Abstract:
An electro-hydraulic control for a six speed power transmission has three shift control valves that are each actuated by a spring and a solenoid valve. The shift valves are positioned in either a spring set or a pressure set position to establish flow paths to five torque transmitting mechanisms (friction devices) that are engaged according to a predetermined schedule to establish six forward speed ratios and one reverse ratio. A pair of high ratio control valves and a pair of low ratio control valves operate to control the actuation pressures for the friction devices. The actuation pressures are distributed through a switching valve. The high ratio control valves control the on coming friction device with an increasing pressure schedule while the low ratio control valves control the off going friction device with a decreasing pressure schedule. A bias port on each of the low ratio valves is responsive to the pressure output of the high ratio control valve to discontinue operation of the low ratio control valve when the on coming friction device has sufficient capacity to transmit the torque. During downshifting, a down shift valve is operable to prevent the pressure of the high ratio control valve from acting on the bias ports. An exhaust switch valve cooperates with the switching valve to ensure that the proper pressure is distributed to the friction devices following an up shift or a down shift.

Description:
TECHNICAL FIELD 
     This invention relates to transmission controls for a power transmission. 
     BACKGROUND OF THE INVENTION 
     Power transmissions of the automatic shifting type have a plurality of selectively establishable gear ratios between the engine and ground engaging mechanism for the vehicle. The ratios are generally established by hydraulically operated friction devices such as clutches and brakes. The engagement and disengagement of these friction devices are controlled by valve mechanisms which direct hydraulic fluid to and from the operating piston of the devices. 
     Some transmission control systems have incorporated electrohydraulic control systems with “clutch to clutch” shift technology. The control systems have utilized two strategies, open loop control and closed loop control. During open loop control, the on-coming friction torque transmitting mechanism (clutch or brake) is filled with fluid and the pressure is ramped up to the inertial pressure required during the shift. The release timing of the pressure in the off-going friction torque transmitting mechanism is based on an estimation of the oncoming torque transmitting mechanism fill time. The fill time of the oncoming torque transmitting mechanism varies due to many design and assembly factors such that the release of the off-going torque transmitting mechanism can be early, causing a flare, or late, causing a tie-up. Some control algorithms have been developed to detect the oncoming clutch fill using an input or output speed signal. However, these have not proved reliable for practical use. 
     During closed loop control, the off-going torque transmitting mechanism capacity is reduced to its critical point by generating a predetermined slip speed in the off-going torque transmitting mechanism. The oncoming torque transmitting mechanism is filled and ramped up to the inertial pressure. As the oncoming torque transmitting mechanism gains capacity, the input speed will drop. As the input speed drop is detected by the microprocessor, the off-going torque transmitting mechanism capacity is reduced to zero. In the closed loop control, there is a controlled engine flare at the beginning of the interchange causing an output torque dip. Also since the off-going torque transmitting mechanism is not released until the input speed drop is detected, a tie-up is present during the ratio interchange. 
     SUMMARY OF THE INVENTION 
     The present invention provides a transmission control system for a six speed automatic transmission. The control system provides clutch-to-clutch shift control with new features to improve robustness and failure mode. 
     The system minimizes the number of components while still ensuring the transmission is protected against any combination of actuator interruption. 
     The control system includes four pressure control valves, two low pressure ratios and two high pressure ratios. During an upshift transition, a switch valve directs an increasing pressure from a high ratio control valve to the on-coming friction device and a decreasing pressure from a low ratio control valve to the off-going clutch. A downshift valve is disposed in the circuit to direct the oncoming pressure to a bias port on the low ratio control valve to discontinue operation of the low ratio control valve and exhaust the of-going friction device. When the shift transition is complete, the switch valve directs fixed pressure to the engaged friction devices. 
     During a downshift, the downshift valve prevents the bias from the high ratio control valve, controlling the off-going friction device, from affecting the pressure output of the low ratio control valve which is controlling the on-coming friction device. An exhaust switching valve is provided to cooperate with the switch valve to insure that the proper friction device is pressurized and that the proper friction device is exhausted. During an up shift, the oncoming device (high ratio friction device) is maintained with a system pressure, and the off-going device (low ratio friction device) is supplied with a low (approx. 2 psi) fluid pressure. During a down shift, the opposite pressure schedule is required. The exhaust switching valve ensures that this will occur. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a powertrain compatible with the present invention transmission control system; 
     FIG. 2 is a diagrammatic representation depicting a transmission control system incorporating the present invention; and 
     FIG. 3 is a table summarizing the torque transmitting mechanism engagement schedule and valve operation of a transmission control system incorporating the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A transmission  10  is shown in FIG.  1  and includes an input shaft E connected to receive torque from an engine, not shown, an output shaft S connected to deliver torque to the drive wheels, not shown, and a multi-speed planetary gear arrangement  12  operatively connected therebetween. The planetary gear arrangement  12  described is just one of those shown in U.S. Pat. No. 5,106,352 issued to Lepelletier. 
     The planetary gear arrangement  12  includes five conventional fluid-operated friction devices, three being illustrated and designated as clutches: C 1 , C 2 , and C 3 , and two as brakes: B 1  and B 2 , which are well known in the art. The brakes are depicted schematically as band type brakes, however, it is well known to utilize a disc type friction brake in place of a band brake in the transmission art. 
     The planetary gear arrangement  12  has a first gearset  14  including a gear  14   a  fixed to the input shaft E and a gear  14   b  in constant meshing engagement with gear  14   a  and connected to the first control clutch C 1  and the second control clutch C 2 . 
     A second gearset  16  includes a gear  16   a  fixed to the input shaft E and a gear  16   b  in constant meshing engagement with gear  16   a  and connected to the third control clutch C 3 . 
     A double planetary gearset  18  has a first gearset  20  including a sun gear  22 , a ring gear  24  and a planet carrier assembly  26 . The planetary carrier assembly  26  includes a plurality of single pinions  28  rotatably mounted thereon and meshing with the sun gear  22  and the ring gear  24 . The double gearset  18  has a second gearset  30  including a sun gear  32 , a ring gear  34  and a planet carrier assembly  36 . The planetary carrier assembly  36  includes a plurality of single pinions  38  rotatably mounted thereon and meshing with the sun gear  32  and the ring gear  34 . 
     A one-way mechanism R 1  is arranged in parallel with the first control brake B 1  to facilitate transitions between first and second gear in a manner known in the art. 
     The planetary gear arrangement further includes four rotatable members referred to as  40 ,  42 ,  44 , and  46 . First member  40  is associated with the first control clutch C 1  and the ring gear  24 . Second member  42  is formed by the planet carrier  26  of the gearset  20 , fixed for rotation with the ring gear  34  of the gearset  30  and the output shaft S. The third member  44  is associated with the planet carrier  36  of the gearset  30 , the third control clutch C 3 , the one-way mechanism R 1 , and the first control brake B 1 . The fourth member  46  is associated with the sun gears  22  and  32  of the gear sets  20  and  30  and fixed for rotation with each other, and with the second control clutch C 2  and the second control brake B 2 . 
     The planetary gear arrangement  12  provides six forward speed ratios and one reverse transmission ratio with the appropriate pair of friction devices engaged as charted in FIG.  3 . The first forward speed ratio is provided with the actuation of first control clutch C 1  and first control brake B 1 . The first member  40  is driven and the third member  44  is held against rotation. 
     The second forward drive ratio is established by disengaging first control brake B 1  and engaging second control brake B 2 , while the clutch C 1  remains engaged. The first member  40  is driven and the fourth member  46  is held against rotation. 
     The third forward drive ratio is established by disengaging second control brake B 2  while engaging the second control clutch C 2  and maintaining the clutch C 1  engaged. The first and fourth members  40  and  46  and the double planetary gearset  18  are driven as a unit. 
     The fourth forward drive ratio is established by releasing second control clutch C 2 , engaging the third control clutch C 3 , while maintaining the first control clutch C 1  engaged. The first and third members  40  and  44  are driven. 
     The fifth drive ratio is provided by engaging second control clutch C 2  while disengaging first control clutch C 1  and maintaining third control clutch C 3  engaged. The third and fourth members  44  and  46  are driven. 
     The sixth drive ratio is provided by engaging the second control brake B 2  and maintaining the third control clutch C 3  engaged, while disengaging the second control clutch C 2 . This transmits torque through the third member  44  while holding the fourth member  46  against rotation. 
     A reverse drive ratio is provided through the engagement of the second control clutch C 2  and the first control brake B 1 . The fourth member  46  is driven while the third member  44  is held stationary. 
     The engagement and disengagement of the fluid-operated friction devices are controlled through an electro-hydraulic control system  50  of the present invention, diagrammed schematically in FIG.  2 . 
     The electro-hydraulic control system  50  includes a pump  54  to supply hydraulic fluid to an electro-hydraulic control  52 . The electro-hydraulic control  52  incorporates an electronic control module (ECU) that includes a conventional preprogrammed digital computer and hydraulic devices (HYDRAULIC) including conventional pressure control valves and conventional directional valves such as a manual valve. 
     The electro-hydraulic control system  50  also includes three shift logic valves  56 ,  58 , and  60 , two high ratio control valves  62  and  64 , two low ratio control valves  66  and  68 , two pressure control valves  70  and  72 , a reverse control valve  74 , and a backfill pressure regulator valve  76 . The control system  50  further includes a steady state/transition switch logic valve  78  (referred to as S/T switch valve), a downshift valve  80 , and a drive/exhaust switch valve  82  (referred to as D 5 /ex valve). 
     The shift logic valve  56  is comprised of a shift valve  84  and a control valve  86 . The control valve  86  is a conventional off-on type solenoid valve controlled by the ECU. The shift valve  84  is a directional flow control valve having twelve ports  84 A,  84 B,  84 C,  84 D,  84 E,  84 F,  84 G,  84 H,  84 I,  84 J,  84 K, and  84 L, which are selectively connectable with six ports  84 M,  84 N,  840 ,  84 P,  84 Q, and  84 R. In the spring set position shown, the ports  84 B,  84 C,  84 F,  84 G,  84 J,  84 L are blocked; the port  84 A is connected to  84 M, the port  84 D is connected to  84 N, the port  84 E is connected to  840 , the port  84 H is connected to  84 P, the port  84 I is connected to  84 Q, and the port  84 K is connected to  84 R. In the pressure set position, that is when the control valve  86  is energized by the ECU to control the fluid pressure delivered through a passage  87  to the shift valve  84 , the ports  84 A,  84 D,  84 E,  84 H,  84 I, and  84 K are blocked, while the ports  84 B,  84 C,  84 F,  84 G,  84 J, and  84 L are connected to the ports  84 M,  84 N,  840 ,  84 P,  84 Q, and  84 R respectively. 
     The shift logic valve  58  is comprised of a shift valve  88  and a control valve  90  which are interconnected by a passage  91 . The pressure in the passage  91  is controlled by the control valve  90 , which is an off-on type solenoid valve controlled by the ECU. The shift valve  88  has a spring set position shown and a pressure set position which is achieved when the passage  91  is pressurized. The shift valve  88  has twelve ports  88 A,  88 B,  88 C,  88 D,  88 E,  88 F,  88 G,  88 H,  88 I,  88 J,  88 K, and  88 L, which are selectively connectable with six ports  88 M,  88 N,  88 O,  88 P,  88 Q, and  88 R. In the spring set position shown, the ports  88 A,  88 C,  88 E,  88 G,  88 J, and  88 L are connected with the ports  88 M,  88 N,  88 O,  88 P,  88 Q, and  88 R respectively, while the ports  88 B,  88 D,  88 F,  88 H,  88 I, and  88 K are blocked. In the pressure set position, the ports  88 B,  88 D,  88 F,  88 H,  88 I, and  88 K are connected with the ports  88 M,  88 N,  88 O,  88 P,  88 Q, and  88 R respectively, while the ports  88 A,  88 C,  88 E,  88 G,  88 J, and  88 L are blocked. 
     The shift logic valve  60  is comprised of a shift valve  92  and a control valve  94 , which are interconnected by a passage  95 . The pressure in the passage  95  is controlled by the control valve  94  which is an off-on type solenoid valve controlled by the ECU. The shift valve  92  has fourteen ports  92 A,  92 B,  92 C,  92 D,  92 E,  92 F,  92 G,  92 H,  92 I,  92 J,  92 K,  92 L,  92 M, and  92 N, which are selectively connectable with seven ports  92 O,  92 P,  92 Q,  92 R,  92 S,  92 T,  92 U, and  92 V. In the spring set position shown, the ports  92 A,  92 C,  92 F,  92 G,  92 I,  92 L, and  92 M are connected with the ports  92 O,  92 P,  92 Q,  92 R,  92 S,  92 T, and  92 U respectively, while the ports  92 B,  92 D,  92 E,  92 H,  92 J,  92 K, and  92 N are blocked. In the pressure set position, the ports  92 B,  92 D,  92 E,  92 H,  92 J,  92 K and  92 N are connected with the ports  92 O,  92 P,  92 Q,  92 R,  92 S,  92 T, and  92 U respectively, while the ports  92 A,  92 C,  92 F,  92 G,  92 I,  92 L and  92 M are blocked. 
     The pressure control valve  70  is a variable pressure type solenoid valve that is controlled in a well-known manner by the ECU. The valve  70  may be of the pulse width modulated (pwm) type which has an output pressure proportional to the voltage duty cycle imposed on the solenoid by the ECU. The valve  70  has an inlet port  70 A connected with a passage  96  that is supplied with a constant pressure from the control  52 . The passage  96  also supplies fluid to the solenoids for the control valves  86 ,  90 , and  94 . The pressure control valve  70  has an outlet port  70 B that is connected with a passage  98  which in turn is connected with control ports  62 A and  64 A of the high ratio control valves  62  and  64 , respectively. 
     The pressure control valve  72  is a variable pressure type solenoid valve that is controlled in a well-known manner by the ECU. The valve  72  may be of the pwm type. The valve  72  has an inlet port  72 A connected with the passage  96 . The valve  72  has an outlet port  72 B that is connected with a passage  100  which in turn is connected with control ports  66 A and  68 A of the low ratio control valves  66  and  68 , respectively as well as a control port  74 A of the reverse control valve  74 . 
     The high ratio control valve  62  has an inlet port  62 B, an outlet port  62 C, an exhaust port  62 D and a feedback control port  62 E. The inlet control port  62 B is connected with a passage  102  that is supplied with pressurized fluid by the control  52  whenever the driver selects a drive position with the manual valve. The pressure in the outlet port  62 C is proportional to the pressure in the passage  98  which is provided from the pressure control valve  70 . The outlet port  62 C is connected with the feedback control port  62 E and a passage  104  to the S/T switch logic valve  78 . The exhaust port  62 D is connected with a passage  105  to the D 5 /EX SW VALVE  82 . 
     The high ratio control valve  64  had an inlet port  64 B, an outlet port  64 C, an exhaust port  64 D and a feedback control port  64 E. The inlet control port  64 B is connected with the passage  102  that is supplied with pressurized fluid by the control  52  whenever the driver selects a drive position with the manual valve. The pressure in the outlet port  64 C is proportional to the pressure in the passage  98  which is provided from the pressure control valve  70 . The outlet port  64 C is connected with the feedback control port  64 E and a passage  106  that is in turn connected with the S/T switch logic valve  78 . 
     The low ratio control valve  66  has an inlet port  66 C, an outlet port  66 D, an exhaust port  66 E and a feedback control port  66 F. The inlet port  66 C is connected with the passage  102 . The outlet port  66 D is connected with a passage  108  which is also connected with the feedback control port  66 F. The pressure in the passage  108  is proportional to the pressure in the passage  100  which is controlled by the pressure control valve  72 . 
     The low ratio control valve  68  has an inlet port  68 C, an outlet port  68 D, an exhaust port  68 E and a feedback control port  68 F. The inlet port  68 C is connected with the passage  102 . The outlet port  68 D is connected with a passage  110  which is also connected with the feedback control port  68 F and the S/T switch logic valve  78 . The pressure in the passage  110  is proportional to the pressure in the passage  100  which is controlled by the pressure control valve  72 . 
     S/T SW VALVE 
     The S/T SW VALVE (switch logic)  78  is comprised of a switch valve  112  and a control valve  114 . The control valve  114  is a conventional off-on type solenoid valve controlled by the ECU. During a steady state gear, the control valve  114  is off, whereas during a ratio interchange, the control valve is on. The shift valve  112  is a directional flow control valve having eight ports  112 A,  112 B,  112 C,  112 D,  112 E,  112 F,  112 G, and  112 H that are selectively connectable with four ports  112 I,  112 J,  112 K, and  112 L. In the spring set position shown, the ports  112 A,  112 C,  112 E, and  112 G are connected with the ports  112 I,  112 J,  112 K, and  112 L respectively, while the ports  112 B,  112 D,  112 F, and  112 H are blocked. In the pressure set position, that is when the control valve  114  is energized by the ECU to control the fluid pressure delivered through a passage  116  to the shift valve  112 , the ports  112 A,  112 C,  112 E, and  112 G are blocked, while the ports  112 B,  112 D,  112 F, and  112 H are connected to the  112 I,  112 J,  112 K, and  112 L respectively. The passage  96  supplies fluid to the passage  116 . The port  112 B is connected to the high ratio control valve output port  64 C by the passage  106 . The port  112 D is connected to the high ratio control valve output port  62 C by the passage  104 . The port  112 F is connected to the low ratio control valve output port  68 D by the passage  110 . The port  112 H is connected to the low ratio control valve output port  66 D by the passage  108 . The port  112 I is connected to port  84 B of the shift valve  84  and to port  88 E of the shift valve  88  by a passage  118 . The port  112 K is connected to port  88 A of the shift valve  88  by a passage  120 . The port  112 J is connected to a plurality of ports including port  84 A of shift valve  84 , port  88 I of shift valve  88 , and ports  92 C,  92 E, and  92 I of shift valve  92 , through a passage  122 . The port  112 L is connected to ports  92 A and  92 K of shift valve  92  by a passage  124 . During any gear shifting, The S/T SW VALVE  112  will be at a pressure set position. When the new ratio is fully established, the valve will be switched to the spring set position. 
     D 5 /EX SW VALVE 
     D 5 /EX SW VALVE  82  has two control ports  82 A and  82 B. When the pressure at port  82 B is higher than the pressure at port  82 A the D 5 /EX SW VALVE  82  will be at lower position. At this position, the port  82 F is connected to the port  82 D which is connected to the drive pressure, the port  82 E is connected to the port  82 C which is connected to the 2 psi back fill pressure. When the pressure at port  82 A is higher than the pressure at port  82 B the D 5 /EX SW VALVE  82  will be at upper position. At this position, the port  82 E is connected to the port  82 D which is connected to the drive pressure, the port  82 F is connected to the port  82 C which is connected to the 2 psi back fill pressure. The pressure at port  82 A and  82 B are determined by the state of the low gear clutch pressure control valve  66  and high gear clutch pressure control valve  62  respectively, when the S/T SW VALVE  112  is at pressured position. After a upshift the output pressure of valve  62  will be high, and the output pressure of valve  66  will be low, therefore the pressure at port  82 B will be higher than the pressure at port  82 A. If the S/T SW VALVE  112  is switched to the spring position after a upshift, the D 5 /EX SW VALVE  82  will be latched at lower position. After a downshift the output pressure of valve  66  will be high and the output pressure of the valve  62  will be low, therefore the pressure at port  82 A will be higher than the pressure at port  82 B. If the S/T SW VALVE  112  is switched to the spring position after a downshift, the D 5 /EX SW VALVE  82  will be latched at upper position. 
     Downshift Valve 
     The downshift logic valve  80  is comprised of a downshift valve  126  and a control valve  128 . The control valve  128  is a conventional off-on type solenoid valve controlled by the ECU. The control valve  128  is on during downshift ratio interchange. The downshift valve  126  is a directional flow control valve having four ports  126 A,  126 B,  126 C, and  126 D where  126 B and  126 D are deadheaded ports, that are selectively connectable with two ports  126 E and  126 F. In the spring set position shown, the ports  126 A and  126 C are connected with the ports  126 E and  126 F respectively, to connect passage  122  to port  66 B and passage a  132  to port  68 B for force exhausting of the off-going clutch. In the pressure set position, that is when the control valve  128  is energized by the ECU to control the fluid pressure delivered through a passage  130  to the downshift valve  126 , the deadheaded ports  126 B and  126 D are connected to ports  126 E and F respectively. Port  126 A is connected to passage  122  and therefore to port  112 J of S/T switch valve  112 . Port  126 C is connected to port  84 M of switch valve  84  through the passage  132   
     The low ratio control valve  66  has a second control port  66 B opposing control port  66 A, which may receive fluid pressure from the high ratio control valve  62  through the S/T switch valve port  112 J via passage  122 , and through the downshift valve port  126 E. When the output pressure of the high ratio control valve  62 , and therefore port  66 B, reach a predetermined level, equal to the critical capacity of the oncoming torque transmitting mechanism, the low ratio control valve  66  is exhausted through port  66 E. 
     The low ratio control valve  68  has a second control port  68 B opposing control port  68 A, which may receive fluid pressure from the shift valve port  84 M through passage  132  and through port  126 C of the downshift valve  126 . When the pressure at port  68 B reaches a critical capacity for the on-coming clutch, the low ratio control valve  66  is exhausted through port  68 E. 
     Back Fill Valve 
     When the feedback pressure at port  62 E of high ratio valve  62  is greater than the pressure at the control port  62 A, then fluid is exhausted through port  62 D to passage  105 . Passage  105  communicates with the back fill valve  76 . The back fill valve  76  is a conventional regulator valve that maintains the pressure in the passage  105  and a passage  144  at a substantially fixed level. Thus the pressure at the port  62 D has a minimum pressure as established by the back fill valve  76  which is generally set at approximately 2 psi. The pressure level in the passage  144  is sufficient to maintain the apply pistons in the torque transmitting mechanisms filled with hydraulic fluid to reduce the fill time needed during a ratio interchange. This is common practice with electro-hydraulic controls for automatic shifting transmissions. 
     Reverse Valve 
     The reverse valve  74  is a downstream regulator valve having a control port  74 A, an inlet port  74 B, an outlet port  74 C, an exhaust port  74 D, and a feedback control port  74 E. The control port  74 A connected with passage  100  which is supplied pressurized fluid by the pressure control valve  72 , thereby exhausting the reverse valve when passage  100  is pressurized. The inlet port  74 B is connected by a passage  135  to the control  52 . Passage  135  is pressurized when the driver selects reverse on the manual valve. The outlet port  74 C is connected with a passage  134  that is in turn connected with the port  88 P of the shift valve  88 . Exhaust port  74 D is connected to passage  105  and therefore communicates with the back fill valve  76 . The feedback port  74 E limits the maximum reverse pressure. 
     Shuttle valve 
     Disposed in passage  134  is a shuttle valve  136  which operates to permit fluid flow from port  88 P of shift valve  88  to the second clutch C 2  when the pressure at port  88 P is greater than the pressure at the output port  74 C of the reverse valve  74  for 3 rd  and 5 th  gears. For reverse, fluid flows from ECU  52 , through passage  135 , through reverse valve  74 , displacing the shuttle valve  136  to communicate with the second clutch C 2  for reverse operation. Therefore the reverse valve  74  controls the pressure in the second clutch during reverse. 
     The following describes the interconnection between the rest of the torque transmitting devices and the electro-hydraulic control system  50 . The first clutch C 1  is connected to port  84 N. The third clutch C 3  is connected to port  840 . The apply portion of the first control brake B 1  (L/R B apl) is connected to port  84 R, and the reduce portion of the brake B 1  is directly connected to the ECU through the drive passage  102 . The second control brake B 2  is connected to port  84 Q of shift valve  84 . 
     S 1  Valve 
     The solenoid control valve  86 , as previously mentioned, is an off-on solenoid valve. The valve  86  is operable to establish the pressure in the passage  87 . The passage  87  is fed from the passage  96  through an orifice or restriction  138 . In the off position shown, the control valve  86  connects the passage  87  to exhaust such that the pressure in the passage is low and not sufficient to move the shift valve  84  from the spring set position since the orifice  138  restricts the inflow while the outflow through control valve  86  is not restricted. In the on position, the control valve  86  blocks the outflow from passage such that the pressure in the passage  87  rises to a level sufficient to move the shift valve  84  to the pressure set position. 
     The control valve  90 , as previously mentioned, is an off-on solenoid valve. The valve  90  is operable to establish the pressure in the passage  91 . The passage  91  is fed from the passage  96  through an orifice or restriction  140 . In the off position shown, the control valve  90  connects the passage  91  to exhaust such that the pressure in the passage is low and not sufficient to move the shift valve  88  off the spring set position since the orifice  140  restricts the inflow while the outflow through control valve  90  is not restricted. In the on position, the control valve  90  blocks the outflow from passage such that the pressure in the passage  91  rises to a level sufficient to move the shift valve  88  to the pressure set position. 
     The control valve  94 , as previously mentioned, is an off-on solenoid valve. The control valve  94  is operable to establish the pressure in the passage  95 . The passage  95  is fed from the passage  96  through an orifice or restriction  142 . In the off position shown, the control valve  94  connects the passage  95  to exhaust such that the pressure in the passage is low and not sufficient to move the shift valve  92  from the spring set position since the orifice  142  restricts the inflow while the outflow through control valve  94  is not restricted. In the on position, the control valve  94  blocks the outflow from passage such that the pressure in the passage  95  rises to a level sufficient to move the shift valve  92  to the pressure set position. 
     The manual valve, not shown, in the control  52  is a conventional directional valve that can be manipulated by the operator to a plurality of positions including park, reverse, neutral, and a plurality of forward drive conditions. A passage  146  is connected to main line pressure at the control  52 . The passage  146  is connected between the control  52  and the port  92 M. The drive passage  102  is connected with main line pressure, the maximum pressure in the system, in the control  52  when the manual valve is placed in the drive positions. The passage  135  is connected between the control  52  and the reverse control valve  74  during reverse operation. 
     Operation 
     In park, reverse, and neutral, the control valve  90  is actuated to place the shift valve  88  in the pressure set position thus delivering line pressure from the ECU in passage  146  to apply the first control brake B 1 . In park and neutral, the pressure control valve  72  is set to maximum and the pressure control valve  70  is set to exhaust. This ensures that the reverse clutch C 2  is exhausted. When reverse is selected by the operator, the pressure control valve  72  is controlled in a modulating condition to thereby control the pressure output of the reverse valve  74  such that the torque transmitting mechanism C 2  is engaged at a controlled rate. 
     During a neutral to first shift, there are two possible first ratio selections, automatic and manual. During automatic selection, the one-way mechanism RI provides drive reaction. The shift valves  84  and  92  are in the spring set position and the shift valve  88  is in the pressure set position. The pressure control valve  72  is set at maximum pressure output and the pressure control valve  70  is controlled to provide a modulated pressure. The output pressure from the high ratio control valve  62  is directed through the S/T SW VALVE  112  and shift valves  92 ,  88 , and  84  to the torque transmitting mechanism C 1  which is engaged at a rate controlled by the output pressure of the high ratio control  62 . When the first ratio has been completed, both of the pressure control valves  70  and  72  are set to exhaust. During manual low gear, not illustrated in FIG. 3, the passage  146  is line pressurized and is directed through the shift valves  92 ,  88 , and  84  to pressurize the apply piston of the torque transmitting mechanism B 1 . Brake B 1  in conjunction with the one way mechanism R 1  ensure engine coast braking is present. There is no drive pressure in passage  102  in manual low gear. 
     During a first to second (1-2), first to third (1-3), or second to third (2-3) ratio interchange, the shift valves  84 ,  88 , and  92  are spring set, while the S/T valve  112  is pressure set. During a 1-2 interchange, the pressure control valve  70  is exhausted and the pressure control valve  72  is modulated. The output pressure from the low ratio control valve  68  is directed through valves  112 ,  88 , and  84  to the torque transmitting mechanism B 2 . When the torque transmitting mechanism B 2  reaches the critical capacity, the one-way mechanism R 1  releases and the second forward ratio is established. When the second ratio has been established, the shift valves  84 ,  88 , and  92  remain in the spring set position and the S/T valve  112  is shifted back to the spring set position. The torque transmitting mechanism B 2  is maintained in the engaged condition by pressure from the drive passage  102  through the D 5 /EX SW VALVE  82 , the S/T valve  112 , through the low pressure port  112 K, and through the shift valves  88  and  84 . The pressure control valves  70  and  72  are both set to exhaust. 
     During a 1-3 interchange, the pressure control valve  70  is modulated and the pressure control valve  72  is exhausted. The output pressure of the high ratio control valve  62  is directed through the S/T valve  112 , and shift valves  92  and  88  to the torque transmitting mechanism C 2  which is engaged at a controlled rate. When the torque transmitting mechanism C 2  reaches the critical capacity, the one-way mechanism R 1  releases and the third forward ratio is achieved. When the third forward ratio is fully established, the S/T valve  112  is released to the spring set position and the torque transmitting mechanism C 2  is maintained engaged by pressure from drive passage  102  through the D 5 /EX SW VALVE  82 , the S/T valve  112 , and switch valves  92  and  88 . The pressure control valves  70  and  72  are both set to exhaust. 
     During a 2-3 interchange, both pressure control valves  70  and  72  are modulated. The low pressure control valve  70  is modulated from low pressure to high pressure while the high pressure control valve  72  is modulated from high pressure to low pressure. The pressure output of the low ratio control valve  68  is directed to the torque transmitting mechanism B 2  through the S/T valve  112 , and shift valves  88  and  84 . The pressure output of the high ratio control valve  62  is directed through the S/T valve  112 , and shift valves  92  and  88  to the torque transmitting mechanism C 2 . The output pressure of the high ratio control valve  62  is also imposed on the control port  68 B of the low ratio control valve  68 . When the torque transmitting mechanism C 2  reaches the critical capacity to transmit the required torque, the low ratio control valve  68  is set to exhaust by the pressure bias at port  68 B from the high ratio control valve  62 . When the third forward ratio is fully established, the S/T valve  112  is set to the pressure set position and the torque transmitting mechanism C 2  is maintained engaged by pressure from drive passage  102  through the D 5 /EX SW VALVE  82 , the S/T valve  112 , and shift valves  92  and  88 . The pressure control valves  70  and  72  are both set to exhaust. During a 3-2 downshift, the DOWN SHIFT VALVE  126  is pressurized form the solenoid valve  128  such that the control ports  66 B and  68 B are disconnected from the passages  122  and  132 . The control valve  68  will be controlled to output pressure from a low value to a high value while the pressure from the control valve  62  will be decreased from high pressure to exhaust. The DOWN SHIFT VALVE  126  blocks the initial high pressure output of the control valve  62  from the control port  68 B 
     During a second to fourth (2-4) interchange, the shift valve  92  is pressure set and the shift valves  84  and  88  are spring set. The pressure control valves  70  and  72  are both modulated. The pressure control valve  70  increases the pressure output thereof and the pressure control valve  72  decreases the pressure output thereof. The pressure output of the low ratio control valve  68 , as controlled by the pressure control valve  72 , is directed to the torque transmitting mechanism B 2  through the S/T valve  112 , and shift valves  88  and  84 . Since the pressure output of the low ratio control valve  68  starts high and goes low, the torque transmitting mechanism B 2  is maintained engaged during the initial portion of the 2-4 interchange. Since the output pressure of the high ratio control valve  62  starts low and goes high, the pressure at the torque transmitting mechanism C 3  as delivered through the S/T valve  112  and shift valve  92  is increased at a controlled rate. When the pressure in the torque transmitting mechanism C 3  is sufficient to establish the critical capacity at the torque transmitting mechanism C 3 , the pressure in the passage  132  operating at the control port  68 B of the low ratio control valve  68  causes the output pressure thereof to be exhausted and the torque transmitting mechanism B 2  will be released or disengaged. When the fourth ratio is fully established, the shift valve  88  is moved to the pressure set position and both of the pressure control valves  70  and  72  are set to exhaust. The torque transmitting mechanism B 2  is exhausted through the shift valves  84  and  88  to the passage  144  such that a minimum pressure is maintained thereat. The torque transmitting mechanism C 3  is maintained engaged by pressure from the passage  102  through the D 5 /EX SW VALVE  82 , the S/T valve  112 , and shift valve  92 . The torque transmitting mechanism C 1  is maintained engaged by pressure from. the passage  102  through the shift valves  92 ,  88 , and  84 . During a 4-2 down shift, the DOWN SHIFT VALVE  126  is effective to prevent the high ratio control valve  62  from imposing a control pressure on the low ratio control valve  68 . 
     During a third to fourth (3-4) interchange, the shift valves  88  and  92  are moved to the pressure set position. Both of the pressure control valves  70  and  72  are modulated. The pressure output of the pressure control valve  72  is modulated from high to low and the pressure output of the pressure control valve  70  is modulated from low to high. The torque transmitting mechanism C 1  is maintained engaged through the interchange by pressure from the passage  102  through the shift valves  92 ,  88 , and  84 . The torque transmitting mechanism C 2  is controlled by the pressure output from the low ratio control valve  66  and the torque transmitting mechanism C 3  is controlled by the pressure output from the high ratio control valve  62 . The pressure output of the low ratio control valve  66  is modulated downward and the pressure output of the high ratio control valve  62  is modulated upward. 
     The pressure output of the low ratio control valve  66  is directed by the S/T valve  112 , and shift valves  92  and  88  to the torque transmitting mechanism C 2  to control the disengagement thereof. The pressure output of the high ratio control valve  62  is directed through the S/T valve  112 , and shift valves  92  and  84  to the torque transmitting mechanism C 3  to control the engagement thereof. When the torque transmitting mechanism C 3  is pressurized to the critical torque capacity, the pressure from the high ratio control valve  62  in passage  104 , operating on the control port  66 B will cause the low ratio control valve  66  to exhaust the pressure in the passage  108  and therefore the torque transmitting mechanism C 2  when the critical capacity of the on-coming friction device is achieved. When the fourth ratio is fully established, the shift valve  84  remains in the spring set position and the shift valves  88  and  92  remain pressure set, while both of the pressure control valves  70  and  72  are set to exhaust. The torque transmitting mechanism C 3  is maintained engaged by pressure from the passage  102  through the D 5 /EX SW VALVE  82 , the S/T valve  112 , and shift valve  92 . The torque transmitting mechanism C 1  is maintained engaged by pressure from the passage  102  through the shift valves  92 ,  88 , and  84 . During a 4-3 down shift, The DOWN SHIFT VALVE  126  is effective to prevent a control pressure from the high ratio control valve  62  from imposing a control pressure on the low ratio control valve  66 . 
     During a third to fifth (3-5) interchange, the shift valves  84  and  92  are moved to the pressure set position. Both of the pressure control valves  70  and  72  are modulated. The pressure output of the pressure control valve  72  is modulated from high to low and the pressure output of the pressure control valve  70  is modulated from low to high. The torque transmitting mechanism C 2  is maintained engaged through the interchange by pressure from the passage  102  through the shift valves  84 ,  92 , and  88 . The torque transmitting mechanism C 1  is controlled by the pressure output from the low ratio control valve  68  and the torque transmitting mechanism C 3  is controlled by the pressure output from the high ratio control valve  64 . The pressure output of the low ratio control valve  68  is modulated downward and the pressure output of the high ratio control valve  64  is modulated upward. The pressure output of the low ratio control valve  68  is directed by the S/T valve  112 , and shift valves  88 ,  92  and  84  to the torque transmitting mechanism C 1  to control the disengagement thereof. The pressure output of the high ratio control valve  64  is directed through the S/T valve  112 , and shift valves  88 ,  92  and  84  to the torque transmitting mechanism C 3  to control the engagement thereof. When the torque transmitting mechanism C 3  is pressurized to the critical torque capacity, the pressure from the high ratio control valve  64  in passage  106 , operating on the control port  68 B causes the low ratio control valve  68  to exhaust the pressure in the passage  110  and therefore the torque transmitting mechanism C 1 . When the fifth ratio is fully established, the shift valve  88  remains in the spring set position and the shift valves  84  and  92  remain pressure set, while both of the pressure control valves  70  and  72  are set to exhaust. The torque transmitting mechanism C 3  is maintained engaged by pressure from the passage  102  through the D 5 /EX SW VALVE  82 , the S/T valve  112 , and shift valves  88 ,  92 , and  84 . The torque transmitting mechanism C 2  is maintained engaged by pressure from the passage  102  through the shift valves  84 ,  92 , and  88 . During a 5-3 downshift, the DOWN SHIFT VALVE  126  prevents the high ratio control valve  64  from imposing a control bias on the low ratio control valve  68 . 
     During a fourth to fifth (4-5) interchange, the shift valve  84  is moved to the pressure set position, while shift valves  88  and  92  are spring set. Both of the pressure control valves  70  and  72  are modulated. The pressure output of the pressure control valve  72  is modulated from high to low and the pressure output of the pressure control valve  70  is modulated from low to high. The torque transmitting mechanism C 3  is maintained engaged through the interchange by pressure from the passage  102  through the shift valves  92  and  84 . The torque transmitting mechanism C 1  is controlled by the pressure output from the low ratio control valve  66  and the torque transmitting mechanism C 2  is controlled by the pressure output from the high ratio control valve  62 . The pressure output of the low ratio control valve  66  is modulated downward and the pressure output of the high ratio control valve  62  is modulated upward. The pressure output of the low ratio control valve  66  is directed by the S/T valve  112 , and shift valves  92  and  84  to the torque transmitting mechanism C 1  to control the disengagement thereof. The pressure output of the high ratio control valve  62  is directed through the S/T valve  112 , and shift valves  92  and  88  to the torque transmitting mechanism C 2  to control the engagement thereof. When the torque transmitting mechanism C 2  is pressurized to the critical torque capacity, the pressure from the high ratio control valve  62  in passage  104 , operating on the control port  66 B causes the low ratio control valve  66  to exhaust the pressure in the passage  108  and therefore the torque transmitting mechanism C 1 . When the fifth ratio is fully established, the shift valve  88  remains in the spring set position and the shift valves  84  and  92  remain pressure set, while both of the pressure control valves  70  and  72  are set to exhaust. The torque transmitting mechanism C 3  is maintained engaged by pressure from the passage  102  through the D 5 /EX SW VALVE  82 , the S/T valve  112 , and shift valves  88 ,  92 , and  84 . The torque transmitting mechanism C 2  is maintained engaged by pressure from the passage  102  through the shift valves  84 ,  92 , and  88 . During a 5-4 downshift, the DOWN SHIFT VALVE  126  will prevent the output pressure of the high ratio control valve  62  from imposing a bias on the low ratio control valve  66 . Thus permitting the low ratio control valve  66  to control the oncoming torque transmitting mechanism C 1 . 
     During a fourth to sixth (4-6) interchange, the shift valves  84  and  88  are moved to the pressure set position, while shift valve  92  is spring set. Both of the pressure control valves  70  and  72  are modulated. The pressure output of the pressure control valve  72  is modulated from high to low and the pressure output of the pressure control valve  70  is modulated from low to high. The torque transmitting mechanism C 3  is maintained engaged through the interchange by pressure from the passage  102  through the shift valves  92  and  84 . The torque transmitting mechanism C 1  is controlled by the pressure output from the low ratio control valve  66  and the torque transmitting mechanism B 2  is controlled by the pressure output from the high ratio control valve  62 . The pressure output of the low ratio control valve  66  is modulated downward and the pressure output of the high ratio control valve  62  is modulated upward. The pressure output of the low ratio control valve  66  is directed by the S/T valve  112 , and shift valves  92  and  84  to the torque transmitting mechanism C 1  to control the disengagement thereof. The pressure output of the high ratio control valve  62  is directed through the S/T valve  112 , and shift valves  88  and  84  to the torque transmitting mechanism B 2  to control the engagement thereof. When the torque transmitting mechanism B 2  is pressurized to the critical torque capacity, the pressure from the high ratio control valve  62  in passage  104 , operating on the control port  66 B causes the low ratio control valve  66  to exhaust the pressure in the passage  108  and therefore the torque transmitting mechanism C 1 . When the sixth ratio is fully established, the shift valves  84  and  88  remain in the pressure set position and the shift valve  92  moves to the pressure set position, while both of the pressure control valves  70  and  72  are set to exhaust. The torque transmitting mechanism C 1  is exhausted through the shift valves  84 ,  92  and  88  to the passage  144  such that a minimum pressure is maintained thereat. The torque transmitting mechanism B 2  is maintained engaged by pressure from the drive passage  102  through the D 5 /EX SW VALVE  82 , the S/T valve  112 , and shift valves  88  and  84 . The torque transmitting mechanism C 3  is maintained engaged by pressure from the passage  102  through the shift valves  88 ,  92 , and  84 . During a 6-4 downshift, the DOWN SHIFT VALVE  126  will prevent the high ratio control valve  62  from imposing a bias at the port  66 B of the low ratio control valve  66 . 
     During a fifth to sixth (5-6) interchange, all the shift valves  84 ,  88  and  92  are moved to the pressure set position. Both of the pressure control valves  70  and  72  are modulated. The pressure output of the pressure control valve  72  is modulated from high to low and the pressure output of the pressure control valve  70  is modulated from low to high. The torque transmitting mechanism C 3  is maintained engaged through the interchange by pressure from the passage  102  through the shift valves  88 ,  92 , and  84 . The torque transmitting mechanism C 2  is controlled by the pressure output from the low ratio control valve  66  and the torque transmitting mechanism B 2  is controlled by the pressure output from the high ratio control valve  62 . The pressure output of the low ratio control valve  66  is modulated downward and the pressure output of the high ratio control valve  62  is modulated upward. The pressure output of the low ratio control valve  66  is directed by the S/T valve  112 , and shift valves  92  and  88  to the torque transmitting mechanism C 2  to control the disengagement thereof. The pressure output of the high ratio control valve  62  is directed through the S/T valve  112 , and shift valves  88  and  84  to the torque transmitting mechanism B 2  to control the engagement thereof. When the torque transmitting mechanism B 2  is pressurized to the critical torque capacity, the pressure from the high ratio control valve  62  in passage  104 , operating on the control port  66 B causes the low ratio control valve  66  to exhaust the pressure in the passage  108  and therefore the torque transmitting mechanism C 2 . When the sixth ratio is fully established, the shift valves  84  and  88  remain in the pressure set position and the shift valve  92  moves to the pressure set position, while both of the pressure control valves  70  and  72  are set to exhaust. The torque transmitting mechanism B 2  is maintained engaged by pressure from the passage  102  through the D 5 /EX SW VALVE  82 , the S/T valve  112 , and shift valves  88  and  84 . The torque transmitting mechanism C 3  is maintained engaged by pressure from the passage  102  through the shift valves  88 ,  92 , and  84 . During a 6-5 downshift, the DOWN SHIFT VALVE  126  is shifted by the valve  128  to block the output pressure of the high ratio shift valve  62  from acting on the control port  66 B of the low pressure control valve  66 . 
     During a 1-2, 1-3, 2-3, and 2-4 upshift and the steady state second and third ratios, the apply chamber of the torque transmitting mechanism B 1  is exhausted to the passage  144  through the shift valves  84  and  88 . During a 3-5, 4-5, 4-6, and 5-6 upshift and the steady state fifth and sixth ratios, the apply chamber of the torque transmitting mechanism B 1  is exhausted to the passage  144  through the shift valve  84 . During the 3-4 upshift, the apply chamber is exhausted to the passage  144  through shift valves  84 ,  88 , and  92 . The shift logic valves  84 ,  88  and  92  will be set to the position as defined in the table based on which shift is commanded. The S/T SW VALVE  112  is set at pressured position, except during the 1-2 and 1-3 upshift, The DOWN SHIFT VALVE  126  is set at spring position. The pressure control valve  72  which controls the off going torque transmitting mechanism (low gear torque transmitting mechanism) is set at the level as a function of the transmission input torque. The pressure control valve  70  which controls oncoming torque transmitting mechanism (high gear torque transmitting mechanism) will be commanded from low to high to engage the corresponding coming torque transmitting mechanism. The oncoming torque transmitting mechanism pressure is introduced to the ports  66 B and  68 B through the DOWN SHIFT VALVE  126 . As the coming torque transmitting mechanism pressure reach to its critical capacity, the output pressure of the low gear torque transmitting mechanism pressure control valve will be reduced to zero, therefore, the off going torque transmitting mechanism will be disengaged. As the shift is completed, the output pressure of the high gear torque transmitting mechanism control valves will be high, and the output pressure of the low gear torque transmitting mechanism control valves will be low. Therefore, the D 5 /EX SW VALVE  82  will be at lower position. When the shift is completed, the S/T SW VALVE  112  will be switched to spring position. Since the D 5 /EX SW VALVE  82  already at lower position, the oncoming torque transmitting mechanism (high gear torque transmitting mechanism) will be fed be the pressure in passage  102 , and the off going torque transmitting mechanism (low gear torque transmitting mechanism) will be connected to the 2 psi back fill pressure. 
     During downshifting, the low ratio control valves are maintained with a higher control pressure from the pressure control valve  72  such that the pressure output of the high ratio control valves will not cause the low ratio control valves to exhaust. The interchange timing is not as critical during a downshift since the speed of the engine must be permitted to increase in any event. The shift valves  84 ,  88  and  92  will be set to the position as defined in the table based on which shift is commanded. The S/T SW VALVE  112  is set at pressured position. Except during the 2-1 and 3-1 downshifts, the DOWN SHIFT VALVE  126  is set at pressured position. The pressure control valve  72  which controls the oncoming torque transmitting mechanism (low gear torque transmitting mechanism) is commanded from low to high. The pressure control valve  70  which controls off going torque transmitting mechanism (high gear torque transmitting mechanism) will be commanded from high to low. As the shift is completed, the output pressure of the high gear torque transmitting mechanism control valves will be low, and the output pressure of the low gear torque transmitting mechanism control valves will be high. Therefore, the D 5 /EX SW VALVE  82  will be at upper position. When the shift is completed, the S/T SW VALVE  112  will be switched to spring position. Since the D 5 /EX SW VALVE  82  already at upper position, the oncoming torque transmitting mechanism (low-gear torque transmitting mechanism) will be fed be the D 5  pressure, and the off going torque transmitting mechanism (high gear torque transmitting mechanism) will be connected to the 2 psi back fill pressure. 
     The truth table shown in FIG. 3 sets forth the condition of the torque transmitting mechanisms and the engagement pressure applied thereto during the ratio interchanges and the steady state conditions. A blank space indicates that the torque transmitting mechanism is disengaged. The table also shows the operating condition of the shift valves  84 ,  88 , and  92 , the S/T control valve  114 , and the valves  114  and  128  during the ratio interchanges and the steady state conditions. From the above description, it should now be appreciated by those skilled in the art that during upshift ratio interchanges, the S/T valve directs ratio controlled pressure to the on-coming and off-going friction devices; while during steady state ratios, the S/T valve directs fixed pressure to the engaged friction devices. 
     The foregoing description of the preferred embodiment of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive, nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiment may be modified in light of the above teachings. The embodiment was chosen to provide an illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, the foregoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the following claims.