Abstract:
A torque-transmitting assembly is provided that includes a dog clutch isolated by a device such as a rotary hydrostatic damper from relative loading on the torque input member and torque output member that it is to connect for common rotation and torque transmission. Although its use is not limited to electrically-variable transmissions, the torque transmitting assembly is able to function even with the large inertia and potentially random torque inputs associated with theses types of transmissions.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a torque-transmitting assembly with a dog clutch and a hydrostatic damper that may be used in an electrically variable transmission to transmit torque. 
       BACKGROUND OF THE INVENTION 
       [0002]    A dog clutch is engaged to transmit torque by moving two sets of teeth together to intermesh with one another. A dog clutch may be engaged in a random combination of positions as both sets of teeth circumscribe two rotating shafts that are to be brought together for common rotation by engagement of the clutch. If the teeth are not closely set, there will be a significant amount of uncontrolled motion in the clutch when it is engaged, creating noise in a drivetrain utilizing the clutch. Therefore, in order to minimize the amount of uncontrolled motion when the dog clutch is engaged, the two sets of teeth should be closely set relative to one another when the dog clutch is engaged. This requires that the two sides of the dog clutch be very nearly aligned with one another and therefore synchronized, i.e., turning at the same speed, for engagement to be successful. 
         [0003]    Manual transmissions typically have a plate clutch that releases the transmission input shaft from the engine when disengaged. A dog clutch with one side (i.e., one of the sets of teeth) connected to the transmission input shaft then has only a few components connected thereto, and therefore a relatively small amount of inertia and resistance to rotational movement. This allows a synchronizer to be employed to synchronize that side of the dog clutch to rotate at the same speed as the other side of the dog clutch, allowing for smooth and reliable engagement of the dog clutch. 
         [0004]    The implementation of dog clutches in other types of transmissions, such as electrically-variable transmissions, has thus far been prevented because relatively heavy components, such as a motor/generator with its relatively large inertia, would be connected to either side of the dog clutch. Additionally, in a vehicle with an electrically-variable transmission, the side of the dog clutch operatively connected to the wheels on a vehicle would sometime be subjected to strong random torque inputs when the vehicle is riding over a bumpy surface. Typical synchronizers would not be able to synchronize the speeds of both sides of the dog clutch under such conditions. 
       SUMMARY OF THE INVENTION 
       [0005]    A torque-transmitting assembly is provided that includes a dog clutch isolated by a rotary hydrostatic damper from relative loading on a torque input member and a torque output member that it connects for common rotation and torque transmission. Although its use is not limited to electrically-variable transmissions, the torque transmitting assembly is able to function even with the large inertia and potentially random torque inputs associated with theses types of transmissions. 
         [0006]    More specifically, the torque-transmitting assembly includes a selectively engagable dog clutch in series with a rotary hydrostatic damper. The dog clutch has first and second rotatable components that are selectively engagable with one another to transmit torque from a torque input member to a torque output member. The hydrostatic damper is operatively connected mechanically in series with the dog clutch between the torque input member and the torque output member (i.e., on one side of the dog clutch). The damper dampens random torque inputs to provide a variable resistance to relative rotation of the first and second components of the dog clutch. That is, the resistance to engagement of the dog clutch is dependent only on the damper, and is preferably unaffected by loading of the torque input and output members. 
         [0007]    In one embodiment, the hydrostatic damper has two rotatable members that are relatively rotatable with respect to one another over a range of less than one rotation (e.g., approximately 180 degrees). Preferably, hydrostatic fluid between the two rotatable members may be varied in volume to control the resistance to relative rotation of the members. It is also preferable that a spring is connected between the two members to urge them to a substantially centered orientation within the range of permitted relative rotation, so that equal rotation in either direction will be possible in response to a random torque component. 
         [0008]    Within the scope of the invention, a synchronizer may be utilized between the two rotatable components of the dog clutch to synchronize these components of the dog clutch prior to engagement of the dog clutch teeth. Specifically, the synchronizer has a cone and blocking teeth, and is alignable for common rotation with the first rotatable component when the cone causes the synchronizer to rotate at the same speed as the second rotatable member of the dog clutch to which it is axially adjacent. In this state, the blocking teeth are aligned with the first set of dog clutch teeth, which are internal teeth on the first rotatable component. The first rotatable component of the dog clutch with the first set of dog clutch teeth thereon are thus blocked from engagement with the second set of teeth at this point, until a spring biases the first rotatable component and the synchronizer to a slightly rotated position relative to one another in which the blocking teeth are out of the way of the first set of teeth (i.e., blocking teeth are no longer aligned with the first set of teeth). The first rotatable component may then continue to move axially toward the second rotatable component, under the control of a controller, while maintaining engagement with the second rotating member of the damper, so that the first set of teeth engage with the second set of teeth. 
         [0009]    In another embodiment, the controllable rotary hydrostatic damper partially defines a cavity housing a variable displacement pump. The pump is connected for rotation with the torque input member. The damper is expandable by increasing hydraulic pressure to axially displace the first rotatable component of the dog clutch into engagement with the second rotatable component of the dog clutch, thereby transferring torque from the torque input member to the torque output member. Pumped fluid within the damper dampens any random torque inputs, allowing for a relatively smooth and reliable engagement. The damper is at a minimum volume when the dog clutch is disengaged, so its resistance to rotation is also at a minimum, allowing the two sets of teeth to align and the dog clutch to close. As the dog clutch engages, the damper volume and resistance to rotation increase. 
         [0010]    The torque-transmitting assembly may be used in an electrically-variable transmission between a transmission input member and a transmission output member. The dog clutch may be engaged to change an operating mode of the transmission, preferably with the engagement not being dependent on loading of the transmission input member and output member due to the damping function of a device such as a hydrostatic damper as described above. (As used herein, a “mode” or an “operating mode” is a particular operating state, whether encompassing a continuous range of speed ratios or only a fixed speed ratio, achieved by engagement of a particular torque-transmitting mechanism or torque-transmitting mechanisms.) The shift may be from an input-split mode to a compound-split mode. Preferably, a friction-based torque-transmitting mechanism is released when the dog clutch is engaged to shift between the two operating modes. 
         [0011]    In one embodiment, the electrically-variable transmission has two motor/generators and two differential gear sets, which are preferably planetary gear sets, each having first, second and third members. The transmission input member is continuously connected for common rotation with the first member of the first planetary gear set. The second member of the first planetary gear set and the first member of the second planetary gear set are connected for common rotation with the transmission output member. The first motor/generator is connected for common rotation with the third member of the first planetary gear set. The second motor/generator is conneceted for common rotation with the second member of the second planetary gear set. A friction brake is selectively engagable to ground the third member of the second planetary gear set to a stationary member, thereby establishing an input-split mode of operation. The dog clutch is selectively engagable to connect the third member of the first planetary gear set for common rotation with the third member of the second planetary gear set, thereby establishing a compound-split mode of operation. 
         [0012]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic cross-sectional illustration of an electrically variable transmission including a torque-transmitting assembly with a rotary hydrostatic damper and a dog clutch; 
           [0014]      FIG. 2  is a perspective exploded view of the torque-transmitting assembly used in the electrically-variable transmission of  FIG. 1 ; and 
           [0015]      FIG. 3  is a perspective exploded view of an alternative embodiment of a torque-transmitting assembly that may be used in the electrically-variable transmission of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows an electrically-variable transmission  10  with a transmission input member  12  and a transmission output member  14 . The transmission  10  includes a transmission gearing arrangement  16 . The transmission gearing arrangement has first and second differential gear sets, which in this embodiment are planetary gear sets  20 ,  30 . The planetary gear set  20  includes a sun gear member  22 , a ring gear member  24  and a carrier member  26  that rotatably supports planet gears  28  that intermesh with both the sun gear member  22  and the ring gear member  24 . The second planetary gear set  30  includes a sun gear member  32 , a ring gear member  34  and a carrier member  36  that rotatably supports planet gears  38  that intermesh with both the sun gear member  32  and the ring gear member  34 . 
         [0017]    The transmission  10  further includes a first motor/generator  40 A and a second motor/generator  40 B. The first motor/generator  40 A includes a rotor  42 A that is operatively connected for common rotation with the sun gear member  22  via a sleeve shaft  44 A and a stator  46 A that is grounded to a stationary member  48 , such as a housing or casing of the transmission  10 . The second motor/generator  40 B includes a rotor  42 B that is operatively connected for common rotation with the sun gear member  32  via a sleeve shaft  44 B and a stator  46 B that is grounded to the stationary member  48 . 
         [0018]    The transmission input member  12  is connected for common rotation with the ring gear member  24 . The carrier member  26  is connected for common rotation with the carrier member  36  via hubs  47  and  50  as well as intermediate shaft  52 . The intermediate shaft  52  rotates commonly with, and may be integral with the transmission output member  14 . 
         [0019]    The transmission  10  has two selectively engagable torque-transmitting mechanisms. The first is a torque-transmitting assembly  56  that has a dog clutch  58  in series with a rotary hydrostatic damper  60 . The second is a friction-based torque-transmitting mechanism, brake  62 , selectively engagable to ground the ring gear member  34  to the stationary member  48 . (A friction-based rotary clutch could be used within the scope of the invention, but a brake is preferred, for the reasons set forth below.) The use of a friction brake  62  and a dog clutch  58  increases the efficiency of the electrically-variable transmission  10 , as both of these torque-transmitting mechanisms may be engaged with relatively low power and losses in comparison with rotating friction clutches. Rotating friction clutches typically require either a strong spring and throw out bearing, such as on a manual transmission, or a rotating hydraulic seal and a high pressure oil supply, such as on an automatic transmission, both of which have high associated energy losses due to increased friction and the need for pumping power, respectively. The dog clutch  58  requires only a low pressure oil to actuate, (either by piston or fork, as described in the embodiments below) and low pressure oil is already necessary in the electrically variable transmission to lubricate the gears in the transmission gearing arrangement  16 . 
         [0020]    A controller  64  controls power flow between an electric storage device  66  (such as a battery) and the respective motor/generators  40 A,  40 B to control their respective functioning as a motor or as a generator, as is understood by those skilled in the art. The controller  64  also controls the torque-transmitting assembly  56  to selectively engage the dog clutch  58 , as will be discussed in greater detail below. Specifically, the controller  64  controls the torque-transmitting assembly  56  to cause axial motion of a rotatable component  70  of the dog clutch  58 , causing a set of teeth  74  on the first rotatable component  70  (the first set of teeth) to engage with a set of teeth  76  on a second rotatable component  72  (the second set of teeth) of the dog clutch  58 . In this embodiment, a synchronizer  95  with blocking teeth  93  allows for smooth engagement of the dog clutch  58 , as will be described in more detail with respect to  FIG. 2 . The first rotatable component  70  is annular, as illustrated in  FIG. 2 . However, in  FIG. 1 , the cross-sectional view of the first rotatable component, a top section is shown representing a disengaged position in which the first rotatable component is referred to as  70 , while a bottom section is shown representing an alternate engaged position, in which the first rotatable component is referred to as  70 A. Thus, to engage, the first rotatable component  70  moves in the direction of arrow A, while to disengage the first rotatable component  70 A moves in the direction of arrow B. It should be appreciated that the entire first rotatable component is either in the engaged position (represented by  70 A) or the disengaged position (represented by  70 ), and the top and bottom sections are not independently movable with respect to one another. 
         [0021]    Those skilled in the art will readily recognize that engagement of the friction brake  62  while the dog clutch  58  remains disengaged establishes an input-split mode of operation. Disengaging the friction brake  62  and engaging the dog clutch  58  shifts from the input-split mode of operation to a compound-split mode of operation. By utilizing the torque-transmitting assembly  56 , as more specifically described with respect to  FIG. 2 , or the alternative torque-transmitting assembly  156  described with respect to  FIG. 3 , the shift from the input-split mode to the compound-split mode can be synchronous, as the hydrostatic damper  60  is able to dampen random differences in speed between a sleeve shaft  44 A and a sleeve shaft  44 B (which may be considered the torque input member and the torque output member, in either order) of the torque-transmitting assembly  56 . The load (i.e., torque) differentials or random differences in speeds experienced by the respective sleeve shafts  44 A,  44 B correspond with random load differentials experienced by the transmission input member  12  and the transmission output member  14 . By isolating the load and/or speed differentials in the hydrostatic damper  60 , the sets of teeth  74 ,  76  of the dog clutch  58  may be engaged due to axial motion of the first rotatable component  70  (indicated by arrow A in  FIG. 1 ), with relatively little resistance to engagement even though the resistance to relative rotation of the shafts  44 A and  71  (which rotates commonly with second rotatable component  72 ) may be high, as the transmission  10  may be relatively stiff (dynamically) in torsion. 
         [0022]    Referring now to  FIG. 2 , the torque-transmitting assembly  56  of  FIG. 1  is shown in greater detail. The damper  60  has a first rotatable member  80  that rotates commonly with the sleeve shaft  44 A. A pair of external vanes  82  extends in a common plane from the first rotatable member  80 , intersecting an axis of rotation C of the sleeve shaft  44 A. The damper  60  further includes a second rotatable member  84  through which the sleeve shaft  44 A extends. A centering torsion spring  86  connects at one end to the second rotatable member  84  and at another end through the sleeve shaft  44 A. A pair of opposed internal vanes  88  extend inward into a hollow center of the second rotatable member  84 . The spring  86  mounts the second rotatable member  84  to the sleeve shaft  44 A and is pretensioned to urge the second rotatable member  84  into the substantially centered orientation shown with respect to the first rotatable member  80 , in which the vanes  82  and  88  are roughly perpendicular, allowing relative rotation of the second rotatable member  84  with respect to the first rotatable member  80  in approximately ninety degrees in either direction over a total range of approximately one hundred-eighty degrees. 
         [0023]    The torque-transmitting assembly  56  includes a synchronizer  95  that has external blocking teeth  93  and a cone  91 . The cone  91  is adjacent a cavity  92  in the second rotatable component  72  that is configured to receive the cone  91 . The first rotatable component  70  (which may be referred to as a collar) includes the first set of teeth  74 , which are internal teeth continuously engaged with external teeth  94  on the second rotatable member  84  of the damper  60 . A groove  90  in the first rotatable component  70  receives a fork (not shown) that is moved by a controller (such as controller  64  or  FIG. 1 ) to axially slide the first rotatable component  70  to the right. The axial movement is small enough so that the teeth  74  remain engaged with the teeth  94  and the second rotatable member  84  continues to rotate commonly with the first rotatable component  70 . A controller slides the first rotatable component  70  in this manner when the synchronizer cone  91  (and the first rotatable component  70 ) are turning at the same speed as the second rotatable component  72  of the dog clutch  58 , as indicated by sensors operatively connected with the first and second rotatable members  70 ,  72  of the dog clutch  58 . 
         [0024]    A first spring  96  has one end held in an opening  97 A in the first rotatable component  70  and another end twisted to lie in a ramped slot  98 A of the synchronizer  95 . Another opening  97 B and ramped slot  98 B similarly receive a second, like spring (not shown). The ramped nature of the slots  98 A and  98 B allow the first spring  96  (and second spring) to be nested in the slots when the first rotatable component  70  moves to the right to engage the second rotatable component  72 . The spring  96  presses the cone  91  into the cavity  92  with a light force to begin to synchronize the speeds of the synchronizer  95  and the second rotatable component  72 . This interaction between the cone  91  and the cavity  92  slightly rotates the synchronizer  95  relative to the first rotatable component  70 , to the extent permitted by the spring  96 , to align the blocking teeth  93  with the internal teeth  74 , thus blocking engagement of the internal teeth  74  with the external teeth  76 . Once the synchronizer  95  and the second rotatable component  72  are rotating at the same speed, the spring force of the spring  96  rotates the synchronizer slightly relative to the first rotatable component  70  to move the blocking teeth out of the way of the internal teeth  74  to allow the first rotatable component to move further axially and the internal teeth  74  to then engage the external teeth  76 . Thus, by controlling the first rotatable component  70  to slide and cause engagement of the dog clutch  58  only when the speeds of the first and second rotatable components  70 ,  72  are the same, synchronized engagement is accomplished, while the one hundred-eighty degree range of motion or “play” between the first and second rotatable members  80 ,  84  of the damper  60  absorbs any small amount of random motion between the two shafts  44 A,  71 . 
         [0025]    Referring to  FIG. 3 , an alternative embodiment of a torque-transmitting assembly  156  is depicted that may be used in place of torque-transmitting assembly  56  in the electrically-variable transmission  10  of  FIG. 1 . The torque-transmitting assembly  156  includes a dog clutch  158  and a variable displacement rotary hydrostatic damper  160  capable of continuous rotation (i.e. without being limited in its angle of rotation) when the dog clutch  158  is disengaged. The dog clutch  158  has a first rotatable component  170  with a first set of teeth  174  that are selectively engagable with a second set of teeth  176  on a second rotatable component  172  of the dog clutch  158 . The second rotatable component  172  rotates commonly with shaft  171 , which would be identical in location to sleeve shaft  71  in the electrically variable transmission  10   FIG. 1 . 
         [0026]    The damper  160  includes a hub  180  connected for rotation with shaft  144 A, which would be identical in location to sleeve shaft  44 A in the electrically-variable transmission  10  of  FIG. 1 . A casing  181  surrounds the hub  180  and is closed on one end by an end cover  183  and on an opposing end by the first rotatable component  170  of the dog clutch  158 . A spacer  187  fits within an eccentric circular or oval cavity  185  formed through the casing  181  and is held in a definite axial position along shaft  144 A by a retaining collar  199 , which is press fit securely onto shaft  144 A but which allows the spacer  187  to rotate freely with respect to the shaft  144 A. The shaft  144 A extends through aligned openings in the end cover  183  and the spacer  187 . A containing ring  189  is free to rotate within a hollowed opening  192  in the first rotatable component  170 . The hollowed opening  192  does not extend completely through the first rotatable component  170 , so that the first rotatable component  170  serves, along with the end cover  183 , to close off the cavity  185  when the torque-transmitting assembly  156  is assembled. 
         [0027]    When the dog clutch  158  is disengaged, spacer  187  is positioned flush with the right end of the casing  181  and the hub  180  is positioned in the containing ring  189  in the hollowed opening  192 , with pump vanes  193  held almost entirely within receiving slots  194  in the containing ring  189 . A small amount of each pump vane  193 , along its left edge, is held within the eccentric or oval cavity  185  in the casing  181 , to hold the pump vane  193  in the correct position for engagement of the dog clutch  158 . This position of the vanes  193  just slightly within the cavity  185 , and with the spacer  187  very close to the containing ring  189 , defines the minimum displacement for the rotary hydraulic damper  160 . In this position, the damper  160  can produce almost no torque, so the first rotatable component  170 , the casing  185 , the spacer  187  and the end cover  183  can rotate almost freely with respect to the containing ring  189 , the pump vanes  193 , the hub  180 , the shaft  144 A, and the retaining collar  199 . 
         [0028]    To engage the dog clutch  158 , oil is fed through an opening  195  in the casing  181 . The oil flows between the right side of the casing  181  and the spacer  187  and the left side of the containing ring  189 , creating hydraulic pressure that moves the containing ring  189 , the first rotatable component  170 , the casing  181  and the end cover  183  to the right with respect to the spacer  187  and the hub  180 , to engage the teeth  174  and  176  of the dog clutch  158 . Thus, the oil drives the containing ring  189  apart from the spacer  187 , expanding oil chambers contained within the cavity  185  of the casing  181  between the spacer  187  and the ring  189 . This axial movement increases the displacement within the expanding oil chambers which are each defined by the hub  180 , the casing  181 , the vanes  193 , the spacer  187  and the ring  189 . Thus, the stiffness of the damper  160  (i.e., its ability to transmit torque), which is dependent on the displacement of the chambers, is integral with the axial movement of the first rotatable component  170  and the attached components (i.e., the containing ring  189 , the casing  181  and the end cover  183 ). These axially-movable components function as a hydraulic piston in response to the rising hydraulic pressure. When the dog clutch  158  is engaged, the casing  181  has moved axially to the right relative to the spacer  187  so that the retaining collar  199  is at the left end of the casing, against the end cover  183  at full engagement. Oil is allowed to escape from this side of the cavity  185  through an opening  197 . To disengage the dog clutch  158 , oil is pumped into opening  197  in the end cover  183  and allowed to escape through opening  195  from among the pump vanes, to easily disengage the clutch  158  by moving end cover  183 , the casing  181 , and the first rotatable component  170  back to the left. Pump vanes  193  are kept in alignment with the cuts in the ring  189  by the relative lengths of the components, so that the vanes  193  are always engaged with the ring  189  by at least a small distance along the axis, even when the clutch is fully engaged. 
         [0029]    It should be appreciated that the torque-transmitting assemblies of  FIGS. 2 and 3  may be used for other torque-transmission purposes than in an electrically-variable transmission and may be used for other electrically-variable transmissions than that depicted in  FIG. 1 . 
         [0030]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.