Abstract:
An electrically-variable transmission includes an input shaft, an output shaft, two electric motor/generators, and four nodes between which three parallel power paths are defined. Two of the power paths are mechanical and one of the power paths is electrical. The electric motor generators provide continuously variable speed ratios; manipulation of the power paths at the nodes provides a plurality of continuously variable operating modes for increased efficiency and smaller motor size. The transmission also provides an equal forward/reverse system with an input split.

Description:
TECHNICAL FIELD 
     This invention relates to a transmission that includes four nodes and three parallel power paths, including two mechanical power paths and an electrical power path, between an input shaft and an output shaft. 
     BACKGROUND OF THE INVENTION 
     An electrically-variable transmission (EVT) splits mechanical 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. 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 batteries, as well as an engine power source. The batteries are 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, the electrical power unit accepts power from either the vehicle or the engine and stores 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. 
     There have been a number of electrically-variable transmissions proposed for vehicle operation. Examples of proposed electrically-variable transmissions are shown in U.S. Pat. No. 5,558,589 issued to Schmidt on Sep. 24, 1996, and assigned to the assignee of the present invention; U.S. Pat. No. 6,090,005 issued to Schmidt et al. on Jul. 8, 2000, and assigned to the assignee of the present invention; and U.S. Pat. No. 5,931,757 issued to Schmidt on Aug. 3, 1999, and assigned to the assignee of the present invention. The above-identified U.S. Pat. No. 5,931,757 defines the structure and operation of a variable two-mode, input-split, electro-mechanical transmission for a parallel hybrid electric propulsion system. U.S. Pat. No. 5,558,589 discloses a two-mode, compound-split, electro-mechanical vehicular transmission, and U.S. Pat. No. 5,558,595 issued to Schmidt et al. on Sep. 24, 1996, discloses a one-mode, input-split transmission. These and other patents describe various electrically-variable type transmissions. 
     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 where one of the electrical power units is stationary, thereby reducing the electrical power input and providing a pure mechanical power flow path which is, of course, more efficient than a pure electrical power flow path. 
     Other hybrid type power transmissions are shown in U.S. Pat. No. 5,571,058 issued to Schmidt on Nov. 5, 1996; U.S. Pat. No. 5,577,973 issued to Schmidt on Nov. 26, 1996; U.S. Pat. No. 5,558,173 issued to Sherman on Sep. 24, 1996; and U.S. Pat. No. 5,558,175 issued to Sherman on Sep. 24, 1996, all of which are assigned to the assignee of the present invention. 
     SUMMARY OF THE INVENTION 
     A vehicle transmission is provided. The transmission includes an input member, an output member, a stationary member, four nodes, a first electric motor/generator, a second electric motor/generator, and an energy storage device. A first node is operatively connected to the input member. A rotatable interconnecting member forms a mechanical first power path between the first node and a second node. A rotatable interconnecting member interconnects the first node and a third node. A rotatable interconnecting member interconnects the third node and a fourth node and forms a mechanical second power path parallel to the first power path. A rotatable interconnecting member operatively interconnects the fourth node and the second node. 
     The first motor/generator is operatively connected to the third node, and the second motor/generator is operatively connected to the fourth node. The energy storage device operatively interconnects the first motor/generator and the second motor/generator such that the energy storage device and the first and second motor/generators at least partially form an electrical third power path parallel to the first and second power paths between the third and fourth nodes. 
     The third and fourth nodes, the first and second motor generators, and the energy storage device are substantially similar in design and function to EVTs. The addition of the first and second nodes and the first mechanical power path parallel to an EVT enables the various EVT modes to be reused. Thus, a two-mode EVT may become a four-mode EVT with the addition of the first and second nodes and the first power path. Mechanical points are thus increased compared to the prior art, thereby increasing efficiency and reducing motor torques. Equal forward and reverse performance is also enabled with a simple input split power flow configuration. 
     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 
         FIG. 1  is a schematic illustration of a vehicle transmission according to the invention; 
         FIG. 2  is a graphical representation of the speeds of elements of the transmission of  FIG. 1  in an exemplary operation of the vehicle transmission; 
         FIG. 3  is a schematic illustration of an alternative transmission configuration; 
         FIG. 4  is a graphical representation of the speeds of elements of the transmission of  FIG. 3  in an exemplary operation of the vehicle transmission; 
         FIG. 5  is a schematic illustration of another alternative transmission configuration; and 
         FIG. 6  is a graphical representation of the speeds of elements of the transmission of  FIG. 5  in an exemplary operation of the vehicle transmission. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , the reference numeral  10  generally designates a hybrid electric powertrain including a transmission  11 . The transmission  11  includes a first node  12 , a second node  14 , a third node  16 , and a fourth node  18 . In the context of the present invention, a “node” is a junction of three or more power paths through which power is distributable between or among the power paths. For example, a “node” may receive power from a power path and distribute the power between or among two separate power paths. Similarly, a “node” may receive power from two power paths and transmit the power to a third power path. Examples of devices that may function as nodes include a planetary gearset with a sun, ring, and carrier, a dual path clutch, a differential, a Ravigneaux gearset, etc. Power paths may include input shafts, output shafts, electric motor/generators, rotatable interconnecting members, etc. 
     The first node  12  is operatively connected to an input member, i.e., input shaft  20 , which, in the embodiment depicted, is also the output shaft of engine  22 . Engine  22  may take a variety of different forms, but as explained below, is preferably designed for constant speed operation during forward vehicle motion subsequent to a vehicle launch phase. 
     The first node  12  is a dual path clutch in the embodiment depicted, but may have other configurations within the scope of the claimed invention. For example, the first node  12  may include a reduction planetary gearset. An output member, i.e., output shaft  24 , is operatively connected to the second node  14 , which, in the embodiment depicted, is a compound planetary gearset. Output shaft  24  of transmission  11  is also operatively connected to vehicle drive wheels (not shown). 
     A first rotatable interconnecting member, i.e., shaft  26 , interconnects the first and second nodes  12 ,  14  and forms a mechanical first power path from the input shaft  20  to the output shaft  24 . 
     The third node  16  includes planetary gearset  28 , and the fourth node  18  includes planetary gearset  30 . The transmission  11  also includes first and second electrical machines  32 ,  34 , i.e., electric motor/generators, coupled to the gearsets  28 ,  30 . Electrical machines  32  and  34  are coaxially aligned with the gearsets  28 ,  30  as shown. An electrical storage device, such as battery  36 , is provided for supplying current to machines  32  and/or  34  when operating in a motoring mode, and receiving charging current from machines  32  and/or  34  when operating in a generating mode. An electronic control unit (ECU)  38 , including a microprocessor-based controller and suitable inverter circuitry, couples the battery  36  to machines  32 ,  34 , and controls the same in response to various input signals, including the driver torque request signal (not shown) and the output shaft speed signal (not shown). In a preferred embodiment, the machines  32 ,  34  are configured as induction machines, although other configurations are also possible. Thus, machine  32  is depicted as having a fixed stator  32   a  electrically coupled to ECU  38  and a rotor  32   b  mounted on a sleeve shaft  40 . Similarly, machine  34  is depicted as having a fixed stator  34   a  electrically coupled to ECU  38  and a rotor  34   b  mounted on sleeve shaft  42 . 
     In addition to the planetary gearsets  28 ,  30 , the transmission  11  includes a pair of selectively engageable friction clutches  46 ,  48 . In customary fashion, each planetary gearset  28 ,  30  includes an outer (ring) gear circumscribing an inner (sun) gear, and a plurality of planet gears rotatably mounted on a carrier such that the planet gears meshingly engage both the outer gear and the inner gear. Thus, the gearset  28  includes a ring gear  50 , a sun gear  52 , and a set of planet gears  54  mounted on a carrier  56 ; the gearset  30  includes a ring gear  58 , a sun gear  60 , and a set of planet gears  62  mounted on a carrier  64 . 
     A second interconnecting member  66  interconnects the first node  12  and the ring gear  50 , and in the embodiment depicted the first node  12  provides direct connection of shaft  20  to ring gear  50 . The planet carriers  56  and  64  are interconnected for common rotation with a third interconnecting member, i.e., sleeve  68 . Thus, sleeve  68  interconnects the third node  16  and the fourth node  18 , and provides a mechanical second parallel power path from the input shaft  20  and the output shaft  24 . 
     Sun gear  52  is coupled to the rotor  32   b  of electric machine  32  via sleeve shaft  40 , and the sun gear  60  is coupled to the rotor  34   b  of electric machine  34  via sleeve shaft  42 . Clutch  46  selectively couples the ring gear  58  to a stationary member, i.e., transmission housing  70 . Clutch  48  selectively couples the ring gear  58  to the sleeve shaft  40 . Thus, sleeve  40  also forms a mechanical power path between the third node and the fourth node when clutch  48  is engaged. Within the scope of the claimed invention, an “interconnecting member” that interconnects two nodes may or may not cooperate with one or more other interconnecting members to interconnect the two nodes. Furthermore, and within the scope of the claimed invention, a power path may or may not be interruptable by a selectively engageable torque transmitting device, such as clutch  48 . 
     Electric machines  32 ,  34  are electrically interconnected via battery  36 . Machines  32 ,  34  and battery  36  thus partially form an electrical third parallel power path between the third node  16  and the fourth node  18 . The first, second, and third power paths are parallel to one another, and define power paths through the transmission  11  between the input shaft  20  and the output shaft  24 . 
     The second node  14  includes a compound planetary gearset  74  having sun gear  78 , ring gear  82 , a first set of planet gears  86  meshingly engaged with the sun gear  78 , and a second set of planet gears  90  meshingly engaged with the first set of planet gears  86  and the ring gear  82 . The first and second set of planet gears  86 ,  90 , are rotatably mounted on planet carrier  94 . Sleeve  68  is coupled to sun gear  78  for rotation therewith, and shaft  26  is coupled to ring gear  82  for rotation therewith. Clutch  98  is selectively engageable to couple ring gear  82  with housing  70 . A planetary lock clutch  102  is selectively engageable to couple planet carrier  94  and ring gear  82 . The planet carrier  94  is coupled to output shaft  24 . 
     It should be noted that subsystem  106  of the transmission  11 , including the third node  16 , the fourth node  18 , the electric machines  32 ,  34 , and battery  36 , is substantially similar in configuration and function to the electronically variable transmission described in U.S. Pat. No. 6,478,705, issued Nov. 12, 2002 to Holmes et al, which is hereby incorporated by reference in its entirety. The compound planetary gearset  74  is employed to provide additional modes to the EVT of the &#39;705 patent by reusing the EVT modes and to provide equal forward/reverse output torque. 
       FIG. 2  is a graphical depiction of the speeds of various transmission components with respect to the speed of the output shaft in an exemplary operation of transmission  11 . Referring to  FIGS. 1 and 2 , the speed of the input shaft  20  is depicted by line  110 , the speed of electric machine  32  is depicted by line  114 , the speed of electric machine  34  is depicted by line  118 , and the speed of sun gear  78  is depicted by line  122 . In a first forward range or mode  126  of CVT operation, i.e., prior to output shaft speed  130 , the dual path clutch of the first node  12  is open, clutch  46  is engaged, clutch  48  is disengaged, and clutch  102  is engaged. Gearset  28  operates in a differential mode, and gearset  30  operates in a torque multiplication mode. Input shaft speed  110 , and correspondingly the speed of the engine, is substantially constant throughout the operation of the transmission to simplify description. The ECU causes the speed of the electric machine  32  to start at a negative value and increase with increasing output shaft speed. Simultaneously, the speed of the electric machine  34  starts at zero and increases with increasing output shaft speed. The speed of sun gear  78  rises proportionally with the output shaft speed. This is the same first mode operation in forward or reverse, as selected at the second node  14 . 
     At output shaft speed  130 , the speed of electric machine  32  is zero, and the transmission is shifted from the first CVT range or mode  126  to a second CVT range or mode  134 . At such point, the speeds of sun gear  52  and ring gear  58  are substantially equal due to the engagement of clutch  46 , so that clutch  48  is engaged (and clutch  46  disengaged) with essentially no resulting torque disturbance to shift from the first mode to the second mode. In the second mode, the speed of electric machine  32  continues to increase with increasing output shaft speed, and the speed of electric machine  34  decreases with increasing output shaft speed. The speed of sun gear  78  continues to increase. Once a 1:1 ratio is achieved, at speed  138 , the dual path clutch at the first node  12  is synchronously engaged and clutch  102  is synchronously disengaged, since all elements in the transmission path are rotating at the same speed, to commence a third mode  142  of operation. Once the dual path clutch is engaged, the output from sun gear  78  is slowed down, effectively working backwards through the first mode and the second mode. A fourth mode  146  begins when the speed of electric machine  32  is zero at output speed  150 , clutch  48  is disengaged, and clutch  46  is engaged. 
     The transmission  11  is also characterized by a reverse mode  154 . At zero output speed, either the planet lock clutch  102  or clutch  98  is selected. The ratio of the compound planetary gearset  74  is such that when holding ring gear  82 , a negative unity ratio is achieved. Thus, the EVT path may be operated precisely as it is in the forward first mode, thereby providing equal reverse. 
     Referring to  FIG. 3 , wherein like reference numbers refer to like components from  FIG. 1 , an alternative transmission  11 ′ having an alternative EVT subsystem  106 ′ is schematically depicted. Subsystem  106 ′ does not include the clutches  46 ,  48  of  FIG. 1 ; rather, ring gear  58 ′ is rigidly mounted to housing  70 . Subsystem  106 ′ also includes a carrier lock  154  to selectively couple the carrier  56  to shaft  68  for rotation therewith. Clutch  158  selectively couples carrier  56  to housing  70 . Carrier lock  154  and clutch  158  allows the engine to be started by electric machine  32  with the mechanical output from the third node  16  disconnected. Subsystem  106 ′ provides only a single mode input split. The operation of subsystem  106 ′ is substantially similar to the EVT described in U.S. Pat. No. 5,558,595, issued Sep. 24, 1996 to Schmidt et al, which is hereby incorporated by reference in its entirety. 
     Referring to  FIG. 4 , an exemplary operation of the transmission of  FIG. 3  is schematically depicted. Input shaft speed, depicted by line  166 , is held substantially constant to simplify description. In a first forward mode  170 , the dual path clutch is open, and the planet lock  102  is applied. With the engine  22  on, clutch  154  is also engaged. Should the engine be off, clutch  158  may be engaged to enable unit  32  to provide a quick start means. The speed of electric machine  32 , depicted by line  174 , is negative and increases in speed with increasing output shaft speed. The speed of electric machine  34 , depicted by line  178 , starts at zero and increases with increasing output shaft speed. The dual path clutch is applied at output shaft speed  180 , when the speed of electric machine  32  equals the speed of input shaft  20 , to commence a second mode  182  of operation at which time clutch  102  is synchronously released and the dual path clutch at node  12  is synchronously engaged. As in the first embodiment, the transmission subsystem  106 ′ then slows the sun gear  78  to increase output speed. It should be noted that three mechanical points  186  result from the operation of the transmisison of  FIG. 3 . A reverse mode  187  is also achieved similar to that as described in the first embodiment. 
     Referring to  FIG. 5 , yet another alternative powertrain  10 ″ configuration is schematically depicted. The powertrain  10 ″ of  FIG. 5  is substantially identical to the powertrain  10  of  FIG. 1 , except that the planetary gearset  30 ″ of the fourth node  18 ″ is compound. More specifically, a first set of planet gears  62   a  mesh with sun gear  60 , and a second set of planet gears  62   b  mesh with the first set of planet gears  62   a  and with the ring gear  58 . The first and second sets of planet gears  62   a ,  62   b  are rotatably mounted on carrier  64 ′, which is connected to shaft  68 . An exemplary operation of powertrain  10 ″ is schematically depicted in  FIG. 6 , with the speed of electric machine  32  with respect to output shaft speed depicted by line  194 , and the speed of electric machine  34  with respect to output shaft speed depicted by line  190 . In a first mode  198 , the planet lock  102  is engaged, the dual path clutch  12  is open, clutch  46  is engaged and clutch  48  is disengaged. Both electric machines  32 ,  34  operate at negative speeds, with electric machine  32  starting at a negative value and increasing with increasing output speed, and electric machine  34  starting at zero speed and decreasing with increasing output speed. 
     When the speed of electric machine  32  equals zero at output speed  200 , clutch  48  is engaged and clutch  46  is disengaged to begin a second mode  202  of powertrain operation, in which the speed of electric machine  32  continues to increase, and the speed of electric machine  34  increases with increasing output shaft speed. When the speeds of electric machine  32  and electric machine  34  are the same at output speed  203 , the dual path clutch  12  is engaged and clutch  102  is disengaged to start a third mode  204 , wherein the speed of electric machines  32 ,  34  decrease with increasing output shaft speed. When the speed of electric machine  32  is zero at output speed  205 , clutch  48  is disengaged and clutch  46  is engaged to commence a fourth mode  206 . It should be noted that the arrangement of powertrain  10 ″ and the operation depicted in  FIG. 6  provide six mechanical points  186 . A reverse mode  208  is acheieved similar to that as described in the embodiment of  FIGS. 1 and 2 . 
     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.