Abstract:
A transmission for a hybrid vehicle including a combustion engine and an electric propulsion system may include a forward clutch assembly, a fluid chamber, a fluid supply, and a forward clutch holding valve. The forward clutch assembly may include a hydraulically actuated clutch member in communication with the fluid chamber. The forward clutch holding valve may be in communication with the fluid chamber and the fluid supply. The valve may provide communication between the fluid supply and the fluid chamber when in a first position and may seal the fluid chamber when in a second position, thereby maintaining a fixed quantity of fluid within the fluid chamber.

Description:
FIELD 
     The present disclosure relates to hybrid vehicles, and more specifically to transmissions for hybrid vehicles. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Internal combustion engines produce drive torque that is transferred to a drivetrain. The drive torque is transferred through a transmission that multiplies the drive torque by a gear ratio. Transmissions generally include multiple gear ratios through which the drive torque is transferred. Automatic transmissions automatically shift between gear ratios based on driver input and vehicle operating conditions. Traditionally, automatic transmissions include a forward clutch and a reverse clutch for actuation between forward and reverse driving conditions through the use of a pressurized hydraulic fluid. The hydraulic fluid is typically pressurized during operation of the engine. 
     Hybrid powertrains typically include an electric machine and an energy storage device (ESD) such as battery or super capacitor. In one mode, the electric machine drives the transmission using energy stored in the ESD. In another mode, the electric machine is driven by the engine to charge the ESD. When operated in the first mode, the hybrid vehicle may be operated without the use of the engine. When operated without the use of the engine, an auxiliary pressurizing mechanism, such as an electric pump, is typically used to pressurize the hydraulic transmission fluid to provide for engagement of the forward clutch. 
     SUMMARY 
     Accordingly, a transmission for a hybrid vehicle including a combustion engine and an electric propulsion system may include a forward clutch assembly, a fluid chamber, a fluid supply, and a forward clutch holding valve. The forward clutch assembly may include a hydraulically actuated clutch member in communication with the fluid chamber. The forward clutch holding valve may be in communication with the fluid chamber and the fluid supply. The valve may provide communication between the fluid supply and the fluid chamber when in a first position and may seal the fluid chamber when in a second position, thereby maintaining a fixed quantity of fluid within the fluid chamber. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic illustration of a hybrid vehicle according to the present disclosure; 
         FIG. 2  is a functional block diagram illustration of a transmission of the hybrid vehicle of  FIG. 1 ; 
         FIG. 3  is a schematic illustration of a forward clutch portion of the transmission of  FIG. 2 ; 
         FIG. 4  is an additional schematic illustration of the forward clutch portion of the transmission of  FIG. 2 ; and 
         FIG. 5  is a flow chart illustrating operation of the transmission of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an exemplary hybrid vehicle  10  is schematically illustrated. The hybrid vehicle  10  includes a combustion engine  12  and an electric machine  14 , which selectively drive a transmission  16 . Drive torque may be transmitted from engine  12  and/or electric machine  14  to transmission  16  through a coupling device  18 . Transmission  16  may be an automatic transmission and coupling device  18  may include a torque converter. 
     Hybrid vehicle  10  may be operable in first and second modes. Control module  20  may be in communication with and may receive and send control signals to engine  12  and transmission  16  to control operation thereof in the first and second modes. In a first mode of operation, engine  12  may be operated, providing drive toque for hybrid vehicle  10  and/or charging of electric machine  14 . In the second mode, engine  12  may be powered off. In the second mode, drive torque for hybrid vehicle  10  may be provided solely by electric machine  14 . Whether operating in the first or second modes, drive torque is transmitted to transmission  16  in order to drive hybrid vehicle  10 . 
     With additional reference to  FIG. 2 , a functional block diagram of transmission  16  is illustrated. Transmission  16  may include a fluid source  22  providing hydraulic fluid for transmission  16 . Fluid source  22  may include a pumping mechanism powered by engine  12  for pressurizing the hydraulic transmission fluid for actuation of transmission  16 , as discussed below. Fluid source  22  may be in communication with a control valve  24  and a locking valve  26 . Control valve  24  may be in fluid communication with a forward clutch regulator valve  28  and a reverse clutch regulator valve  30 . Control valve  24  may provide selective communication between fluid source  22  and the forward and reverse clutch regulator valves  28 ,  30 . Transmission  16  may be actuated between forward, reverse, and neutral conditions by the pressurized hydraulic fluid provided by fluid source  22  during operation of engine  12 . More specifically, forward and reverse clutch regulator valves  28 ,  30  may be in fluid communication with forward and reverse clutch assemblies  32 ,  34 . Selectively providing the pressurized hydraulic fluid to forward and reverse clutch assemblies  32 ,  34  allows actuation between the forward, reverse, and neutral conditions. 
     A forward clutch holding valve  36  may be disposed between and in fluid communication with forward clutch regulator valve  28  and forward clutch assembly  32 . Locking valve  26  may also be in fluid communication with forward clutch holding valve  36 , as discussed below. With additional reference to  FIGS. 3 and 4 , forward clutch holding valve  36  may include a valve housing  38  containing a valve  40  therein. Valve housing  38  may include an inlet port  42 , an outlet port  44 , and first and second valve actuation ports  46 ,  48 . An inner bore  50  may include first and second portions  52 ,  54  housing valve  40  therein. 
     Valve  40  may include a central portion  56  having first and second portions  58 ,  60  extending therefrom. Central portion  56  may be disposed in bore second portion  54  and may have an outer diameter generally corresponding to the inner diameter of bore second portion  54 . Valve first portion  58  may be disposed in bore first portion  52  and may have an outer diameter generally corresponding to the inner diameter of bore first portion  52 . The outer diameter of valve first portion  58  may be less than the outer diameter of valve central portion  56  creating an annular surface  62  on a first side of central portion  56 . Valve second portion  60  may have an outer diameter that is less than the outer diameter of valve central portion  56  creating an annular surface  64  on a second side of central portion  56 . A biasing member  66 , such as a spring, may extend between a first end  68  of bore second portion  54  and valve annular surface  64 . The outer diameter of valve second portion  60  may be less than the outer diameter of valve first portion  58 . As such, annular surface  64  on the second side of central portion  56  may have a greater surface area than annular surface  62 . First end  68  of bore second portion  54  may act as a first stop for valve  40 , as discussed below. 
     Valve housing inlet port  42  may extend into bore first portion  52 . A flow path  70  may extend from an end  72  of bore first portion  52  to outlet port  44 . End  72  may act as a second stop for valve  40 , as discussed below. First and second valve actuation ports  46 ,  48  may extend into bore second portion  54 . 
     Forward clutch assembly  32  may include a hydraulic chamber  74 , a clutch piston  76 , and a series of clutch plates  78 . Hydraulic chamber  74  may be in communication with clutch piston  76 . Clutch piston  76  may be operably coupled to clutch plates  78  for selective engagement thereof, as discussed below. A first fluid path  80  extends between hydraulic chamber  74  and valve housing outlet port  44 . A second fluid flow path  82  extends between inlet port  42  and forward clutch regulator valve  28  and a third fluid flow path  84  extends between first valve actuation port  46  and forward clutch regulator valve  28 . A fourth fluid flow path  86  extends between second valve actuation port  48  and locking valve  26 . 
     With additional reference to  FIG. 5 , flow chart  100  generally shows the operation of transmission  16 . As indicated in step  110 , engine  12  is initially operated to allow for pressurization of fluid source  22 , as discussed above. Transmission  16  may then provide for a forward drive condition by providing pressurized fluid from forward clutch holding valve  36 . As indicated at step  112 , forward clutch holding valve  36  may be opened to provide for engagement of forward clutch assembly  32 , as indicated at step  114 . 
     More specifically, as seen in  FIG. 3 , valve  40  may be displaced to an open position, allowing fluid communication between inlet port  42  and outlet port  44 . Valve  40  may be displaced to the open position by pressurized fluid provided by forward clutch regulator valve  28  entering valve housing  38  at first valve control port  46  and acting upon annular surface  62  of valve  40 . The force created by the pressurized fluid may be greater than that applied by biasing member  66 , resulting in the opening of forward clutch holding valve  36 . Pressurized fluid may therefore travel through first fluid path  80  and into hydraulic chamber  74 , where it acts upon clutch piston  76 , urging clutch plates  78  into engagement. 
     As indicated at step  116 , and seen in  FIG. 4 , forward clutch holding valve  36  may be closed. Operation of hybrid vehicle  10  may then be operated in an engine-off condition while maintaining engagement of the forward clutch assembly without the use of an auxiliary fluid pump or fluid source. Forward clutch holding valve  36  may be closed before the engine-off condition to maintain fluid pressure in hydraulic chamber  74 . More specifically, locking valve  26  may provide pressurized fluid to bore second portion  54 , resulting in a force being applied on annular surface  64  of valve central portion  56 . The combination of the force applied by the pressurized fluid on annular surface  64  and the force applied by biasing member  66  may be greater than the force applied by the pressurized fluid acting upon annular surface  62 , resulting in displacement of valve  40  to the closed position. 
     When in the closed position (seen in  FIG. 4 ), valve first portion  58  abuts bore end  72 , sealing outlet port  44  from inlet port  42 . As such, hydraulic chamber  74  is in a sealed condition, where fluid neither exits nor enters, resulting in a generally constant pressure being applied to clutch piston  76 . The pressure in hydraulic chamber  74  is sufficient for engagement of clutch plates  78  by clutch piston  76  when hydraulic chamber  74  is sealed. Therefore, clutch plates  78  remain in an engaged condition when hydraulic chamber  74  is sealed. 
     As indicated at step  118 , engine  12  may then be powered off resulting in the pressure provided by locking valve  26  and forward clutch regulator valve  28  being greatly reduced. When in the engine-off condition, valve  40  may be held in the closed position through the force applied by biasing member  66  maintaining engagement of the forward clutch assembly  32 , as indicated at step  120 . As such, forward clutch engagement may be maintained in hybrid vehicle  10  without the use of an auxiliary source of pressurized fluid. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.