  65 . Passage  184  supplies hydraulic lubricant to bearing  84 , and passage  242  supplies hydraulic lubricant to bearing  82 . Actuating pressure communicates a source of high pressure fluid through passages  234 ,  235 ,  236  to cylinder  238 , in which piston  232  moves. Seals  192 ,  194 , located at opposite axial sides of radial passage  235  and adjacent halfshaft  20 , prevent hydraulic fluid from leaking past the seals.  
         [0040]     In embodiment of  FIG. 7 , the left side bevel gear  220  is continually engaged with center bevel pinion  168 , is splined at  224  to the left halfshaft  204 , and is splined at  225  to the friction discs  226  of the clutch  250 . Clutch  250  is actuated by a piston  252 , which that reciprocates within a hydraulic cylinder  254 . Cylinder  254  is connected to a source of hydraulic control pressure through axial passage  256 , and radial passages  257  formed in housing  52 . Bearing  82  is lubricated through passage  242  formed in housing  42 , and bearing  84  is lubricated through passage  184  formed in housing  52 . Seals  192 ,  194 , located at opposite axial sides of radial passage  258 , but relatively distant from halfshaft  20 , prevent hydraulic fluid leaking past the seals.  
         [0041]     The differential mechanism of the embodiment shown in  FIG. 8  is a dual planetary gear unit  270  having a sun gear  272  splined at  274  to the left side halfshaft  276 . A planet pinion carrier  278  is splined at  280  to the right side halfshaft  282 . A ring gear  284 , driveably secured to output wheel  65  is in continuous meshing engagement with a set of planet pinions  286 , rotatably supported on carrier  278 . A second set of planet pinions  288 , also rotatably supported on carrier  278 , are in continuous meshing engagement with sun gear  272  and with the first set of planet pinions  286 .  
         [0042]     Friction discs  290  of the clutch  292  are splined at  294  to the radial outer surface of pinion carrier  278 . The spacer plates  296  of the clutch  292  are splined at  298  to the radial inner surface of a hydraulic cylinder  300 . An actuating piston  302  moves within cylinder  300  when the space behind piston  302  is alternately pressurized through passages  304 ,  306  from a source of hydraulic fluid pressure and as the cylinder is vented through those passages. Cylinder  300  and connecting member  308  are driveably secured by splines to output wheel  65  and rotate at the speed of wheel  64 . Cylinder  300  is supported by bearing  82  on housing  42 , and connecting member  308  is supported by bearing  84  on housing  52 . Passages  184  and  242  carry hydraulic lubricant to bearings  84  and  82 , respectively. Seals  192 ,  194 , located at opposite axial sides of radial passage  306  adjacent halfshaft  282 , prevent hydraulic fluid from leaking past the seals. Hydraulic control pressure is supplied through passages  304 ,  306  alternately to actuate piston  302  and to vent cylinder  300 . Passages  304 ,  306  are formed in a cylinder  307 , which is rotatably supported by bushings  183  on the radial outer surface of halfshaft  282 .  
         [0043]     Piston  302  applies its actuating force to the clutch  292  in opposition to a Belleville spring  360 , which is supported pivotably at  362  on the inner surface of cylinder  300  and bears against a pressure plate  364 . When cylinder  300  is vented, spring  360  forces piston  302  rightward to the position shown in  FIG. 8 , where the clutch  292  is disengaged. The actuating piston force is amplified through the mechanical advantage produced by the leveraged condition of the spring.  
         [0044]     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.