Abstract:
The present invention provides a control system employing a single solenoid valve operable to provide a variable fluid flow to effect cooling if the motor/generator assemblies contained within an electrically variable hybrid transmission. The control system of the present invention selectively controls the cooling of at least one motor/generator assembly of an electronically variable hybrid transmission by selectively controlling valves of various types and configurations.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a control system for selectively controlling the fluid flow rate to effect the cooling of at least one motor/generator assembly of an electrically variable hybrid transmission.  
       BACKGROUND OF THE INVENTION  
       [0002]     An electrically variable hybrid transmission has been proposed for vehicles to improve fuel economy and reduce exhaust emissions. The electrically variable transmission splits mechanical power between an input shaft and an output shaft into a mechanical power path and an electrical power path by means of differential gearing. The mechanical power path may include clutches and additional gears. The electrical power path may employ two electrical power units, or motor/generator assemblies, each of which may operate as a motor or a generator. With an electrical storage system, such as a battery, the electrically variable transmission can be incorporated into a propulsion system for a hybrid electric vehicle.  
         [0003]     The hybrid propulsion system uses an electrical power source, such as batteries, as well as an engine power source. The electrical power source is connected with the motor/generator units through an electronic control unit, which distributes the electrical power as required. The electronic control unit also has connections with the engine and vehicle to determine the operating characteristics, or operating demand, so that the motor/generator assemblies are operated properly as either a motor or a generator. When operating as a generator, the motor/generator assembly accepts power from either the vehicle or the engine and stores power in the battery, or provides that power to operate another electrical device or another motor/generator assembly.  
         [0004]     Additionally, the stators for each electric motor/generator assembly contained within the electrically variable hybrid transmission may each require differing rates of cooling that are dependent on the duty cycle of each motor/generator. The cooling of the stator is typically performed by bathing the stator with a calibrated flow rate of transmission fluid allowing the heat generated by operation of the motor/generators to be transferred to the fluid. A continuously high cooling rate is simple to implement, however, additional pump loads and spin losses may produce a decrease in efficiency over a selectively variable motor/generator cooling system.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention provides a cooling control system employing a single solenoid valve, to selectively control the fluid flow rate to the motor/generator cooling system of an electrically variable hybrid transmission.  
         [0006]     Accordingly, the present invention provides a variable motor/generator cooling control system for an electrically variable hybrid vehicular transmission having a solenoid valve, a line pressure source of pressurized fluid, at least one motor/generator; and at least one relay valve. The relay valve has a first position and a second position which is controlled by the solenoid valve, and is operable to selectively distribute the pressurized fluid from the line source to the at least one motor/generator for cooling.  
         [0007]     The variable motor/generator cooling control system of the present invention may also include a motor/generator feed passage having a plurality of branches of varying restriction to place the at least one motor/generator in selective fluid communication with the relay valve. Orifices disposed therein may effect the restriction in the plurality of branches. The plurality of branches of the present invention may include a first branch and a second branch. The first branch has no orifice, the second branch has multiple orifices, and the motor/generator feed passage has a single orifice. The relay valve may communicate the pressurized fluid from the line pressure source at one flow rate to the at least one motor/generator via one of the plurality of branches when the relay valve is in the first position. Alternately, the relay valve may distribute the pressurized fluid from the line pressure source at another flow rate to the at least one motor/generator via another of the plurality of branches when the relay valve is in the second position.  
         [0008]     The solenoid valve may control the at least one relay valve by selectively, variably pressurizing a control passage. The solenoid valve may be a variable pressure type solenoid valve. Additionally, the present invention may provide a multiplex valve having a first position and a second position. The multiplex valve is operable to selectively distribute the pressure within the control passage to the at least one relay valve when the multiplex valve is in the first position. Alternately, the multiplex valve will selectively distribute the pressure within the control passage to an additional component of the variable motor/generator cooling control system when the multiplex valve is in the second position. The additionally component may be a damper lock out clutch trim valve.  
         [0009]     A second embodiment of the present invention provides a variable motor/generator cooling control system for an electrically variable hybrid vehicular transmission having a relay valve having a first position and a second position, a regulator valve, a line pressure source of pressurized fluid, and a plurality of motor/generators each of which is individually in selective fluid communication with the regulator valve via one of a plurality of feed passages. A solenoid valve is also provided and is operable to control the relay valve and the regulator valve to selectively communicate the pressurized fluid from the line pressure source to each of the plurality of motor/generators for cooling. The solenoid valve of the present invention may be a variable pressure type solenoid valve operable to control the relay valve and the regulator valve by selectively and variably pressurizing a control passage.  
         [0010]     Each of the plurality of feed passages may include at least one orifice. Additionally, the line pressure source may be in fluid communication with the regulator valve via a line pressure source passage. The line pressure passage may include an orifice.  
         [0011]     The present invention also provides a variable motor/generator cooling control system for an electrically variable hybrid vehicular transmission comprising having at least one motor/generator, a line pressure source of pressurized fluid, and at least one relay valve operable to provide the pressurized fluid from the line pressure source to the at least one motor/generator for cooling. The variable motor/generator cooling control system also includes a solenoid valve operable to control the relay valve by selectively and variably pressurizing a control passage. The solenoid valve may be a variable pressure type solenoid valve. The control system may also include a regulator valve disposed between, and in selective fluid communication with, the at least one motor/generator and the at least one relay valve.  
         [0012]     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is an exemplary schematic diagram of a variable motor/generator cooling system for an electrically variable hybrid transmission illustrating an engine off operating condition;  
         [0014]      FIG. 2  is an exemplary schematic diagram of the variable motor/generator cooling system for an electrically variable hybrid transmission illustrating an engine on, low cooling flow to both motor/generator A and motor/generator B operating condition;  
         [0015]      FIG. 3  is an exemplary schematic diagram of the variable motor/generator cooling system for an electrically variable hybrid transmission illustrating an engine on, high cooling flow to motor/generator A and low cooling flow to motor/generator B operating condition;  
         [0016]      FIG. 4  is an exemplary schematic diagram of the variable motor/generator cooling system for an electrically variable hybrid transmission illustrating an engine on, low cooling flow to motor/generator A and high cooling flow to motor/generator B operating condition;  
         [0017]      FIG. 5  is an exemplary schematic diagram of the variable motor/generator cooling system for an electrically variable hybrid transmission illustrating an engine on, high cooling flow to motor/generator A and high cooling flow to motor/generator B operating condition;  
         [0018]      FIG. 6  is a schematic diagram showing an alternate embodiment of the variable motor/generator cooling system for an electrically variable hybrid vehicular transmission illustrating an engine on, high flow cooling to motor/generator A and motor/generator B operating condition;  
         [0019]      FIG. 7  is a schematic diagram showing an alternate embodiment of the variable motor/generator cooling system for an electrically variable hybrid vehicular transmission illustrating an engine on, high flow cooling to motor/generator A and no cooling to motor/generator B operating condition;  
         [0020]      FIG. 8  is a schematic diagram showing an alternate embodiment of the variable motor/generator cooling system for an electrically variable hybrid vehicular transmission illustrating an engine on, proportional cooling between motor/generator A and motor/generator B operating condition;  
         [0021]      FIG. 9  is a schematic diagram showing an alternate embodiment of the variable motor/generator cooling system for an electrically variable hybrid vehicular transmission illustrating an engine on, no cooling to motor/generator A and high flow cooling to motor/generator B operating condition; and  
         [0022]      FIG. 10  is a schematic diagram showing an alternate embodiment of the variable motor/generator cooling system for an electrically variable hybrid vehicular transmission illustrating an engine on, no cooling to motor/generator A and no cooling to motor/generator B operating condition. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Referring to the drawings, wherein like characters represent the same or corresponding parts throughout the several views, there is seen in  FIGS. 1 through 5  a multiplexed control system  10  having a solenoid valve  12 , a multiplex valve  14 , a damper trim valve  16 , a relay valve  18 , and a relay valve  20 . The solenoid valve  12  is a variable pressure-type solenoid valve that may include a variable bleed or a pulse width modulated solenoid valve. Those skilled in the art of control systems will appreciate that there may be other types of solenoid valves compatible with the multiplexed control system  10  of the present invention. The solenoid valve  12  is a normally low type in that the solenoid valve  12  will not allow the passage of pressurized fluid if electrical power to the solenoid valve  12  is discontinued. However, a normally high type may be used depending on the application and the desired default state of the multiplexed control system  10  upon electrical power interruption.  
         [0024]     The solenoid valve  12  is in fluid communication with an exhaust passage  22 , a control pressure source  24 , and a control passage  25 . The exhaust passage  22  ensures that pressurized fluid is evacuated from within the solenoid valve  12  upon deactuation of the solenoid valve  12 . The control pressure source  24  provides a pressurized fluid signal to allow the control passage  25  to be selectively pressurized at varying pressure levels by the actuation of the solenoid valve  12 .  
         [0025]     The multiplex valve  14  has a bore  26  and a valve spool  28  slidably disposed therein. The valve spool  28  has lands  30 ,  32 , and  34 . Additionally, a valley  36  is situated between lands  30  and  32 , while a valley  38  is situated between lands  32  and  34 . The valve spool  28  is biased within bore  26  by a spring  40 . The multiplex valve  14  is in fluid communication with an auxiliary pressure source  42 , the exhaust passage  22 , a damper trim valve control passage  44 , the control passage  25 , a motor/generator control passage  46 , and an exhaust passage  48 . The valve spool  28  operates to selectively open and block each of these passages depending on the position of the valve spool  28  within the bore  26 .  
         [0026]     The damper trim valve  16  has a bore  50  and a valve spool  52  slidably disposed therein. The valve spool  52  has lands  54  and  56 , with a valley  58  situated therebetween. The valve spool  52  is biased within bore  50  by a spring  60 . The damper trim valve  16  is in fluid communication with the damper trim valve control passage  44 , an exhaust passage  62 , a damper lock-out clutch feed passage  64 , and a line pressure source  66 . The valve spool  52  operates to selectively open and block each of these passages depending on the position of the valve spool  52  within the bore  50 . The damper lock-out clutch feed passage  64  is the conduit through which pressurized fluid will selectively flow to effect engagement of a damper lock-out clutch  68 .  
         [0027]     The relay valve  18  has a bore  70  and a valve spool  72  slidably disposed therein. The valve spool  72  has lands  74  and  76 , with a valley  78  situated therebetween. The valve spool  72  is biased within bore  70  by a spring  80 . The spring  80  is contained within a spring chamber  82  formed by the land  76 , the bore  70 , and an end wall  84 . The land  76  has a differential area  85  that is operable to provide a desired pressure differential between opposite ends of the valve spool  72 . The relay valve  18  is in fluid communication with the motor/generator control passage  46 , a motor/generator A cooling feed passage  86 , a line pressure source  66 ′, a differential pressure passage  88 , and an exhaust passage  90 . The valve spool  72  operates to selectively open or block each of these passages depending on the position of the valve spool  72  within the bore  70 .  
         [0028]     The motor/generator A cooling feed passage  86  is the conduit through which pressurized fluid may flow to effect cooling of motor/generator A  92 . The amount of cooling flow available to motor/generator A  92  is determined by the amount of pressure provided by the line pressure source  66 ′ as well as through which branch,  94  or  96 , of the motor/generator A cooling feed passage  86  the fluid is allowed to flow. The branch  94  has a single orifice  98 , which will cause a minor restriction in flow when compared to the multiple orifice set  100  of branch  96 . The selection of branch  94  or  96  will ultimately depend on the position of the valve spool  72  within the bore  70 .  
         [0029]     The relay valve  20  has a bore  102  and a valve spool  104  slidably disposed therein. The valve spool  104  has lands  106 ,  108  and  110 . Additionally, a valley  112  is situated between the lands  106  and  108 , while a valley  114  is situated between the lands  108  and  110 . The valve spool  104  is biased within bore  102  by a spring  116 . The relay valve  20  is in fluid communication with the motor/generator control passage  46 , an exhaust passage  118 , the differential pressure passage  88 , a control pressure source  24 ′, a motor/generator B cooling feed passage  120 , a line pressure source  66 ″, and an exhaust passage  122 . The valve spool  104  operates to selectively open or block each of these passages depending on the position of the valve spool  104  within the bore  102 .  
         [0030]     The motor/generator B cooling feed passage  120  is the conduit through which pressurized fluid may flow to effect cooling of motor/generator B  124 . The amount of cooling flow available to the motor/generator B  124  is determined by the amount of pressure provided by the line pressure source  66 ″ as well as through which branch,  126  or  128 , of the motor/generator B cooling feed passage  120  the fluid is allowed to flow. The branch  126  has a single orifice  130 , which will cause a relatively minor restriction in fluid flow when compared to the multiple orifice set  132  of branch  128 . The selection of branch  126  or  128  will ultimately depend on the position of the valve spool  104  within the bore  102 .  
         [0031]     The line pressure sources  66 ,  66 ′, and  66 ″ are typically maintained at the same pressure, however they need not be. Likewise, the control pressure sources  24  and  24 ′ are typically maintained at the same pressure level however they need not be. Additionally, orifices  134 A and  134 B may be provided as an additional measure of fluid flow control.  
         [0000]     Electric Mode—Engine Off  
         [0032]     In  FIG. 1  there is seen an exemplary schematic diagram of the multiplexed control system  10  for selectively controlling the damper lock-out clutch  68  and the cooling of motor/generator A  92  and motor/generator B  124 , illustrating the engine off operating condition. Hybrid electric vehicles may selectively energize motors by battery power to effect movement of the hybrid electric vehicle. This engine off mode is sometimes referred to as “Electric Mode”. During this state of operation, an auxiliary pressure source  42 , such as an electrically controlled hydraulic pump, is employed to maintain fluid pressure within the electrically variable hybrid transmission. Since operation in the “Electric Mode” is limited, and torque requirements on the motor/generators are low and brief in duration, a large amount of cooling is not required by the motor/generator A  92  and the motor/generator B  124 .  
         [0033]     The damper lock-out clutch  68  should be engaged when stopping and starting the internal combustion engine, which occurs when transitioning into and out of “Electric Mode”. This clutching is required to avoid the torsional vibrations associated with an engine moving into and out of its torsional resonant point. As the vehicle enters an operating mode in which the internal combustion engine may be stopped, the auxiliary pressure source  42  is activated by the vehicle control system (not shown). This pressurized fluid from the auxiliary pressure source  42  forces the valve spool  28  of the multiplex valve  14  into a pressure set position. The valley  36  will allow fluid communication between the control passage  25  and the damper trim valve control passage  44 .  
         [0034]     The solenoid valve  12  may now precisely control the fluid pressure within the damper trim valve control passage  44  by allowing regulated fluid from the control pressure source  24  into the control passage  25 . As the solenoid valve  12  permits the increase of the pressure within the damper trim valve control passage  44 , the valve spool  52  of the damper trim valve  16  will move from its spring set position, as shown in  FIGS. 2 through 5 , to bias against the spring  60 . The valve spool  52  will move into a trim position, as shown in  FIG. 1 , when the fluid pressure operating on land  54  overcomes the force of spring  60 . At which point, the damper lock-out clutch  68  will stop exhausting fluid pressure through the damper lock-out clutch feed passage  64  into the exhaust passage  62  via the valley  58 . Instead, the land  54  will block the exhaust passage  62  and the land  56  will permit pressurized fluid from the line pressure source  66  to enter the damper lock-out clutch feed passage  64  via valley  58 . The increased fluid pressure within the damper lock-out clutch feed passage  64  will enable engagement of the damper lock-out clutch  68 .  
         [0035]     Concurrently, the position of the valve spool  28  within the multiplex valve  14  will cause any fluid pressure within the motor/generator control passage  46  to be exhausted by the exhaust passage  48  via valley  38 . This will ensure that both the valve spool  72  of the relay valve  18  and the valve spool  104  of the relay valve  20  will remain in the spring set position thereby providing a minimal amount of cooling fluid to motor/generator A  92  and motor/generator B  124  via branch  96  and  128  respectively.  
         [0000]     Engine On—Low Cooling Flow to Motor/Generator A and Motor/Generator B  
         [0036]      FIG. 2  is an exemplary schematic diagram of the multiplexed control system  10  for selectively controlling the damper lockout clutch engagement and motor/generator cooling, illustrating the engine on, low cooling flow to both the motor/generator A  92  and the motor/generator B  124  operating condition. The auxiliary pressure source  42  is turned off following engine restart thereby relieving the fluid pressure acting upon the valve spool  28  of the multiplex valve  14 . The spring  40  will bias the valve spool  28  into a spring set position. The damper trim valve control passage  44  will then exhaust though the exhaust passage  22  by way of valley  36 . The lack of fluid pressure acting on land  54  will allow the spring  60  to bias the valve spool  52  of the damper trim valve  16  into a spring set condition. As a result, the land  56  will move into position to block the line pressure source  66  and allow the disengagement of the damper lock-out clutch  68  by exhausting fluid pressure through the damper lock-out clutch feed passage  64  into the exhaust passage  62  via valley  58 . This condition will remain for the duration of the engine on conditions.  
         [0037]     At low pressure values within the control passage  25 , both the valve spool  72  within the relay valve  18  and the valve spool  104  within the relay valve  20  will remain in the spring set position. In this state, the land  76  of the valve spool  72  will block the pressurized fluid of the line pressure source  66 ′ from entering branch  94  of the motor/generator A feed passage  86 .  
         [0038]     Instead, the pressurized fluid from the line pressure source  66 ′ will be directed into branch  96  where it must traverse a multiple orifice set  100  prior to entering the motor/generator A feed passage  86  and ultimately to effect cooling of motor/generator A.  
         [0039]     Likewise, the land  110  of the valve spool  104  will block the pressurized fluid of the line pressure source  66 ″ from entering branch  126  of the motor/generator B feed passage  120 . Instead, the pressurized fluid from the line pressure source  66 ″ will be directed into branch  128  where it must traverse a multiple orifice set  132  prior to entering the motor/generator B feed passage  120  and ultimately to effect cooling of motor/generator B  124 . Additionally, with the valve spool  104  in the spring set position, the land  108  will block fluid flow from the control pressure source  24 ′ to the differential pressure passage  88 .  
         [0040]     The high flow restriction of the multiple orifice sets  100  and  132  produce a low fluid flow rate condition within the motor/generator A feed passage  86  and the motor/generator B feed passage  120 , respectively. Those skilled in the art will recognize that the flow rate may be tailored to the specific application by adjusting the amount of restriction within branches  96  and  128  and/or adjusting the pressure value of the line pressure sources  66 ′ and  66 ″.  
         [0000]     Engine On—Low Cooling Flow to Motor/Generator B and High Cooling Flow to Motor/Generator A  
         [0041]      FIG. 3  is an exemplary schematic diagram of the multiplexed control system  10  for selectively controlling the damper lockout clutch engagement and motor/generator cooling, illustrating the engine on, high cooling flow to the motor/generator A  92  and low cooling flow to the motor/generator B  124  operating condition. As the solenoid valve  12  actuates to allow greater fluid communication between the control passage  25  and the control pressure source  24 , the fluid pressure will increase within both the control passage  25  and the motor/generator control passage  46 . The increased pressure within the motor/generator control passage  46  will bias the valve spool  72  of the relay valve  18  into a pressure set position against the spring  80 . The position of the valve spool  72  within the bore  70  will allow pressurized fluid from the line pressure source  66 ′ to flow into both branches  94  and  96 , of the motor/generator A feed passage  86 , via valley  78 . Motor/generator A  92  will now receive fluid though the single orifice  98  at a much higher flow rate than when the valve spool  72  is in the spring set position.  
         [0042]     The spring  116  of the relay valve  20  is of sufficient stiffness to bias the valve spool  104  in the spring set position, thereby ensuring that the fluid flow to the motor/generator B  124  will remain at a low level. The line pressure source  66 ″ will continue to provide pressurized fluid to the motor/generator B feed passage  120  via the branch  128 . The high flow restriction of the multiple orifice set  132  will produce a low fluid flow rate condition within the motor/generator B feed passage  120 .  
         [0000]     Engine On—Low Cooling Flow to Motor/Generator A and High Cooling Flow to Motor/Generator B  
         [0043]      FIG. 4  is an exemplary schematic diagram of the multiplexed control system  10  for selectively controlling the damper lockout clutch engagement and motor/generator cooling, illustrating the engine on, low cooling flow to the motor/generator A  92  and high cooling flow to the motor/generator B  124  operating condition. As the solenoid valve  12  actuates to allow even greater fluid communication between the control passage  25  and the control pressure source  24 , the fluid pressure will further increase in both the control passage  25  and the motor/generator control passage  46 . As a result, the fluid pressure within the motor/generator control passage  46  will bias the valve spool  104  of the relay valve  20  into a pressure set position. The position of the valve spool  104  within the bore  102  will allow pressurized fluid from the line pressure source  66 ″ to flow into both branch  126  and  128 , of the motor/generator B feed passage  120 , via valley  114 . Motor/generator B  124  will now receive fluid though a single orifice  130  at a much higher flow rate than when the valve spool  104  is in the spring set position.  
         [0044]     By moving valve spool  104  into the pressure set position, the valley  112  will allow the control pressure source  24 ′ to pressurize the differential pressure passage  88 . The differential pressure passage  88  will in turn pressurize the spring chamber  82 , and act upon the differential area  85  of land  76  to bias the valve spool  72  of the relay valve  18  into the spring set position. In this position, the land  76  of the valve spool  72  will block the pressurized fluid of the line pressure source  66 ′ from entering branch  94  of the motor/generator A feed passage  86 . Instead, the pressurized fluid from the line pressure source  66 ′ will be directed into branch  96  where it must traverse the multiple orifice set  100  prior to entering the motor/generator A feed passage  86  and to ultimately effect the cooling of motor/generator A  92 . The high restriction of the multiple orifice set  100  will produce a low fluid flow rate condition within the motor/generator A feed passage  86 .  
         [0000]     Engine On—High Cooling Flow to Motor/Generator A and High Cooling Flow to Motor/Generator B  
         [0045]      FIG. 5  is an exemplary schematic diagram of the multiplexed control system  10  for selectively controlling the damper lockout clutch engagement and motor/generator cooling, illustrating the engine on, high cooling flow to the motor/generator A  92  and high cooling flow to the motor/generator B  124  operating condition. As the solenoid valve  12  actuates to allow even greater fluid communication between the control passage  25  and the control pressure source  24 , the fluid pressure will further increase within both the control passage  25  and the motor/generator control passage  46 . As a result, the motor/generator control passage  46  will bias the valve spool  104  of the relay valve  20  into a pressure set position. The position of the valve spool  104  within the bore  102  will allow pressurized fluid from the line pressure source  66 ″ into both branches  126  and  128  via valley  114 . Motor/generator B  124  will now receive fluid though a single orifice  130  at a much higher flow rate than when the valve spool  104  is in the spring set position.  
         [0046]     Additionally, The increased pressure within the motor/generator control passage  46  is now of a sufficient magnitude to bias the valve spool  72  contained within the relay valve  18  into the pressure set position by overcoming both the spring force of spring  80  and the force acting upon the differential area  85  of land  76 . The position of the valve spool  72  within the bore  70  will introduce pressurized fluid from the line pressure source  66 ′ into both branch  94  and  96  via valley  78 . Motor/generator A  92  will now receive fluid though a single orifice  98  at a much higher flow rate than when the valve spool  72  is in the spring set position.  
         [0047]     Referring now to  FIGS. 6 through 10 , there is seen an alternate embodiment of a variable motor/generator cooling system  210  having a solenoid valve  212 , a regulator valve  214 , and a relay valve  216 . The solenoid valve  212  is a variable pressure-type solenoid valve and may be a variable bleed solenoid valve or pulse width modulated solenoid valve. Those skilled in the art of control systems may recognize other types of solenoid valve compatible with the variable motor/generator cooling system  210 . The solenoid valve  212  is a normally low type solenoid valve. Therefore, it will not allow pressurized fluid to pass if the electrical power to the solenoid valve  212  is interrupted. A normally high type may also be used depending on the application and the desired default state of the variable motor/generator cooling system  210  upon power loss.  
         [0048]     The solenoid valve  212  is in fluid communication with an exhaust passage  218 , a control pressure source  220 , and a control passage  222 . The exhaust passage  218  ensures that no pressurized fluid remains within the solenoid valve  212  upon deactuation. The control pressure source  220  provides a pressurized fluid signal to allow the control passage  222  to be selectively pressurized at varying pressure levels by the actuation of the solenoid valve  212 .  
         [0049]     The regulator valve  214  has a bore  224  and a valve spool  226  slidably disposed therein. The valve spool  226  has lands  228 ,  230 , and  232 . Additionally, a valley  234  is situated between the lands  228  and  230 , while a valley  236  is situated between the lands  230  and  232 . The valve spool  226  is biased within bore  224  by a spring  238 . The regulator valve  214  is in fluid communication with the control passage  222 , a relay valve first passage  240 , a relay valve second passage  242 , a motor/generator A cooling feed passage  244 , a motor/generator B cooling feed passage  246 , and a first branch  248  and a second branch  250  of a line pressure source passage  252 . The valve spool  226  operates to selectively open and block each of these passages depending on the position of the valve spool  226  within the bore  224 .  
         [0050]     The relay valve  216  has a bore  254  and a valve spool  256  slidably disposed therein. The valve spool  256  has lands  258  and  260 . Additionally, a valley  262  is situated between the lands  258  and  260 . The valve spool  256  is biased within bore  254  by a spring  264 . The relay valve  216  is in fluid communication with the control passage  222 , an exhaust passage  266 , the relay valve first passage  240 , and the relay valve second passage  242 . The valve spool  256  operates to selectively open and block each of these passages depending on the position of the valve spool  256  within the bore  254 .  
         [0051]     A line pressure source  268  is operable to maintain the pressure within the line pressure source passage  252 . The line pressure source passage  252 , the motor/generator A cooling passage  244 , and the motor/generator B cooling passage  246  each have a flow control orifice  270 ,  272 , and  274  respectively disposed therein. A motor/generator A  276  is in fluid communication with the motor/generator A cooling passage  244 , while a motor/generator B  278  is in fluid communication with the motor/generator B cooling passage  246 .  
         [0000]     Engine On—High Cooling Flow to Motor/Generator A and Motor/Generator B  
         [0052]      FIG. 6  shows a variable motor/generator cooling system  210  for an electrically variable hybrid vehicular transmission illustrating the engine on, high flow cooling to the motor/generator A  276  and the motor/generator B  278  mode of operation. In this mode, the solenoid valve  212  will not permit fluid from the control pressure source  220  to pressurize the control passage  222 . As a result, the valve spool  226  of the regulator valve  214  and the valve spool  256  of the relay valve  216  will remain biased in the spring set position. To effect cooling of the motor/generator A  276 , pressurized fluid from the line pressure source  268  will traverse orifice  270  and enter the line pressure source passage  252 . The fluid will subsequently flow into branch  250  and traverse valley  236 , thereafter entering the motor/generator A cooling feed passage  244 . The pressurized fluid must then traverse the orifice  272  prior to entering the motor/generator A  276 .  
         [0053]     To effect cooling of the motor/generator B  278 , pressurized fluid within the branch  248  is communicated to the relay valve second passage  242  via the valley  234 . The valley  262  of the valve spool  256  will allow pressurized fluid to flow from the relay valve second passage  242  into the relay valve first passage  240 . The pressurized fluid will then flow around the land  232  of the valve spool  226 , and into the motor/generator B cooling passage  246 . The orifice  274  provides a measure of flow control for the pressurized fluid entering the motor/generator B  278 . Fluid pressure from the relay valve first passage  240  acting upon the underside of land  232  of the valve spool  226  will ensure that the valve spool  226  will remain in the spring set position.  
         [0054]     Those skilled in the art will recognize that the fluid flow rate to the motor/generator A  276  and the motor/generator B  278  may be varied by increasing or decreasing the fluid pressure within the line pressure source  268  as well as increasing or decreasing the size of orifices  270 ,  272 , and  274 .  
         [0000]     Engine On—High Cooling Flow to Motor/Generator A and No Cooling Flow to Motor/Generator B  
         [0055]      FIG. 7  shows a variable motor/generator cooling system  210  for an electrically variable hybrid vehicular transmission illustrating the engine on, high flow cooling to the motor/generator A  276  and no cooling to the motor/generator B  278  mode of operation. As the solenoid valve  212  actuates to allow greater communication of pressurized fluid between the control pressure source  220  and the control passage  222 , the valve spool  256  will bias against the spring  264 . When the fluid pressure within the control passage  222  is of sufficient magnitude to overcome the spring force exerted by the spring  264 , the valve spool  256  will move to a pressure set position, as shown in  FIGS. 7 through 10 . In this position, the land  258  of the valve spool  256  will block the relay valve first passage  240  thereby interrupting fluid flow to the motor/generator B feed passage  246 . The fluid pressure within the control passage  222  is of insufficient magnitude to overcome the spring force exerted on the valve spool  226  by the spring  238 . Therefore, the valve spool  226  will remain in the spring set position.  
         [0056]     Additionally, pressurized fluid within the relay valve second passage  242  will become trapped within the valley  262 , thereby disallowing the flow of fluid within the relay valve second passage  242 . The pressurized fluid within the line pressure source passage  252  will flow into branch  250  and subsequently into the motor/generator A cooling feed passage  244 , via valley  236 , where the fluid must traverse the orifice  272  prior to entering the motor/generator A  276 . This mode of operation will provide the maximum amount of fluid flow to the motor/generator A  276  and no fluid flow to the motor/generator B  278 .  
         [0000]     Engine On—Proportional Cooling Flow to Motor/Generator A and Motor/Generator B  
         [0057]      FIG. 8  shows a variable motor/generator cooling system  210  for an electrically variable hybrid vehicular transmission illustrating a proportional cooling between the motor/generator A  276  and the motor/generator B  278  mode of operation. As the solenoid valve  212  actuates to allow greater communication of pressurized fluid between the control pressure source  220  and the control passage  222 , the fluid pressure within the control passage  222  will eventually be of a sufficient magnitude to overcome the spring force exerted on the valve spool  226  by the spring  238 . The valve spool  226  will bias against the spring  238  and move within the bore  224  of the regulator valve  214  until it reaches a pressure regulation point, as shown in  FIG. 8 .  
         [0058]     In this position, the valley  236  will communicate the pressurized fluid within the branch  250  of the line pressure source passage  252  proportionately between the motor/generator A cooling feed passage  244  and the motor/generator B cooling feed passage  246 . By varying the fluid pressure within the control passage  222 , the valve spool  226  will vary the proportion of fluid that flows to the motor/generator A  276  and the motor/generator B  278 . Those skilled in the art will recognize that the proportional fluid distribution characteristic can be adjusted by varying the geometric characteristics of the valve spool  226  and the orifices  270 ,  272 , and  274 . Additionally, as the valley  236  allows fluid communication between the branch  25  and the relay valve first passage  240 , the relay valve first passage  240  will provide a pressure feedback signal to the underside of the land  232  to balance the forces acting on the valve spool  226 .  
         [0000]     Engine On—No Cooling Flow to Motor/Generator A and High Cooling Flow to Motor/Generator B  
         [0059]      FIG. 9  shows a variable motor/generator cooling system  210  for an electrically variable hybrid vehicular transmission illustrating a no cooling to motor/generator A  276  and high flow cooling to motor/generator B  278  mode of operation. As the solenoid valve  212  actuates to provide the control passage  222  with a fluid pressure greater than that of the feedback pressure signal operating on the land  232 , the valve spool  226  will bias against the spring  238  to an even greater extent, as shown in  FIG. 9 . The position of the valve spool  226  within the valve bore  224  will cause the land  230  to block fluid flow to the motor/generator A cooling feed passage  244 . In doing so, the fluid flow to the motor/generator A  276  is discontinued. The fluid flow rate to the motor/generator B  278  will increase as the pressurized fluid within the branch  250  is now communicated to the motor/generator B cooling feed passage  246  via the valley  236 .  
         [0000]     Engine On—No Cooling Flow to Motor/Generator A and No Cooling Flow to Motor/Generator B  
         [0060]      FIG. 10  shows a variable motor/generator cooling system  210  for an electrically variable hybrid vehicular transmission illustrating an engine on, no cooling to the motor/generator A  276  and no cooling to the motor/generator B  278  mode of operation. As the solenoid valve  212  actuates to allow the maximum fluid communication between the control pressure source  220  and the control passage  222 , the valve spool  226  will bias against the spring  238  and move to a pressure set position, as shown in  FIG. 10 . In this position, the lands  228  and  230  of the valve spool  226  will operate to block fluid flow from both branches  248  and  250 , respectively, of the line pressure source passage  252 . Thus, fluid flow to the motor/generator A cooling feed passage  244  and the motor/generator B cooling feed passage  246 , and ultimately to the motor/generator A  276  and the motor/generator B  278  will be disallowed.  
         [0061]     By providing multiple modes of motor/generator cooling, multiple motor/generator assemblies may be independently cooled at varying rates depending on the duty cycle of each motor/generator. Increases in efficiency may be achieved though reduced pump loads and spin losses by selectively controlling the fluid flow to effect the cooling of each motor/generator  
         [0062]     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.