Abstract:
An automotive transmission is equipped with a variety of gears that may be combined to yield one or more output speeds as compared to an input speed. One or more electromechanical actuators is used to engage or disengage a particular desired mix of gears. The electromechanical actuator engages one mix of gears or another to set the desired ratio of input speed to output speed. The transmission may be used to provide a straight-through, an underdrive speed range, or an overdrive speed range in an automotive transmission.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to power transmission devices, and in particular to an electromechanical actuator useful for adding or removing elements of a power transmitter, including auxiliary, automatic and manual transmissions, axles, and transaxles. 
     BACKGROUND OF THE INVENTION 
     Power transmissions are complicated machines, packing many mechanical devices into ever-smaller packages in order to meet cost and weight goals. A present-day transmission may use hydraulic bands to change gearing ratios and thus speeds. A simple two-speed transmission, such as one depicted in U.S. Pat. No. 5,588,928, is used to describe the involved gear and friction elements, and their functions during gear changes.  FIG. 1  depicts a transmission consisting of a simple planetary gear unit  1  having an annulus gear  2  coupled with input shaft  3 , a sun gear  4  connected with brake drum  5 , and a planet carrier  6  connected with output shaft  7 . Planet gears  8  mesh with annulus gear  2  and sun gear  4 . A self-synchronizing friction band  10  is engaged to hold the drum  5  and the sun gear  4  attached thereto stationary to set the transmission in low gear. The transmission is upshifted to direct drive by applying multi-plate clutch  9  and by disengaging the friction band  10  to lock the planetary gear set for unitary rotation. 
     In  FIG. 2 , the friction band  10  encircling the drum  5  has friction lining  11  attached to its inner surface. The band  10  also has lugs  12 ,  13  secured to each end of the band; one lug  12  to the apply end and another lug  13  to the reaction end. Typically, the friction band actuating system  14  is housed inside a servo chamber  15  extending transversely in a transmission case  16 . The main components in the system are the apply piston  17  and the reaction piston  18 . Both pistons are subjected to the same pressure regulated by an exhaust control valve  19 , which is attached to the reaction piston guide rod  20 , responding to the axial movement of reaction piston  18 . Chamber  15  is enclosed by a servo cover  22 , which includes cylindrical surfaces and oil passages for both pistons as well as an elastomer ring  24  for sealing purposes. A complicated system to apply and release hydraulic pressure causes the band or bands to contract or relax, thus engaging or releasing a drive shaft encircled by the bands. Control system  25  for the selfsynchronized friction band includes a shift valve  26  and a mode valve  27 , including ball  28  and spring  29 . Ball  30  with seat  23  forms another valve. Hydraulic fluid or oil is supplied and directed through a series of pistons, accumulators, and chambers to control the bands. 
     Such complicated devices as this brake-band actuated transmission tend to have many components that must interact in a prescribed manner for correct operation. These parts and the resulting transmission are costly. The transmissions are subject to oil leaks. Wear may occur in many parts of the transmission, including the valve seats, the pistons, and the bands themselves. What is needed is a power transmitter having fewer parts and operating in a simpler fashion to add speed ranges to a mechanical transmission. Also, what is needed is a power transmitter that will shift and transmit power with fewer components and less cost, and in which the components are capable of acting simply and reliably to deliver mechanical power. 
     SUMMARY 
     One aspect of the invention is an electromechanical actuator for engaging a shaft. The electromechanical actuator comprises a housing that is fixedly mounted. Within the housing is a plurality of roller elements, such as roller bearings or needle bearings. There is a split ring around the shaft and within the housing, the ring urging the roller elements against an inside surface of the housing. The electromechanical actuator also comprises an engaging device, wherein the engaging device urges the split ring against the shaft. Another aspect of the invention is a method of manufacturing an electromechanical actuator. The method comprises molding a cage having a plurality of separating elements and a surface for engaging an engaging device. The method also comprises manufacturing an outer race and an inner race, at least one of the outer race and inner race having a cammed surface, and the method also comprises manufacturing a plurality of roller elements. 
     Another aspect of the invention is an auxiliary transmission, such as a transmission for an automobile or a truck. The auxiliary transmission comprises an input shaft, an output shaft, and a housing. The auxiliary transmission also comprises a planetary transmission connected with the shafts, and a sleeve connected with the planetary transmission. The auxiliary transmission also comprises an electromechanical actuator having a cammed surface, the actuator in rotatable contact with the sleeve and fixed to the housing. The auxiliary transmission has a first gear ratio when the sleeve rotates and a second gear ratio when the electromechanical actuator is engaged and prevents rotation of the sleeve. 
     Another aspect of the invention is an actuator, the actuator comprising an inner race for connecting with a first drive and an outer race for connecting with a second drive. The actuator further comprises a cage and a plurality of roller elements, the cage between the inner and outer races. At least one of an inner surface of the outer race and an outer surface of the inner race is a cammed surface. Another aspect of the invention is a two-speed transmission. The two-speed transmission comprises an input shaft and an output shaft, and a planetary transmission connecting the input shaft and the output shaft. The two-speed transmission also comprises an electromechanical actuator having a cammed surface and an engagement device for rotating a portion of the electromechanical actuator. The transmission has a first output ratio when the electromechanical actuator is in a first position and has a second output ratio when the electromechanical actuator is in a second position. 
     The electromechanical actuator of the present invention is bi-directional, that is, it may be operated with a mating shaft in either a clockwise or counter-clockwise direction of rotation. These and many other aspects and advantages of the invention will be seen in the figures and preferred embodiments of the invention described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a diagrammatic representation of a prior art two-speed transmission. 
         FIG. 2  is a cross-sectional view of a prior art clutch mechanism. 
         FIG. 3  is a cross-sectional view of an electromechanical actuator according to the present invention. 
         FIG. 4  is a schematic diagram of an application of the electromechanical actuator of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of an auxiliary transmission using an embodiment of an electromechanical actuator. 
         FIG. 6  is a schematic view of a three-speed transmission using embodiments of an electromechanical actuator. 
         FIG. 7  is a plan view of a vehicle using a two speed transmission. 
         FIG. 8  is a cross-sectional view of an embodiment of a two-speed transmission having two electromechanical actuators. 
         FIG. 9  is an exploded perspective view of a portion of the electromechanical actuator. 
         FIGS. 10–11  are cross sectional views of the inner and outer races. 
         FIGS. 12–13  are cross-sectional views of embodiments of two-speed transmissions using two of the electromechanical actuators of  FIG. 9 . 
         FIG. 14  is a cross-sectional view of a two-speed transmission using a single electromechanical actuator to shift gear ratios. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 3  is an embodiment of an electromechanical actuator  32  according to the present invention. The electromechanical actuator comprises an electric solenoid  33  mounted to housing  35 . Roller elements  31  are contained within the housing. The roller elements roll between the housing and an inner ring  38 , split along its length, so that the ring may be expanded or contracted by forces acting on the edges of the split. The electromechanical actuator acts on a shaft  39  that rotates within the split ring. When a user wishes to stop or prevent rotation of the shaft, the user actuates solenoid  33 . The solenoid then plunges plunger  34  into the split ring  38  between roller elements  31 . The plunger forces ring  38  to engage the rotating shaft  39 , stopping the shaft if it had been rotating, or preventing rotation if the shaft was already stopped. The inner surface of the housing may have a cammed profile of slightly raised surfaces  37 , gently radiused with a radius of curvature at least slightly greater than the radius of the roller elements. These raised surfaces, or arcuate surfaces, gently urge the roller elements radially inward in a circumferential motion, and thus contribute to engaging and stopping the shaft when it is rotating. Other radii of curvature may be used or added for the cammed profile on split ring  38 . This electromechanical actuator may be used in conjunction with any desired shaft. 
     One application is pictured in  FIG. 4 , in which the electromechanical actuator  32  is used as a parking brake for axle half-shafts  36 . An auto has a transaxle  40  with half-shafts  36  to provide power to wheels  44 . The electromechanical actuator  32  may be mounted to a non-rotating axle housing  41 . During normal operation, the electromechanical actuator is not engaged, and the transaxle provides power to the wheels  44 . When the car is parked, and the operator desires to engage a parking brake, the operator actuates the solenoid of electromechanical actuator  32 . Plunger  34  causes interference of half-shaft  36  with the split ring  38  of the electromechanical actuator, and the auto is prevented from rolling. 
     The illustration is for an auto with a transaxle and two-wheel front drive, but the electromechanical actuator is usable also for rear wheels of a rearwheel drive car having a differential. The actuator housing should be mounted to a structure that does not rotate, in order to react the load upon a structure that does not move relative to the actuator housing. Instead of a solenoid-type actuator, other electro-mechanical devices may be used in embodiments of the present invention, such as a ballscrew, a ball-and-ramp device, and a cone friction clutch. 
     The electromechanical actuator may be used in transmission applications, such as auxiliary transmissions and multi-speed transmissions.  FIG. 5  depicts a cross-section of an auxiliary transmission  45  using the electromechanical actuator  69 . Auxiliary transmission  45  includes a first housing portion  47  and a second housing portion  51 . The auxiliary transmission includes an input shaft  49 , such as from an engine or a primary transmission of a motor vehicle or truck. Output shaft  50  typically transmits power to a differential or other power transmitter of the vehicle or truck. Input shaft  49  is fixedly connected to ring gear  42  that meshes with planetary transmission  57 , and planet gears  59 . Planet gears  59  rotate on planet pins  61 . In one embodiment, there are four planet gears  59  rotating on four pins  61 . The pins are supported by carriers  58  and  63 . Planet pin  58  has an internal spline  60  and planet pin  63  has an internal spline or gear  66 . The shafts and carriers in turn are mounted on anti-friction bearings  67  supported by housing  47  or  51  or housing portion  62 . 
     Output shaft  50  mounts to housing portion  51  by bearing  67  on one end and has external splined gear  53  at the opposite end meshing with internal spline  60  from carrier  58 . Sleeve  52  mounts concentric to output shaft  50  and has external spline  55  for meshing with planetary gears  59 . The spline  55  acts as a sun gear in the planetary transmission  57 . Sleeve  52  also has a second splined gear  64  for meshing with internal spline  66  of carrier  63 . Electromechanical actuator  69  mounts concentric with and outside sleeve  52 . Electromechanical actuator  69  is preferably mounted fixedly to housing  51  to prevent rotation when engaged with sleeve  52 . The electromechanical actuator includes housing  71 , roller elements  73  and split ring  75  adjacent sleeve  52 . The electromechanical actuator also includes solenoid  77 . Control wires  79  pass through housing  51  via orifice  81 . 
     Operation of the auxiliary transmission and electromechanical actuator are as follows. Input power enters through the input shaft  49  and ring gear  42 . When ring gear  42  rotates, planet gears  59  also rotate. Since there is no restraint on carriers  58  and  63 , they rotate also, and thus spline  60  and sleeve  52  rotate. With spline  60  rotating, the output shaft  50  rotates also. The planetary gears are of no effect, since the entire inner assembly now rotates at the rotational speed of the input shaft, with the exception of the electromechanical actuator and its housing and controls. 
     When the electromechanical actuator is actuated, the split ring clamps onto sleeve  52  and prevents its rotation. Now when the input shaft  49  and ring gear  42  turn, the sleeve  52 , spline  64  and spline/sun gear  55  cannot rotate. The input shaft and its ring gear continue in gear contact with the planets  59 . The planets  59 , their pins  61  and their carriers  58  and  63  now rotate. Planet carrier  58  with internal spline  60  is in gear contact with the output shaft  50  through its external spline  53  at the inside end of the output shaft. In this position, the gear reduction takes place through the action of the ring gear and its pitch diameter relative to the planet gears and sun gear used. In one embodiment, a gear reduction of 1.4:1 is used. Other gear ratios may also be used as desired, such as a speed increase, or overdrive. 
       FIG. 6  depicts another embodiment of the invention, its application to a multi-speed transmission. Driveshaft  88  is attached to a ring gear  92 . Ring gear  92  is concentric with drive shaft  88 . Ring gear  92  meshes with a planetary gear set  94  having single gears and with a planetary gear set  95  having double gear elements. Double planetary gear set  95  has an inner ring contact gear  114  that is rigidly attached to outer gear  116  by shaft  110 . The diameter of the planetary gears in each gear set may be varied along with the number of teeth to alter the gear ratio as desired within the transmission. In this embodiment, planetary gear  116  is shown having a larger diameter and a greater number of teeth than the planetary gear  96 , which in turn has a larger diameter and more teeth than inner planetary gear  114 . 
     Both planetary gear sets  94  and  95  are supported by a common planet carrier  100 . Planet carrier  100  is rigidly attached to and concentrically located about driven shaft  90 . Planetary gear set  94  and planetary gear set  95  are rotatably attached by suitable shaft bearing assemblies  112  and  98  respectively. Rotary movement is transferred to driven output shaft  90  from ring gear  92  through either or both of planetary gear sets  94  and  95 . The transfer of rotation through the planetary gear sets  94  and  95  is determined by the rotational condition of inner and outer sun gears  102  and  118 , respectively, which act as speed control gears. In one preferred embodiment, sun gears  102  and  118  are the same diameter, but they may have different diameters depending on the desired gear ratios. Inner sun gear  102  meshes with the single planetary gear system  94  and is non-rotatably attached to one end of a hollow shaft  104  which is positioned about and concentrically over and is capable of rotation about, driven output shaft  90 . At its opposite end, a clutch disc  115  is attached to shaft  104 . 
     Outer sun gear  118  meshes with outer planetary gear  116  and is also attached to one end of a hollow shaft  108 . Shaft  108  is positioned concentrically over shaft  104  for rotation about shaft  104 . At an end opposite sun gear  118 , a rotor  117  is non-rotatably attached to shaft  108 . Rotor  117  also has a clutch caliper  119  for engaging clutch disk  115 . An electromechanical actuator, such as cone friction clutch  105 , according to the present invention is positioned over and concentric with shaft  104  and another electromechanical actuator, cone friction clutch  106  is positioned concentric with and over shaft  108 . The clutch and electromechanical actuators  105  and  106  are used to control the rotation of the sun gears  102  and  118  and effect speed changes within the transmission. 
     When the clutch is engaged, the transmission is in direct drive, with the speed of rotation of the output shaft equaling the speed of rotation of the input shaft. With the clutch engaged, all elements of the transmission that rotate move in unison, with all shafts and planetaries rotating. Therefore, the output rotational speed will equal the input rotational speed. To engage a first underdrive of the transmission, the clutch is released and electromagnetic actuator  106  is engaged. With actuator  106  engaged, shaft  108  cannot turn and sun gear  118  is fixed in position. Therefore, when ring gear  92  turns, planetary gear set  95  rotates about sun gear  118 . Rotation of planetary gear set  95  causes rotation of planet carrier  100  and also rotation of output shaft  90 . Shaft  104  and sun gear  102  are free to rotate, and they rotate idly along with planetary gear set  94 . The speed of the output shaft  90  is set by the ratios of the gear pitch diameters of ring gear  92 , inner planet gear  114 , outer planet gear  116 , and outer sun gear  118 . 
     A second underdrive speed is obtained by releasing electromagnetic actuator  106  and engaging only electromagnetic actuator  105 . With electromagnetic actuator  105  engaged, shaft  104  and inner sun gear  102  cannot rotate. As ring gear  92  rotates, single planetary gear set  94  rotates about sun gear  102 , which causes planet carrier  100  and output shaft  90  to rotate. Outer sun gear  118  revolves idly, as does double planetary gear set  95 . The speed of the output shaft  90  is set by the ratios of the diameters of ring gear  92 , planet gear  96 , and inner sun gear  102 . As is well known in the art, the same gears may be used in a reversing fashion to achieve an overdrive transmission by reversing the functions of the input and output shafts. In this case, a first overdrive may be obtained by actuating only electromagnetic actuator  106  and a second overdrive may be obtained by engaging only electromagnetic actuator  105 . 
       FIG. 7  is a plan view of an application using a two speed transmission  121 . A motor vehicle  120 , such as an automobile or truck, comprises an engine  122  and a transmission  124  mounted on a frame  126 . A first drive shaft  128  transmits power from the transmission to an auxiliary transmission  121 . The first drive shaft may function as an input shaft to the auxiliary transmission  121 . A second drive shaft  132  carries power from the auxiliary transmission  121  to a rear differential  138  and then to wheel shafts or halfaxles  139  to power the rear wheels of the vehicle. The drive shafts may be connected to the auxiliary transmission by U-joints  134  or other joints. The auxiliary transmission  121  may be a transmission according to the embodiment of  FIG. 5 , or may be a simpler, 2-speed version of the embodiment of  FIG. 6 . Control wires from the auxiliary transmission may be routed to an electronic control unit  136 , where a switch or other control is available to the operator of the vehicle. 
     A detailed view of a two-speed auxiliary transmission  130  is depicted in  FIG. 8 . Two-speed auxiliary transmission  130  includes a flange gear  141  and input shaft  142  having a extension  143 . The transmission may also have a sun gear  145  and bushing  144 . The output from the transmission includes ring gear  147  and output shaft  148  with axle pinion gear  149 . A planetary transmission  150  within the two-speed transmission  130  includes sun gear  145 , planet gears  153 , planet pins  155  and carrier  157 . The sun gear also has an extension  151  for mounting to electromechanical actuators  165  and  170 . Extension  143  is fixedly linked to carrier  157 . 
     In this embodiment, actuator  165  acts as an idler, while actuator  170  acts to shift the two-speed transmission from one gear ratio to another when an operator of the vehicle desires. The outer race of actuator  170  is in fixed contact with the housing  160 , while its inner race is in rotatable contact with the gear extension  151 . The outer race of actuator  165  is in fixed contact with carrier  157 , while its inner race is in rotatable contact with sun gear extension  151 . In this embodiment, the two-speed transmission may be operated in straight-through mode or in under-drive mode. Other embodiments may have straight-through and an over-drive mode. In straight-through mode, actuator  170  does not engage, and sun gear  145  and sun gear extension  151  rotate. Input torque from input shaft  142  drives the sun gear  145 , causing the sun gear  145  and extension  151  to rotate at the input shaft speed. Extension  143 , tied to planet carriers  157 , also rotates, and therefore the planetary transmission  150  as a whole also rotates. Ring gear  147  rotates at the same speed as the input shaft, as does output shaft  148  and axle pinion gear  149 . 
     An underdrive mode may be used if the planetary transmission  150  has been designed and constructed by selection of ring gear  147  and planet gears  153  so that their input/output ratios will be some desired ratio, such as 1.4:1, that is, 1 output revolution per 1.4 input revolutions, for an underdrive mode. To utilize the underdrive mode, an operator or controller actuates electromechanical actuator  170  to engage. The cage of actuator  170  rotates through a portion of a revolution, locking the inner race to the outer race through roller bearing elements, and preventing rotation of sun gear extension  151  and therefore preventing rotation of sun gear  145 . When the input shaft  142  turns, sun gear extension  151  cannot rotate, nor can sun gear  145 . Extension  143  rotates at the speed of the input shaft  142 , as does carrier  157 . This causes the planet gears  153  of the planetary transmission to rotate about the sun gear. The ring gear rotates as driven by the planet gears, driving the output shaft  148  and axle pinion gear  149  at a desired underdrive ratio, such as 1.4:1. Thus, the operator of the vehicle can select a straight-through or an underdrive mode of operation. 
     Details of the electromechanical actuator  170  are shown in  FIG. 9 . The actuator includes an inner race  171 , a plurality of roller elements  175 , a cage  176 , and an outer race  179 . The inner race  171  may be splined on its inner surface or otherwise designed to mate with a shaft or rotating member, such as sun gear extension  151 , or the surface may be smooth. Preferably, arcuate, cammed surfaces can exist on the inner circumference of outer race  179 , or the inner circumference of inner race  171  may have arcuate, cammed surfaces. The outer circumference of inner race  171  may comprise a plurality of arcuate surfaces  179  to match roller elements  175 , or the outer circumference may be smooth as shown. The inner race may also include a split  173  and a notch  174  for engaging a matching tab  177  on cage  176 . Cage  176  also includes a plurality of isolating members or fingers  178  for separating roller elements  175 . There may be two counter opposing return springs  169  (or two pair of return springs) held within cage  176  at 180° positions, for centering the inner and outer races and the cage in a neutrallycentered, free-wheeling position. A cross-sectional view of the inner race  171  is shown in  FIG. 10 , and a cross-sectional view of the outer race is shown in  FIG. 11 . 
     Cage  176  is preferably molded from a strong, relatively stiff plastic material having wear-resistant qualities, or the cage may be molded from powdered metal. The cage includes a plurality of fingers  178  to separate roller elements from each other. The outer circumference may have an engagement feature  172  on a portion of its surface, such as gear teeth for a gear sector. The engagement feature is meant to engage a mechanical device to rotate the cage a few degrees, thus engaging the electromechanical actuator. While cage  170  depicts helical gear sector  172 , other features that may be used to interface a mechanical device include a splined or cammed surface on the outer circumference of cage  176 . 
     As depicted in  FIG. 10 , the inner race  171  has a smooth outer circumference  103  and a smooth inner circumference  113 , and also has a split  173  and a notch  174 . The split allows the inner race to expand slightly in a radial direction. However, the split also tends to interfere with desirable roundness of the inner race. This interference may take place both during operation and during manufacture of the inner race itself, since it is very difficult to hold roundness tolerances on a part that has been split. Therefore, the split feature should be placed on the inner ring in one of the later steps used to manufacture the race. The split may be placed by any convenient method of manufacture, such as machining, laser cutting, or water-jet cutting. The split should also be narrow, desirably from 0.001 to 0.020 inches in width, preferably from about 0.005 to about 0.010 inches. The split should also be as short as possible in length, to minimize distortion after the split has been made. One way to minimize work hardening is to leave the inner surface smooth, rather than adding cammed or arcuate surfaces, which also add distortion. The split need not be co-located circumferentially with the notch, but may be placed there, as shown in  FIG. 9 , for convenience. The inner race  171  also preferably has a lubrication pattern imprinted or placed onto its inner circumference  113 , for interfacing with other parts. The lubrication pattern may be small, grooved pattern for retaining small amounts of oil on the surface, such as a series of axial grooves. 
       FIG. 11  depicts a cross-sectional view of outer race  179 . The outer circumference may have a spline  107  for interfacing to another element of the transmission, such as a housing. The inner circumference may have stops  182  to react leaf or compression springs  169  and maintain a preload on the cage and thus the actuator. The remainder of the inner circumference may include a plurality of relatively smooth surfaces  111  interrupted by raised surfaces  109  to separate the roller elements  175 . The raised surfaces also act as cammed surfaces. When the cage is rotated a few degrees, the fingers force the roller elements against raised surfaces  109 , thrusting the bearings radially inward and causing an engagement and lock-up between the inner and outer races. The corner radius of the raised surfaces with the inner circumference of the outer race is desirably at least somewhat larger than the radius of the roller bearing elements  175 , ensuring that the roller elements will be free to translate circumferentially and to rotate. Thus, the electromechanical actuator is engaged by rotating the cage and causing engagement between the inner and outer races. 
     The inner race  171  may be machined from barstock or preferably made from a powdered metal. If it is made from powdered metal, the notch and split may be molded in and distortion minimized during manufacture. The cage  176  is made from metal or preferably from an engineering plastic. The engineering plastics preferably include reinforced or unreinforced nylon, phenolic, or other high-performance engineering plastics. Cages may be made from thermoplastic or thermoset materials, and processes used to make them may include injection molding, compression molding, and other plastics processes. Manufacturing and machining processes for the inner and outer races, and the roller elements, are meant to include any sort process for shaping material, including but not limited to, casting, molding, forging, and machining processes. Other manufacturing processes using in making the components of the electromechanical actuator include turning, broaching, grinding, shaping, machining and honing. Net-shape or near-net shape processes, such as powder metal compaction and sintering processes, are also included in this definition of manufacturing processes. 
     Other embodiments may include a variety of devices for releasably engaging the sun gear extension with a housing of the two-speed transmission. These devices are used in automotive differentials, and include friction cone clutches, ball-and-ramp devices, and solenoids.  FIG. 12  illustrates an auxiliary transmission using a ball and ramp device for engaging the electromechanical actuator. In  FIG. 12 , the two-speed transmission works in the same manner as that described above for  FIG. 8 .  FIG. 13  depicts a solenoid for releasably engaging the transmission. 
       FIG. 12  is another embodiment of a two speed transmission  140  with an idling electromechanical actuator  180  and a second electromechanical actuator  180  in operable contact with a ball-and-ramp device  185 . The electromechanical actuators have inner races  192   a ,  192   b , cages  194   a ,  194   b , and outer races  196   a ,  196   b , along with other internal parts, such as roller elements and springs, as previously described. The inner races  192   a ,  192   b  are in rotatable contact with the sun gear extension  151 , while outer race  196   b  is in fixed contact with the housing  160  and outer race  196   a  is in rotatable contact with carrier  157 . The ball and ramp device  185  may include a rotor  181  and a stator  183 . With respect to the second electromechanical actuator  180 , upon command, rotor  181  may rotate to cause cage  194   b  to rotate engaging inner race  192   b  and outer race  196   b . Since outer race  196   b  is splined or otherwise grounded to housing  160 , inner race  192   b , cage  194   b , and outer race  196   b  are unable to rotate. Thus, sun gear extension  151  and therefore sun gear  145  are also unable to rotate. With the sun gear stationary, the planetary gear system operates as described previously, including planets  153  and ring gear  147 . 
       FIG. 13  depicts another embodiment of a two-speed transmission  190  having two electromechanical actuators  195 ,  197 . In this embodiment, first electromechanical actuator  195  is an electromechanical actuator as previously described, while second actuator  197  includes a solenoid  199 . The first and second actuator have inner races  192   a ,  192   b , cages  194   a ,  194   b , and outer races  196   a ,  196   b , along with other parts as previously described. The solenoid  199  comprises a plunger  191  in a rotating track and coil  193 . Electric power to the solenoid is provided via slip rings (not shown). Upon actuation, the coil  193  may drive the plunger  191  and rotate it a short angle so that cage  194   b  causes engagement of inner race  192   b  with outer race  196   b  of electromechanical actuator  197  through roller elements  175 . As previously described for  FIGS. 8 and 12 , this causes the sun gear extension  151  and sun gear  145  to cease rotating, engaging the two speed transmission and placing the transmission into underdrive. 
     Another embodiment uses a single electromechanical actuator in a two speed auxiliary transmission.  FIG. 14  depicts a two-speed transmission  200  with a single electromechanical actuator  210  and a planetary transmission  220  within housing  206 . In this embodiment, there is a flange gear  201  and a drive shaft  202  with drive shaft extension  203 , sun gear  204  and sun gear extension  205 . The electromechanical actuator  210  may include an inner race  216  in splined connection with sun gear  204  and sun gear extension  205 , and may also include cage  218  and outer race  219 . Not visible are the internal components, included roller elements, springs and the like, as previously described. This embodiment features a ballscrew  223  driving cage  218  and rotating the cage through an angle of a few degrees in response to controller  225 . Upon a signal from controller  225 , the ballscrew  223  may rotate the cage  218 , causing inner race  216  to lock up with outer race  219 , which is grounded to housing  206 . This prevents the sun gear  204  and sun gear extension  205  from rotating. Drive shaft  202  and extension  203  continue to rotate, as does planet carrier  208 . Planet gears  211  rotate about the sun gear  204  on planet pins  215 . The output of the planetary transmission  220  is taken through ring gear  207 , driven by the planet gears, and axle pinion gear  209 . The ratio between the input speed and the output speed of the transmission is set by the ratio of the planet gears  211  to the ring gear  207  in the planetary transmission. The electromechanical actuator  210  may use any other device that is convenient to rotate the cage and engage the electromechanical actuator, such as a ball-and-ramp mechanism or a solenoid, to engage the housing and thus the planetary transmission. 
     It is therefore intended that the foregoing description illustrates rather than limits this invention, and that it is the following claims, including all equivalents, which define this invention. Of course, it should be understood that a wide range of changes and modifications may be made to the embodiments and preferences described above. For instance, an overdrive speed range may be used as well as an under-drive range. Accordingly, it is the intention of the applicants to protect all variations and modifications within the valid scope of the present invention. It is intended that the invention be defined by the following claims, including all of the equivalents thereto.