Abstract:
A transmission latching mechanism includes a component of a transmission gearset, a member secured to and able to rotate with the component, and a piston fixed against rotation and moveable alternately to latch the mechanism, thereby holding the member against rotation and to unlatch the mechanism, thereby releasing the member to rotate.

Description:
[0001]    This application claims priority to and the benefit of U.S. Provisional Application Nos. 61/446,147 and 61/446,149, filed Feb. 24, 2011, the full disclosures of which are incorporated herein by reference. 
         [0002]    This application is a continuation-in-part of pending U. S. application Ser. No. 13/052,362, filed Mar. 21, 2011. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    This invention relates to an automatic transmission for a motor vehicle that includes planetary gearsets and clutches and brakes whose state of engagement and disengagement determines speed ratios produced by the transmission. 
         [0005]    2. Description of the Prior Art 
         [0006]    In a front wheel drive vehicle, the axial space available for the transmission is limited by the width of the engine compartment and the length of the engine. In addition, the trend to increase the number of ratios available generally increases the number of components required. For these reasons, it is desirable to position components concentrically in order to minimize axial length. The ability to position components concentrically is limited, however, by the need to connect particular components mutually and to the transmission case. 
         [0007]    Furthermore, it is desirable for the output element to be located near the center of the vehicle, which corresponds to the input end of the gear box. An output element located toward the outside of the vehicle may require additional support structure and add length on the transfer axis. With some kinematic arrangements, however, the need to connect certain elements to the transmission case requires that the output element be so located. 
         [0008]    One of the transmission control devices, such as the D brake, may be used only as a latching device rather than as a dynamic device. To minimize parasitic viscous drag loss produced in the control device, it would be better if the brake were a latching mechanism rather than a hydraulically-actuated friction brake having interleaved discs and spacer plates. 
       SUMMARY OF THE INVENTION 
       [0009]    A transmission latching mechanism includes a component of a transmission gearset, a member secured to and able to rotate with the component, and a piston fixed against rotation and moveable alternately to latch the mechanism, thereby holding the member against rotation and to unlatch the mechanism, thereby releasing the member to rotate. 
         [0010]    The latching mechanism simplifies the brake, reduces the number of components as compared to the number required for a hydraulically-actuated friction brake, reduces the drag loss by eliminating the friction discs and plates, and requires a smaller space than the space required for a hydraulically-actuated friction brake. 
         [0011]    The latching mechanism is a more robust component and requires lower cost to assemble and install than does a hydraulically-actuated friction brake. 
         [0012]    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 
         [0013]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0014]      FIG. 1  is a cross sectional side view of a multiple speed automatic transaxle; 
           [0015]      FIG. 2  is cross sectional side view of the transaxle showing the front and middle cylinder assemblies; 
           [0016]      FIG. 3  is a side perspective view showing sleeves that are fitted on the front support and middle cylinder assembly, respectively; 
           [0017]      FIG. 4  is a view cross sectional side view of the transfer gears and shaft near the output of the transaxle of  FIG. 1 ; and 
           [0018]      FIG. 5  is a cross section side view taken through the latching mechanism and components of the transmission in the vicinity of the latching mechanism. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Referring now to the drawings,  FIG. 1  illustrates gearing, clutches, brakes, shafts, fluid passages, and other components of a multiple-speed automatic transaxle  10  arranged substantially concentrically about an axis  11 . 
         [0020]    A torque converter includes an impeller driven by an engine, a turbine hydrokinetically coupled to the impeller, and a stator between the impeller and turbine. A transmission input shaft  20  is secured by a spline connection  21  to the turbine. The stator is secured by a spline connection  22  to a front support  24 , which is secured against rotation to a transmission case  26 . 
         [0021]    A double pinion, speed reduction planetary gearset  28  includes a sun gear  30 , secured by a spline connection  31  to input shaft  20 ; a carrier  32 , secured by a spline connection  33  to the front support  24 ; a ring gear  34 , secured by a spline connection  35  to a front cylinder assembly  36 ; a first set of planet pinions  38  supported on carrier  32  and meshing with sun gear  30 ; and a second set of planet pinions  40 , supported on carrier  32  and meshing with ring gear  34  and the first pinions  38 . Ring gear  34  rotates in the same direction as input shaft  20  but at a reduced speed. 
         [0022]    Rear gearset  46  and middle gearset  48  are simple planetary gearsets. Gearset  46  includes a set of planet pinion  50  supported for rotation on carrier  52  and meshing with both sun gear  54  and ring gear  56 . Gearset  48  includes a set of planet pinions  58  supported for rotation on carrier  60  and meshing with both sun gear  62  and ring gear  64 . Sun gear  54  is splined to a shaft that is splined to a shell  66 , on which shaft sun gear  62  is formed, thereby securing the sun gears  54 ,  62  mutually and to the shell  66 . Carrier  52  is fixed to a shell  68 . Carrier  60  and ring gear  56  are fixed to each other and to output pinion  70  through a shell  72 . Ring gear  64  is fixed to shell  74 . 
         [0023]    Front cylinder assembly  36 , which is fixed to ring gear  34 , actuates clutches  76 ,  80 . Plates for clutch  76  includes plates splined to front cylinder assembly  36  alternating with plates splined to shell  74 . When hydraulic pressure is applied to piston  78 , the plates are forced together and torque is transmitted between ring gears  34  and  64 . When the hydraulic pressure is released, ring gears  34  and  64  may rotate at different speeds with low parasitic drag. Similarly, plates for clutch  80  include plates splined to front cylinder assembly  36  alternating with plates splined to shell  66 . When hydraulic pressure is applied to piston  82 , torque is transmitted between ring gear  34  and sun gears  54 ,  62 . Pressurized fluid is routed from a control body  84 , through front support  24 , into front cylinder assembly  36  between rotating seals. 
         [0024]    Middle cylinder assembly  86 , which includes carrier  32 , actuates brake  88 . Plates for brake  88  include plates splined to carrier  32  alternating with plates splined to shell  66 . When hydraulic pressure is applied to piston  90 , the brake holds sun gears  54 ,  62  against rotation. Pressurized fluid is routed from the control body  84 , through front support  24 , between planet pinions  38 ,  40 , into middle cylinder assembly  86 . Due to the location of clutch pack  88 , output element  70  is located in the more favorable position near the front of the gear box. 
         [0025]    Rear cylinder assembly  92  is secured by a spline connection  93  fixed to input shaft  20 . When hydraulic pressure is applied to piston  94 , the plates of clutch  96  transmit torque between input shaft  20  and carrier  52 . Similarly, when hydraulic pressure is applied to piston  98 , the plates of clutch  100  transmit torque between input shaft  20  and sun gears  54 ,  62 . Pressurized fluid is routed from the control body  84 , into rear cylinder assembly  92 . 
         [0026]    When hydraulic pressure is applied to piston  102 , brake  104  holds carrier  52  and shell  68  against rotation. A one-way brake  106  passively prevents carrier  52  and shell  68  from rotating in the negative direction, but allows them to rotate in the forward direction. One-way brake  106  may optionally be omitted and its function performed by actively controlling brake  104 . 
         [0027]    The D brake  104  is used only as a latching device not as a dynamic brake. To minimize parasitic viscous drag loss produced in brake  104  it is desired that excess oil not be present in the brake. Therefore, an oil dam formed by an oil seal  103  between the piston  94  of E clutch  96  and the inner race  107  of one-way brake  106  is provided to limit or prevent oil from entering the D brake  104 . The inner radial end of return spring  108  continually contacts the piston  102  that actuates brake  104 . The outer radial end of return spring  108  continually contacts a fixed structure, so that the spring flexes as the piston  102  moves in the cylinder of the D brake  104 . In this way, return spring  108  also participates in the oil dam by limiting or preventing radial flow of oil into the D brake  104  caused by centrifugal force. 
         [0028]    This arrangement permits brake  88  and clutches  76 ,  80  to be mutually concentric, located at an axial plane, and located radially outward from the planetary gearsets  28 ,  46 ,  48  such that they do not add to the axial length of the gearbox. Similarly, clutches  96 ,  100  and brake  104  are mutually concentric and located radially outward from the planetary gearing  28 ,  46 ,  48 . Clutches  76 ,  80 ,  96 ,  100  and brakes  88 ,  104 ,  106  comprise the control elements. 
         [0029]    As  FIGS. 2A ,  2 B illustrate, the front cylinder assembly  36  is supported for rotation on the fixed front support  24  and carrier  34 . The front cylinder assembly  36  is formed with clutch actuation fluid passages, each passage communicating with one of the cylinders  114 ,  116  formed in the front cylinder assembly  36 . Cylinder  114  contains piston  78 ; cylinder  116  contains piston  82 . One of the fluid passages in front cylinder assembly  36  is represented in  FIG. 2  by interconnected passage lengths  109 ,  110 ,  111 ,  112 , through which cylinder  116  communicates with a source of clutch control hydraulic pressure. Another of the fluid passages in front cylinder assembly  36 , which is similar to passage lengths  109 ,  110 ,  111 ,  112  but spaced angularly about axis  11  from passage lengths  109 ,  110 ,  111 ,  112 , communicates a source of clutch control hydraulic pressure to cylinder  114 . Passage lengths  109  are machined in the surface at the inside diameter of the front cylinder assembly  36 . 
         [0030]    The front cylinder assembly  36  is also formed with a balance volume supply passage, similar to, but spaced angularly about axis  11  from passage lengths  109 ,  110 ,  111 ,  112 . The balance volume supply passage communicates with balance volumes  120 ,  122 . As shown in  FIG. 2A , the balance volume supply passage includes an axial passage length  124 , which communicates with a source of balance volume supply fluid and pressure, and a radial passage length  126 , through which fluid flows into the balance volumes  120 ,  122  from passage  124 . Passage  124  may be a single drilled hole extending along a longitudinal axis and located between the two clutch balance areas of the A clutch and B clutch. Passage  124  carries fluid to cross drilled holes  126 , which communicate with the balance volumes  120 ,  122 . 
         [0031]    Coiled compression springs  128 ,  130 , each located in a respective balance dam  120 ,  122 , urge the respective piston  78 ,  82  to the position shown in  FIG. 2 . Ring gear  34  is secured to front cylinder assembly  36  by a spline connection  132 . 
         [0032]    Middle cylinder assembly  86  includes carrier  32 , which is grounded on the front support  24 . Carrier  32  includes first and second plates  134 ,  135  and pinion shafts secured to the plates, one pinion shaft supporting pinions  38 , and the other pinion shaft supporting pinions  40 . Plate  135  is formed with a cylinder  140  containing a brake piston  90 . 
         [0033]    A source of brake actuating hydraulic pressure communicates with cylinder  140  through a series on interconnected passage lengths  142 ,  143  and a horizontal passage length that extends axially from passage  143 , through a web of carrier  32 , between the sets of planet pinions  38 ,  40 , to cylinder  140 . These brake feed passages are formed in carrier  32 . When actuating pressure is applied to cylinder  140 , piston  90  forces the plates of brake  88  into mutual frictional contact, thereby holding sun gears  54 ,  62  and shell  66  against rotation. A Belleville spring  146  returns piston  90  to the position shown in  FIG. 2 , when actuating pressure is vented from cylinder  140 . 
         [0034]    The front support  24  is formed with passages, preferably spaced mutually about axis  11 . These passages in front support  24  are represented in the  FIGS. 1 and 2  by passage lengths  150 ,  151 ,  152 , through which hydraulic fluid is supplied to clutch servo cylinders  114 ,  116 , brake servo cylinder  140 , and balance dams  120 ,  122 . A passage of each of the front support passages communicates hydraulic fluid and pressure to cylinders  114 ,  116  and balance dams  120 ,  122  of the front cylinder assembly  36  through the fluid passages  109 ,  110 ,  111 ,  112 ,  113 ,  124  formed in the front cylinder assembly  36 . Another passage of each of the front support passages communicates hydraulic fluid and pressure to cylinder  140  of the middle cylinder assembly  86  through the fluid passages  142 ,  143  in carrier  32 . 
         [0035]    The front support  24  includes a bearing support shoulder  154 , which extends axially and over an axial extension  156  of the front cylinder assembly  36 . A bushing  158  and bearing  160  provide for rotation of the front cylinder assembly  36  relative to the front support  24 . This arrangement of the front support  24 , its bearing support shoulder  154 , and front cylinder assembly  36 , however, prevents radial access required to machine a passage or passages that would connect first passage  152  in front support  24  to the second passage  109  in the front cylinder assembly  36 . 
         [0036]    To overcome this problem and provide hydraulic continuity between passage lengths  109 ,  152 , first passage  152  is formed with an opening that extends along a length of first passage  152 , parallel to axis  11 , and through an outer wall of the front support  24 . The opening faces radially outward toward second passage  109 . Similarly, second passage  109  is formed with a second opening that extends along a length of second passage  109 , parallel to axis  11 , and through an inner wall of the front cylinder assembly  36 . The second opening faces radially inward toward first passage  152 . 
         [0037]    A first sleeve  162  is inserted axially with a press fit over a surface at an outer diameter of the front support  24 , thereby covering the opening at the outer surface of passage length  152 . Sleeve  162  is formed with radial passages  164 ,  165 , which extend through the thickness of the sleeve  162 . Seals  176 , located at each side of the passages  164 ,  165  prevent leakage of fluid from the passages. 
         [0038]    A second sleeve  170  is inserted axially with a press fit over the second opening at the inside diameter of the front cylinder assembly  36 , thereby covering and enclosing the length of the second opening in the second passage  109 . Sleeve  170  is formed with radial openings, two of which are represented in  FIG. 2  by openings  172 ,  174 , aligned with the radial passages  164 ,  165  formed in the first sleeve  162 . 
         [0039]    Sleeves  164  and  170  provides hydraulic continuity from the source of fluid pressure carried in the passages of the front support  24  to the balance dams  120 ,  122  and the servo cylinders  114 ,  116 ,  140 , through which clutches  76 ,  80  and brake  88  are actuated. 
         [0040]    Sleeves  162 ,  170  also provide access that enables machining of the first and second passages  152 ,  109  in the surface at the outside diameter of front support  24  and in the surface at the inside diameter of the front cylinder assembly  36 .  FIG. 3  shows sleeves  162 ,  170  and three seals  176 , which are fitted in recesses on sleeve  162  between each of its radial passages  164 ,  165 . 
         [0041]    As  FIG. 4  shows output pinion  70  meshes with a transfer gear  180 , which is formed integrally with transfer pinion  182  on a transfer wheel  184 . A transfer shaft  186 , is secured at one end by a pinned connection  188  to a non-rotating housing component  190 , and at the opposite end is seated in a recess  192  formed in a non-rotating torque converter housing component  194 . Ball bearing  198  supports transfer wheel  184  on the torque converter housing  194 . Housing components  190 ,  194  comprise a reaction component and may be formed integrally or preferably as separate components. 
         [0042]    Ball bearing  198  is supported radially by being seated on a surface  196  of the torque converter housing  194 . A shoulder  199  on torque converter housing  194  contacts the right-hand axial surface of the inner race of bearing  198 , the second surface of bearing  198 . A snap ring  200  contacts the right-hand axial third surface  201  of the outer race of bearing  198 . Shoulder  199  and snap ring  200  limit rightward axial movement of bearing  198 . 
         [0043]    A shoulder  202  formed on gear wheel  184  contacts the left-hand axial first surface of the outer race of bearing  198 . A thrust washer  204  contacts a left-hand axial fourth surface  205  of the inner race of bearing  198 . The thrust washer  204  contacts a shoulder  206  formed on transfer shaft  186 . Shoulders  202  and  206  limit leftward axial movement of bearing  198   
         [0044]    The ring gear  210  of a differential mechanism  212  meshes with transfer pinion  182  and is supported for rotation by bearings  214 ,  216  on housing  190 ,  194 . Rotating power transmitted to output pinion  70  is transmitted through transfer gears  180 ,  182  and ring gear  210  to the input of differential, which drives a set of vehicle wheels aligned with axis  220 . 
         [0045]    A roller bearing  222  supports transfer wheel  184  on transfer shaft  186 . The thickness of a washer  224 , fitted in a recess  226  of housing  190 , is selected to ensure contact between thrust washer  204  and the inner race of bearing  198 . 
         [0046]    The output pinion  70  and transfer gears  180 ,  182  have helical gear teeth, which produce thrust force components in the axial direction parallel to axis  220  and in the radial direction, normal to the plane of  FIG. 5 , which transmitting torque. A thrust force in the right-hand direction transmitted to the transfer gear wheel  184  is reacted by the torque converter housing  194  due to its contact at shoulder  199  with bearing  198 . A thrust force in the left-hand direction transmitted to the transfer gear wheel  184  is reacted by the housing  190  due to contact between snap ring  200  and bearing  198 , contact between bearing  198  and thrust washer  204 , contact between the thrust washer and transfer shaft  186 , and contact between shaft  186 , washer  224  and housing  190 . 
         [0047]    As shown in  FIG. 1A , the D brake  104  includes a first set of thin discs  230  secured to the outer race  232  of one-way brake  106  by a spline connection, which permits the discs  230  to move axially and prevents them from rotating relative to the race  232 , which is fixed to the transmission case or end cover against rotation. 
         [0048]    Similarly, the D brake  104  includes a second set of thin discs  234  secured to the inner race  107  of one-way brake  106  by a spline connection, which permits the discs  234  to move axially and prevents them from rotating relative to the inner race  107 . The first and second discs are interleaved, such that each of the first discs  230  has a second disc  234  located on each axial side of the first disc. 
         [0049]    Inner race  107  is fixed to the carrier  68  of gearset  46 , such that discs  234 , inner race  107  and carrier  68  rotate together as a unit at the same speed. The discs  230 ,  234  become frictional engaged mutually when hydraulic pressure is applied to the cylinder  252  and piston  102  forced the discs into mutual contact, thereby fixing the inner race  107  and carrier  68  against rotation. The discs  234  rotate freely relative to discs  230  when hydraulic pressure is vented from cylinder  252 . 
         [0050]    Preferably the outer and inner races  232 ,  107  of one-way brake  106  are formed of a ferrous alloy of sintered powdered metal, and discs  230 ,  234  are of steel. The reaction splines for the D brake  104  is preferably not formed in the aluminum case or aluminum end cover because of high local bearing stresses that would be induced in the case or end cover by the thin discs  230 ,  234 . The discs  230 ,  234  are thin to reduce parasitic loss in the D brake  104 . The D brake  104  reaction splines are formed as an integral part of the raceways  232 ,  107  of the one-way brake  106 . The brake  106  is then splined to the transmission case. 
         [0051]    Although the one-way transmission control member is described with reference to its being a brake  106 , it may be a clutch, which connects one member of a gearset to another member of the same gearset or a different gearset. Similarly, the hydraulically-actuated transmission control member is described with reference to its being a brake, but it may be a clutch instead. 
         [0052]    Preferably the one-way brake  106  is a rocker one-way brake of the type having a pivoting rockers, each rocker retained is a pocket and actuated by centrifugal force and a compression spring, as described in U. S. Pat. Nos. 7,448,481 and 7,451,862. 
         [0053]      FIG. 5  illustrates the D brake  104  as a latching mechanism  260 , which alternately connects carrier  52  and shell  68  to the transmission case, thereby holding the carrier against rotation, and disconnects carrier  52  and shell  68  from the transmission case so that they can rotate freely. 
         [0054]    Shell  68  is secured by a spline connection  261  to member  262 . The inner race  263  of a one-way brake  264  is secured by a spline connection  265  to member  262 . The outer race  266  of brake  264  is fixed against rotation by being secured to axially directed spline teeth  270  formed on the end cover  272  of the transmission case. 
         [0055]    Latching mechanism  260  includes a piston  274 , which moves substantially parallel to axis  11  and is fixed against rotation by being secured to the axial spline teeth  270  formed on the end cover  272 . Piston is actuated by actuating pressure in the cylinder  252  formed in the end cover  272  to slide rightward on spline teeth  270 , thereby latching mechanism  260 . When actuating pressure in cylinder  252  is vented and release pressure is supplied through passage  271 ,  273  to a volume  282  of cylinder  252 , piston  274  is actuated by release pressure and the force of a return spring  276  to slide leftward on spline teeth  270 , thereby unlatching mechanism  260 . 
         [0056]    A dam  278 , secured to the end cover  272  by a snap ring  280 , supports a dynamic seal  284 , which, together with seal  286 , hydraulically seals the volume  282  located between the piston  274  and the dam  278 . 
         [0057]    Piston  274  is formed with a series of dog teeth  288 , which are spaced mutually about axis  11  and located at the inner surface of the piston. Member  262  is similarly formed with a series of dog teeth  290 , which are spaced mutually about axis  11  and located for engagement by teeth  288  as piston  274  moves rightward in cylinder  252 . 
         [0058]    When cylinder  252  is pressurized and volume  282  is vented, piston  274  moves rightward against the force of spring  276  causing teeth  288  to engage teeth  290 , thereby connecting carrier  52  and shell  68  to the end cover  272  and holding the carrier and shell against rotation. When cylinder  252  is vented and volume  282  is pressurized, piston  274  moves leftward causing teeth  288  to disengage teeth  290 , thereby disconnecting carrier  52  and shell  68  from the end cover  272  and allowing the carrier and shell to rotate freely. 
         [0059]    The one-way brake  264  produces a torque reaction for carrier  52  and shell  68  in one rotary direction and allows the carrier and shell to rotate freely in the opposite direction. Preferably the races  263 ,  266  of one-way brake  264  are formed from a ferrous alloy of sintered powdered metal. 
         [0060]    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.