Abstract:
A transmission system without dynamic seals, specifically, an actuator for a vehicle transmission including a first rotating clutch pack engageable with a planetary gearset a first non-rotating actuator piston for engaging the clutch pack and a first bearing for isolating a first rotation of the clutch pack from the piston. A transmission system is provided using an electromechanical system for shifting the clutches, allowing a smaller pump only for lubrication of the transmission and the torque converter flow.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to a transmission actuator, and more specifically to a transmission actuator without rotational seals. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional automatic transmissions select gears using a combination of planetary gearsets and torque-transmitting mechanisms. For instance, U.S. Pat. No. 6,932,765 (Kao et al), assigned to General Motors, describes six-speed planetary transmission mechanisms with three planetary gearsets, two clutches and three brakes. Each family member may be employed in a power train to provide six forward speed rations and one reverse speed ration when the torque-transmitting mechanisms are engaged in combinations of two in a selected manner. 
         [0003]    As disclosed in U.S. Pat. No. 6,960,150 (Armstrong et al), assigned to General Motors, torque-transmitting mechanisms include piston mechanisms, which are slidably disposed within members of the transmission housing including a front end cover, a rear end cover, and a shell interconnecting the front end cover and the rear end cover. As can be seen in the transmission depicted in  FIGS. 1 and 2 , rear end cover  10  has extension or boss  12 , which rotatably supports sleeve portion  14  of input shaft  16 . Extension  12  and sleeve portion  14  include a plurality of hydraulic passages through which fluid to torque-transmitting mechanisms  18  and  20  is directed. 
         [0004]    Extension  12  is a portion of stationary cover  10  and sleeve  14  is a portion of rotating input shaft  16 . Therefore, seals forming a portion of the hydraulic passage between extension  12  and sleeve  14  must be dynamic or rotational seals. That is, because there is relative rotation between extension  12  and sleeve  14  during operation of the transmission, the seals must be dynamic or rotational seals. 
         [0005]    Similarly, in the transmission depicted in  FIGS. 3 and 4 , cover  50  has extension or boss  52 , which rotatably supports sealing portion  54  of input shaft  56 . Extension  52  and sleeve portion  54  include a plurality of hydraulic passages through which fluid to the torque-transmitting mechanisms  58  and  60  is directed. Extension  52  is a portion of stationary cover  50  and portion  54  is a portion of rotating input shaft  56 . Therefore, seals forming a portion of the hydraulic passage between extension  52  and portion  54  must be dynamic or rotational seals. That is, because there is relative rotation between extension  52  and portion  54  during operation of the transmission, the seals must be dynamic or rotational seals. 
         [0006]    It should be appreciated that the current state-of-the-art uses hydraulic pressure from a pump to control the clutches in the transmission and torque converter, providing lubrication and cooling for the bearings in gears within the transmission, and provide fluid flow to the torque converter. The flow from the pump is routed to a valve body which divides the flow between the proper clutches and lubrication/cooling circuits, and the torque converter. By nature, these tasks have conflicting requirements. The clutch circuits require high pressure and low flow while the lubrication and torque converter flow requires high flow and low pressure. Therefore the design of this pump and related hydraulics requires a trade off to perform all of these tests. 
         [0007]    While generally sufficient to engage the piston mechanisms, dynamic seals are not liquid-tight seals and allow some leakage of hydraulic fluid past the sealing interface. This leakage results in lower transmission efficiency because the transmission pump must continually operate to ensure that the torque-transmitting mechanisms do not slip. Thus there is a long-felt need for a transmission actuator without dynamic seals. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention broadly comprises a transmission system without dynamic seals, specifically, an actuator for a vehicle transmission including a first rotating clutch pack engageable with a planetary gearset a first non-rotating actuator piston for engaging the clutch pack and a first bearing for isolating a first rotation of the clutch pack from the piston. A transmission system is provided using an electromechanical system for shifting the clutches, allowing a smaller pump only for lubrication of the transmission and the torque converter flow. 
         [0009]    In one embodiment, the transmission system includes a torque converter and a pump operatively arranged for only providing lubrication to the transmission system and the torque converter, wherein the pump includes a sump for storing a lubricant, an apply actuator, a supply actuator, and a plurality of passageways connecting the sump, the apply actuator, the supply actuator, and the transmission system for distributing the lubricant throughout the transmission system, wherein the apply actuator controls which passageways are open for running a master cylinder which pressurizes the system, and wherein the release actuator controls which passageways are open for returning the lubricant back to the sump. 
         [0010]    In a preferred embodiment, the apply actuator opens passageways by rotating a series of gears to align openings in the gears with valve spools, wherein there is one valve spool provided in each passageway for restricting or enabling flow as determined by the alignment of the gears. In another embodiment the release actuator opens selected passageways by rotating a cylinder to align openings in the cylinder with the passage ways. 
         [0011]    A general object of this invention is to provide a transmission actuator without dynamic seals. Another object is to optimize the system by using an electromechanical system for shifting the clutches, allowing a smaller pump only for lubrication of the transmission and the torque converter flow. This optimized pump can be smaller and therefore result in lower operating losses in the system and greater overall fuel economy. 
         [0012]    Another object of the invention is to remove clutch operation from the requirement of the pump. 
         [0013]    Still another object of the invention is to use electromechanical actuation to operate the transmission clutches. 
         [0014]    Yet another object of the invention is to use only to electric motors to actuate the entire transmission. 
         [0015]    Yet a further object of the invention is to provide a transmission actuation system that works with existing transmission architectures. 
         [0016]    These and other objects, features and advantages of the present invention will become readily apparent and appreciated by those having ordinary skill in the art in view of the following detailed description of the invention, claims to the invention, and several views of the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which: 
           [0018]      FIG. 1  is a cross-section of a first transmission; 
           [0019]      FIG. 2  is a detail view of encircled region  2  in  FIG. 1 ; 
           [0020]      FIG. 3  is a cross-section of a second transmission; 
           [0021]      FIG. 4  is a cross-section of encircled region  4  in  FIG. 3 ; 
           [0022]      FIG. 5  is a detail view of encircled region  2  with an example embodiment of a present invention actuator; 
           [0023]      FIG. 6  is a detail view of encircled region  4  with an example embodiment of a present invention actuator; 
           [0024]      FIG. 7  is a sectioned perspective view of an actuator motor and hydraulic cylinder according to an example embodiment of the present invention; 
           [0025]      FIG. 8  is a top view of a gear drive for the actuator of  FIG. 7 ; 
           [0026]      FIG. 9  is a sectioned view of a selector valve and check valve for the actuator of  FIG. 7 ; 
           [0027]      FIG. 10  is an exploded view of a valve body assembly incorporating the actuator of  FIG. 7 ; 
           [0028]      FIG. 11  is a sectioned perspective view of an actuator motor and release drum according to an example embodiment of the present invention; 
           [0029]      FIG. 12  is a detail view of the release drum of  FIG. 11  shown in a blocking mode; 
           [0030]      FIG. 13  is a detail view of the release drum of  FIG. 11  shown in a release mode; 
           [0031]      FIG. 14  is a schematic view of a transmission system according to the current invention; 
           [0032]      FIG. 15  is a perspective view of a valve body assembly; 
           [0033]      FIG. 16  is an exploded view of the valve body assembly shown in  FIG. 15 ; 
           [0034]      FIG. 17  is a cross-sectional view of a apply actuator; 
           [0035]      FIG. 18  is a cross-sectional view of a valve; 
           [0036]      FIG. 19  is a cross-section view of a release actuator; 
           [0037]      FIG. 20  is a perspective view comparing the release actuator of  FIG. 19  in a select position and a release position; 
           [0038]      FIG. 21  is a cross-sectional view of a transmission system according to the current invention; 
           [0039]      FIG. 22  is a cross-sectioned perspective view of a torque converter of the transmission system shown in  FIG. 21 ; 
           [0040]      FIG. 23  illustrates a mounted actuation unit for the transmission system of  FIG. 21 ; 
           [0041]      FIG. 24  illustrates a power pack assembly for a transmission system for the transmission system of  FIG. 21 ; 
           [0042]      FIG. 25  is a cross-sectional view of a prior art transmission system; 
           [0043]      FIG. 26  is a cross-sectional view of a transmission system according to the current invention which eliminates dynamic seals; 
           [0044]      FIG. 27  is a cross-sectional view of a transmission system; 
           [0045]      FIG. 28  is an enlarged view of the encircled area of the transmission system shown in  FIG. 27 ; 
           [0046]      FIG. 29  is a cross-sectional view corresponding to the area of the transmission system shown in  FIG. 28 , as modified according to the current invention; 
           [0047]      FIG. 30  is a cross-sectional view of a check-valve mechanism; and, 
           [0048]      FIG. 31  is a cross-sectional view of a transmission system indicating where improvements according to the current invention are generally installed or incorporated in the transmission system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0049]    At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural element of the invention. While the present invention is described with respect to what is presently considered to be the preferred aspects, it is to be understood that the invention as claimed is not limited to the disclosed aspects. 
         [0050]    Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims. 
         [0051]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described. 
         [0052]    An alternative to replace the high pressure flow from the pump in a typical transmission is to use a hydrostatic system consisting of an electronically controlled master and slave cylinder. Conventional technology would require a separate E-motor and master cylinder for each clutch which may not be practical or cost effective. This invention controls the flow to all clutches with one electronically controlled master cylinder and one electronically controlled release actuator by making use of the mechanism designed to shift lay shaft (manual) transmissions using only one motor (see, U.S. Pat. Nos. 7,026,770 and 7,303,043). 
         [0053]    The basic operation of the mechanism described in the above patents uses the two rotation directions of the motor to control the output of the actuator. In one direction the E-motor travels a nut up a lead screw until it reaches the end of it travel at which point the whole mechanism rotates freely. In the other rotation direction a one-way clutch holds the mechanism in the chosen location allowing the nut to travel down the lead screw. 
         [0054]    In the present invention, two of the above actuators are built into a common valve body  1  (see  FIG. 15 ) containing the hardware and fluid passageways  2  ( FIG. 16 ) to direct the fluid to the proper location(s). The first actuator is referred to as the apply actuator  3  which controls which passageways are open and runs a master cylinder  4  ( FIG. 17 ) which pressurizes the system. The selecting of various passageways is accomplished by rotating a series of gears  10  with openings  10   a  ( FIG. 18 ) to allow or restrict movement of valve spools  11 . There is one valve spool in each passageway, thus allowing or preventing flow as desired. 
         [0055]    In order to permit the actuator to retract the master cylinder piston  5 , a one-way valve  6  is included in the system. This allows for recharging of fluid or selecting another passageway for pressurization without permitting the previously engaged clutch or clutches to disengage. Fluid accumulators  7  can also be included into the system as required. 
         [0056]    Because of this one-way valve, the fluid cannot return the same way it was applied. Therefore, an alternative flow path for the fluid to return to the sump must be provided. The flow through these return passageways also must be controlled and is accomplished with a second actuator called a release actuator  8 . This actuator must seal all passageways during the select process and open the desired passageway(s) in the apply mode. This is accomplished by rotating a cylinder  9  with openings  9   a  ( FIG. 19 ) corresponding to the available passageways. This release of the clutch is then controlled by how far and how quickly the cylinder  9  is moved into position. This effectively creates a variable size orifice that controls the flow and therefore the characteristics of the clutch disengagement. 
         [0057]      FIG. 5  is a detail view of encircled region  2  with an example embodiment of a present invention actuator. The following description is made with reference to  FIG. 5 . 
         [0058]    Present invention actuator  100  for vehicle transmission  102  includes rotating clutch pack  104  engageable with gear  106 . In some example embodiments of the invention, gear  106  is a planetary gearset with sun gear  108 , planet gear  110  and carrier  112 , and ring gear  114 , and output hub  116  of clutch pack  104  is drivingly engaged with carrier  112  at spline  118 . Actuator  100  also includes non-rotating actuator piston  120  for engaging clutch pack  104 , and bearing  122  for isolating rotation of clutch pack  104  from piston  120 . In some embodiments, bearing  122  is a release bearing. 
         [0059]    In an example embodiment of the invention, actuator  100  is disposed within housing  10  for transmission  102 . In some example embodiments of the invention, piston  120  is disposed in chamber  124 , and chamber  124  is rotationally fixed to housing  10  by a key and keyway (not shown), for example. In some example embodiments of the invention, actuator  100  also includes clutch carrier  126 . Carrier  126  axially retains clutch pack  104  with snap ring  128 , for example. That is, snap ring  128  engaged with carrier  126  prevents axial displacement of clutch pack  104  when axial force is applied to clutch pack  104 . Bearing  130  isolates rotation of carrier  126  from chamber  124  and reacts axial force of carrier  126  to chamber  124 . 
         [0060]    Arrangement of chamber  124 , piston  120 , bearing  122 , clutch pack  104 , carrier  126  and bearing  130  isolates rotational motion while minimizing thrust loading. Pressure in chamber  124  exerts force on piston  120  which in turn pushes on bearing  122 . Force of bearing  122  is applied to actuator arm  132 . Arm  132  rotates with clutch pack  104  and bearing  122  isolates that rotation from piston  120 . Therefore, because piston  120  is non-rotating, piston seal  133  does not need to be a dynamic seal and can maintain a liquid-tight connection. Arm  132  applies force to clutch pack  104  which in turn pushes on carrier  126  through snap ring  128 . Force of carrier  126  is reacted through bearing  130  to non-rotating portion  134  to chamber  124  through snap ring  136 , for example. Because pressure acting on piston  120  is also acting on chamber  124  in the opposite direction, the forces are balanced and the thrust force is minimized. 
         [0061]    In an example embodiment of the invention, actuator  100  includes release spring  138  for disengaging clutch pack  104 . Disengagement of clutch pack  104  by spring  138  applies a preload to bearing  122 . 
         [0062]    In some example embodiments of the invention, actuator  100  includes rotating clutch pack  140 , non-rotating actuator piston  142  for engaging clutch pack  140 , and bearing  144  for isolating rotation clutch pack  140  from second piston  142 . In the example embodiment of  FIG. 5 , clutch pack  140  is disposed radially outside of clutch pack  104 . However, other configurations of clutch packs  104  and  140  are possible with the present invention. For instance, clutch pack  104  may be disposed radially inside of clutch pack  140 , or clutch pack  104  may be disposed adjacent to clutch pack  140 . 
         [0063]    In some example embodiments of the invention, clutch carrier  126  is an outer clutch carrier for clutch pack  104  and an inner clutch carrier for clutch pack  140 . In an example embodiment of the invention, a portion of actuator arm  132  passes through clearance hole  146  in clutch carrier  126 . In an example embodiment of the invention, carrier  126  is rotatably fixed to input shaft  16  for transmission  102  at tabbed connection  148 , for example. 
         [0064]    In some example embodiments of the invention, carrier  126  axially retains clutch pack  140  by snap ring  150 , for example. Bearing  130  reacts axial force of carrier  126  to chamber  124 . The earlier discussion of thrust forces for piston  120 , bearing  122 , and clutch pack  104  is generally applicable for piston  142 , bearing  144 , and clutch pack  140  and will not be repeated. 
         [0065]    Transmission  102  includes gear  106  engaged with rotating clutch pack  104  through output hub  116 , for example. Transmission  102  also includes gear actuator  100  with non-rotating actuator piston  120 . Bearing  122  isolates rotation of clutch pack  104  from piston  120 . In an example embodiment, gear  106  is axially disposed between actuator  100  and an engine drivingly engaged with the transmission (not shown). 
         [0066]      FIG. 6  is a detail view of encircled region  4  with an example embodiment of a present invention actuator. The following description is made with reference to  FIG. 6 . Present invention actuator  200  for vehicle transmission  202  includes rotating clutch pack  204  engageable with a gear (not shown). In some example embodiments of the invention, gear (not shown) is a planetary gearset and output hub  216  of clutch pack  204  is drivingly engaged with a sun gear of the planetary gearset. Actuator  200  also includes non-rotating actuator piston  220  for engaging clutch pack  204 , and bearing  222  for isolating rotation of clutch pack  204  from piston  220 . In some embodiments, bearing  222  is a release bearing. 
         [0067]    In an example embodiment of the invention, actuator  200  is disposed within housing  50  for transmission  202 . In some example embodiments of the invention, piston  220  is disposed in chamber  224 , and chamber  224  is rotationally fixed to housing  50  by a key and keyway (not shown), for example. In some example embodiments of the invention, actuator  200  also includes clutch carrier  226  and outer carrier  227 . Carriers  226  and  227  axially retain clutch pack  204  with snap rings  228  and  229 , for example. That is, snap rings  228  and  229  engaged with carrier  227  prevent axial displacement of clutch pack  204  when axial force is applied to clutch pack  204 . Bearing  230  isolates rotation of carrier  226  from chamber  224  and reacts axial force of carrier  226  to chamber  224 . 
         [0068]    Arrangement of chamber  224 , piston  220 , bearing  222 , clutch pack  204 , carriers  226  and  227 , and bearing  230  isolates rotational motion while minimizing thrust loading. Pressure in chamber  224  exerts force on piston  220  which in turn pushes on bearing  222 . Force of bearing  222  is applied to actuator arm  232 . Arm  232  rotates with clutch pack  204  and bearing  222  isolates that rotation from piston  220 . Therefore, because piston  220  is non-rotating, piston seal  233  does not need to be a dynamic seal and can maintain a liquid-tight connection. Arm  232  applies force to clutch pack  204  which in turn pushes on carrier  226  through carrier  227  and snap rings  228  and  229 . Force of carrier  226  is reacted through bearing  230  to chamber  224 . Because pressure acting on piston  220  is also acting on chamber  224  in the opposite direction, the forces are balanced and the thrust force is minimized. 
         [0069]    In an example embodiment of the invention, actuator  200  includes release spring  238  for disengaging clutch pack  204 . Disengagement of clutch pack  204  by spring  238  applies a preload to bearing  222 . 
         [0070]    In some example embodiments of the invention, actuator  200  includes rotating clutch pack  240 , non-rotating actuator piston  242  for engaging clutch pack  240 , and bearing  244  for isolating rotation clutch pack  240  from second piston  242 . In the example embodiment of  FIG. 6 , clutch pack  240  is disposed adjacent to clutch pack  204 . However, other configurations of clutch packs  204  and  240  are possible with the present invention. For instance, clutch pack  204  may be disposed radially inside or outside of clutch pack  240 , as shown in  FIG. 5 . 
         [0071]    In some example embodiments of the invention, clutch carriers  226  and  227  are an inner clutch carrier for clutch pack  240  and an outer clutch carrier for clutch pack  204 , respectively. In an example embodiment of the invention, a portion of actuator arm  232  passes through clearance hole  246  in planet carrier  247 , drivingly engaged clutch carrier  226 . In an example embodiment of the invention, carrier  226  is rotatably fixed to planet carrier  247  at tabbed connection  248 , for example. 
         [0072]    In some example embodiments of the invention, carrier  249  axially retains clutch pack  240  by snap ring  250 , for example. Connector  252  reacts force of carrier  249  through snap ring  254 . Bearing  256  reacts axial force of carrier  226  to chamber  224 . The earlier discussion of thrust forces for piston  220 , bearing  222 , and clutch pack  204  is generally applicable for piston  242 , bearing  244 , and clutch pack  240  and will not be repeated. 
         [0073]    Transmission  202  includes gear (not shown) engaged with rotating clutch pack  204  through output hub  216 , for example. Transmission  202  also includes gear actuator  200  with non-rotating actuator piston  220 . Bearing  222  isolates rotation of clutch pack  204  from piston  220 . In an example embodiment, actuator  200  is axially disposed between a gear (not shown) and an engine drivingly engaged with the transmission (not shown). 
         [0074]      FIG. 7  is a sectioned perspective view of an actuator motor and hydraulic cylinder according to an example embodiment of the present invention.  FIG. 8  is a top view of a gear drive for the actuator of  FIG. 7 .  FIG. 9  is a sectioned view of a selector valve and check valve for the actuator of  FIG. 7 . The following description is made with reference to  FIGS. 7-9 . Actuator  300  includes electric motor  302  and hydraulic cylinder  304 . Channel  306  includes check valve  308  and selector valve  310 . Check valve  308  is for maintaining pressure in channel  306  and may be a spring loaded ball in an orifice, for example. Motor  302  is arranged to displace cylinder  304  and operate valve  310  to selectively pressurize channel  306 . 
         [0075]    In some example embodiments of the invention, rotation of motor  302  in direction  312  displaces cylinder  304  and rotation of motor  302  in direction  314  operates valve  310 . Two-way operation of motor-cylinder-valve arrangement is similar to the actuator described in U.S. Pat. Nos. 7,026,770 and 7,303,043, the entire disclosure of which is hereby incorporated by reference herein. Motor  302  is coupled with spindle  316  via gear wheel set  318 . When spindle  316  turns, spindle nut  320  can migrate in the longitudinal direction of spindle  316  until it reaches a torsional lock (end stop  322 , for example). For example, rotation of motor  302  in direction  312  displaces nut  320  and cylinder  304  to pressurize fluid in chamber  323 . 
         [0076]    Rotation of motor  302  in direction  314  retracts cylinder  304  until nut  320  reaches stop  322 . Once nut  320  reaches stop  322 , nut  320  is turned with spindle  316 . When disposed against stop  322 , nut  320  is drivingly engaged with gear  324  of gear train  326 , so rotation of nut  320  also rotates selector gears  328  and  330 . Selector gears  328  and  330  control position of valve  310 . That is, when pin portion  332  of valve  310  is disposed on annular face  334  of gear  328 , valve  310  blocks flow of fluid between chamber  336  and channel  338 . When gear  328  is rotated so that pin  332  is aligned with hole  340 , pressure in chamber  336  overcomes force of return spring  342  to displace pin  332  into hole  340 . As a result, valve  310  is displaced allowing fluid exchange between chamber  336  and channel  338 . 
         [0077]    Piston chamber  343  and chamber  336  are in fluid communication. Check valve  308  operates to allow flow of fluid from chamber  336  to channel  338 , but prevent flow in the reverse direction. Therefore, when cylinder  304  is retracted, fluid in channel  338  remains pressurized. 
         [0078]      FIG. 10  is an exploded view of a valve body assembly incorporating the actuator of  FIG. 7 . The following description is made with reference to  FIGS. 7-10 . Valve body assembly  344  includes valve body  346 , gasket  348  and cover  350 . Motor  302 , cylinder  304 , and accumulator  358  are disposed within valve body  346 . 
         [0079]    Chambers and channels in assembly  344  form a hydraulic path. Pressurized fluid in chamber  336  flows through channel  338  and holes  352  in gasket  348  to channels (not shown) in cover  350 . Holes  354  in gasket  348  connect channels in cover (not shown) to return channels  356 . Holes  357  in cover  350  connect pressurized fluid with pistons for engaging transmission clutches (pistons  120  and  142 , and transmission clutches  104  and  140 , for example). In some example embodiments of the invention, accumulator  358  is disposed in channel  356 . That is, accumulator  358  disposed after check valve  308  in a hydraulic path beginning at cylinder  304  and chamber  336 . In an example embodiment of the invention, accumulator  358  includes a diaphragm spring (not shown). 
         [0080]      FIG. 11  is a sectioned perspective view of an actuator motor and release drum according to an example embodiment of the present invention.  FIG. 12  is a detail view of the release drum of  FIG. 11  shown in a blocking mode.  FIG. 13  is a detail view of the release drum of  FIG. 11  shown in a release mode. The following description is made with reference to  FIGS. 10-13 . In some example embodiments of the invention, actuator  300  includes electric motor  360  and release drum  362  with release port  364 . Motor  360  is arranged to align release port  364  to selectively de-pressurize channel  356 . 
         [0081]    Drum  362  includes axis  366 . Rotation of motor  360  in direction  368  rotates drum  362  about axis  366  and rotation of motor  360  in direction  370  displaces drum  362  along axis  366 . Discussion of motor  302  and spindle nut  320  applies to motor  360  and drum  362  and will not be repeated. Rotation of drum  362  circumferentially aligns port  364  with channel  356 , but drum  362  must be axially displaced before port  364  can release pressure in channel  356 . Therefore, pressure in unselected channels is not released during the selection process. In an example embodiment, motor  360  and drum  362  are disposed in valve body with motor  302 , cylinder  304 , and accumulator  358 . 
         [0082]    The following description is made with reference to  FIGS. 1-13 . Example embodiments of the present invention also include a transmission for a vehicle. Transmission  400  ( FIG. 1 ) includes gear  402 , brake  404 , and clutch  406 . Brake  404  and clutch  406  are actuated via individual pressure channels  306  ( FIG. 9 ). Channels  306  each include check valves  308  for maintaining pressure in channels  306 . Transmission  400  also includes electric motor  302  ( FIG. 11 ) and hydraulic cylinder  304 . Electric motor  302  displaces cylinder  304  to pressurize channels  306 . 
         [0083]    Transmission  400  includes valve  310  ( FIG. 9 ) operated by motor  302  to selectively pressurize channels  306 . Rotation of the motor  302  in direction  312  displaces cylinder  304  and rotation of motor  302  in direction  314  operates valve  310 . In an example embodiment, accumulator  358  ( FIG. 10 ) is disposed in a hydraulic path between check valve  308  and brake  404  or clutch  406 . Accumulator  358  may include a diaphragm spring. 
         [0084]    In an example embodiment of the invention, transmission  400  includes valve body  346  ( FIG. 10 ), and cylinder  304 , motor  302 , and accumulator  358  are disposed within valve body  346 . In some example embodiments of the invention, transmission  400  includes electric motor  360  ( FIG. 11 ) and release drum  362  with release port  364 . Motor  360  aligns release port  364  to selectively de-pressurize channels  356 . Rotation of motor  360  in direction  368  rotates drum  362  and rotation of motor  360  in direction  370  axially displaces drum  362 . In an example embodiment of the invention, transmission  400  includes hydraulic pump  408  for cooling flow. Pump  408  is drivingly engaged with the engine (not shown) for the vehicle. 
         [0085]    Thus, it is seen that the objects of the invention are efficiently obtained, although changes and modifications to the invention should be readily apparent to those having ordinary skill in the art, without departing from the spirit or scope of the invention as claimed. Although the invention is described by reference to a specific preferred embodiment, it is clear that variations can be made without departing from the scope or spirit of the invention as claimed.