Abstract:
A method for controlling a transmission includes using signals of first solenoids to control first and second clutches, servos of first gears and servos of second gears, using signals of a second solenoid to establish a flow rate to cool the clutches and to actuate the servo that is associated with a selected gear, and using signals of a third solenoid to direct the flow rate to one of the clutches and to engage the selected gear.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a powertrain for a motor vehicle, particularly to the hydraulic control circuit of powershift transmission located in the powertrain. 
     2. Description of the Prior Art 
     A dual clutch transmission (DCT), also called a powershift transmission, is a geared mechanism employing two input clutches used to produce multiple gear ratios in forward drive and reverse drive. It transmits power continuously using synchronized clutch-to-clutch shifts. 
     The transmission incorporates gearing arranged in a dual layshaft configuration between the transmission input and its output. One input clutch transmits torque between the input and a first layshaft associated with certain gears; the other input clutch transmits torque between the transmission input and a second layshaft associated with the other gears. The transmission produces gear ratio changes by alternately engaging a first input clutch and running in a current gear, disengaging the second input clutch, preparing a power path in the transmission for operation in the target gear, disengaging the first clutch, engaging the second clutch and preparing another power path in the transmission for operation in the next gear. 
     A powershift transmission launches the vehicle from a stopped or nearly stopped condition using a start clutch. Due to engine downsizing and boosting for a given vehicle size, boost is not present at launch causing potentially insufficient transmission gear ratio for launching. 
     A powershift transmission generally has a specific number of gears and provides little design flexibility for accommodating an increase in the number of gears to five, six or seven speeds. 
     A powershift transmission also has complex electro-hydraulic controls to accommodate required synchronizer states. Some designs have relied on multiplexing clutch controls with synchronizer control in an attempt to deduce cost, which results in reduced operating performance, such as longer shift period, loss of repeatable high quality shifts, and an increased number of failure states. 
     SUMMARY OF THE INVENTION 
     A method for controlling a transmission includes using signals of first solenoids to control first and second clutches, servos of first gears and servos of second gears, using signals of a second solenoid to establish a flow rate to cool the clutches and to actuate the servo that is associated with a selected gear, and using signals of a third solenoid to direct the flow rate to one of the clutches and to engage the selected gear. 
     The invention comprehends a system for controlling a transmission including a first clutch for connecting a power source to odd-numbered gears, a second clutch for connecting a power source to even-numbered second gears, first servos for engaging the odd-numbered gears, second servos for engaging the even-numbered gears, a first solenoid producing first signals that control the first clutches, a second solenoid producing second signals that control the second clutch, the first and second signals determining whether the first servos or the second servos are controlled to engage a selected gear, a third solenoid producing signals that establish a flow rate to cool the clutches and to direct flow to one of the servos that is associated with the selected gear, and a fourth solenoid producing signals that direct the flow rate to one of the clutches and to direct flow to the selected gear. 
     The electro-hydraulic control requires fewer solenoids and valves than the number required for a conventional transmission control without multiplexing the clutch variable force solenoid (VFS) that provides synchronizer flow control. 
     The use multiplexed on/off solenoids reduces cost of the control system compared to the cost of conventional variable force solenoids. 
     The electro-hydraulic control includes stand-alone, clutch control VFSs, allowing greater independence between clutch control and synchronizer selection. The control has a dedicated VFS for synchronizer flow and pressure control, and synchronizer selection is a result of the valve selection network, which receives input signal from the clutch solenoids and clutch cooling control solenoids. 
     Normally multiplexing is considered undesirable due to potential interference between the tasks being performed. But since the need to provide lube and cooling flow to the input clutches occurs at a low frequency, a solenoid will normally be used for this function and will always switch from that function momentarily to control the servo valves. The duration of servo valve control is short and always has priority over lube and cooling flow to the input clutches. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of transmission gearing that produces seven forward speeds and reverse drive; 
         FIG. 2  is a schematic diagram showing an end view of the gearing of  FIG. 1 ; and 
         FIG. 3  is a schematic diagram of a hydraulic control system for the transmission of  FIGS. 1 and 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a powershift transmission  10  includes first and second coaxial input shafts  11 ,  12 , an output gear  14  driveably connected to the vehicle wheels (not shown); first, second and third layshafts  16 ,  18 ,  20 , respectively; a 1-neutral synchronizer  22 ; a 6-2 synchronizer  24 ; a 3-5 synchronizer  26 ; a 4-R synchronizer  28 ; and a L synchronizer  30 . Outer shaft  11  is driveably connected to an engine  13  through an input clutch  15 . Inner shaft  12  is driveably connected to the engine through an input clutch  17 . 
     Each layshaft  16 ,  18 ,  20  includes an output pinion  32 ,  34 ,  36 , secured to the respective layshaft. Each synchronizer is secured to the layshaft on which it is supported and includes a selector sleeve having a neutral position from which it is moved axially along the shaft to secure a gear to the shaft. Input clutches  15 ,  17  include sets of clutch plates, which alternately engage and disengage mutually. 
     Secured to input shaft  12  are input pinions  38 ,  42 ,  46 ,  48 . Secured to input shaft  11  are input pinions  40 ,  44 . First gear  50  meshes with pinion  38  and is journalled on layshaft  16 . Second gear  52  meshes with pinion  40  and is journalled on layshaft  16 . Third gear  54  meshes with pinion  42  and is journalled on layshaft  18 . Fourth gear  56  meshes with pinion  44  and is journalled on layshaft  18 . Fifth gear  58  meshes with pinion  46  and is journalled on layshaft  18 . Sixth gear  60  meshes with pinion  44  and is journalled on layshaft  16 . Reverse gear  64  meshes with idler gear  68  and low gear  66  and is journalled on layshaft  18 . Low gear  66  is journalled on layshaft  20 . An idler gear  68 , secured to second gear  52 , is also journalled on layshaft  16  for rotation with gear  52  as a unit. 
     In operation, each of the gear ratios is produced by transmitting power from the engine  13 , through one of the input clutch  15 ,  17 , to the input shaft  11 ,  12  that corresponds to the desired gear. First gear results when the sector sleeve of synchronizer  22  is moved leftward into engagement with first gear  50  and the selector sleeves of the other synchronizers are in their neutral positions, thereby connecting input shaft  12  to output gear  14  through the mesh between pinion  38  and gear  50 , and the mesh between output pinion  32  and output gear  14 . 
     Second gear results when the selector sleeve of synchronizer  24  is moved rightward into engagement with idler  68  and the selector sleeves of the other synchronizers are in their neutral positions, thereby connecting input shaft  11  to output gear  14  through the mesh between pinion  40  and gear  52 , and the mesh between output pinion  32  and output gear  14 . 
     Third gear results when the selector sleeve of synchronizer  26  is moved leftward into engagement with third gear  54  and the selector sleeves of the other synchronizers are in their neutral positions, thereby connecting input shaft  12  to output gear  14  through the mesh between pinion  42  and gear  54 , and the mesh between output pinion  34  and output gear  14 . 
     Fourth gear results when the selector sleeve of synchronizer  28  is moved leftward into engagement with fourth gear  56  and the selector sleeves of the other synchronizers are in their neutral positions, thereby connecting input shaft  11  to output gear  14  through the mesh between pinion  44  and gear  56 , and the mesh between output pinion  34  and output gear  14 . 
     Fifth gear results when the selector sleeve of synchronizer  26  is moved rightward into engagement with fifth gear  58  and the selector sleeves of the other synchronizers are in their neutral positions, thereby connecting input shaft  12  to output gear  14  through the mesh between pinion  46  and gear  58 , and the mesh between output pinion  34  and output gear  14 . 
     Sixth gear results when the selector sleeve of synchronizer  24  is moved leftward into engagement with sixth gear  60  and the selector sleeves of the other synchronizers are in their neutral positions, thereby connecting input shaft  11  to output gear  14  through the mesh between pinion  44  and gear  60 , and the mesh between output pinion  32  and output gear  14 . 
     Reverse gear results when the selector sleeve of synchronizer  28  is moved rightward into engagement with reverse gear  64 , and the selector sleeves of the other synchronizers are in their neutral positions. The reverse gear power path through transmission  10  includes input shaft  11 , pinion  40 , second gear  52 , idler  68 , reverse gear  64 , synchronizer  28 , layshaft  18 , output pinion  34  and output gear  14 . 
     The low or deep low launch gear results when the selector sleeve of synchronizer  30  is moved rightward into engagement with low launch gear  66 , and the selector sleeves of the other synchronizers are in their neutral positions. The low gear power path through transmission  10  includes input shaft  11 , pinion  40 , second gear  52 , idler  68 , reverse gear  64 , low gear  66 , synchronizer  30 , layshaft  20 , output pinion  36  and output gear  14 . 
     The final drive ratio, i.e., the mesh between pinions  32 ,  34 ,  36  and gear  14 , has a speed ratio of about 4.5. The speed ratio produced in first gear by the mesh between pinion  38  and first gear  50  is about 4.5. Therefore, the first gear speed ratio produced by transmission  10  is about 20:1 (4.5×4.5). In low gear, however, transmission  10  produces a speed ratio, which is the result of a forward gear ratio (2nd gear), a reverse ratio, a low gear ratio and the final drive ratio (4.5). Therefore, a speed ratio of 20:1 is no longer a limit; instead speed ratios much greater than 20:1, e.g. speed ratios greater than 24:1, can be easily produced by transmission  10 . 
       FIG. 3  is a schematic diagram of a hydraulic control circuit  80  for producing gear ratio changes in the transmission of the type shown in  FIGS. 1 and 2 . A fixed displacement pump  82  draws automatic transmission fluid (ATF) through a filter  84  from a sump  86 . A main regulator  88  controls line pressure carried in line  89 . Pressure in line  90 , output from a valve controlled by a variable force solenoid (VFS)  92 , actuates input clutch  15 , and pressure in line  94 , output from a valve controlled by a VFS  96 , actuates input clutch  17 . 
     When the state of an on/off solenoid  100  is low, i.e., off, the flow rate to lube valve  106  from lube flow valve  102 , which is controlled by solenoid  100 , is low, i.e., about 0.50 liters per minute (lpm) going to clutch lube circuits  108  and  109 . Depending on the high/low state of the on/off solenoid  104 , lube direction valve  106  directs the flow rate output from valve  102  to clutch  15  or clutch  17  through lines  108 ,  109 , respectively. For example, if the state of on/off solenoid  100  is low and the state of an on/off solenoid  104  is high, a low flow rate is directed through line  109  to input clutch  17 . If the state of on/off solenoid  100  is high and the state of an on/off solenoid  104  is high, a low flow rate is directed through line  108  to input clutch  15 . 
     If the input clutch  17  for the odd-numbered gears is applied, VFS  112  controls the servos and the related synchronizers  24 ,  28  for the even-numbered gears and reverse gear. If the input clutch  15  for the even-numbered gears is applied, VFS  112  controls the servos and related synchronizers  22 ,  26  for the odd-numbered gears. 
     After a gear change event, in which one of the input clutches  15 ,  17  is newly engaged causing its temperature to rise, the desired flow rate of ATF lube to that input clutch increases to about 15.0 lpm. To produce an increase in flow rate, the state of on/off solenoid  100  goes high, valve  102  shuttles to a high flow rate position, and lube flow to the recently engaged input clutch increases to about 15.0 lpm. 
     The control circuit  80  also includes a servo control  110 , which controls the synchronizer  22 ,  24 ,  26 ,  28 ,  30 , whose state of engagement with a selected gear determines the operating gear produced by transmission  10 . The servo control  110  includes a high flow rate VFS  112 , a servo direction valve  114 , and a servo valves  116 ,  118 ,  120 . 
     The input of high flow rate VFS  112 , which has a normally low state, is connected to the source of line pressure  89 . The output of high flow rate VFS  112  is connected by line  122  to the input of servo direction valve  114 . 
     Pressure signals produced by VFS  92  and VFS  96  are shared or multiplexed with the servo direction valve  114 , whose left/right positional state determines whether an even-numbered gear or an odd-numbered gear of transmission  10  is to be connected by a synchronizer to the shaft on which the subject gear is journalled. For example, if servo direction valve  114  shuttles rightward due to input clutch  17  being engaged and input clutch  15  being disengaged, line  122  is connected to line  126 , indicating that a synchronizer that actuates an even-numbered gear is being activated. If servo direction valve  114  shuttles leftward due to input clutch  15  being engaged and input clutch  17  being disengaged, line  122  is connected to line  124 , indicating that a synchronizer that actuates an odd-numbered gear is being activated. 
     Lines  124 ,  126  connect the output of servo valve  114  to the input of servo valve  116 . High/low pressure signals produced by on/off solenoid  100  are shared or multiplexed with the servo valve  116 . The high/low pressure signal of on/off solenoid  100  in combination with the positional state of servo valve  114  determine whether the output of servo valve  116  is carried in line  128  or  130  to servo valve  118 , or in lines  132  or  134  to servo valve  120 . 
     For example, if servo direction valve  114  shuttles leftward and the state of on/off solenoid  100  is low, line  124  is connected to line  128  through servo valve  116 , indicating that synchronizer  22  is being actuated. If servo direction valve  114  shuttles leftward and the state of on/off solenoid  100  is high low, line  124  is connected to line  130  through servo valve  116 , indicating that synchronizer  26  is being actuated. If servo direction valve  114  shuttles rightward and the state of on/off solenoid  100  is low, line  126  is connected to line  132  through servo valve  116 , indicating that synchronizer  24  is being actuated. If servo direction valve  114  shuttles rightward and the state of on/off solenoid  100  is high, line  126  is connected to line  134  through servo valve  116 , indicating that synchronizer  28  is being actuated. 
     Pressure signals produced by on/off solenoid  104  are shared or multiplexed through lines  136 ,  138  with servo valves  118 ,  120 , respectively. The state of servo valve  118  in combination with the state of lines  128 ,  130  determines which of the odd-numbered gears associated with synchronizer  22  is being activated. Similarly, the state of servo valve  118  in combination with the state of line  130  determines which of the odd numbered gears associated with synchronizer  26  is being activated. 
     For example for odd-numbered gear synchronizer engagement, when the state of on/off solenoid  104  is low and synchronizer  22  is being activated, pressure in line  128  is directed to line  140 , thereby moving the sleeve of synchronizer  22  to disengage first gear moving the synchronizer to neutral. When the state of on/off solenoid  104  is high and synchronizer  22  is being activated, pressure in line  128  is directed to line  142 , thereby moving the sleeve of synchronizer  22  to engage first gear. Similarly, when the state of on/off solenoid  104  is low and synchronizer  26  is being activated, pressure in line  130  is directed to line  144 , thereby moving the sleeve of synchronizer  26  to engage fifth gear. When the state of on/off solenoid  106  is high and synchronizer  26  is being activated, pressure in line  130  is directed to line  146 , thereby moving the sleeve of synchronizer  26  to engage third gear. 
     For even-numbered gear synchronizer engagement, when the state of on/off solenoid  104  is low and synchronizer  24  is being activated, pressure in line  132  is directed to line  150 , thereby moving the sleeve of synchronizer  24  to engage second gear. When the state of on/off solenoid  104  is high and synchronizer  24  is being activated, pressure in line  132  is directed to line  148 , thereby moving the sleeve of synchronizer  24  to engage sixth gear. Similarly, when the state of on/off solenoid  104  is low and synchronizer  28  is being activated, pressure in line  134  is directed to line  152 , thereby moving the sleeve of synchronizer  28  to engage reverse gear. When the state of on/off solenoid  104  is high and synchronizer  28  is being activated, pressure in line  134  is directed to line  154 , thereby moving the sleeve of synchronizer  28  to engage fourth gear. 
     In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.