Abstract:
A transmission shaft is divided into a first shaft portion releasably connectable to a first electric motor/generator via a first gear set and a second shaft portion connected to a second electric motor/generator via a second gear set. The first and second shaft portions are operatively connected to one another for rotation together. The first shaft portion is selectively slidable with respect to the second shaft portion to connect and disconnect the first shaft portion and the first gear set.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application 60/602,976 filed Aug. 19, 2004, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     A clutch operable as an engine disconnect clutch within a transmission system. 
     BACKGROUND OF THE INVENTION 
     The electrically-variable transmission (EVT) has been proposed for vehicles to improve fuel economy and reduce emissions. The EVT splits power between an input shaft and an output shaft into a mechanical power path and an electrical power path by means of differential gearing. The mechanical power path may include clutches and additional gears. The electrical power path may employ two electrical power units, each of which may operate as a motor or as a generator (“motor/generator”). With an electric storage battery, the EVT can be incorporated into a propulsion system for a hybrid electric vehicle. 
     The hybrid vehicle or hybrid propulsion system uses an electrical power source, such as a battery, as well as an engine power source. The battery is connected with the electrical drive units through an electronic control unit (ECU), which distributes the electrical power as required. The ECU also has connections with the engine and vehicle to determine operating characteristics, or operating demand, so that the electrical power units are operated properly as either a motor or a generator. When operating as a generator, an electrical power unit accepts power from either the vehicle or the engine and stores the power in the battery, or provides that power to operate another electrical device or another electrical power unit on the vehicle or on the transmission. 
     One of the benefits of having an electrically-variable transmission incorporating more than one mode of operation is that each mode of operation will generally incorporate at least one mechanical point at which no electrical energy is present in either motor/generator, thereby reducing losses. 
     A power transmission in an electromechanical transmission is described in commonly assigned United States Provisional Application entitled “Electrically Variable Transmission with Selective Fixed Ratio Operation,” U.S. Ser. No. 60/590,427, Holmes et al., filed Jul. 22, 2004 and is hereby incorporated by reference in its entirety. 
     One current issue with gasoline/electric vehicles is their ability to effectively operate in reverse. Previous gasoline/electric vehicles generally operate in reverse in two ways. One method of operating in reverse is to use the electric motor to propel the vehicle in reverse. Since the engine attempts to propel the vehicle forward, the electric motor must overpower the running engine. Such counteraction between the engine and the electric motor causes large losses because only a portion of electric motor power is used to reverse the vehicle. A second method of operating in reverse uses the electric motor to drive the vehicle in reverse while the engine is not running. This method, however, does not permit the vehicle to generate energy while reversing. Thus, it only permits the vehicle to operate in reverse until the battery is depleted or discharged. Once the battery has exhausted all of its energy and is fully discharged the vehicle will not be capable of reversing any further. 
     SUMMARY OF THE INVENTION 
     The invention provides a dog clutch that is operable as an engine/motor disconnect clutch within a hybrid system such as a gasoline/electric transmission system. The clutch is housed on the main shaft of the transmission. The main shaft is divided into a first main shaft portion releasably connected to a first planetary carrier of a first gear set and a second main shaft portion connected to a sun gear of a second gear set and connectable to the first main shaft portion. First and second motors/generators are connected to the first and second gears sets, respectively. The clutch includes a hydraulically actuatable piston slidably located in the input shaft and a spring-biased first main shaft portion juxtaposed with the piston and located on the second main shaft portion. A first planetary carrier or member of the first gear set is releasably engaged with the first main shaft portion, which, through the second main shaft portion, is engaged with a sun gear or member of the second gear set. When the clutch is actuated, pressurized fluid acts on the piston which slides the first main shaft portion against the spring bias to disengage the first gear set from the first main shaft portion and the second main shaft portion and, thus, to disengage the first gear set from the second gear set. Accordingly, since the engine is connected with the first gear set and the second motor/generator is connected with the second gear set, the clutch may disconnect the engine from the second motor/generator, which is particularly advantageous when the vehicle is operating in reverse. 
     The present invention provides a means to propel a gasoline/electric vehicle in reverse in such a way that the engine and motor do not counteract and the vehicle is able to generate storable energy while operating in reverse. 
     More specifically, the present invention provides a clutch adapted for engagement in a transmission having a plurality of gear sets. The clutch comprises an input shaft having at least one fluid inlet for pressurized fluid, a rotatable first main shaft portion being engageable with a first gear set, and a rotatable second main shaft portion having a spring and being engageable with a second gear set. The first main shaft portion is slidably movable with respect to the second main shaft portion and rotatable therewith and is in a bias relationship with the spring for movement in a first direction. A piston is slidably movable for actuating movement of the first main shaft portion. The piston may be in fluid flow communication with sufficiently pressurized fluid at the fluid inlet for movement in a second direction opposite the first direction. The first gear set and the first main shaft portion are relatively engageable and disengageable. The spring biases the first main shaft portion to engage the first gear set when the piston is not in fluid flow communication with sufficiently pressurized fluid at the fluid inlet. Sufficiently pressurized fluid at the fluid inlet forces the piston to disengage the first main shaft portion from the first gear set. When the sufficiently pressurized fluid is depleted at the fluid inlet, the spring biases the first main shaft portion to re-engage the first gear set. 
     The present invention also provides a main shaft adapted for use in an electrically-variable transmission system having a first electrical power unit connected with a first gear set and a second electrical power unit connected with a second gear set. The main shaft comprises a first main shaft portion engageable with a member of the first gear set and a second main shaft portion axially aligned with the first main shaft portion and engaged with a member of the second gear set. The main shaft also comprises a piston axially aligned with the first main shaft portion and the second main shaft portion and axially movable with respect to one of the first and second main shaft portions. The member of the first gear set is engageable with the first main shaft portion, the second main shaft portion, and the member of the second gear set when the piston has axially moved in a first direction. The member of the first gear set is disengageable from the first main shaft portion, the second main shaft portion, and the member of the second gear set when the piston has axially moved in a second direction, opposite the first direction. 
     The present invention further provides a method of selectively engaging and disengaging a main shaft having a first main shaft portion engageable with a first gear set and a second main shaft portion engageable with a second gear set in a transmission. The method comprises slidably engaging the first main shaft portion with the second main shaft portion and biasing the first main shaft portion in a first direction with respect to the second main shaft portion to engage the first main shaft portion with the first gear set. The method further comprises providing sufficiently pressurized fluid to the first main shaft portion to slide the first main shaft portion in a second direction to disengage the first main shaft portion from the first gear set and rebiasing the first main shaft portion in the first direction when the sufficiently pressurized fluid is exhausted. 
     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 DRAWING 
         FIG. 1  is a fragmentary cross-sectional view of an EVT transmission including a clutch in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a clutch  10  in accordance with the present invention for use in combination with and modification of an electrically-variable transmission (EVT)  14 . The clutch  10 , which is shown as a dog clutch, operates coaxially with the transmission main shaft  18 , which may be connected to an engine input shaft portion  22  through a first or input gear set  34  of the hybrid transmission  14 , which receives power from an engine. Input/engine torque is transferred to the transmission main shaft  18  through a damper (not shown), the engine input shaft  22 , and then to the first ring gear  82  of the first gear set  34 . The transmissions main shaft  18  contains a first main shaft portion  54  and a second main shaft portion  26 . The clutch  10  effectively engages and disengages the first planetary carrier  38  of the first gear set  34  with respect to the transmission&#39;s first main shaft portion  54 . 
     Referring to the first gear set  34 , having a plurality of members  38 ,  39 ,  82 ,  86 , the first planetary carrier  38  carries planet gears  86  which are meshingly engaged with a ring gear  82  and sun gear  39 . The first sun gear  39  is connected to a first electrical power unit  40  of the transmission. An electrical power unit may operate as a motor to drive the transmission first sun gear  39  or as a generator to charge a battery. The second main shaft portion  26  is equipped with a spring  42  and is engaged with a second gear set  46  having a plurality of members, including a second member or sun gear  50  which is connected to a second electrical power unit  51 . “Connected” implies that each sun gear  39 ,  50  is connected either indirectly through a rotor hub  52 ,  53  or similar structure, as illustrated in  FIG. 1 , or directly to the electrical power unit  40 ,  51 . The rotor hub structures  52 ,  53  are respectively “wineglass” and “umbrella” shaped as shown and described in commonly-assigned “Transmission Packaging and Rotor Support Structure,” to Klemen et al., U.S. Ser. No. 60/602,983 filed Aug. 19, 2004, which is incorporated herein in its entirety. 
     The first main shaft portion  54  is slidably located on the second main shaft portion  26  in biased relationship with the spring  42 , which biases the first main shaft portion bias is in a first direction. “Slidably” implies that the first main shaft portion  54  is engaged with the second main shaft portion  26  but may move or shuttle axially back and forth along the second main shaft portion  26 . The first main shaft portion  54  may have a plurality of first main shaft portion splines  80  engageable with a plurality of second main shaft portion splines  81 , which allow relative axial movement between the first main shaft portion  54  and the second main shaft portion  26 . The spring  42  may be fixed or stopped at one end to the second main shaft portion  26  by a washer  70 , as illustrated in  FIG. 1 , or by a c-clamp, a spring locator, or any other positive stop or similar device. The second end of the spring  42  is in a biased relationship with the first main shaft portion  54 . A piston  58  is slidably located in the input shaft portion  22 , which has one or more fluid inlets  30 . In a second embodiment of the present invention, which is not illustrated, the piston  58  and the first main shaft portion  54  may comprise a single or unitary structure. Additionally, an apply chamber  84  may be located between the fluid inlet  30  and the piston  58 . The piston  58  is in fluid flow communication with the fluid inlet  30  such that pressurized fluid at the fluid inlet  30  will bias the piston  58  in a second direction, opposite the first direction of the spring  42  bias. 
     An internal first spline  62 , connected to the first planetary carrier  38  of the gear set  34 , is engaged with the external second spline  66  located on the first main shaft portion  54 . When the first main shaft portion  54  is biased in the first direction by the spring  42 , the second spline  66  is engaged with the first spline  62  and, thus, the first planetary carrier  38  is effectively engaged with the second sun gear  50  through the first main shaft portion  54  and the second main shaft portion  26 . When the first planetary carrier  38  is effectively engaged with the second sun gear  50 , the first electrical power unit  40  is effectively engaged with the second electrical power unit  51  through the first or “wineglass-shaped” rotor hub  52 , the first gear set  34 , the first main shaft portion  54 , the second main shaft portion  26 , and the second “umbrella-shaped” rotor hub  53 . The splines  62 ,  66  may be any pair of interconnectable members that provide for engagement and disengagement between the first gear set  34  and the first main shaft portion  54 . 
     When sufficiently pressurized fluid is at the fluid inlet  30 , the piston  58  will be biased in the second direction, opposite the spring bias. Sufficiently pressurized fluid is fluid having a pressure which is large enough to overcome the spring bias so that the piston  58  will slide or shuttle the first main shaft portion  54  in the second direction, compressing the spring  42 . Once the first main shaft portion  54  has slid or shuttled in the second direction, the first or internal spline  62  and the second or external spline  66  disengage. When the splines  62 ,  66  are disengaged, the first electrical power unit  40  and first gear set  34  are disengaged from the first main shaft portion  54  and, thus, from the second main shaft portion  26 , the second gear set  46 , and the second electrical power unit  51 . When the first electrical power unit  40  is disengaged from the second electrical power unit  51 , the first electrical power unit  40  may charge the battery while the second electrical power unit  51  may be controlled by an electronic control unit to operate as a power unit for the transmission&#39;s second main shaft portion  26 . Disengaged dog clutch  10  disconnects the engine (not shown) and first electrical power unit  40  from the second electrical power unit  51  and output member  83 . 
     When the sufficiently pressurized fluid at the fluid inlet  30  is exhausted, the spring  42  will force or rebias the first main shaft portion  54  and the piston  58  back in the first direction, wherein the first spline  62  and the second spline  66  will re-engage, as shown in  FIG. 1 . The re-engagement of the first spline  62  and second spline  66  will re-engage the first electrical power unit  40  and first gear set  34  with the second electrical power unit  51  and second gear set  46  so that both electrical power units  40 ,  51  may be controlled by an electronic control unit to operate as power units for the transmission main shaft  18 . 
     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.