Abstract:
An active thermal hydraulic control system for a transmission is provided. The active thermal hydraulic control system improves fuel economy by storing transmission fluid in areas away from rotating components during hot operation. However, during other conditions the transmission fluid is kept in the sump. The active thermal hydraulic control system includes an active thermal valve. The active thermal valve is an electro-mechanical device which converts electrical energy into thermal energy which melts a wax pellet which in turn moves a plunger. Movement of the plunger controls the opening and closing of a valve that communicates between the sump and the side or front cover of the transmission. The system improves fuel economy by as much as 0.5% by storing excess hydraulic fluid away from rotating components.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/976,819 filed Apr. 8, 2014. The disclosure of the above application is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to an active thermal hydraulic fluid level control system for an automatic transmission, and more particularly to a control system for actively controlling hydraulic fluid level between a sump and a side or front cover in an automatic transmission. 
       BACKGROUND 
       [0003]    A typical automatic transmission includes a hydraulic control system that is employed to provide cooling and lubrication to components within the transmission and to actuate a plurality of torque transmitting devices such as clutches and brakes. The hydraulic control system typically includes a sump located at a bottom of the transmission that collects the hydraulic fluid from the remainder of the hydraulic control system. The sump stores the hydraulic fluid to be suctioned back into the hydraulic control system by a pump. A minimum level of hydraulic fluid is required in the sump in order to feed the hydraulic control system for all ranges of transmission operation and to account for dynamic movement of the hydraulic fluid within the sump. It is desirable to keep the amount of hydraulic stored in the sump to this minimum level since hydraulic fluid in the sump interferes with the rotating components of the transmission. The rotating components, including for example gears, clutch plates, and interconnecting members, traveling through the stored hydraulic fluid within the sump experience increased drag, thus increasing spin losses and in turn decreasing the efficiency of the transmission. 
         [0004]    The minimum level of hydraulic fluid that must be stored in the sump varies based on various factors including the operating temperature of the hydraulic fluid. Therefore it is desirable to store excess hydraulic fluid out of the sump and in a separate area that does not interfere with rotating components. One solution is to actively control the level of hydraulic fluid between the sump and a front or side cover of the transmission using a passive thermal valve. These passive thermal valves allow hydraulic fluid to flow between the sump and the front cover based on the temperature of the hydraulic fluid. While these systems are useful for their intended purpose, there is a need in the art for an active control system that minimizes cost and mass and that allows excess hydraulic fluid to be stored out of the sump during normal operating conditions but not during certain other conditions, such as end-of-line testing or transportation of the transmission. 
       SUMMARY 
       [0005]    An active thermal hydraulic control system for a transmission is provided. The active thermal hydraulic control system improves fuel economy by storing transmission fluid in areas away from rotating components during hot operation. However, during other conditions the transmission fluid is kept in the sump. The active thermal hydraulic control system includes an active thermal valve. The active thermal valve is an electro-mechanical device which converts electrical energy into thermal energy which melts a wax pellet which in turn moves a plunger. Movement of the plunger controls the opening and closing of a valve that communicates between the sump and the side or front cover of the transmission. The system improves fuel economy by as much as 0.5% by storing excess hydraulic fluid away from rotating components. 
         [0006]    In one aspect, an assembly for use in a transmission of a motor vehicle includes a first fluid reservoir, a second fluid reservoir, and a control valve assembly. The control valve assembly includes a heat source, a wax element configured to undergo a phase change in response to the heat source, a valve moveable between a first position and a second position by the phase change of the wax element, and a sleeve having a first port and a second port. The first port is in direct fluid communication with the first fluid reservoir and the second port is in direct fluid communication with the second fluid reservoir and the valve allows fluid communication between the first port and the second port when in the first position and prevents fluid communication between the first port and the second port when in the second position. 
         [0007]    In another aspect, the first fluid reservoir is located in a sump of the transmission and the second fluid reservoir is located in a side cover of the transmission. 
         [0008]    In yet another aspect, the wax element includes a pressure resistant vessel filled with a temperature tuned wax, wherein the wax undergoes the phase change at a specific temperature. 
         [0009]    In yet another aspect, the wax element further includes a pin partially slidably disposed within the pressure resistant vessel and extending out into the sleeve to contact the valve. 
         [0010]    In yet another aspect, a biasing member is disposed within the sleeve to bias the valve to the second position. 
         [0011]    In yet another aspect, the heat source is a coil disposed around the wax element to which a current is applied to generate heat. 
         [0012]    In yet another aspect, the wax element undergoes the phase change when an operating temperature of the transmission exceeds a threshold. 
         [0013]    In yet another aspect, a separator wall is disposed between the first fluid reservoir and the second fluid reservoir, and the control valve assembly is connected to the separator wall and the sleeve is extended through the separator wall. 
         [0014]    In yet another aspect, the separator wall includes a support collar that receives the sleeve of the control valve assembly. 
         [0015]    In yet another aspect, the first port is disposed in a distal end of the sleeve and the second port is disposed in a side surface of the sleeve. 
         [0016]    In yet another aspect, the valve covers the second port when the valve is in the second position. 
         [0017]    Further features, aspects, and advantages will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0019]      FIG. 1  is a schematic diagram of an exemplary front wheel drive transmission according to the principles of the present invention; 
           [0020]      FIG. 2  is an enlarged cross section of a portion of the exemplary front wheel drive transmission shown in  FIG. 1 ; 
           [0021]      FIG. 3  is a front or side view of the exemplary front wheel drive transmission of  FIG. 1  with a side or front cover removed; 
           [0022]      FIG. 4  is a side view of a control valve assembly used in the exemplary front wheel drive transmission according to the principles of the present invention; 
           [0023]      FIG. 5A  is a cross-sectional view taken in the direction of arrows  5 - 5  in  FIG. 4  of the control valve assembly in a first position; and 
           [0024]      FIG. 5B  is a cross-sectional view taken in the direction of arrows  5 - 5  in  FIG. 4  of the control valve assembly in a second position. 
       
    
    
     DESCRIPTION 
       [0025]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0026]    With reference to  FIG. 1 , a schematic diagram of an exemplary transmission is generally indicated by reference number  10 . The transmission  10  is an automatic, front wheel drive, multiple speed transmission. However it should be appreciated that the transmission may be a manual transmission or any other type of transmission without departing from the scope of the present invention. The transmission  10  includes a typically cast, metal housing  12  which encloses and protects the various components of the transmission  10 . The housing  12  includes a variety of apertures, passageways, shoulders and flanges which position and support these components. The transmission generally  10  includes an input shaft  14 , an output shaft  16 , a starting device  18 , and a gear arrangement  20 . The input shaft  14  is connected with a prime mover (not shown) such as an engine. The prime mover may be an internal combustion gas or Diesel engine or a hybrid power plant. The input shaft  14  receives input torque or power from the prime mover. The output shaft  16  is preferably connected with a final drive unit (not shown) which may include, for example, propshafts, differential assemblies, and drive axles. The input shaft  14  is coupled to and drives the gear arrangement  20  through the starting device  18 . The starting device  18  is illustrated as a torque converter in the example provided, though various other hydrodynamic and mechanical devices may be used without departing from the scope of the present invention. 
         [0027]    The gear arrangement  20  generally provides multiple forward and reverse speed or gear ratios between the input shaft  14  and the output shaft  16 . The gear arrangement  20  may have various forms and configurations but generally includes a plurality of gear sets or a continuously variable unit having a chain or belt and movable pulley pairs, a plurality of shafts or interconnecting members, and at least one torque transmitting mechanism. The gear sets may include intermeshing gear pairs, planetary gear sets, or any other type of gear set. The plurality of shafts may include layshafts, countershafts, sleeve or center shafts, reverse or idle shafts, or combinations thereof. The torque transmitting mechanisms may include clutches, brakes, synchronizer assemblies or dog clutches, or combinations thereof, without departing from the scope of the present invention. 
         [0028]    Operation of the starting device  18  and gear arrangement  20 , including selection of gear ratios via clutch and brake engagement, is controlled by an electronic transmission control module (ETCM)  22  and a hydraulic control system  24 . The ETCM  22  is preferably an electronic control device having a preprogrammed digital computer or processor, control logic, memory used to store data, and at least one I/O peripheral. The control logic includes a plurality of logic routines for monitoring, manipulating, and generating data. The ETCM  22  controls the actuation of the torque transmitting mechanisms in the gear arrangement  20  via the hydraulic control system  24 . The hydraulic control system  24  generally includes electrically controlled solenoids and valves that selectively communicate hydraulic fluid throughout the transmission  10  in order to control, lubricate, and cool the various components of the transmission  10 . 
         [0029]    The hydraulic fluid used by the hydraulic control system  24  is primarily stored in a sump or reservoir  26 . The sump  26  is preferably located at a bottom of the transmission  10 . A pump (not shown) produces a suction that draws the hydraulic fluid from the sump  26  and into the hydraulic control system  24  where the hydraulic fluid is used to engage torque transmitting mechanisms and to cool and lubricate the transmission  10 . 
         [0030]    The transmission  10  further includes a front or side cover  28  attached to a side or front of the transmission  10 . The side cover  28  protects components of the hydraulic control system  24  within the transmission  10  and functions as a secondary transmission oil storage reservoir, as will be described in greater detail below. 
         [0031]    Turning to  FIGS. 2 and 3 , the transmission housing  12  includes a separator wall  12   a  that extends vertically from a bottom of the housing  12  to a top of the housing  12 . A rim or flange  12   b  extends perpendicularly out from the separator wall  12   a . The flange  12   b  is disposed around the entire outer periphery of the separator wall  12   a , forming a pocket or cavity  32 . Various components of the transmission  10  are disposed within the cavity  32 , for example a transmission valve body  34  of the hydraulic control system  24 . The transmission valve body  34  contains many of the pressure regulation valves, directional valves and solenoids that control the transmission  10 . 
         [0032]    The side cover  28  is configured to connect and seal to the flange  12   b , thus enclosing the cavity  32 . For example, the side cover  28  includes a wall or rim  28   a  that extends perpendicularly out from a main portion  28   b . The rim  28   a  is disposed around the entire outer periphery of the side cover  28 . The rim  28   a  includes a plurality of bolt holes  36  that align with a plurality of bolt holes  38  formed on the flange  12   b . A plurality of bolts  40  or other fasteners connect the side cover  28  to the housing  12  overtop the cavity  32 . A seal (not shown) is disposed on or radially inward of the rim  28   a  in order to seal the side cover  28  to the flange  12   b  of the housing  12 . 
         [0033]    A lower portion or secondary reservoir  32   a  of the cavity  32  acts as a secondary hydraulic fluid reservoir to the sump  26 . The secondary reservoir  32   a  is not in communication with any rotating components of the transmission  10 . Communication of the hydraulic fluid from the secondary reservoir  32   a  to the sump  26  is controlled via an active thermal control valve assembly  50 . The control valve assembly  50  is disposed within the secondary reservoir  32   a  of the cavity  32  near a bottom of the transmission housing  12 . 
         [0034]    Turning to  FIG. 4 , the control valve assembly  50  is preferably an actively controlled wax pellet thermostat valve or an electro-mechanical armature. The control valve assembly  50  includes a coil housing  52  connected to a flange or sleeve  54 . A plurality of inlet ports  56  are formed in a side surface  54   a  of the sleeve  54 . An outlet port  58  is formed in a distal end  54   b  of the sleeve  54 . 
         [0035]    With reference to  FIGS. 5A and 5B  and continued reference to  FIG. 4 , a coil or other resistance element  60  is disposed about or wrapped around a closed end  54   c  of the sleeve  54 . The coil  60  is connected to a connector port  61  disposed on an outside of the coil housing  52 . The connector port  61  is interconnected to the ETCM  22  or to another power source. The coil  60  is enclosed and protected by the coil housing  52 . A phase change or wax element  62  is disposed within the sleeve  54  proximate the closed end  54   c  and radially inwardly of the coil  60 . The wax element  62  includes a pressure resistant vessel  64  filled with a special temperature tuned wax  66 . The wax  66  is designed to melt at a specific temperature. A pin  68  is partially slidably disposed within the vessel  64  and extends out into the sleeve  54 . A centering guide  70  is connected to a distal end  68   a  of the pin  68 . An alternate design to the wax pellet is to utilize an electro-mechanical actuator which converts the electrical energy from the coil to mechanical movement in an armature. 
         [0036]    A valve  72  is slidably disposed within the sleeve  54 . The valve  72  is in contact with the centering guide  70  (or directly with the pin  68 ) on a first side  72   a  of the valve  72 . A biasing member  74 , such as a spring, is in contact with the valve  72  on an opposite side  72   b . The valve  72  is moveable between a first position, shown in  FIG. 5A , and a second position shown in  FIG. 5B . The biasing member  74  biases the valve  72  to the first position. In the first position, the inlet ports  56  are in communication with the outlet port  58 . In the second position, the valve  72  closes off the inlet ports  56  such that they do not communicate with the outlet port  58 . 
         [0037]    The valve  72  is moved to the second position against the bias of the spring  74  when the wax  66  melts due to a heat source. For example, when the temperature of the wax  66  crosses the phase change temperature from solid to liquid, the wax  66  expands. Expansion of the wax  66  within the vessel  64  pushes out the pin  68 . The pin  68  contacts the valve  72  and moves the valve  72  to the second position, thus closing off the inlet ports  56  in the sleeve  54 . The valve  72  returns to the first position when the temperature of the wax  66  falls below the melt temperature, the wax  66  contracts, and the spring  74  moves the valve  72  and pin  68  back to the first position. 
         [0038]    The temperature of the wax  66  may be actively controlled by inducing an electrical current in the coil  60 . The current in the coil  60  generates heat around the wax element  62 , thereby selectively inducing a phase change in the wax  66 . The normal operating conditions of the transmission  10  may also create thermal conditions that melt the wax  66 . 
         [0039]    Returning to  FIG. 2 , the control valve assembly  50  is connected to the separator wall  12   a  of the housing  12  by a bracket  80  and pin  82 . The distal end  54   a  of the sleeve  54  extends through a support collar  12   c  formed in the separator wall  12   a  such that the inlet ports  56  are disposed in the secondary reservoir  32   a  and the outlet port  58  is disposed within the sump  26 . Thus, communication between the sump  26  and the secondary reservoir  32   a  is controlled by activation of the control valve assembly  50 . For example, the fluid level in the sump may be kept reduced by storing fluid within the secondary reservoir  32   a  by commanding a current in the coil  60 , thus inducing a phase change in the wax  66  and moving the valve  72  to close the control valve assembly  50 . Closing of the control valve assembly  50  hydraulically isolates the secondary reservoir  32   a  from the sump  26  thereby keeping the fluid level within the sump  26  to a predefined minimum. This predefined minimum is controlled by a distance of the control valve assembly  50  from a bottom of the sump  26 . When the transmission cools and the current in the coil  60  is reduced, the wax  66  may again solidify, moving the control valve assembly  50  into the open position. Transmission fluid can then communicate from the secondary reservoir  32   a  through the inlet ports  56 , out the outlet port  58  and into the sump  26 . 
         [0040]    Keeping the level of hydraulic fluid in the sump  26  to a minimum enables components of the gear arrangement  20  such as planetary gear sets, shafts or members, and clutches or brakes to rotate with a minimum of spin losses. The result is a more efficient transmission providing improved fuel economy. 
         [0041]    The description of the invention is merely exemplary in nature and variations that do not depart from the general essence of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.