Patent Abstract:
An electro-hydraulic control system is provided, preferably for a countershaft transmission, that uses logic valves to multiplex trim systems to more than one torque-transmitting mechanism, thereby minimizing the number of required components. Additionally, the electro-hydraulic control system preferably has more than one failure mode so that the transmission operates at a respective predetermined speed ratio in the event of an interruption in electrical power.

Full Description:
TECHNICAL FIELD 
       [0001]    The invention relates to an electro-hydraulic control system for a transmission; specifically, an electro-hydraulic control system having multiplexed trim valves that is preferably for a countershaft transmission. 
       BACKGROUND OF THE INVENTION 
       [0002]    Multi-speed power transmissions, particularly those using planetary gear arrangements, require a hydraulic system to provide controlled engagement and disengagement, on a desired schedule, of the clutches and brakes or torque-transmitting mechanisms that operate to establish the ratios within the planetary gear arrangement. 
         [0003]    These control systems have evolved from substantially pure hydraulic control systems, wherein all of the control signals are produced by hydraulic devices, to electro-hydraulic control systems, wherein a number of the control signals are produced by an electronic controller. The electronic controller emits electrical control signals to solenoid valves, which then issue controlled hydraulic signals to the various operating valves within the transmission control. 
         [0004]    With many of the early pure hydraulic and first generation electro-hydraulic control systems, the power transmission utilized a number of freewheel or one-way devices which smooth the shifting or ratio interchange of the transmission during both upshifting and downshifting of the transmission. This relieves the hydraulic control system from providing for the control of overlap between the torque-transmitting mechanism that was coming on and the torque-transmitting mechanism that was going off. If this overlap is excessive, the driver feels a shudder in the drivetrain, and if the overlap is too little, the driver experiences engine flare or a sense of coasting. The freewheel device prevents this feeling by quickly engaging when the torque imposed thereon is reversed from a freewheeling state to a transmitting state 
         [0005]    The advent of electro-hydraulic devices gave rise to what is known as clutch-to-clutch shift arrangements to reduce the complexity of the transmission and the control. These electro-hydraulic control mechanisms are generally perceived to reduce cost and reduce the space required for the control mechanism. 
         [0006]    In addition, with the advent of more sophisticated control mechanisms, the power transmissions have advanced from two-speed or three-speed transmissions to five-speed and six-speed transmissions. In at least one presently available six-speed transmission, just five friction devices are employed to provide six forward speeds, neutral condition, and a reverse speed. 
         [0007]    Countershaft transmissions are often a desirable design option as they typically have low spin losses and offer wide ratio coverage. The relatively large number of clutches sometimes associated with countershaft transmissions may require double transition shifts. To reduce the number of components to the extent possible, clutches are sometimes reused in different speed ratio ranges. 
         [0008]    It is desirable to provide drive-home capabilities within the transmission in the event that the electronic system undergoes a malfunction or discontinuance of operation. The drive-home feature of a power transmission is an important factor in that it permits the vehicle operator to return home with the vehicle so that the proper repairs can be undertaken at a repair station rather than in the field where the vehicle underwent the malfunction. 
       SUMMARY OF THE INVENTION 
       [0009]    An electro-hydraulic control system is provided that uses logic valves to multiplex trim systems to more than one torque-transmitting mechanism, thereby minimizing the number of required components. Additionally, the electro-hydraulic control system preferably has more than one failure mode so that the transmission operates at a respective predetermined speed ratio in the event of an interruption in electrical power. 
         [0010]    The electro-hydraulic control system controls the selective engagement of a plurality of torque-transmitting mechanisms in a transmission that provides multiple speed ratios. The electro-hydraulic control system has a trim valve and a logic valve that is selectively movable between a first position and a second position. The trim valve selectively communicates pressurized fluid to the logic valve. The logic valve multiplexes the trim valve by directing the pressurized fluid to a first toque-transmitting mechanism for engagement thereof when in the first position and to a second torque-transmitting mechanism for engagement thereof when in the second position. As used herein, a valve is “multiplexed” when it has more than one function, such as when it is able to at least partially control engagement of more than one torque-transmitting mechanism. Preferably, the electro-hydraulic control system has multiple logic valves each multiplexing a different trim valve to control engagement of different pairs of the torque-transmitting mechanisms. 
         [0011]    The electro-hydraulic control system preferably includes a three position dog clutch actuator valve that controls the position of a dog clutch in the transmission. The position of two of the logic valves along with a solenoid valve may control the position of the dog clutch actuator valve, which in turn determines the position of a third of the logic valves. 
         [0012]    Preferably, the trim valves are each part of a different trim system that also includes a solenoid valve energizable by the controller to move the trim valve, thereby permitting the flow of pressurized fluid therethrough. Some of the solenoids are normally open-type valves while others are normally closed-type valves such that the trim valves, the logic valves and the dog clutch actuator valve are positioned to establish different preferred “failure modes” in the event of an electrical power failure. The electro-hydraulic control system establishes one “failure mode” that is a speed ratio included in a first set of the speed ratios attainable by the transmission if there is an electrical power failure when the transmission is operating in any of the speed ratios in the first set, and establishes another “failure mode” that is a different speed ratio included in a second set of speed ratios attainable by the transmission if there is an electrical power failure when the transmission is operating in any of the speed ratios of the second set. 
         [0013]    When system established the failure mode that is a speed ratio in the second set, the dog clutch actuator valve is in a neutral position which latches two of the logic valves to prevent movement thereof. Another logic valve is energizable to selectively break the latch and allow movement of these two logic valves. The latching of the logic valves X and Y provides the ability to achieve the high speed, power-off failure mode. 
         [0014]    Preferably, the transmission is a countershaft transmission with seven torque-transmitting mechanisms, including the dog clutch, as well as a torque-converter clutch to lockup a torque converter. The electro-hydraulic control system described above controls engagement and disengagement of these torque-transmitting mechanisms to attain nine forward and at least two reverse speed ratios. (A speed ratio is also referred to herein as a speed ratio range.) 
         [0015]    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 
         [0016]      FIG. 1  is a schematic representation of a countershaft transmission having torque-transmitting mechanisms engaged and disengaged via an electro-hydraulic control system within the scope of the invention; 
           [0017]      FIGS. 2A and 2B  are a schematic representation of a hydraulic control portion of the electro-hydraulic control system of  FIG. 1  having valves to control engagement and disengagement of the torque-transmitting mechanisms of the transmission of  FIG. 1 ; and 
           [0018]      FIG. 3  is a table indicating the state of many of the valves shown in  FIGS. 2A and 2B  for each speed ratio achievable by the transmission of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring to the drawings, wherein like reference numbers represent the same or corresponding parts throughout the several views, there is shown in  FIG. 1  a powertrain  10 . The powertrain  10  includes a power source or engine  12 , a torque converter  14  and a countershaft transmission  16 . The torque converter  14  is connected with the engine  12  and with a transmission input member  18  via a turbine  20 . Selective engagement of a torque converter clutch TCC allows the engine  12  to be directly connected with the input shaft  18 , bypassing the torque converter  14 . The input member  18  is typically a shaft, and may be referred to as an input shaft herein. The torque converter  14  includes the turbine  20 , a pump  24  and a stator  26 . The converter stator  26  is grounded to a casing  30  through a typical one-way clutch that is not shown. A damper  28  is operatively connected to the engaged torque converter clutch TCC for absorbing vibration. 
         [0020]    The transmission  16  includes a plurality of intermeshing gears, a first countershaft  32 , a second countershaft  34 , an intermediate shaft  36  and an output member  38 , which may be a shaft. The transmission  16  further includes a plurality of torque-transmitting mechanisms, including the torque converter clutch TCC, six rotating clutches: C 1 , C 2 , C 3 , C 4 , C 5  and C 7 ; and one stationary clutch C 6 . Torque is transferred from the input member  18  to the output member  38  along various powerflow paths through the transmission  16  depending on which of the plurality of selectively engagable torque-transmitting mechanisms are engaged. 
         [0021]    Clutch C 4  is selectively engagable to connect the input member  18  for rotation with the intermediate shaft  36 . Gear  40  rotates with the input member  18  and continuously intermeshes with gear  42 , which rotates with the second countershaft  34 . Gear  44  rotates with input member  18  and continuously intermeshes with gear  46 , which rotates with the first countershaft  32 . Gear  48  rotates with sleeve shaft  51  which is concentric with first countershaft  32  and is selectively connectable with the first countershaft  32  by engagement of clutch C 3 . Gear  48  continuously intermeshes with gear  50 , which rotates with intermediate shaft  36 . Gear  50  also continuously intermeshes with gear  52 , which rotates with sleeve shaft  53 , which is concentric with second countershaft  34  and is selectively connectable for rotation with second countershaft  34  by engagement of clutch C 5 . Gear  54  rotates with sleeve shaft  55  which is concentric with and selectively connectable for rotation with first countershaft  32  by engagement of clutch C 1 . Gear  54  continuously intermeshes with gear  56  (in a different plane than the two-dimensional schematic, as indicated by the dashed lines therebetween). Gear  56  rotates about and is selectively connectable for rotation with a sleeve shaft  57  by the positioning of a dog clutch DOG in a reverse position indicated as R. The sleeve shaft  57  is selectively connectable for rotation with the second countershaft  34  by engagement of clutch C 2 . Gear  58  rotates with the sleeve shaft  55  and continuously intermeshes with gear  60 , which rotates with the intermediate shaft  36 . Gear  60  continuously intermeshes with the gear  62 , which is selectively connectable for rotation with the sleeve shaft  57  by positioning of the dog clutch DOG in a forward position indicated by F in the  FIG. 1 . 
         [0022]    The transmission  16  further includes a planetary gear set  64  with a sun gear member  66  connected for rotation with the intermediate shaft  36 , a ring gear member  68  selectively connectable for rotation with the intermediate shaft  36  by engagement of clutch C 7 , a carrier member  70  connected for rotation with the output member  38  and rotatably supporting planet gears  72  that intermesh with both the sun gear member  66  and the ring gear member  68 . A clutch C 6  is selectively engagable to ground the ring gear member  68  to the stationary member  30 . 
         [0023]    In a preferred embodiment, the following gear tooth counts are used: gear  40  has 39 teeth; gear  42  has 37 teeth; gear  46  has 40 teeth; gear  44  has 31 teeth; gear  48  has 34 teeth; gear  50  has 31 teeth; gear  52  has 34 teeth; gear  54  has 62 teeth; gear  56  has 46 teeth; gear  58  has 26 teeth; gear  60  has 44 teeth; gear  62  has 26 teeth; ring gear member  68  has 85 teeth and sun gear member  66  has 35 teeth. By the selective engagement of the torque-transmitting mechanisms TCC, C 1 , C 2 , C 3 , C 4 , C 5 , C 6 , C 7  and DOG according to the table of  FIG. 3 , and assuming the tooth counts listed above, the following sample numerical speed ratios are attained between the input member  12  and the output member  14  for the following speed ratio ranges: second reverse speed ratio range (R 2 ): 2.18; first reverse speed ratio range (R 1 ): 7.42; first forward speed ratio (1st 7.49; second forward speed ratio (2nd): 5.51; third forward speed ratio (3rd): 4.03; fourth forward speed ratio (4th): 2.97; fifth forward speed ratio (5th): 2.18; sixth forward speed ratio (6th): 1.61; seventh forward speed ratio (7th): 1.18; eighth forward speed ratio (8th): 1.00; ninth forward speed ratio (9th): 0.87. Alternate solenoid-energizing schemes are available for the first, third, fifth and seventh speed ratio ranges with one or more of the logic valves in different positions for the same range. For example, three different alternate seventh forward speed ratios (7th′), (7th″) and (7th′″) are available by energizing solenoids associated with different ones of the logic valves X, Y, Z and W, as discussed below and indicated in  FIG. 3 . 
         [0024]    The selective engagement and disengagement of the torque-transmitting mechanisms is controlled by an electro-hydraulic control system  74 , which is shown in further detail in  FIGS. 2A and 2B . The electro-hydraulic control system  74  includes an electronic controller  76 , which may be one or more control units and is referred to as ECU in  FIG. 1 , as well as a hydraulic control portion  100  referred to as HYD in  FIG. 1 . The electronic controller  76  is programmable to provide electrical control signals to the hydraulic control portion  100  to establish the fluid pressures that control engagement and disengagement of the torque-transmitting mechanisms TCC, C 1 , C 2 , C 3 , C 4 , C 5 , C 6 , C 7  and DOG. Electrical signals are also sent to the electronic controller  76  based on fluid pressure in the hydraulic control portion  100  to provide feedback information such as information indicative of valve positions. The locations of various pressure switches which provide such feedback are indicated as pressure switches SW 1 , SW 2 , SW 3 , SW 4 , SW 5 , SW 6 , SW 7  and SW 8  in  FIGS. 2A and 2B . 
         [0025]    Referring to  FIGS. 2A and 2B , the hydraulic control portion  100  includes a main regulator valve  104 , a control regulator valve  106 , an EBF (exhaust back flow) regulator valve  108 , a converter flow valve  110 , and a lube regulator valve  112 . The main regulator valve  104  is in fluid communication with a hydraulic pump  114 , such as a variable volume pump, that draws fluid from a reservoir  116  for delivery to a main passage  118 . The control regulator valve  106  is in fluid communication with the main regulator valve  104 , and establishes a reduced control pressure within passage  117 , which is then communicated to other valves described below, depending upon their position. The EBF regulator valve  108  is operable to vent pressurized fluid within passage  117  to exhaust should an over pressurized condition occur. Pump  119  is an engine-driven pump that also draws fluid from reservoir  116  and that controls the lubrication pressure to a lubrication system  121  and provides cooling fluid to a transmission cooling system  123 . 
         [0026]    The hydraulic control portion  100  includes many solenoid valves, such as variable pressure type solenoid valves PCS 1 , PCS 2 , PCS 3 , PCS 4 , PCS 5 , PCS 6 , and PCS 7 , and shift-type (i.e., on/off type) solenoid valves SS 1 , SS 2  and SS 3 . Each solenoid valve is in electric signal communication with the control unit  76  and is actuated upon receipt of a control signal therefrom. The solenoid valves PCS 1 , PCS 7  and PCS 5  are normally high or normally open-type solenoid valves, while the remaining solenoid valves PCS 2 , PCS 3 , PCS 4 , PCS 6 , SS 1 , SS 2  and SS 3  are normally low or normally closed-type solenoid valves. As is well known, an open solenoid valve will distribute output pressure in the absence of an electrical signal to the solenoid. As used herein, a normally high-type solenoid is energized by a control signal to be placed in and to remain in a closed position, while a normally low-type valve is energized to be placed in and to remain in a closed position. 
         [0027]    The hydraulic control portion  100  also includes a plurality of trim valves  120 ,  122 ,  124 ,  126 ,  128  and  130 . Trim valve  120 , solenoid valve PCS 1  and a spring-biased relief valve  132  are a first trim system that, as will be further explained below, is multiplexed to control engagement and disengagement of both clutch C 1  and clutch C 4 . Trim valve  122 , solenoid valve PCS 2  and accumulator valve  134  are a second trim system that is multiplexed to control engagement and disengagement of both clutch C 2  and C 5 . Trim valve  124 , solenoid valve PCS 3  and accumulator valve  136  are a third trim system that is multiplexed to control engagement and disengagement of both clutch C 3  and C 7  (for clutch C 7 , only for some speed ratios). Trim valve  126 , solenoid valve PCS 4 , converter flow valve  110  and accumulator valve  138  are a fourth trim system that controls engagement of the torque-converter clutch TCC. Trim valve  128 , solenoid valve PCS 6  and accumulator valve  140  are a fifth trim system that controls engagement and disengagement of clutch C 6 . Trim valve  130 , solenoid valve PCS 7  and accumulator valve  142  are a sixth trim system that controls engagement of clutch C 7  in those speed ratios for which the third trim system is not controlling. For each trim system, actuation of the associated solenoid valve causes actuation of the respective trim valve and clutch (or one of the respective clutches in the case of multiplexed trim valves). Solenoid valve PCS 5  and the main regulator valve  104  control the main pressure level in main passage  118  from the pump  114 . 
         [0028]    The hydraulic control portion  100  further includes logic valves X, Y, Z and W, and a dog clutch actuator valve  144 . Solenoid SS 1  receives an electrical control signal from the control unit  76  to actuate or shift, thereby shifting logic valve X. The position of logic valve X controls in part the position of dog clutch actuator valve  144 , as the downward shift on the logic valve X (moving from a spring-set position to a pressure-set position) caused by energizing solenoid SS 1  allows pressurized fluid provided from passage  118  in passage  143  to pass through the logic valve X into passage  146  in communication with the dog clutch actuator valve  144 . Solenoid valve SS 2  receives an electrical control signal from the control unit  76  to actuate or shift, thereby shifting logic valve Y, allowing pressurized fluid provided from passage  118  in passage  143  to pass through logic valves X and Y into outlet passage  148  in communication with dog clutch actuator valve  144 . Solenoid valve SS 3  receives an electrical control signal from the control unit  76  to actuate or shift, thereby allowing pressurized fluid from passage  164  to outlet passage  151  in communication with both logic valve W and dog clutch actuator valve  144 . The pressurized fluid in passage  151  causes the logic valve W to shift downward in  FIG. 2B , allowing fluid in passage  155  to be exhausted. 
         [0029]    The position of logic valve Z is controlled by the position of the dog clutch actuator valve  144 . (It should be appreciated that the dog clutch actuator valve  144  has two separately movable valve components, a spool valve  157  and a plug valve  159 .) Specifically, when the dog clutch actuator valve  144  is in a reverse position (as depicted in  FIG. 2B ) controlled pressure fluid provided to passage  161  from passage  117  is not provided to logic valve Z through passage  163 . However, when the dog clutch actuator valve is in either the neutral position or the forward position, the controlled pressure fluid from passage  161  is provided to passage  163  through restricted passage  165 A to move the logic valve Z from a spring-set position to a pressure-set position. Restricted passage  165 B is in fluid communication with switch SW 8  and restricted passage  165 C is in fluid communication with passage  153 . Two exhaust ports. EX 1  and EX 2 , are in fluid communication with the dog clutch actuator valve  144  and two switches SW 7  and SW 8  are in communication with the valve  144  to monitor its position based on pressure readings. Pressure switch SW 7  exhausts through exhaust port EX 1 , depending on the position of the spool valve  157 . Also depending on the position of the spool valve  157 , Pressure switch SW 8  exhausts through the cavity formed by the portion of the central bore of dog clutch actuator valve  144  (which is attached to a sump), shown just below pressure switch SW 8 . 
         [0030]    Referring to  FIG. 3 , a table shows the steady-state conditions of the following valves during available speed ratios (also referred to as ranges): logic valves W, X, Y and Z, dog clutch actuator valve  144 , and pressure control solenoid valves PCS 1 , PCS 2 , PCS 3 , PCS 4 , PCS 5 , PCS 6  and PCS 7 . With respect to the logic valves W, X, Y and Z, an “0” in the chart indicates that the valve is in a spring-set position (“unstroked”) and a “1” indicates that the valve is in a pressure-set position (“stroked”). With respect to the dog clutch actuator valve  144 , an “R” indicates that the dog clutch actuator valve  144  is in a reverse position (with the spool valve  157  and plug valve  159  each in their relatively lowest positions as they appear in  FIG. 2B ). Switch SW 7  will indicate a relatively low pressure condition (i.e., a low logic state) and switch SW 8  will indicate a relatively high pressure condition (i.e., a high logic state). Exhaust ports EX 1  and EX 2  will exhaust. An “F” indicates that the dog clutch actuator valve  144  is in a forward position, with the spool valve  157  in its relatively highest position with an uppermost part of the spool valve  157  shown in  FIG. 2B  experiencing exhaust pressure fluid in passage  146  and a lowest portion of the plug valve  159  experiencing exhaust pressure in passage  148 , and flow of controlled pressure from passage  117  permitted across the valve to passage  163 . Switch SW 7  will indicate a relatively high pressure condition and switch SW 8  will indicate a relatively low pressure condition. Exhaust ports EX 1  and EX 2  will exhaust. An “N” indicates that the dog clutch actuator valve  144  is in a neutral position in which the upper and lower ends of the valve are subjected to main pressure fluid from passages  146  and  148 , respectively, and flow of controlled pressure fluid from passage  117  permitted across the valve  144  to both passages  153  and  163 . Switches SW 7  and SW 8  will both indicate a relatively high pressure condition. Exhaust ports EX 1  and EX 2  will exhaust. 
         [0031]    With respect to the columns in  FIG. 3  for the respective pressure control solenoid valves PCS 1 , PCS 2 , PCS 3 , PCS 4 , PCS 6  and PCS 7 , the clutch listed for a particular speed ratio in a column for a particular solenoid valve indicates that the solenoid valve is in fluid communication with that clutch during that speed ratio. If the box listing the clutch is not shaded, then the solenoid is not energized in the case of a normally closed-type solenoid or is energized in the case of a normally open-type solenoid, and the listed clutch is not engaged. If the box is shaded, then the solenoid is energized in the case of a normally closed-type solenoid or is not energized in the case of a normally-open type solenoid, and the listed clutch is thereby engaged. With respect to PCS 5 , “MM” indicates that the pressure control solenoid PCS 5  is being energized as necessary to control an output pressure in passage  149  that controls a pressure bias on the main regulator valve  104 . The pressure control solenoid PCS 5 , by varying the pressure within passage  149 , is operable to vary the operating characteristics of the main regulator valve  104 , thereby modulating the pressure within the passage  118 . The column of  FIG. 2  labeled “Exhaust” indicates which of the clutches are being exhausted (emptied of pressurized fluid) during each of the various speed ratios. 
         [0032]    As is apparent from the chart of  FIG. 3 , the pressure control solenoid PCS 1  and the first trim system of which it is a part is multiplexed to control the engagement and disengagement of both clutches C 1  and C 4 . The pressure control solenoid PCS 2  and the second trim system of which it is a part is multiplexed to control the engagement and disengagement of both clutches C 2  and C 5 . The pressure control solenoid PCS 3  and the third trim system of which it is a part is multiplexed to control the engagement and disengagement of both clutches C 3  and C 7  (at least for ranges reverse (R 2 ), reverse (R 1 ), startup and neutral conditions, and the first forward speed ratio range (1st). For ranges above the first forward speed ratio range (1st), pressure control solenoid PCS 7  controls the engagement and disengagement of clutch C 7 . Pressure control solenoid PCS 4  controls the engagement of the torque-converter clutch TCC. Pressure control solenoid PCS 6  controls the engagement of clutch C 6 , except in speed ratio ranges (7th″). (7th′″), (8th) and (9th). In these speed ratios, clutch C 6  is not engaged, and is also not affected by the state of the pressure control solenoid PCS 6 . The dashed lines in the chart of  FIG. 3  indicate that the respective pressure control solenoid and trim system are decoupled from the respective clutch. The column labeled “Exhaust” indicates, for each speed ratio range, clutches that are being exhausted through the logic valves. The remaining clutches that are not engaged are exhausted through the associated trim valves. 
         [0033]      FIGS. 2A and 2B  depict the hydraulic control portion  100  with the positioning of the valves corresponding to the second reverse speed ratio range (R 2 ) of  FIG. 3 . When operating in the reverse speed ratio range (R 2 ), the trim valves  122  and  124  are pressure-set and trim valve  120  is spring-set by energizing the solenoids PCS 2 , PCS 3 , and PCS 1 , respectively. The remaining trim valves  126 ,  128  and  130 , and the logic valves X, Y, Z and W remain in a spring-set position. With the above-stated valve configuration, the main pressure in passage  118  is in fluid communication with clutches C 2  and C 7 , which will engage, while clutches C 3 , C 4 , and C 5  will exhaust. To effect the engagement of clutch C 2 , pressurized fluid from the passage  150  is communicated to the outlet passage  152  of the trim valve  122 . Because it is in the spring-set position, the logic valve Y will communicate the fluid within the passage  152  to the clutch C 2 . To effect the engagement of the clutch C 7 , pressurized fluid within the passage  154  is communicated to the outlet passage  156  of the trim valve  124 . Because it is in the spring-set position, the logic valve Z will communicate the fluid within passage  156  to the clutch C 7 . 
         [0034]    When operating in the first reverse speed ratio range (R 1 ), the trim valves  122  and  128  are pressure-set and trim valve  120  is spring-set by energizing solenoids PCS 2 , PCS 6  and PCS 1 , respectively. The remaining trim valves  124 ,  126  and  130 , and the logic valves X, Y, Z and W remain in a spring-set position. With the above-stated valve configuration, the main pressure in passage  118  is in fluid communication with clutches C 2  and C 6 , which will engage, while clutches C 3 , C 4 , and C 5  will exhaust. To effect the engagement of clutch C 2 , pressurized fluid from the passage  150  is communicated to the outlet passage  152  of the trim valve  122 . Because it is in the spring-set position the logic valve Y will communicate the fluid within the passage  152  to the clutch C 2 . To effect the engagement of clutch C 6  pressurized fluid within passage  158  is communicated to outlet passage  160  of trim valve  128 . Because they are in the spring-set position, logic valve X and logic valve Y communicate the fluid within passage  118  to passage  158 . 
         [0035]    When starting the engine  12  of  FIG. 1  (indicated in  FIG. 3  as “startup”), the logic valve X and the trim valve  128  are pressure-set and trim valve  120  is spring-set by energizing the solenoids SS 1 , PCS 6 , and PCS 1 , respectively. The remaining trim valves  120 ,  124 ,  126  and  130 , and logic valves Y, Z and W remain in a spring-set position. With the above-stated valve configuration, the main pressure in passage  118  is in fluid communication with clutch C 6 , which will engage, while clutches C 1 , C 3 , and C 5  will exhaust. To effect the engagement of clutch C 6 , pressurized fluid within passage  158  is communicated to outlet passage  160  of trim valve  128 . The pressure-set position of logic valve X and the spring-set position of logic valve Y allow fluid in passage  118  to be communicated to passage  158 . 
         [0036]    When operating in the neutral state, indicated as “N” in  FIG. 3 , the trim valve  128  is pressure-set and trim valve  120  spring set by energizing solenoids PCS 6  and PCS 1 , respectively. The remaining trim valves  124 ,  126  and  130 , and the logic valves X, Y, Z and W remain in a spring-set position. With the above-stated valve configuration, the main pressure in passage  118  is in fluid communication with clutch C 6 , which will engage, while clutches C 3 , C 4  and C 5  will exhaust. To effect the engagement of clutch C 6 , pressurized fluid within passage  158  is communicated to outlet passage  160  of trim valve  128 . Because they are in the spring-set position, logic valve X and logic valve Y communicate the fluid within passage  118  to passage  158 . 
         [0037]    When operating in the first forward speed ratio range (1st), the trim valves  120  and  128  are pressure-set by not energizing solenoid PCS 1  and energizing PCS 6 , respectively. (Note that, because PCS 1  is normally open, in a steady state condition, no energizing control signal is required in order to pressure-set the trim valve  120 .) The remaining trim valves  122 ,  124 ,  126  and  130 , and the logic valves X, Y, Z and W remain in a spring-set position. With the above-stated valve configuration, the main pressure in passage  118  is in fluid communication with clutches C 1  and C 6 , which will engage, while clutches C 3 . C 4 , and C 5  exhaust. To effect engagement of clutch C 1 , pressurized fluid within passage  150  is communicated to outlet passage  162  of trim valve  120 . To effect the engagement of clutch C 6 , pressurized fluid within passage  158  is communicated to outlet passage  160  of trim valve  128 . Because they are in the spring-set position, logic valve X and logic valve Y communicate the fluid within passage  118  to passage  158 . 
         [0038]    When operating in the alternate first forward speed ratio range (1st′), in addition to pressure-setting trim valves  120  and  128  as in the first forward speed ratio range (1st), trim valve  126  is also pressure-set by energizing solenoid valve PCS 4 . Solenoid valve SS 3  is also energized to shift the dog clutch actuator valve  144  to a forward position, thus blocking exhaust of controlled pressure fluid from passage  117  in passage  161  provided to passage  163  through restricted passage  165 A, to move the logic valve Z from a spring-set position to a pressure-set position. Solenoid valve SS 3  is no longer energized after the dog clutch actuator valve  144  moves to the forward position, as confirmed by the pressure switches SW 7  and SW 8  shown in communication with the dog clutch actuator valve  144 , and control pressure in passage  151  is exhausted, to eliminate unnecessary loading of the dog clutch DOG. With the above-stated valve configuration, the main pressure in passage  118  is in fluid communication with clutches C 1  and C 6 , which will engage. The main pressure in passage  118  is communicated to the converter flow valve  110  via passage  164  across trim valve  126  to passage  167 . Clutches C 4 , and C 5  exhaust. 
         [0039]    When operating in the second forward speed ratio range (2nd), the trim valves  122 ,  126  and  128  are pressure-set and trim valves  120  and  130  are spring-set by energizing solenoids PCS 2 , PCS 4 , PCS 6 , PCS 1  and PCS 7 , respectively. If the second forward speed ratio range is attained in a shift from the first alternate speed ratio range (1st′), then the dog clutch actuator valve  144  remains in the forward position and the logic valve Z in a pressure-set position due to the previous actuation of the dog clutch actuator valve  144  in the first alternate forward speed ratio range (1st′). The remaining trim valves  120  and  124  remain in a spring-set position. With the above-stated valve configuration, clutches C 2 , TCC and C 6  will be in an engaged position while clutches C 4  and C 5  exhaust. To effect engagement of clutch C 2 , pressurized fluid within passage  150  is communicated to outlet passage  152  of trim valve  122 . To effect the engagement of clutch C 6 , pressurized fluid within passage  158  is communicated to outlet passage  160  of trim valve  128 . Because they are in the spring-set position, logic valve X and logic valve Y communicate the fluid within passage  118  to passage  158 . To effect engagement of clutch TCC, trim valve  126  is pressure-set by energizing solenoid valve PCS 4 , so that the main pressure in passage  118  is communicated to the converter valve  110  via passage  164  across trim valve  126  to passage  167 . 
         [0040]    When operating in the third forward speed ratio range (3rd), the trim valves  124 ,  126  and  128  are pressure-set and trim valves  120  and  130  are spring-set by energizing solenoids PCS 3 , PCS 4 , PCS 6 , PCS 1  and PCS 7 , respectively. The dog clutch actuator valve  144  remains in the forward position and the logic valve Z in a pressure-set position due to the previous actuation of the dog clutch actuator valve  144  in the first alternate forward speed ratio range (1st′) or in the second forward speed ratio range (2nd), as described above. The remaining trim valve  122  remains in a spring-set position. With the above-stated valve configuration, clutches C 3 , TCC and C 6  will be in an engaged position while clutches C 4  and C 5  will exhaust. To effect engagement of clutch C 3 , pressurized fluid from passage  118  within passage  154  is communicated to outlet passage  156  of the trim valve  124  and through the pressure-set logic valve Z to clutch C 3 . To effect engagement of clutch TCC, trim valve  126  is pressure-set by energizing solenoid valve PCS 4 . To effect engagement of clutch C 6 , pressurized fluid within passage  158  is communicated to outlet passage  160  of trim valve  128 . Because they are in the spring-set position, logic valve X and logic valve Y communicate the fluid within passage  118  to passage  158 . 
         [0041]    When operating in the alternate third forward speed ratio range (3rd′), the trim valves  124 ,  126  and  128  are pressure-set and trim valves  120  and  130  are spring set by energizing solenoids PCS 3 , PCS 4 , PCS 6 , PCS 1  and PCS 7 , respectively, to cause engagement of clutches C 3 , TCC and C 6 , as described above with respect to the third forward speed ratio range (3rd). The dog clutch actuator valve  144  remains in the forward position and the logic valve Z in a pressure-set position due to the previous actuation of the dog clutch actuator valve  144  in the first alternate forward speed ratio range (1st′) or in the second forward speed ratio range (2nd), as described above. Additionally, solenoid valve SS 2  is energized to move the logic valve Y to a pressure-set position, thus allowing main pressure from passage  118  in communication with passage  169  to flow across the logic valve Y to outlet passage  148 , moving the plug valve  159  of the dog clutch actuator valve  144  upward. Additionally, the shifting of logic valve Y puts exhaust pressure rather then main pressure into communication with the switches SW 2  and SW 1  at the trim valves  120  and  128 , respectively. 
         [0042]    When operating in the fourth forward speed ratio range (4th), trim valves  122 ,  126  and  128  are pressure-set and trim valves  120  and  130  are spring-set by energizing solenoids PCS 2 , PCS 4 , PCS 6 , PCS 1  and PCS 7 , respectively. The dog clutch actuator valve  144  remains in the forward position and the logic valve Z in a pressure-set position due to the previous actuation of the dog clutch actuator valve  144  in the first alternate forward speed ratio range (1st′) or in the second forward speed ratio range (2nd), as described above. Solenoid valve SS 2  is energized to place logic valve Y in a pressure-set position. With the above-stated valve configuration, clutches C 5 , TCC and C 6  will be in an engaged position while clutches C 2  and C 4  will exhaust. Engagement of the clutches TCC and C 6  are as described above with respect to the third forward speed ratio range (3rd). To effect engagement of clutch C 5 , solenoid PCS 2  is energized to move trim valve  122  to a pressure-set position. Pressurized fluid from passage  118  in communication with passage  150  is communicated to outlet passage  152  across trim valve  122  and then across the pressure-set logic valve Y into communication with clutch C 5 . 
         [0043]    When operating in the fifth forward speed ratio range (5th), trim valves  120 ,  126  and  130  are pressure-set. Solenoid PCS 4  is energized to pressure-set trim valve  126 , but solenoids PCS 1  and PCS 7  are not energized to pressure-set trim valves  120  and  130 , as these are normally open-type solenoid valves. The dog clutch actuator valve  144  remains in the forward position and the logic valve Z in a pressure-set position due to the previous actuation of the dog clutch actuator valve  144  in the first alternate forward speed ratio range (1st′) or in the second forward speed ratio range (2nd), as described above. Solenoid valve SS 2  is energized to place logic valve Y in a pressure-set position. With the above-stated valve configuration, clutches C 1 , TCC and C 7  will be in an engaged position while clutches C 2  and C 4  will exhaust. To effect engagement of clutch C 1 , pressurized fluid within passage  150  is communicated to outlet passage  162  of trim valve  120 . With the logic valve X in the spring-set position, fluid in passage  162  communicates with the clutch C 1  across the logic valve X. To effect the engagement of clutch TCC, trim valve  126  is pressure-set by energizing solenoid PCS 4 . To effect the engagement of clutch C 7 , pressurized fluid within passage  154  is communicated to outlet passage  173  and across the pressure-set logic valve Z to the clutch C 7 . With the logic valve Y in a pressure-set position, pressurized fluid in passage  152  can exhaust. 
         [0044]    When operating in the alternate fifth forward speed ratio range (5th′), trim valves  120 ,  126  and  130  are pressure-set, by energizing solenoid PCS 4 , but not solenoids PCS 1  or PCS 7 , as described above with respect to the fifth forward speed ratio range (5th). The dog clutch actuator valve  144  remains in the forward position and the logic valve Z in a pressure-set position due to the previous actuation of the dog clutch actuator valve  144  in the first alternate forward speed ratio range (1st′) or in the second forward speed ratio range (2nd), as described above. With the above-stated valve configuration, the clutches C 1 , TCC and C 7  are engaged (as described above with respect to the fifth forward speed ratio range (5th)) while the clutches C 4  and C 5  exhaust. 
         [0045]    When operating in the sixth forward speed ratio range (6th), trim valves  122 ,  126  and  130  are pressure-set. Solenoids PCS 2  and PCS 4  are energized to pressure-set trim valves C 2  and TCC, respectively, but solenoid valve PCS 7  is not energized, as it is normally open. The dog clutch actuator valve  144  remains in the forward position and the logic valve Z in a pressure-set position due to the previous actuation of the dog clutch actuator valve  144  in the first alternate forward speed ratio range (1st′) or in the second forward speed ratio range (2nd), as described above. With the above-stated valve configuration, clutches C 2 , TCC and C 7  will engage while clutches C 4  and C 5  will exhaust. To effect engagement of clutch C 2 , pressurized fluid within passage  150  is communicated to outlet passage  152  of trim valve  122 . The clutches TCC and C 7  are engaged as described above with respect to the fifth forward speed ratio range (5th). 
         [0046]    When operating in the seventh forward speed ratio range (7th), trim valves  124 ,  126  and  130  are pressure-set. Solenoids PCS 3  and PCS 4  are energized to pressure-set trim valves  124  and  126 , respectively, but solenoid valve PCS 7  is not energized, as it is normally open. The dog clutch actuator valve  144  remains in the forward position and the logic valve Z in a pressure-set position due to the previous actuation of the dog clutch actuator valve  144  in the first alternate forward speed ratio range (1st′) or in the second forward speed ratio range (2nd), as described above. With the above-stated valve configuration, clutches C 3 , TCC and C 7  will engage while clutches C 4  and C 5  will exhaust. To effect engagement of clutch C 3 , pressurized fluid from passage  118  within passage  154  is communicated to outlet passage  156  of the trim valve  124  and through the pressure-set logic valve Z to clutch C 3 . The clutches TCC and C 7  are engaged as described above with respect to the fifth forward speed ratio range (5th). 
         [0047]    When operating in the seventh alternate forward speed ratio range (7th′), trim valves and solenoids are energized as described with respect to the seventh forward speed ratio range (7th), except that solenoid valve SS 2  is also energized to place the Y valve into a pressure-set position, thus providing pressurized fluid to channel  148 , control pressure to channel  175 , and exhaust fluid to channel  171 , causing the pressure at switch SW 2  in communication with trim valve  120  to be exhaust pressure and pressure at switch SW 1  in communication with trim valve  128  to be control pressure. 
         [0048]    When operating in the seventh alternate forward speed ratio range (7th″), trim valves and solenoids are energized as described with respect to the seventh forward speed ratio range (7th), except that solenoid valves SS 1  and SS 2  are also energized. Energizing solenoid valve SS 1  places logic valve X in a pressure-set position to allow pressurized fluid from passage  143  to passage  146  and shifts the dog actuator clutch valve  144  to a neutral position, while preventing the pressurized fluid in passage  143  from reaching passage  174 , changing the monitored pressures at the switches SW 3  and SW 4  associated with trim valves  122  and  124  from high pressure to low pressure and the monitored pressure at the lower switch SW 8  associated with the dog clutch actuator valve  144  from exhaust pressure to control pressure. With the dog clutch actuator valve  144  in a neutral position, logic valve Z is in a pressure-set position. Solenoid valve SS 2  is also energized to place logic valve Y into a pressure-set position, thus providing pressurized fluid to channel  148  and exhaust fluid to channel  171 , causing the pressure at switch SW 2  associated with trim valve  120  to be at exhaust pressure and pressure at switch SW 1  associated with trim valve  128  to be at control pressure. 
         [0049]    When operating in the seventh alternate forward speed ratio range (7th′″), trim valves and solenoids are energized as described with respect to the seventh forward speed ratio range (7th), except that solenoid valves SS 1 , SS 2  and SS 3  are also energized. Energizing solenoid valves SS 1  and SS 2  has the effects described above with respect to speed ratio range (7th″). Energizing solenoid valve SS 3  as well moves logic valve W to a pressure-set position, thus exhausting fluid in channel  155 . 
         [0050]    When operating in the eighth forward speed ratio range (8th), trim valves  124 ,  126  and  130  are pressure-set. Solenoid valve PCS 4  is energized to pressure-set trim valve  126 , but solenoid valves PCS 1  and PCS 7  are not, as these are normally open-type solenoid valves. Solenoid valves SS 1  and SS 2  are also energized to move the logic valves X and Y, respectively, to pressure-set positions, causing the dog clutch actuator valve  144  to be in a neutral position. With logic valve X in a pressure-set position, pressurized fluid from passage  143  is communicated to passage  146 , while preventing the pressurized fluid in passage  143  from reaching passage  174 , causing the monitored pressures at the switch SW 3  associated with trim valve  122  to be at exhaust pressure, that at the switch SW 4  associated with trim valve  124  to be at control pressure, and that at the lower switch SW 8  associated with the dog clutch actuator valve  144  to be at control pressure. With the dog clutch actuator valve  144  in a neutral position, logic valve Z is in a pressure-set position. With the above-stated valve configuration, clutches C 4 , TCC and C 7  will engage while clutches C 1 , C 2  and C 6  will exhaust. To effect engagement of clutch C 4 , pressurized fluid from passage  150  crosses the pressure-set trim valve  120  to outlet passage  162  and across pressure-set logic valve X into communication with clutch C 4 . To effect the engagement of clutch TCC, trim valve  126  is pressure-set by energizing solenoid valve PCS 4 . To effect engagement of clutch C 7 , pressurized fluid from passage  154  crosses pressure-set trim valve  130  to communicate with passage  173  and then crosses pressure-set logic valve Z into communication with clutch C 7 . The pressure-set position of logic valve X allows pressurized fluid to pass from passage  143  across the pressure-set logic valve X to passage  146 , shifting the dog clutch actuator valve  144  to a neutral state or position, allowing control pressure fluid to contact the lower switch SW 8  associated with the dog clutch actuator valve  144 . Furthermore, the pressure-set position of logic valve Y allows some of the pressurized fluid crossing logic valve X to be routed to passage  148 . 
         [0051]    When operating in the ninth forward speed ratio range (9th), trim valves  122 ,  126  and  130  are pressure-set. Solenoid valves PCS 2  and PCS 4  are energized to pressure-set trim valves  122  and  126 , but solenoid valve PCS 7  is not energized, as it is normally-open type solenoid valve. Solenoid valves SS 1  and SS 2  are also energized so that logic valves X and Y, respectively, are in pressure-set positions and the dog clutch actuator valve  144  is in a neutral position. With the above-stated valve configuration, clutches TCC and C 7  will engage (as described above with respect to the eighth forward speed ratio range (8th)) as well as clutch C 5 , while clutches C 1 , C 2  and C 6  will exhaust. To effect engagement of clutch C 5 , pressurized fluid from forward  150  communicates with outlet passage  152  across the pressure-set trim valve  122  and then with clutch C 5  through the pressure-set logic valve Y. Because the control system  100  is designed with the dog clutch actuator valve  144  in the neutral position in the higher speed ratio ranges (the alternate seventh forward speed ratio ranges (7th″) and (7th′″)), as well as in the eighth (8th) and ninth (9th) forward speed ratio ranges, spin losses are reduced in the transmission  10  of  FIG. 1 . 
       Multiplexing of Trim Systems 
       [0052]    As is evident from the Figures and from the above description, the first trim system, which includes solenoid valve PCS 1  and trim valve  120 , is multiplexed to control engagement of clutches C 1  and clutch C 4 . Shifting of the logic valve X between a spring-set position and a pressure-set position determines which of the clutches C 1  and C 4  will be engaged via the pressurized fluid fed through the pressure-set trim valve  120  and the logic valve X. 
         [0053]    Furthermore the second trim system, which includes solenoid valve PCS 2  and trim valve  124  is multiplexed to control engagement of clutches C 2  and C 5 . Shifting of logic valve Y between a spring-set position and a pressure-set position determines which of the clutches C 2  and C 5  will be engaged via pressurized fluid fed through the pressure-set trim valve  124  to the logic valve Y. 
         [0054]    Still further, the third trim system, which includes the solenoid valve PCS 3  and the trim valve  124  is multiplexed to control engagement of the C 3  and C 7  clutches, at least in speed ratio ranges (R 2 ), (R 1 ), startup, neutral, and first forward speed ratio range (1st). In speed ratio ranges above the first forward speed ratio range (1 st ), engagement of clutch C 7  is controlled by the sixth trim system, which includes solenoid valve PCS 7  and trim valve  130 . Shifting of logic valve Z between a spring-set position and a pressure-set position determines which of the clutches C 3  and C 7  will be engaged via pressurized fluid fed through the pressure-set trim valve  124  to the logic valve Z. The shifting of logic valve Z is controlled by the position of the dog clutch actuator valve  144 , which in turn is controlled by the positions of the logic valves X and Y and by solenoid valve SS 3 . 
       Double Transition Shifts and Skip Shifts 
       [0055]    As is evident from  FIG. 3  and from the above description, a shift from the fourth forward speed ratio range (4th) to the fifth forward speed ratio range (5th) involves a four clutch, double transition shift. That is, clutches C 5  and C 6  are disengaged while clutches C 1  and C 7  are engaged. Thus, even with the multiplexing of the trim systems, this four clutch shift is achieved by the control system  100 . A four clutch, double transition shift is also realized. As is evident from  FIG. 3 , numerous other shifts also involve double transition shifts (i.e., a shift that requires that more than one clutch be engaged or disengaged). The system  100  is also able to accomplish many skip shifts, including a shift from the first reverse speed ratio range (R 1 ) to the first forward speed ratio range (1st); a shift from the second reverse speed ratio range (R 2 ) to the first forward speed ratio range (1st); a shift from the first alternative forward speed ratio range (1st′) to the third forward speed ratio range (3rd); a shift from the third forward speed ratio range (3rd) to the fifth forward speed ratio range (5th); a shift from the fifth forward speed ratio range (5th) to the seventh forward speed ratio range (7th); and a shift from the second alternative seventh forward speed ratio range (7th″) to the ninth forward speed ratio range (9th). 
       Logic Valves Used to Control Power Off/Drive-Home Modes 
       [0056]    The hydraulic control system  100  is configured to provide a functional “drive-home” system in the event of an interruption or failure in electrical power, which would prevent selective energizing of the solenoid valves. The hydraulic control system  100  is designed to default to two different speed ratio ranges (referred to as failure modes), i.e., there are two different failure modes, depending on which speed ratio range the system  100  is providing when failure occurs. Specifically, if power failure occurs while the transmission  10  is operating in any of the first reverse speed ratio range (R 1 ), the second reverse speed ratio range (R 2 ) or is in neutral (N), the hydraulic control system  100  will automatically operate in a neutral state (i.e., an operating condition which will not allow driving the vehicle in either forward or reverse). This “failure” to a neutral state occurs for several reasons. First, in each of the first reverse speed ratio range (R 1 ), the second reverse speed ratio range (R 2 ) or the neutral (N) speed ratio range, the dog clutch actuator valve  144  is in a reverse position during normal operation (i.e., when electrical energy is available). Additionally, because solenoid valve PCS 1  is a normally open-type valve, trim valve  120  will be pressure-set in the absence of an energizing control signal. This causes the pressurized fluid in passage  150  to communicate with outlet passage  162  and be directed through the logic valve X (which allows flow to clutch C 1  when in the spring-set position) to clutch C 1 . Because the trim valves  122 ,  124 ,  128  and  130  and the logic valves Z and Y are in spring-set positions during a power failure with the dog clutch actuator valve  144  in a reverse position, trim valve  128  does not allow pressurized fluid flow to clutch C 6 , logic valve Z does not allow pressurized fluid flow to clutches C 3  and C 7 , and logic valve Y does not allow pressurized fluid flow to clutches C 2  and C 5 . With only clutch C 1  engaged, the transmission  10  of  FIG. 1  operates in a neutral state. 
         [0057]    If power failure occurs when the transmission  10  is in any of the speed ratio ranges (1st), (1st′), (2nd). (3rd), (3rd′), 4th), (5th), (5th′), (6th). (7th), and (7th′), referred to herein as “low” speed ratio ranges, the hydraulic control system  100  will automatically operate in the fifth forward speed ratio range (5th). This “failure” to the fifth forward speed ratio range (5th) occurs for several reasons. First, in each of the first forward speed ratio range (1st) through the seventh alternate forward speed ratio range (7 th ′), the dog clutch actuator valve  144  is in a forward position during normal operation (i.e., when electrical energy is available), causing logic valve Z to be pressure-set Additionally, because solenoid valve PCS 1  is a normally open-type valve, trim valve  120  will be pressure-set in the absence of an energizing control signal. This causes the pressurized fluid in passage  150  to communicate with outlet passage  162  and be directed through the logic valve X (which allows flow to clutch C 1  when in the spring-set position) to clutch C 1 . Solenoid valve PCS 7  is also a normally-open type solenoid valve, so trim valve  130  will be pressure-set in the absence of an electrical control signal and will provide pressurized fluid from passage  154  to outlet passage  173  and through the pressure-set logic valve Z to clutch C 7 . Because the trim valves  120 ,  124 , and  128  and the logic valves X and Y are in spring-set positions during a power failure with the dog clutch actuator valve  144  in a reverse position, trim valve  128  does not allow pressurized fluid flow to clutch C 6 , and logic valve Y does not allow pressurized fluid flow to clutches C 2  and C 5 . With only clutches C 1  and C 75  engaged, the transmission  10  of  FIG. 1  operates in the fifth forward speed ratio range, except without engagement of the torque-converter clutch TCC. 
         [0058]    If power failure occurs when the transmission  10  is in any of the speed ratio ranges (7th″), (7th′″), (8th), or (9th), referred to herein as “high” speed ratio ranges, the hydraulic control system  100  will automatically operate in the eighth forward speed ratio range (8th). This “failure” to the eighth forward speed ratio range (8th) occurs for several reasons. First, in each of the alternate seventh forward speed ratio range (7th″) through the ninth forward speed ratio range (9th), the dog clutch actuator valve  144  is in a neutral position during normal operation (i.e., when electrical energy is available), causing logic valve Z to be pressure-set. When power is interrupted, the neutral position of the dog clutch actuator valve  144  causes logic valves X and Y to remain pressure-set (i.e., the dog clutch actuator valve  144  latches the logic valves X and Y), as they are in each of the alternate seventh forward speed ratio range (7th″) through the ninth forward speed ratio range (9th), even though solenoid valves SS 1  and SS 2  are not energized, because there are no exhaust routes open for the pressurized fluid in passages  146  and  148  acting on logic valves X and Y, and for the controlled pressure fluid acting on logic valves X and Y through the spring-set logic valve W which communicates passage  153  with passage  155 . During normal operation, the solenoid SS 3  can be energized to place logic valve W in a pressure-set position (either in steady state, or temporarily) to prevent fluid communication between passages  153  and  155 , thus preventing the dog clutch actuator  144  from having a latching effect on logic valves X and Y. 
         [0059]    The logic valves X and Y also function to “lock out” clutch C 6  during forward ratio ranges (7th″), (7th′″), (8th) and (9th). This occurs because, in these operating ranges, the logic valves X and Y are both in pressure-set positions. Thus, logic valve X and logic valve Y prevent pressurized fluid from passage  118  from reaching passage  158 , while logic valve Y allows control pressure fluid from passage  117  to passage  179 , preventing trim valve  128  from being placed in a pressure-set position by solenoid valve PCS 6 . 
         [0060]    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.

Technology Classification (CPC): 5