Abstract:
A transmission includes two blocking valves that control fluid pressure to a plurality of clutches. The blocking valves are characterized by a plurality of states that result in at least three transmission operating conditions. Each of the three operating conditions is characterized by fluid pressure being unavailable to a respective one of the plurality of clutches.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/042,386, filed Apr. 4, 2008, and which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to hydraulic control systems for vehicular transmissions. 
       BACKGROUND OF THE INVENTION 
       [0003]    In general, a motor vehicle transmission includes an input shaft and an output shaft. The input shaft is typically coupled to the vehicle engine through a fluid coupling such as a torque converter, and the output shaft is coupled to the vehicle drive wheels through a differential gear set. The transmission employs a number of gear elements and selectively engageable friction elements (referred to herein as clutches) that are controllable to vary the speed ratio between the transmission input and output shafts. 
         [0004]    Transmissions are typically characterized by a plurality of fixed speed ratios. Each of the fixed speed ratios is achievable by engaging a particular combination of clutches. An electrically variable transmission includes at least one motor/generator, and is typically characterized by at least one electrically variable mode or range of operation in which the speed ratio between the input shaft and the output shaft is not fixed, but instead varies with the speed of the rotor of the motor/generator. An electrically variable transmission may be configured such that multiple electrically variable modes or ranges are achievable by engaging particular combinations of clutches. Other combinations of clutches in an electrically variable transmission may result in fixed speed ratio modes. 
         [0005]    Shifting from a currently established fixed ratio or electrically variable mode to a new fixed ratio or electrically variable mode involves, in most cases, disengaging a clutch (off-going clutch) and engaging another clutch (on-coming clutch). Clutches may be engaged by the action of pressurized fluid against a piston in a clutch apply chamber. Accordingly, transmissions typically include a hydraulic circuit for supplying pressurized fluid to the apply chambers of the clutches. 
       SUMMARY OF THE INVENTION 
       [0006]    A transmission includes first, second, third, and fourth clutches that engage in response to fluid pressure. The transmission also includes a main passage, a first passage, a second passage, and a third passage. A pump is configured to supply fluid pressure to the main passage. A first valve is configured to control fluid communication between the first clutch and the first passage. A second valve is configured to control fluid communication between the second clutch and the second passage. A third valve is configured to control fluid communication between the third clutch and the third passage. A fourth valve is configured to control fluid communication between the fourth clutch and the main passage. 
         [0007]    Fifth and sixth valves are configured to control fluid communication between the main passage and the first, second, and third passages such that the fifth and sixth valves selectively provide first, second, and third operating conditions. In the first operating condition, the first passage is not in fluid communication with the main passage and the second and third passages are in fluid communication with the main passage. Accordingly, the first clutch is not engageable in the first operating condition. 
         [0008]    In the second operating condition, the second passage is not in fluid communication with the main passage and the first and third passages are in fluid communication with the main passage. Accordingly, the second clutch is not engageable in the second operating condition. 
         [0009]    In the third operating condition, the third passage is not in fluid communication with the main passage and the first and second passages are in fluid communication with the main passage. Accordingly, the third clutch is not engageable in the third operating condition. 
         [0010]    Thus, in each of the three operating conditions caused by the fifth and sixth valves, a respective clutch is not engageable. Accordingly, the transmission provided may prevent undesired shift sequencing and clutch combinations. In an exemplary embodiment, the default settings of the valves is such that the clutches are engaged in a combination that provides a pre-established transmission mode. Accordingly, in the event of a loss of power to the transmission controller, the transmission will enter the pre-established transmission mode. 
         [0011]    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 
         [0012]      FIG. 1  is a schematic depiction of a powertrain including an electrically variable transmission with a plurality of clutches; 
           [0013]      FIG. 2  is a truth table depicting a shift logic for the transmission of  FIG. 1 ; 
           [0014]      FIG. 3  is a schematic depiction of the hydraulic clutch actuation control system for the transmission of  FIG. 1 ; 
           [0015]      FIG. 4  is a schematic depiction of a portion of the hydraulic clutch actuation control system of  FIG. 3 , including four trim valves and first and second blocking valves; 
           [0016]      FIG. 5  is a schematic depiction of the first blocking valve of  FIG. 4  in a first position; 
           [0017]      FIG. 6  is a schematic depiction of the first blocking valve of  FIG. 4  in a second position; 
           [0018]      FIG. 7  is a schematic depiction of the second blocking valve of  FIG. 4  in a first position; 
           [0019]      FIG. 8  is a schematic depiction of the second blocking valve of  FIG. 4  in a second position; and 
           [0020]      FIG. 9  is a truth table depicting the availability of the clutches of  FIG. 1  during various states of the blocking valves. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Referring to the drawings wherein like characters represent the same or corresponding parts throughout the several views, there is seen in  FIG. 1  a powertrain  10  having an engine  12  and an electrically variable hybrid transmission  14 . The engine  12  in one embodiment is a reciprocating, internal combustion engine, and may, for example, be spark ignition or compression ignition. The electrically variable hybrid transmission  14  includes an input shaft  18 , an output shaft  20 , three planetary gearsets  22 ,  24 , and  26 , five torque transmitting mechanisms C 1 , C 2 , C 3 , C 4 , and C 5  (also referred to herein as “clutches”), and two electrical power units or motor/generators  30 ,  32 . 
         [0022]    Planetary gearset  22  includes a ring gear member  36 , a sun gear member  40 , and a planet carrier  44  that rotatably supports a plurality of planet gear members  48 . Each of the planet gear members  48  meshingly engages the sun gear member  40  and the ring gear member  36 . Planetary gearset  24  includes a ring gear member  52 , a sun gear member  56 , and a planet carrier  60  that rotatably supports a plurality of planet gear members  64 . Each of the planet gear members  64  meshingly engages the sun gear member  56  and the ring gear member  52 . Planetary gearset  26  includes a ring gear member  68 , a sun gear member  72 , and a planet carrier  76  that rotatably supports a plurality of planet gear members  80 A,  80 B. Each of the planet gear members  80 A meshingly engages the sun gear member  72  and a respective one of the planet gear members  80 B. Each of the planet gear members  80 B meshingly engages the ring gear member  68  and a respective one of the planet gear members  80 A. 
         [0023]    Motor/generator  30  includes a stator  84  and a rotor  88 . Motor/generator  32  includes a stator  92  and a rotor  96 . Ring gear member  36  is operatively connected to the input shaft  18  for unitary rotation therewith. Sun gear member  40  is operatively connected to rotor  88  for unitary rotation therewith. Planet carrier  44 , planet carrier  60 , and sun gear member  72  are operatively interconnected for unitary rotation. Sun gear member  56  is operatively connected to rotor  96  for unitary rotation therewith. The output shaft  20  is operatively connected to ring gear member  68  for unitary rotation therewith. 
         [0024]    Clutch C 1  is selectively engageable to operatively connect planet carrier  76  to a stationary member such as transmission housing  100 . Clutch C 2  is selectively engageable to operatively connect planet carrier  76  to rotor  96  and sun gear member  56  for unitary rotation. Clutch C 3  is selectively engageable to operatively connect ring gear member  52  to the housing  100 . Clutch C 4  is selectively engageable to operatively connect ring gear member  52  to sun gear member  40  and rotor  88  for unitary rotation. 
         [0025]    Motor/generators  30 ,  32  are in electrical communication with an energy storage device (not shown) such as a battery or an ultracapacitor, and are controlled by a control unit (not shown). 
         [0026]    Referring to  FIGS. 1 and 2 , the planetary gear arrangement, as shown in  FIG. 1 , provides four electrically variable modes of operation and three fixed ratio mode of operation. In the four electrically variable modes, the speed ratio between the input shaft  18  and the output shaft  20  is variable and depends on the speed of one or both of the motor/generators  30 ,  32 . In the fixed ratio modes, the speed ratio between the input shaft  18  and the output shaft  20  is fixed. In the first electrically variable mode, i.e., Mode  1 , clutches C 1  and C 3  are engaged, and clutches C 2  and C 4  are disengaged. In the first fixed ratio mode, i.e., G 1 , clutches C 1 , C 3 , and C 4  are engaged, and clutch C 2  is disengaged. In the second electrically variable mode, i.e., Mode  2 , clutches C 1  and C 4  are engaged, and clutches C 2  and C 3  are disengaged. In the second fixed ratio mode, i.e., G 2 , clutches C 1 , C 2 , and C 4  are engaged, and clutch C 3  is disengaged. In the third electrically variable mode, i.e., Mode  3 , clutches C 2  and C 4  are engaged, and clutches C 1  and C 3  are disengaged. In the third fixed ratio mode, i.e., G 3 , clutches C 2 , C 3 , and C 4  are engaged and clutch C 1  is disengaged. In the fourth electrically variable mode, i.e., Mode  4 , clutches C 2  and C 3  are engaged, and clutches C 1  and C 4  are disengaged. 
         [0027]    Referring to  FIG. 3 , a hydraulic clutch actuation control system  120  is schematically depicted. The system  120  includes an engine driven hydraulic pump  124 , such as a fixed displacement pump, that draws fluid from a reservoir  128  for delivery to a main passage  132 . Alternately, an electrically controlled hydraulic pump  136  is provided for operation in an electric mode (i.e., when the engine  12  is not transmitting power to the transmission and only motor/generators  30 ,  32  provide power). A check valve  140  operates to selectively distribute pressurized fluid to the main passage  132  from one of pumps  124 ,  136 , depending upon which pump  124  or  136  is operating. A pressure relief valve  144  is provided in fluid communication with the outlet of the hydraulic pump  124  to guard against over pressurization of the main passage  132 . Likewise, a pressure relief valve  148  is provided in fluid communication with the outlet of the electrically controlled hydraulic pump  136  to guard against over pressurization of the main passage  132 . The pressure relief valves  144  and  148  will exhaust fluid though a passage should an over pressurized condition manifest itself within the main passage  132 . 
         [0028]    The system  120  also includes four trim valves  152 ,  156 ,  160 ,  164  and two shift valves, or blocking valves  168 ,  170 . Each clutch C 1 , C 2 , C 3 , C 4  is operatively connected to a respective one of the trim valves  152 ,  156 ,  160 ,  164 , which controls the application and release of the clutch. That is, each clutch C 1 , C 2 , C 3 , C 4  is applied by the application of hydraulic pressure, as understood by those skilled in the art. Pressurized fluid from the pumps  124 ,  136  is supplied to valves  164 ,  168 ,  170  via main passage  132 . 
         [0029]    Passage  172  provides fluid communication between each of the valves  152 ,  156 ,  160 ,  164 ,  168 ,  170  and the motor/generators  30 ,  32 . Passage  172  functions as backfill and provides cooling to the motor/generators  30 ,  32 . Passage  176  provides fluid communication between valve  152  and clutch C 1 . Passage  180  provides fluid communication between valve  156  and clutch C 2 . Passage  184  provides fluid communication between valve  160  and clutch C 3 . Passage  188  provides fluid communication between valve  164  and clutch C 4 . 
         [0030]    Main passage  132  provides fluid communication between the pumps  124 ,  136  and valves  164 ,  168 ,  170 . Accordingly, main passage  132  supplies high pressure fluid from one of pumps  124 ,  136  (depending on which of the pumps is operating and the status of valve  140 ) to each of valves  164 ,  168 ,  170 . Passage  192  provides fluid communication between valve  168  and valve  170 . Passage  196  provides fluid communication between valve  168  and valve  152 . Passage  200  provides fluid communication between valve  168  and valve  156 . Passage  204  provides fluid communication between valve  168  and valve  170 . Passage  208  provides fluid communication between valve  168  and valve  160 . 
         [0031]    Each valve  152 ,  156 ,  160 ,  164 ,  168 ,  170  includes a respective valve member  240 ,  244 ,  248 ,  252 ,  256 ,  260 , respectively, that is selectively movable to control which of the various passages connected to each valve are in fluid communication with one another. Referring to  FIG. 5 , valve  168  includes a valve body  264  defining a cavity in which member  256  is selectively, slidably translatable between first and second positions. Spring  268  biases the valve member  256  in the first position, as shown in  FIG. 5 . In the first position, member  256  permits fluid communication between passage  192  and passage  196 ; between passage  132  and passage  200 ; and between passage  204  and passage  208 . 
         [0032]    Member  256  is shown in its second position in  FIG. 6 . When member  256  is in its second position, member  256  permits fluid communication between passage  196  and passage  132 ; between passage  200  and passage  204 ; and between passage  208  and passage  132 . 
         [0033]    Referring to  FIG. 7 , valve  170  includes a valve body  272  defining a cavity in which member  260  is selectively, slidably translatable between first and second positions. Spring  276  biases the valve member  260  in the first position, as shown in  FIG. 7 . In the first position, member  260  permits fluid communication between passage  172  and passage  204 ; between passage  132  and passage  192 ; and between passage  172  and passage  212 . Member  260  is shown in its second position in  FIG. 8 . In its second position, member  260  permits fluid communication between passage  204  and passage  132 ; and between passage  192  and passage  172 . 
         [0034]    Referring again to  FIG. 4 , member  240  is selectively movable within the body of valve  152  between a first position in which the member  240  obstructs fluid communication between passage  176  and passage  196 , and a second position in which the member  240  permits fluid communication between passage  176  and passage  196 . A spring biases the member  240  in its first position. Member  244  is selectively movable within the body of valve  156  between a first position in which the member  244  obstructs fluid communication between passage  180  and passage  200 , and a second position in which the member  244  permits fluid communication between passage  180  and passage  200 . A spring biases the member  244  in its first position. Member  248  is selectively movable within the body of valve  160  between a first position in which the member  248  obstructs fluid communication between passage  184  and passage  208 , and a second position in which the member  248  permits fluid communication between passage  184  and passage  208 . A spring biases the member  248  in its first position. Member  252  is selectively movable within the body of valve  164  between a first position in which the member  252  obstructs fluid communication between passage  188  and passage  132 , and a second position in which the member  252  permits fluid communication between passage  188  and passage  132 . A spring biases the member  252  in its first position. In their respective first positions, each of members  240 ,  244 ,  248 ,  252  provide fluid communication between a respective one of passages  176 ,  180 ,  184 ,  188  and backfill (exhaust) passage  172 . 
         [0035]    The system  120  also includes six solenoid valves  216 ,  220 ,  224 ,  228 ,  232  and  236 . Each solenoid valve is operative to control fluid pressure exerted on a respective one of members  240 ,  244 ,  248 ,  252 ,  256 ,  260 . Each of the solenoid valves  216 ,  220 ,  224 ,  228 ,  232  and  236 , when open (or high), permits fluid pressure to act on a respective one of members  240 ,  244 ,  248 ,  252 ,  256 ,  260  to move the respective member to its second position. Each of the solenoid valves  216 ,  220 ,  224 ,  228 ,  232  and  236 , when closed (or low) does not permit sufficient pressure to act against a respective one of members  240 ,  244 ,  248 ,  252 ,  256 ,  260  to overcome the spring bias and the respective member remains in its first position. 
         [0036]    Solenoid valves  232 ,  236  are on/off type solenoid valves, and solenoid valves  216 ,  220 ,  224 ,  228  are variable pressure (proportional control) type solenoid valves. Solenoid valves  216 ,  224 ,  232 , and  236  are normally low or normally closed type solenoid valves, and solenoid valves  220 ,  228  are normally high or normally open type solenoid valves. A normally open (or normally high) solenoid valve will distribute pressurized fluid or an output pressure when not energized (in the absence of an electrical signal to the solenoid). A normally low (or normally closed) solenoid valve does not supply pressure when not energized. As used herein, the default state of a valve  152 ,  156 ,  160 ,  164 ,  168 ,  170  corresponds to the position of the valve member  240 ,  244 ,  248 ,  252 ,  256 ,  260  when the corresponding solenoid valve  216 ,  220 ,  224 ,  228 ,  232 ,  236  is not energized. 
         [0037]    Referring to  FIGS. 4 and 9 , there are four possible operating configurations of blocking valves  168  and  170 , which are determined by the activation status of the solenoid valves  232 ,  236 . The four possible operating configurations of blocking valves  168 ,  170  result in four transmission operating conditions, each having a different availability of clutches C 1 -C 4 . In  FIG. 9 , the status of solenoid valve  232  is depicted in the column labeled “X Blk” and the status of solenoid valve  236  is depicted in the column labeled “Y Blk.” The numeral “1” indicates that the solenoid valve is activated or energized, and the number “0” indicates that the solenoid valve is deactivated, or not energized. 
         [0038]    In a first operating configuration, as depicted in the first row of the table of  FIG. 9 , both solenoid valves  232 ,  236  are energized and therefore members  256 ,  260  are in their respective second positions. In a second operating configuration, as depicted in the second row of the table of  FIG. 9 , solenoid valve  232  is not energized and solenoid valve  236  is energized, and therefore member  256  is in its first position and member  260  is in its second position. In a third operating configuration, as depicted in the third row of the table of  FIG. 9 , solenoid valve  232  is energized and solenoid valve  236  is not energized, and therefore member  256  is in its second position and member  260  is in its first position. In a fourth operating configuration, as depicted in the fourth row of the table of  FIG. 9 , both solenoid valves  232 ,  236  are not energized, and therefore members  256 ,  260  are in their respective first positions. 
         [0039]    Clutch C 1  is engageable only if sufficient fluid pressure is present in passage  196 . Clutch C 2  is engageable only if sufficient fluid pressure is present in passage  200 . Clutch C 3  is engageable only if sufficient fluid pressure is present in passage  208 . Sufficient fluid pressure is obtained in a passage  196 ,  200 ,  208  by providing fluid communication between the passage  196 ,  200 ,  208  and the main passage  132 . The presence of sufficient fluid pressure in passages  196 ,  200 ,  208  is dependent upon the status of the blocking valves  168 ,  170 . Thus, the availability of any of the electrically variable modes and the fixed ratio modes is dependent upon the status of the blocking valves  168 ,  172 . Clutch C 4  is engageable independent of the status of blocking valves  168 ,  170 , because valve  164  is in direct fluid communication with main passage  132  and can provide fluid communication between main passage  132  and the clutch C 4  via passage  188 . More specifically, valve  164  provides direct fluid communication between passage  188  and the main passage  132  when member  252  is in its second position, and therefore the application of clutch C 4  is not dependent upon the status of the blocking valves  168 ,  170 . 
         [0040]    In the first operating configuration, pressurized fluid from the pumps  124 ,  136  is available to all of valves  152 ,  156 ,  160 , and  164  (i.e., all of valves  152 ,  156 ,  160 ,  164  are in fluid communication with the main passage  132 ). Accordingly, all of the clutches C 1 -C 4  are engageable, and therefore all electrically variable and fixed ratio modes are available. More specifically, in the first operating configuration, passage  196  is in fluid communication with the main passage  132  via valve  168 , and therefore pressure is available to clutch C 1 . Passage  200  is in fluid communication with main passage  132  via valve  168 , passage  204 , and valve  170 , and therefore pressure is available to clutch C 2 . Passage  208  is in fluid communication with main passage  132  via valve  168 , and therefore pressure is available to clutch C 2 . 
         [0041]    In the second operating configuration, clutch C 1  is not available because passage  196  is not in fluid communication with the main passage  132 . Accordingly, only Mode  3 , G 3 , and Mode  4  are possible in the second operating configuration. With member  260  in its second position and member  256  in its first position, passage  200  is in fluid communication with the main passage  132  via valve  168 , and passage  208  is in fluid communication with the main passage  132  via valve  168 , passage  204 , and valve  170 . Passage  196  is in fluid communication with the backfill passage  172  (and therefore not sufficiently pressurized) via valve  168 , passage  192 , and valve  170 . 
         [0042]    In the third operating configuration, clutch C 2  is not available because passage  200  is not in fluid communication with the main passage  132 . Accordingly, only Mode  1 , G 1 , and Mode  2  are possible in the third operating configuration. With member  256  in its second position and member  260  in its first position, passage  196  is in fluid communication with main passage  132  via valve  168 , and passage  208  is in fluid communication with main passage  132  via valve  168 . Passage  200  is in fluid communication with the backfill passage  172  (and therefore not sufficiently pressurized) via valve  168 , passage  204 , and valve  170 . 
         [0043]    In the fourth operating configuration, clutch C 3  is not available because passage  208  is not in fluid communication with the main passage  132 . Accordingly, only Mode  2 , G 2 , and Mode  3  are possible in the fourth operating configuration. With members  256 ,  260  in their respective first positions, passage  196  is in fluid communication with main passage  132  via valve  168 , passage  192 , and valve  170 ; passage  200  is in fluid communication with main passage  132  via valve  168 . Passage  208  is in fluid communication with the backfill passage  172  (and therefore not sufficiently pressurized) via valve  168 , passage  204 , and valve  170 . 
         [0044]    The concurrent application of clutches C 1 , C 2 , and C 3  may cause the transmission  14  to lock up, and therefore it is desirable to avoid the condition in which all of clutches C 1 , C 2 , and C 3  are applied. By operating the transmission  14  only in the second, third, and fourth operating configurations shown in  FIG. 9 , all four electrically variable modes and all three fixed ratio modes of transmission operation are usable and the application of clutches C 1 , C 2  and C 3  concurrently is not possible. 
         [0045]    The four available logic combinations of the two blocking valves  168 ,  170  thus provide four operating zones (low ranges only, mid ranges only, high ranges only, and all driving ranges available). In the event of power loss to the transmission controller (not shown), two normally high solenoids  220 ,  228  are used to actuate two clutch control valves  156 ,  164  to provide the correct combination of clutches to provide EVT MODE  3  operation. During power-off conditions, the blocking valves  168 ,  170  are mechanized not to block the MODE  3  clutches (i.e., clutch C 2  and clutch C 4 ). By providing only one blocked clutch in any given operating configuration, all transitions to higher or lower modes can occur with at most a single blocking valve transition. 
         [0046]    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.