Abstract:
A power transmission includes a plurality of torque transmitting mechanisms controlled by an electro-hydraulic control system to provide a reverse drive ratio, a neutral condition and a plurality of forward drive ratios. The electro-hydraulic control has three shift valves, two variable pressure control valves, and a manual control valve. Each of the shift valves have a hydraulically on position, established by a respective solenoid valve, and a hydraulically off position, established by a spring. The manual control valve is moveable to a neutral condition, a reverse drive condition and a forward drive condition. In each of the positions during a neutral to reverse, neutral to forward, or forward/reverse interchange, the shift valves are conditioned to be hydraulically on thereby permitting the manual control valve to be the controlling valve member for completing the interchange. When the reverse ratio is established, the manual control valve directs fluid pressure from one of the variable pressure control valves to one of the shift valves to assist the respective spring and urge the shift valve to the hydraulically off position. During the reverse ratio, neutral condition and the first forward ratio one of the torque transmitting mechanisms is continually engaged.

Description:
TECHNICAL FIELD 
     This invention relates to electro-hydraulic controls for a power transmission and more particularly to hydraulic controls having a manual control valve for selecting transmission drive conditions. 
     BACKGROUND OF THE INVENTION 
     Electro-hydraulic control systems employed in automatic transmissions can operate with or without a manual selector valve. Traditionally the most common practice is to use a manual selector valve that is manipulated by the operator to perform “garage shifts”. Garage shifts are the valve manipulations performed when the vehicle is at rest. These garage shifts include reverse to neutral, neutral to reverse, neutral to forward drive, forward drive to neutral, reverse to forward drive, and forward drive to reverse. However in many of the current automatic transmissions having electro-hydraulic control systems, the garage shifts to reverse and drive are controlled by the electronic control unit (ECU) which enforces the manipulation of solenoid control valves to ensure the proper positioning of the shift valves or relay valves which control the distribution of hydraulic fluid to and from the torque transmitting mechanisms (clutches and brakes) in the transmission. The garage shifts into neutral continue to be controlled by the manual control valve. 
     The more current automatic transmissions, especially those used in heavy trucks, have increased the number of forward speed ratios to improve performance and efficiency of these vehicles. However, to conserve space in the powertrain, the transmissions utilize as few torque transmitting mechanisms as possible. One such transmission is described in U.S. Pat. No. 4,070,927 issued to Polak and assigned to the assignee of this application. The Polak gear scheme reuses the torque transmitting mechanisms to control three simple planetary gear sets to produce six forward speeds. For example, one of the torque transmitting mechanisms is engaged during the reverse, third and fifth ratios, another torque transmitting mechanism is engaged in both the second and sixth forward ratios, and yet another torque transmitting mechanism is engaged in both the reverse ratio and the first forward ratio. When this gearing arrangement is used to provide a five speed transmission, only two of the torque transmitting mechanisms are reused. The reuse of the torque transmitting mechanisms requires that the electro-hydraulic control be sufficiently flexible to provide the proper operation of these devices. Two such electro-hydraulic controls are described in U.S. Pat. Nos. 5,601,506 and 5,616,093 both of which were issued to Long et al. and assigned to the assignee of this application. These controls will operate equally well for both a five speed and a six speed transmission. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved electro-hydraulic control system for an automatic transmission. 
     In one aspect of the present invention, the electro-hydraulic control has three solenoid actuated, spring return shift valves for distributing hydraulic fluid during the operation of the transmission and the hydraulic logic of the electro-hydraulic control requires the hydraulic fluid to flow through the manual control valve during reverse operation thereby giving the operator control of the neutral-reverse garage shift. In another aspect of the present invention, the hydraulic logic overrides the electronic logic during reverse to ensure one of the shift valves is in a spring set condition. In yet another aspect of the present invention, the offgoing torque transmitting mechanism, during a reverse to neutral interchange, is exhausted through a flow restricted passage and the one shift valve. 
     In still another aspect of the present invention, all three of the shift valves have a solenoid controlled hydraulic signal imposed thereon during the reverse drive, the neutral condition, and the first forward ratio. In a further aspect of the present invention, an alternate reverse engagement control circuit is provided in the event of an electrical or mechanical malfunction of the solenoid controlled shift valves. In a yet further aspect of the present invention, the hydraulic logic requires hydraulic fluid flow through the manual control valve during the first forward drive condition to provide the operator with more complete selection of the forward drive operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a powertrain incorporating the present invention. 
     FIG. 2 is a diagrammatic representation of an electro-hydraulic control system, shown in a neutral condition, incorporating the present invention. 
     FIG. 3 is a diagrammatic representation of an electro-hydraulic control system, shown in reverse ratio selection, incorporating the present invention. 
     FIG. 4 is a diagrammatic representation of an electro-hydraulic control system, shown in first ratio forward drive selection, incorporating the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A powertrain  10 , shown in FIG. 1, includes an engine  12 , a torque converter  14 , electro-hydraulic controls  14 A, and a multi-speed transmission  16 . The engine  12  is a conventional device. The torque converter  14  includes a conventional torque converter and clutch. The electro-hydraulic control  14  includes a hydraulic control portion that includes the present invention and an electronic control unit (ECU) that includes a conventional programmable digital computer. The ECU receives signals from a plurality of sensors, not shown, and issues control commands to various elements in the powertrain  10 . The signals utilized by the ECU may include engine speed, torque converter output speed, transmission output speed, hydraulic fluid pressures in the transmission  16  and a torque proportional various torque levels in the powertrain  10 . 
     The transmission  16  is preferably constructed in accordance with the transmission described in U.S. Pat. No. 4,070,927 issued to Polak and assigned to the assignee of the present invention. The transmission  16  includes an input shaft  18 , an output shaft  20 , three simple planetary gear sets  22 ,  24 , and  26 , two rotating torque transmitting mechanisms  28 , and  30 , and three stationary torque transmitting mechanisms  32 ,  34 , and  36 . The torque transmitting mechanisms are selectively engaged in pairs, by hydraulic commands from the electro-hydraulic control  14 , to provide a plurality of forward drive ratios and one reverse drive ratio. The torque transmitting mechanism  32  is engaged during a neutral condition in the transmission  16 . 
     The reverse drive ratio is established with the engagement of the stationary torque transmitting mechanism  36 ; the torque transmitting mechanism  32  was engaged during the neutral condition. The first forward drive ratio is established with the engagement of the torque transmitting mechanism  28 ; the torque transmitting mechanism  32  was engaged during the neutral condition. Therefore on a garage shift from neutral to the reverse drive ratio or from neutral to the first forward drive ratio only one torque transmitting mechanism is engaged to complete the interchange. The same is true on a first to reverse and a reverse to first interchange. This interchange is made with the swapping of the torque transmitting mechanisms  36  and  28 . 
     The first to second forward drive ratio interchange is completed with the synchronized disengagement of the torque transmitting mechanism  32  and the engagement of the torque transmitting mechanism  34  while the torque transmitting mechanism  28  remains engaged. The second to third forward drive ratio interchange is completed with the synchronized disengagement of the torque transmitting mechanism  34  and the engagement of the torque transmitting mechanism  36 ; the torque transmitting mechanism  28  remains engaged. The third to fourth forward drive ratio interchange is completed with the synchronized disengagement of the torque transmitting mechanism  36  and the engagement of the torque transmitting mechanism  30 ; the torque transmitting mechanism  28  remains engaged. The fourth to fifth forward drive ratio interchange is completed with the synchronous disengagement of the torque transmitting mechanism  28  and the engagement of the torque transmitting mechanism  36 ; the torque transmitting mechanism  30  remains engaged. A fifth to sixth forward drive ratio interchange is also possible with the synchronous engagement of the torque transmitting mechanism  34  and the disengagement of the torque transmitting mechanism  36 ; the torque transmitting mechanism  30  remains engaged. The sixth ratio is not utilized with the present invention so that the control  14 A can provide improved pressure regulation during the fifth forward ratio. 
     A portion of the electro-hydraulic control  14 A is shown in FIGS. 1 through 4. The control includes a manual control valve  38 , three shift valves  40 ,  42 ,  44 , a torque converter clutch (TCC) valve  46 , an exhaust pressure control valve  48 . The control  14 A also has a pressure source  50 , which includes a pump and pressure controls, not shown, that supplies fluid pressure to operate the various mechanisms in the transmission  16 . The pressure source  50  also feeds pressurized fluid to a conventional pressure control valve  52  that in turn supplies a filtered and controlled main pressure to a first variable pressure solenoid valve  54 , which is in fluid communication with the shift valve  40 , a second variable pressure solenoid valve  56 , which is in fluid communication with the shift valve  42 , and a plurality of conventional off-on solenoid valves  58 ,  60 ,  62  and  64  that are in fluid communication with the shift valve  40 , shift valve  42 , shift valve  44  and the TCC valve  46  respectively. The shift valve  42  is in fluid communication with both of the torque transmitting mechanisms  32  and  36  and the shift valve  44  is in fluid communication with the torque transmitting mechanism  34 . The variable pressure solenoid valves  56  and  54  are conventional variable pressure output mechanisms such as those described in U.S. Pat. No. 5,643,125 issued to Long et al. on Jul. 7, 1997 and assigned to the assignee of this application. The variable pressure solenoid valve  54  is a normally open solenoid valve such that the pressure output is minimum (approximately zero) when the electronic signal thereto is minimum while the variable pressure solenoid valve  56  is a normally closed solenoid valve such that the pressure output thereof is at maximum (pressure output of valve  54 ) when the electronic signal thereto is minimum. 
     The pressure source  50  is in fluid communication with the shift valve  44  and the TCC valve  46  through a main passage  66 . The shift valve  44  is in fluid communication with the manual control valve  38  through a passage  68 , the shift valve  42  through passages  70 ,  72  and  74 , the shift valve  40  through passages  76 ,  78 , and  80 , and a pressure switch  82  through a passage  84 . The pressure switch  82  and passage  84  are also in fluid communication with the control valve  52  through a plurality of restrictions  86 . The shift valve  42  is in fluid communication with the manual control valve  38 , the exhaust control valve  48 , the TCC valve  46  and the shift valve  40  through a passage  88 . 
     The shift valve  42  is also connected with the manual control valve  38  through a passage  90 , the shift valve  40  through a passage  92 , the TCC valve  46  through the passage  94 , a pressure switch  96  through a passage  98 , and the manual control valve  38 , and the TCC valve  46  through a passage  100 . The shift valves  42  and  44  are interconnected through a passage  102  which is also connected with the solenoid valve  60 . The pressure switch  96  is in fluid communication with the valve  52  through a plurality of restrictions  104 . 
     The shift valve  40  is in fluid communication with a switch  108  and with the control pressure valve  52 . The manual control valve  38  is in fluid communication with a switch  110  through a passage  112  which is also in fluid communication with the control pressure valve  52  through a plurality of restrictions  114 . The manual control valve  38  is also in fluid communication with the torque transmitting mechanisms  28  and  30  through respective passages  116  and  118 . The TCC valve  46  and the shift valve  40  are interconnected for fluid communication via passage  120 . 
     The shift valve  40  has a valve spool  122 , slidably disposed in a valve bore  124  and cooperating therewith to form a pressure chamber  126  that is connected with the solenoid valve  58  and a spring chamber  128  that houses a spring  130 . When the chamber  126  is pressurized, the valve spool  122  is urged to a pressure set or hydraulically on position and when the chamber  126  is exhausted, the spring  130  urges the valve spool  122  to a spring set or hydraulically off position. 
     The shift valve  42  has a valve spool  132 , slidably disposed in a valve bore  134  and cooperating therewith to form a pressure chamber  136  that is connected with the solenoid valve  60  and a spring chamber  138  that houses a spring  140 . When the chamber  136  is pressurized, the valve spool  132  is urged to a pressure set or hydraulically on position and when the chamber  136  is exhausted, the spring  140  urges the valve spool  132  to a spring set or hydraulically off position. 
     The shift valve  44  has a valve spool  142 , slidably disposed in a valve bore  144  and cooperating therewith to form a pressure chamber  146  that is connected with the solenoid valve  62  and a spring chamber  148  that houses a spring  150 . When the chamber  146  is pressurized, the valve spool  142  is urged to a pressure set or hydraulically on position and when the chamber  146  is exhausted, the spring  150  urges the valve spool  142  to a spring set or hydraulically off position. 
     FIG. 2 depicts the electro-hydraulic control  14 A in the neutral condition, that is the manual control valve  38  is in the neutral (N) position. All of the solenoid valves  58 ,  60 , and  62  are electrically on and the shift valves  40 ,  42 , and  44  are in the hydraulically on condition. The variable pressure solenoid valve  56  is communicating with the torque transmitting mechanism  32  through the shift valve  42  and supplying pressure thereto the complete the engagement thereof. All of the other torque transmitting mechanisms are disengaged. The manual control valve  38  closes the passages  90 ,  100 , and  112 , and exhausts the torque transmitting mechanisms  30  and  28  through the exhaust control valve  48 . The switches  82 ,  96 ,  108  and  110  are all pressurized to indicate to the ECU that the electro-hydraulic control is in the neutral condition. 
     FIG. 3 depicts the electro-hydraulic control  14 A with the manual control valve  38  in the reverse condition (R). In this condition, the manual control valve  38  exhausts the torque transmitting mechanisms  28  and  30  through respective orifices or restrictions in passage  152  and  154 , connects the passage  100  with the passage  68 , and exhausts the passage  112 . With the passage  112  exhausted, the switch  110  is exhausted to inform the ECU that the manual control valve  38  has achieved the reverse condition. The shift valve  40  connects the variable pressure solenoid valve  54  with the passage  78  which connects with the passage  68  through the shift valve  44 . The passage  68  is connected through the manual control valve  38  with the passage  100  which is connected with the spring chamber  146  of the shift valve  42  to force the valve spool  132  to the spring set position. The pressure in the spring chamber  138  and the force of the spring  140  will impose a greater force on the valve spool  132  that the pressure in the pressure chamber  136 . 
     Thus on a neutral to reverse shift, the solenoids  58 ,  60 , and  62  remain electrically on and the chambers  126 ,  136 , and  146  remain pressurized. The passage  100  is also connected through a restriction  156  with the TCC valve  46  which is connected through a restriction  158  with the passage  94  that connects through the shift valve  42 , in the spring set position, with the torque transmitting mechanism  32 . Until the shift valve  42  reaches the spring set position, the passage  94  is closed by the valve spool  132 . Also in the spring set position, the shift valve  42  connects the variable pressure solenoid valve  56  with the torque transmitting mechanism  36  which is engaged thereby. The restrictions  156  and  158  tend to slow the pressure rise in the passage  94  and therefore the torque transmitting mechanism  32 . The reverse drive ratio is establish in the transmission  16 , as explained previously, by the engagement of the torque transmitting mechanisms  32  and  36 . It will be now apparent that, during normal operation, the reverse drive ratio is established and controlled by positioning of the manual control valve. 
     A shift to the neutral condition occurs by simply exhausting the passage  100  through the manual control valve. If the shift valve  40  becomes stuck in the hydraulically off condition and either or both of the shift valves  42  and  44  are stuck in the hydraulically on position by the system logic in the ECU, the reverse range can still be attained. With the manual control valve  38  in the neutral position, the torque transmitting mechanism  32  is controlled by the variable pressure solenoid valve  56  and the torque transmitting mechanism  36  is connected to the variable pressure solenoid valve  54  through the shift valve  40 , the passage  76 , the shift valve  44 , the passage  74  and the shift valve  42 . The ECU will control the pressure output of the variable pressure solenoids  54  and  56  to properly engage the reverse ratio for limp home operation. 
     FIG. 4 depicts the electro-hydraulic control conditioned for the first forward drive ratio with the manual control valve  38  moved to the forward (F) position. The shift valves  40 ,  42  and  44  are all in the hydraulically on condition during the shift from neutral to first interchange. The torque transmitting mechanism  32  is controlled by the output pressure from the variable pressure solenoid valve  56 . The output pressure from the variable pressure solenoid valve  54  is directed through the shift valve to the passage  78  to the shift valve  44 , through the shift valve  44  to the passage  68  to the manual control valve  38 , and through the manual control valve  38  to the torque transmitting mechanism  28 . The engagement of the torque transmitting mechanism  28  is, therefore, controlled by the output pressure of the variable pressure solenoid valve  54 . The neutral condition can be attained by simply moving the manual control valve  38  to the neutral condition. This gives the operator control over the neutral/forward interchange. 
     In preparation for a first to second interchange, the shift valves  40  and  44  are conditioned to the hydraulically off condition. In this condition, the fluid pressure from the pressure source  50  is directed through the shift valve  44  to the passage  68 , which is connected with the manual control valve  38 , for delivery to the torque transmitting mechanism  28 . It should be noted that the movement of the shift valve  44  at this stage merely interchanges passage  68  from passage  78  to the pressure source  50 . Also, the switch  82  is exhausted through the passage  84  and the spring chamber  148  to inform the ECU that the hydraulic valves are conditioned to permit a first to second interchange when required by the operating parameters of the vehicle. 
     From the above description, it will be apparent to those skilled in the art that the present invention permits the selection of neutral, reverse, and first forward drive conditions and interchanges therebetween with only the manual control valve being manipulated, and that the forward and reverse conditions are not achieved otherwise unless required by a malfunction, such as a stuck valve or electric power discontinuance.