Abstract:
A unique regulator valve arrangement is provided for an automatic transmission which provides variable line pressure. The line pressure is actively regulated through the regulator valve configuration with a variable force solenoid. The arrangement allows line pressure to be maintained at a minimal value according to a given condition while avoiding clutch slip.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a hydraulic control system used in an automatic transmission for a vehicle, and more particularly to a pressure control configuration for regulating line pressure in the hydraulic control system. 
     BACKGROUND 
     A conventional automatic transmission used in vehicles generally includes a multi-stage gear mechanism, a torque converter connected thereto, and a plurality of clutch elements actuated by hydraulic pressure for selecting one of the gears of the gear mechanism. A hydraulic control system for an automatic transmission operates by selectively supplying hydraulic pressure from a hydraulic pump to the clutch elements by a plurality of control valves such that shifting may be realized automatically according to the driving situation. 
     The hydraulic control system generally includes a hydraulic fluid source, a line pressure controller for regulating hydraulic pressure supplied from the fluid source to line pressure, and a hydraulic pressure distributor for determining a hydraulic flow path corresponding to the respective transmission speeds according to the hydraulic pressure from the shift controller and suitably distributing the operational pressure to each friction element. 
     In traditional automatic transmissions, the line pressure is usually maintained at two different levels while in the “Drive” position. The first pressure remains constant while in first and second gears, and depending on application is around 135 psi. When the transmission shifts from second to third, the pressure lowers to around 85 psi depending on the application. The pressure remains at that pressure as the transmission shifts to fourth gear. 
     It would be desirable to provide a transmission that had the ability to vary the line pressure according to an optimal running condition. For example, in some conditions it would be favorable to run the transmission at a lower pressure while in the higher gears. If a lower line pressure can be maintained without inducing clutch slip, the longevity of the transmission as well as the fuel economy of the vehicle would be increased. Similarly, it may be desired to increase the line pressure in a low gear situation where clutch holding torque capacity is needed. A variable pressure configuration would allow the transmission to operate at an optimal pressure according to the condition and avoid relying on two predetermined pressures. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a hydraulic control system for an automatic transmission including a planetary gear system having a plurality of clutch elements to alter the torque ratio of the transmission. 
     It is another object of the present invention to provide a line pressure control device for variably regulating hydraulic pressure supplied from the fluid source. 
     It is yet another object of the present invention to provide a line pressure regulating valve influenced by a solenoid which is in communication with the transmission control module which is using signals from the input and output sensors as well as engine throttle angle. 
     It is a further object of the present invention to provide a line pressure control device for regulating hydraulic pressure which provides increased fuel economy and transmission life. 
     It is still another object of the present invention to replace the multitude of parts comprising a traditional regulator valve with one single valve. 
     The present invention obtains these and other objects by providing a new configuration for a regulator valve in an automatic transmission. The configuration according to this invention includes a first fluid port communicating with the manual valve, a second fluid port communicating with the fluid pump and a third fluid port influenced by a solenoid communicating with the fluid pump. The solenoid is energized according to the desired line pressure needed for a given situation. The solenoid is actuated accordingly to achieve the lowest line pressure available avoiding clutch slip. By maintaining line pressure at an optimal level, the durability of the transmission components as well as the fuel efficiency of the vehicle is increased. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a schematic view of the hydraulic control system of the automatic transmission according to the principles of the present invention. 
     FIG. 1 a  is a table illustrating the applied clutches for each gear ratio of the transmission according to the principles of the present invention. 
     FIG. 2 is a schematic view of the hydraulic control system of the automatic transmission in drive “D” position according to the principles of the present invention. 
     FIG. 3 is a schematic view of the hydraulic control system of the automatic transmission in reverse “R” position according to the principles of the present invention. 
     FIG. 4 is a view of the general steps of the preferred method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 1, a four-speed automatic transmission  10  is shown, according to the principles of the present invention. The automatic transmission  10  includes a torque converter  12  which is operably connected to a multiple planetary gear system. The multiple planetary gear system includes a first planetary gear assembly  16 , and a second planetary gear assembly  18 . The first planetary gear assembly  16  includes a sun gear  22 , an annulus gear  24 , a planetary carrier assembly  26 , and a plurality of rotatably mounted planetary gears  28 . The second planetary gear assembly  18  includes a sun gear  38 , an annulus gear  40 , a planetary carrier assembly  42 , and a plurality of rotatably mounted planetary gears  44 . 
     The sun gear  22  of the first planetary gear assembly  16  is selectively driven by engagement of an underdrive clutch  46  with an input shaft  48  which is driven by a turbine  50  of the torque converter  12 . The annulus gear  24  of the first planetary gear assembly  16  is attached to the planetary carrier  42  of the second planetary gear assembly  18 . Both of these elements are selectively engaged by an overdrive clutch  52  which engages the annulus gear  24  of first planetary gear assembly  16 , and the planetary carrier  42  of the second planetary gear assembly  18  to the input shaft  48 . The planetary carrier  26  of the first planetary gear assembly  16  is attached to an output shaft  54  and is also attached to the annulus gear  40  of the second planetary gear assembly  18 . A reverse clutch  60  operably connects the sun gear  38  of the second planetary gear assembly  18  to the input shaft  48 . A 2-4 brake  62  is provided to engage the sun gear  38  of the second planetary gear assembly  18  to the transmission housing  63 . A low/reverse brake  53  is provided to engage the annulus gear  24  of the first planetary gear assembly  16  and the planetary carrier  42  of the second planetary gear assembly  18  to the housing  63 . 
     FIG. 1A illustrates the different operating modes of the automatic transmission, as shown in FIG.  1 . In particular, in order to obtain a reverse gear operation, the reverse clutch  60  and low/reverse brake  53  must be applied. In order to provide improved neutral-to-reverse shift quality, the low/reverse brake  53  is applied in neutral. In order to obtain first gear, the underdrive clutch  46  and the low/reverse brake  53  must be applied. In order to obtain second gear, the underdrive clutch  46  and the 2-4 brake  62  must be applied. In order to obtain direct gear (3 rd ), the underdrive clutch  46  and the overdrive clutch  52  must be applied. In order to obtain overdrive (4 th ), the overdrive clutch  52  and the 2-4 clutch must be applied. 
     Turning now to FIGS. 2 and 3, the hydraulic control system  70  for controlling the operation of transmission  10  will now be described. When the manual valve is in the drive “D” position (FIG.  2 ), the regulator valve  74  distributes hydraulic fluid  75  under pressure to the torque converter limit valve  78  via fluid passage  80 . Fluid is also open to the solenoid switch valve  82  and to the manual valve  84  via passage  105  and  86  respectively. The torque converter limit valve  78  communicates fluid to the torque converter switch valve  69  via passage  127 . The regulator valve  74  has a first fluid port  101  communicating with the manual valve  84  via passage  86 , a second fluid port  102  communicating with the hydraulic fluid pump  110  and a third fluid port  103  influenced by a variable force solenoid  120  communicating with the hydraulic fluid pump  110  and the manual valve  84  via passage  105 . A pressure transducer  107  monitors and measures the pressure at all times. The variable force solenoid  120  is actuated to establish the desired line pressure for optimum running conditions and it is based on the information obtained at the input shaft  48  and output shaft  54  by the input speed sensor  49  and output speed sensor  55  respectively. The signals  32  and  34  from speed sensors  49  and  55  are received by a powertrain control module  30 . The powertrain control module uses the information along with a signal  36  obtained from the engine regarding throttle angle and torque to generate and send a signal  39  to the variable force solenoid  120 . The variable force solenoid  120  maintains the appropriate fluid pressure at the end of the regulator valve  74  to vary supply line pressure at an optimal level according to the given situation. For example, when the vehicle is under minimal loading conditions, it is desirable to run the transmission at a reduced line pressure. As such, based on the optimum desired line pressure, the variable force solenoid  120  is energized and signal pressure is supplied to the regulator valve  74  at fluid port  103 . This results in the reduction of line pressure. Similarly, when the vehicle is under a high loading condition, the transmission could undergo clutch slip realized through speed sensors  49  and  55 . In this situation, the variable force solenoid  120  would not provide any signal pressure at port  103 . This provides an increased line pressure. 
     Pressurized fluid is delivered to the torque converter control valve  64  via passage  88 . The torque converter control valve  64  communicates pressurized fluid to the torque converter switch valve  69  via hydraulic passage  71 . The torque converter switch valve  69  communicates pressurized fluid to the torque converter clutch  67  via passage  65 . Hydraulic fluid is also communicated between the torque converter clutch  67  and the torque converter switch valve  69  via passage  66 . Fluid is also communicated from torque converter switch valve  69  to ball check valves  94  and  95  through passage  92 . Ball check valves  94  and  95  allow fluid to flow to overdrive clutch  52  and reverse clutch  60  accordingly. 
     Hydraulic fluid is communicated between the torque converter control valve  64  and the torque converter switch valve  69  via passage  77 . Hydraulic fluid is communicated between the torque converter switch valve  69  and a cooler device  87  via passage  89 . The hydraulic fluid from the cooler  87  is communicated back to the pump  110  via passage  91  (not specifically shown). 
     Hydraulic fluid is delivered to the passages  86 ,  96 ,  88 ,  98  and  105  from manual valve  84 . Passage  86  communicates the regulator valve  74  to the manual valve  84 . Passage  96  communicates fluid to normally closed solenoid  106  and ball check valve  116 . Passage  88  communicates fluid to converter clutch control valve  64  while passage  98  transmits fluid through normally open solenoid  108  that returns fluid to the solenoid switch valve  82  as well as communicates fluid to the underdrive clutch  46 . Passage  98  also allows fluid to flow through normally closed solenoid  112  to overdrive clutch  52 . In addition, passage  98  delivers fluid through ball check valve  116  and temperature controller  118  to underdrive clutch  46 . 
     Turning now to FIG. 3, the transmission is shown with the manual valve  84  in the reverse “R” position. To obtain reverse gear, the reverse clutch  60  and the low reverse clutch  53  must be applied. The regulator valve  74  distributes hydraulic fluid under pressure to the torque converter limit valve  78  via fluid passage  80 . Fluid is also open to port  102  which communicates with the pump  110  and the manual valve  84  via passage  105 . The variable force solenoid  120  is closed preventing fluid from flowing through port  103 . Fluid also communicates with the solenoid switch valve  82  via passage  126 . Passage  126  allows fluid to travel past ball check valve  124  through passage  120  and to the manual valve  84 . Fluid travels from the manual valve  84  through passage  130 , communicating with open ball check valve  132 , to apply reverse clutch  60 . Fluid also travels through passage  122  from the manual valve  84  to apply the low reverse clutch  53 . 
     Referring now to FIG. 4, in a first general step  150  the preferred method of the present invention provides a transmission  10  with a planetary gear system  16 ,  18  having a plurality of clutch elements to alter the torque ratio of the transmission, the transmission including input and output speed sensors  49  and  55 . 
     In a second general step  152 , the preferred method of the present invention provides a hydraulic fluid source  75 . 
     In a third general step  154 , the preferred method of the present invention provides a pressure regulating device  120  to supply signal pressure at the pressure regulating valve  74 . 
     In a fourth general step  156 , the preferred method of the present invention the pressure regulating device  120  is actively actuated to attain and maintain the minimal line pressure sufficient to avoid clutch slip. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.