Transmission shifting hydraulic control system

A hydraulic control for an automatic shifting transmission has a plurality of shift logic valves, a high ratio control valve, a low ratio control valve and respective pressure control valves for controlling the bias pressure on the ratio control valves. The shift logic valves control the distribution of fluid to a plurality of torque transmitting mechanisms from the proper ratio control valve. During an upshift sequence, the high ratio control valves establishes the engagement pressure in the oncoming torque transmitting mechanism and the low ratio control valve establishes the engagement pressure in the offgoing torque transmitting mechanism. The pressure from the high ratio control valve is also delivered to a control port on the low ratio control valve to force the exhausting of the offgoing torque transmitting mechanism when the oncoming torque transmitting mechanism reaches its critical torque capacity. Following the ratio interchange, the shift logic valves are then positioned to disconnect the ratio control valves from the torque transmitting mechanisms and connect the oncoming torque transmitting mechanism with another source of pressure. During and subsequent to the ratio interchange, the shift logic valves maintain at least one other torque transmitting mechanism engaged with pressure from the other source of pressure.

TECHNICAL FIELD
 This invention relates to hydraulic control mechanisms and more
 particularly to hydraulic systems for controlling the shift sequence of a
 power transmission.
 BACKGROUND OF THE INVENTION
 One-way torque transmitting mechanisms have been employed in many automatic
 shifting transmissions to accommodate the ratio interchange in the
 transmission. The one-way torque transmitting mechanism is provided to
 either transmit torque from the engine to a gear member or transmit torque
 from the gear member to ground. As is well-known, the one way torque
 transmitting mechanism will release the controlled gear member upon a
 reversal of torque that occurs during the ratio interchange. This permits
 a smooth transition between ratios. The one-way mechanisms are mechanical
 devices that require space in the transmission and also add weight to the
 transmission.
 To eliminate the use of one-way torque transmitting mechanisms, 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 oncoming 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 offgoing 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 offgoing
 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 offgoing torque transmitting mechanism
 capacity is reduced to its critical point by generating a predetermined
 slip speed in the offgoing 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 offgoing 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 offgoing 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
 It is an object of the present invention to provide an improved
 transmission control system.
 In one aspect of the present invention, a plurality of shift logic valves
 and pressure control valves are interconnected to control the interchange
 and continuous engagement of a plurality of torque transmitting
 mechanisms. In another aspect of the present invention, the pressure
 control valves are comprised of two oncoming torque transmitting mechanism
 control valves and two offgoing torque transmitting mechanism control
 valves. In yet another aspect of the present invention, the oncoming
 torque transmitting mechanism control valves and the offgoing torque
 transmitting mechanism control valves are arranged in operative pairs with
 an oncoming torque transmitting mechanism control valve and an offgoing
 torque transmitting mechanism control valve in each pair.
 In still another aspect of the present invention, an interlock passage is
 connected between each offgoing torque transmitting mechanism control
 valve and the output pressure of the paired oncoming torque transmitting
 mechanism control valve. In a further aspect of the present invention, the
 output pressure of the oncoming torque transmitting mechanism control
 valve will cause the output pressure of the offgoing torque transmitting
 mechanism control valve to be reduced below the critical capacity of the
 offgoing torque transmitting mechanism during an upshift ratio
 interchange.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT
 A lever diagram 10, representing the gearing of a planetary transmission,
 having two lever arms 12 and 14 is shown in FIG. 3. The lever arm 12 has
 three nodes 16, 18 and 20 that represent a sun gear member, a planet
 carrier assembly member and a ring gear member respectively. The lever arm
 14 has three nodes 22, 24 and 26 that represent a sun gear member, a
 planet carrier assembly member and a ring gear member respectively. The
 nodes 20 and 24 are both connected with an output member 28. An input
 member 30 is connected directly with the node 26.
 The input member 30 is selectively connectable with the node 16 through a
 selectively engageable torque transmitting mechanism 32 and with the node
 18 through a selectively engageable torque transmitting mechanism 34. The
 nodes 18 and 22 are selectively interconnectable by a selectively
 engageable torque transmitting mechanism 36. The node 18 is also
 selectively connectable with a stationary or ground portion 38 of the
 transmission through a one-way torque transmitting mechanism 40 and a
 selectively engageable torque transmitting mechanism 42. The node 16
 selectively connectable with the stationary portion 38 through a
 selectively engageable torque transmitting mechanism 44.
 The torque transmitting mechanisms 32, 34 and 36 are preferably fluid
 operated frictionally engaged clutch mechanisms. The torque transmitting
 mechanism 42 is preferably a fluid operated band type brake mechanism,
 however, a fluid operated disc type brake mechanism can also be employed.
 When a band type brake is employed, the mechanism will have an apply
 chamber 42A and a release chamber 42b. The torque transmitting mechanism
 44 is preferably a fluid operated disc type brake mechanism. The one-way
 torque transmitting mechanism 40 is preferably a roller type mechanism. In
 a current production transmission, having the same lever diagram, a
 friction torque transmitting mechanism and one-way torque transmitting
 mechanism are disposed in series between the node 16 and 15 portion 38 in
 addition to the torque transmitting mechanism 44. In the same
 transmission, a friction torque transmitting mechanism and one-way torque
 transmitting mechanism are disposed in series between the nodes 18 and 22
 in addition to the torque transmitting mechanism 36. The present invention
 permits the removal of these mechanisms.
 The planetary gear set represented by the lever diagram 10 will provide
 four forward ratios, a neutral condition, and a reverse ratio. When the
 first or low forward ratio is desired, the torque transmitting mechanism
 36 is engaged. Input torque at the node 26 causes the node 22 to react at
 node 18 against ground through the torque transmitting mechanism 36 and
 one-way torque transmitting mechanism 40 which results in forward
 underdrive ratio between the input member 30 and the output member 28. If
 engine braking is desired, the torque transmitting mechanism 38 is engaged
 thereby establishing a positive reaction point at the node 18.
 To establish the second forward ratio, the torque transmitting mechanism 44
 is engaged and the torque transmitting mechanism 36 remains engaged. This
 changes the reaction point from node 18 to node 16 resulting in a higher
 underdrive ratio between the input 30 and the output 28. To establish the
 third forward ratio, the torque transmitting mechanism 44 is disengaged
 and the torque transmitting mechanism 34 is engaged. This establishes a
 direct connection between the node 22 and the input resulting in a direct
 drive between the input member 30 and the output member 28. To establish
 the fourth and highest forward ratio, the torque transmitting mechanism 36
 is disengaged and the torque transmitting mechanism 44 is engaged. This
 establishes the node 16 as a reaction point and an overdrive ratio between
 the input 30 and the node 20 is present. Since the node 20 is directly
 connected with the output member 28 an overdrive ratio between the input
 member 30 and the output member 28 is present.
 A neutral condition is established by exhausting all of the torque
 transmitting mechanisms except for the torque transmitting mechanism 42. A
 reverse condition is established by engaging the torque transmitting
 mechanism 32 and the torque transmitting mechanism 42 remains engaged.
 This conditions the node 16 as an input point and the node 18 as a
 reaction point resulting in a reverse ratio at the node 20 and therefore
 the output member 28.
 The torque transmitting mechanisms 32, 34, 36, 40, 42 and 44 are
 hydraulically operated and controlled by an electro-hydraulic mechanism 46
 shown in FIG. 2. The electro-hydraulic mechanism 46 includes a pump 48
 that supplies hydraulic fluid to an electro-hydraulic control 50. The
 electro-hydraulic control 50 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 mechanism also includes three shift logic valves 52, 54,
 and 56, two high ratio control valves 58 and 60, two low ratio control
 valves 62 and 64, a reverse control valve 66, two pressure control valves
 68 and 70 and a backfill valve 72.
 The shift logic valve 52 is comprised of a shift valve 74 and a control
 valve 76. The control valve 76 is a conventional off-on type solenoid
 valve controlled by the ECU. The shift valve is a directional flow control
 valve having eight ports 74A, 74B, 74C, 74D, 74E, 74F, 74G, and 74H that
 are selectively connectable with four ports 74I, 74J, 74K, and 74L. In the
 spring set position shown, the ports 74 B, C, E, and G are blocked, the
 port 74A is connected with the port 74I, the port 74D is connected with
 the port 74J, the port 74 F is connected with the port 74 K, and the port
 74 H is connected with the port 74L. In the pressure set position, that is
 when the valve 76 is energized by the ECU to control the fluid pressure
 delivered through a passage 78 to the valve 74, the ports 74A, D, F, and H
 are blocked while the ports 74B, C, E, and F are connected to the ports
 74I, J, K, and L respectively.
 The shift logic valve 54 is comprised of a directional valve 80 and a
 control valve 82 that are interconnected by a passage 84. The pressure in
 the passage 84 is controlled by the valve 82 which is an off-on type
 solenoid valve controlled by the ECU. The valve 80 has a spring set
 position shown and a pressure set position which is achieved when the
 passage 84 is pressurized. The directional valve 80 has ten ports 80A,
 80B, 80C, 80D, 80E, 80F, 80G, 80H, 80I, and 80j that are selectively
 connectable with five ports 80K, 80L, 80M, 80N, and 80 P. In the spring
 set position shown, the ports 80B, C, F, H, and I are connected with the
 ports 80K, L, M, N, and P respectively while the ports 80A, D, E, G, and J
 are blocked. In the pressure set position, the ports 80A, D, E, G, and J
 and connected with the ports 80K, L, M, N, and P respectively while the
 ports 80B, C, F, H, and I are blocked.
 The shift logic valve 56 is comprised of a directional valve 86 and a
 control valve 88 that are interconnected by a passage 90. The pressure in
 the pass 90 is controlled by the valve 88 which is an off-on type solenoid
 valve controlled by the ECU. The valve 86 has twelve ports 86A, 86B, 86C,
 86D, 86E, 86F, 86G, 86H, 86I, 86J, 86K, and 86L that are selectively
 connectable with six ports 86M, 86N, 86P, 86Q, 86R, and 86S. In the spring
 set position shown, the ports 86A, D, E, H, I, and L are selectively
 connected with the ports 86N, M, P, Q, R, and S respectively while the
 ports 86B, C, F, G, J, and K are blocked. In the pressure set position,
 the ports 86B, C, F, G, J, and K are connected with the ports 86N, M, P,
 Q, R, and S respectively while the 86A, D, E, H, I, and L are blocked.
 The pressure control valve 68 is a variable pressure type solenoid valve
 that is controlled in a well-known manner by the ECU. The valve 68 may be
 of the pulse width modulated (pwm) type which will have an output pressure
 proportional to the voltage duty cycle imposed on the solenoid by the ECU.
 The valve 68 has an inlet port 68A connected with a passage 92 that is
 supplied with a constant pressure from the control 50. The passage 92 also
 supplies fluid to the solenoids for the valves 76, 82, and 88. The valve
 68 has an outlet port 68B that is connected with a passage 94 which in
 turn is connected with control ports 58A and 60A of the valves 58 and 60,
 respectively.
 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 pwm type. The valve 70 has an inlet port 70A connected with the
 passage 92. The valve 70 has an outlet port 70B that is connected with a
 passage 96 which in turn is connected with control ports 62A and 64A of
 the valves 62 and 64, respectively as well as a control port 66A of the
 valve 66.
 The high ratio control valve 58 had an inlet port 58B, an outlet port 58C,
 an exhaust port 58D and a feedback control port 58E. The inlet control
 port 58B is connected with a passage 98 that is supplied with pressurized
 fluid by the control 50 whenever the driver selects a drive position with
 the manual valve. The pressure in the outlet port 58C is proportional to
 the pressure in the passage 94 which is provided from the valve 68. The
 port 58C is connected with a passage 100 that is in turn connected with
 the port 86H and a control port 62B on the valve 62.
 The high ratio control valve 60 had an inlet port 60B, an outlet port 60C,
 an exhaust port 60D and a feedback control port 60E. The inlet control
 port 60B is connected with the passage 98 that is supplied with
 pressurized fluid by the control 50 whenever the driver selects a drive
 position with the manual valve. The pressure in the outlet port 60C is
 proportional to the pressure in the passage 94 which is provided from the
 valve 68. The port 60C is connected with a passage 102 that is in turn
 connected with the ports 86C, 74E and a control port 64B on the valve 64.
 The exhaust port 60D is connected with a passage 104 that communicates
 with the backfill valve 72. Thus the pressure at the port 60D has a
 minimum pressure as established by the back fill valve 72 which is
 generally set at approximately 2 psi.
 The low ratio control valve 62 has an inlet port 62C, an outlet port 62D,
 an exhaust port 62E and a control port 62F. the inlet port 62C is
 connected with the passage 98, the outlet port 62D is connected with a
 passage 106 which is also connected with the control port 62F. The
 pressure in the passage 106 is proportional to the pressure in the passage
 96 which is controlled by the valve 70. However, when the high ratio
 control valve 58 is operated and the pressure in the passage 100 reaches a
 predetermined level, equal to the critical capacity of the oncoming torque
 transmitting mechanism, the low ratio control valve 62 will be exhausted.
 The passage 106 is connected with the ports 74D and 86A.
 The low ratio control valve 64 has an inlet port 64C, an outlet port 64D,
 an exhaust port 64E and a control port 64F. The inlet port 64C is
 connected with the passage 98, the outlet port 64D is connected with a
 passage 108 which is also connected with the control port 62F. The
 pressure in the passage 108 is proportional to the pressure in the passage
 96 which is controlled by the valve 70. However, when the high ratio
 control valve 60 is operated and the pressure in the passage 108 reaches a
 predetermined level, equal to the critical capacity of the oncoming torque
 transmitting mechanism, the low ratio control valve 64 will be exhausted.
 The passage 108 is connected with the port 86B.
 The valve 76, as previously mentioned, is an off-on solenoid valve. The
 valve 76 is operable to establish the pressure in the passage 78. The
 passage 78 is fed from the passage 92 through an orifice or restriction
 110. In the off position shown, the valve 76 connects the passage 78 to
 exhaust such that the pressure in the passage is low and not sufficient to
 move the valve 74 to the spring set position since the orifice 110
 restricts the inflow which the outflow through valve 76 is not restricted.
 In the on position, the valve 76 blocks the outflow from passage such that
 the pressure in the passage 78 rises to a level sufficient to move the
 valve 74 to the pressure set position.
 The valve 82, as previously mentioned, is an off-on solenoid valve. The
 valve 82 is operable to establish the pressure in the passage 84. The
 passage 84 is fed from the passage 92 through an orifice or restriction
 112. In the off position shown, the valve 82 connects the passage 84 to
 exhaust such that the pressure in the passage is low and not sufficient to
 move the valve 80 to the spring set position since the orifice 112
 restricts the inflow which the outflow through valve 82 is not restricted.
 In the on position, the valve 82 blocks the outflow from passage such that
 the pressure in the passage 84 rises to a level sufficient to move the
 valve 74 to the pressure set position.
 The valve 88, as previously mentioned, is an off-on solenoid valve. The
 valve 88 is operable to establish the pressure in the passage 90. The
 passage 90 is fed from the passage 92 through an orifice or restriction
 114. In the off position shown, the valve 88 connects the passage 90 to
 exhaust such that the pressure in the passage is low and not sufficient to
 move the valve 86 to the spring set position since the orifice 114
 restricts the inflow which the outflow through valve 88 is not restricted.
 In the on position, the valve 88 blocks the outflow from passage such that
 the pressure in the passage 90 rises to a level sufficient to move the
 valve 86 to the pressure set position.
 The valve 72 is a conventional regulator valve that maintains the pressure
 in the passage 104 at a substantially fixed level as previously mentioned.
 The pressure level in the passage 104 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.
 The manual valve, not shown, in the control 50 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 drive
 conditions. A passage 116 is connected to main line pressure at the
 control 50. The passage 116 is connected between the control 50 and the
 port 86J. The passage 98 is connected with main line pressure in the
 control 50 when the manual valve is placed in the drive positions. A
 passage 118 is connected between the control 50 and the reverse control
 valve 66 during reverse operation.
 The reverse control valve 66 is a downstream regulator valve that control
 the pressure in the torque transmitting mechanism 32. The valve 66 has an
 inlet port 66B connected with the passage 118, and outlet port 66C
 connected by a passage 120 connected with the torque transmitting
 mechanism 32 and a control port 66D. Fluid pressure at the control ports
 66A and 66D reduce the pressure at the outlet port 66C. Thus the pressure
 at the torque transmitting mechanism 32 is controlled proportional to the
 pressure produced at the pressure control valve 70.
 In park, reverse and neutral, the valves 76 and 88 are actuated to place
 the valves 74 and 86 respectively in the pressure set position. In park
 and neutral, the pressure control valve 70 is set to maximum and the
 pressure control valve 68 is set to exhaust. This ensures that the torque
 transmitting mechanism 32 will be exhausted. When reverse is selected by
 the operator, the pressure control valve 70 controlled in a modulating
 condition to thereby control the pressure output of the valve 66 such that
 the torque transmitting mechanism 32 is engaged at a controlled rate.
 During a neutral to first shift, the shift logic valves 52 and 56 are in
 the pressure set position and the shift logic valve 54 is in the spring
 set position. The pressure control valve 70 is set at maximum pressure
 output and the pressure control valve 68 is controlled to provide a
 modulated pressure. The output pressure from the high ratio control 60 is
 directed through valves 86, 80 and 74 to the torque transmitting mechanism
 36 which is engaged at a rate controlled by the output pressure of the
 high ratio control 60 and the one-way torque transmitting mechanism 40
 establishes the reaction member. When the first ratio has been completed,
 the shift logic valve 52 returns to the spring set position and both of
 the pressure control valves 68 and 70 are set to exhaust. There are two
 possible first ratio selection, manual and automatic. The automatic
 selection is described above. During manual first, the passage 116 is
 pressurized and the apply piston 42A of the torque transmitting mechanism
 42 is pressurized to provide a low capacity brake to ensure engine coast
 braking is present.
 During a first to second (1-2), first to third (1-3), or second to third
 (2-3) ratio interchange, the shift logic valves 52 and 56 are spring set
 and the shift logic valve 54 is pressure set. During a 1-2 interchange,
 the pressure control valve 68 is exhausted and the pressure control valve
 70 is modulated. The output pressure from the low ratio control valve 62
 is directed through valves 74, 80 and 86 to the torque transmitting
 mechanism 44. When the torque transmitting mechanism 44 reaches the
 critical capacity, the one-way torque transmitting mechanism 40 will
 release and the second forward ratio is established. When the second ratio
 has been established, all of the shift logic valves 52, 54, and 56 will be
 at the spring set position. The torque transmitting mechanism 44 will be
 maintained in the engaged condition by pressure from the passage 98
 through the valves 80 and 86. The pressure control valves 68 and 70 are
 both set to exhaust.
 During a 1-3 interchange, the pressure control valve 68 is modulated and
 the pressure control valve 70 is exhausted. The output pressure of the
 high ratio control valve 58 is directed through the valves 86 and 80 to
 the torque transmitting mechanism 34 which is engaged at a controlled
 rate. When the torque transmitting mechanism 34 reaches the critical
 capacity, the one-way torque transmitting mechanism will release and the
 third forward ratio is achieved. When the third forward ratio is fully
 established, the shift logic valve 56 is set to the pressure set position
 and the torque transmitting mechanism 34 is maintained engaged by pressure
 from passage 98 through the valves 86 and 80. The pressure control valves
 68 and 70 are both set to exhaust.
 During a 2-3 interchange, both pressure control valves 68 and 70 are
 modulated. The pressure control valve 68 is modulated from low pressure to
 high pressure while the pressure control valve 70 is modulated from high
 pressure to low pressure. The pressure output of the low ratio control
 valve 62 is directed to the torque transmitting mechanism 44 through the
 valves 74, 80 and 86. The pressure output of the high ratio control valve
 58 is directed through the valves 86 and 80 to the torque transmitting
 mechanism 34. The output pressure of the high ratio control valve 58 is
 also imposed on the control port 62B of the low ratio control valve 62.
 When the torque transmitting mechanism 34 reaches the critical capacity to
 transmit the required torque, the low ratio control valve 62 is set to
 exhaust by the pressure bias from the high ratio control valve 58. When
 the third forward ratio is fully established, the shift logic valve 56 is
 set to the pressure set position and the torque transmitting mechanism 34
 is maintained engaged by pressure from passage 98 through the valves 86
 and 80. The pressure control valves 68 and 70 are both set to exhaust.
 During a second to fourth (2-4) interchange, the shift logic valves 52 and
 54 are pressure set and the shift logic valve 56 is spring set. The
 pressure control valves 68 and 70 are both modulated. The pressure control
 valve 68 increases the pressure output thereof and the pressure control
 valve 70 decreases the pressure output thereof. The pressure output of the
 low ratio control valve, as controlled by the pressure control valve 70,
 is directed to the torque transmitting mechanism 36 through the valves 86,
 80 and 74. Since the pressure output of the low ratio control valve 62
 starts high and goes low, the torque transmitting mechanism 36 is
 maintained engaged during the initial portion of the 2-4 interchange.
 Since the output pressure of the high ratio control valve 58 starts low
 and goes high, the pressure at the torque transmitting mechanism 34 as
 delivered through the valves 86 and 80 is increased at a controlled rate.
 When the pressure in the torque transmitting mechanism 34 is sufficient to
 establish the critical capacity at the torque transmitting mechanism 34,
 the pressure in the passage 100 operating at the control port 62B of the
 low ratio control valve 62 will cause the output pressure thereof to be
 exhausted and the torque transmitting mechanism 36 will be released or
 disengaged. When the fourth ratio is fully established, the shift logic
 valve 54 is moved to the spring set position and both of the pressure
 control valves 68 and 70 are set to exhaust. The torque transmitting
 mechanism 36 is exhausted through the shift logic valves 52, 54 and 56 to
 the passage 104 such that a minimum pressure is maintained thereat. The
 torque transmitting mechanism 34 is maintained engaged by pressure from
 the passage 98 through the valves 74, 86, and 80. The torque transmitting
 mechanism 44 is maintained engaged by pressure from the passage 98 through
 the valves 80 and 86.
 During a third to fourth (3-4) interchange, all of the shift logic valves
 52, 54 and 56 are moved to the pressure set position. Both of the pressure
 control valves 68 and 70 are modulated. The pressure output of the
 pressure control valve 70 is modulated from high to low and the pressure
 output of the pressure control valve 68 is modulated from low to high. The
 torque transmitting mechanism 34 is maintained engaged through the
 interchange by pressure from the passage 98 through the valves 86 and 80.
 The torque transmitting mechanism 36 is controlled by the pressure output
 from the low ratio control valve 64 and the torque transmitting mechanism
 44 is controlled by the pressure output from the high ratio control valve
 60. The pressure output of the low ratio control valve 64 is modulated
 downward and the pressure output of the high ratio control valve 60 is
 modulated upward. The pressure output of the low ratio control valve 64 is
 directed by the valves 86, 80 and 74 to the torque transmitting mechanism
 36 to control the disengagement thereof. The pressure output of the high
 ratio control valve 60 is directed through the valves 74, 80, and 86 to
 the torque transmitting mechanism 44 to control the engagement thereof.
 When the torque transmitting mechanism 44 is pressurized to the critical
 torque capacity, the pressure from the high ratio control valve in passage
 102, operating on the control port 64B will cause the low ratio control
 valve 64 to exhaust the pressure in the passage 108 and therefore the
 torque transmitting mechanism 36. When the fourth ratio is fully
 established, the shift logic valves 54 and 56 are moved to the spring set
 position and both of the pressure control valves 68 and 70 are set to
 exhaust. The torque transmitting mechanism 36 is exhausted through the
 shift logic valves 52, 54 and 56 to the passage 104 such that a minimum
 pressure is maintained thereat. The torque transmitting mechanism 34 is
 maintained engaged by pressure from the passage 98 through the valves 74,
 86, and 80. The torque transmitting mechanism 44 is maintained engaged by
 pressure from the passage 98 through the valves 80 and 86.
 During a 1-2, 1-3, 2-4, and 3-4 upshift and the steady state third ratio,
 the apply chamber 42A of the torque transmitting mechanism 42 is exhausted
 to the passage 104 through the shift logic valve 54. During the steady
 state second and fourth ratios, the apply chamber 42A is exhausted to the
 passage 104 through both shift logic valves 54 and 56.
 The control 46 uses two low ratio control valves and two high ratio control
 valves to accommodate the differing torque requirements of the torque
 transmitting mechanisms during the 3-4 interchange. It is possible to use
 a single low ratio control valve and a high ratio control valves if
 variable gain valves are incorporated. For the present control it is
 believed that the use of four valves provides a more efficient mechanism.
 During downshifting, the low ratio control valves are maintained with a
 higher control pressure from the pressure control valve 70 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 truth 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 logic valves 52, 54, and
 56 and the pressure control valves 68 and 70 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 the upshift ratio
 interchanges, except from first gear, are made without benefit of one-way
 mechanisms and with out a tie-up between friction devices. The low ratio
 one-torque transmitting mechanism 40 can also be eliminated, if desired,
 by controlling the pressure in the apply chamber thereof with one of the
 ratio control valves during and up shift.