Abstract:
A powertrain includes a first pump and a second pump. A conduit defines a passageway for providing hydraulic pressure from the first pump or the second pump to a transmission. A valve assembly is configured to selectively supply hydraulic pressure to the passageway solely from the first pump, solely from the second pump, and from both the first and second pumps. The valve assembly thus enables the first and second pump to augment one another, thereby enabling the size of at least one of the pumps to be smaller than would otherwise be possible without the valve assembly.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to valve assemblies configured to selectively supply hydraulic pressure to a transmission from two pumps.  
       BACKGROUND OF THE INVENTION  
       [0002]     Hybrid powertrains typically employ an engine and an electric motor operatively connected to a transmission. The engine is stopped and restarted under certain conditions in order to improve fuel economy. When the engine is off, it is desirable to keep the transmission engaged in order to reduce the delay time to put power to the wheels when the driver commands it. Automatic transmissions require hydraulic pressure to be applied to clutches in order to maintain engagement. The hydraulic pressure is provided by an oil pump.  
         [0003]     In prior art transmissions, the oil pump is driven by the engine. With the engine off, an alternative means to supply pressure to the clutches must be provided. Some prior art hybrid powertrains include an auxiliary pump driven by the electric motor to supply hydraulic pressure to clutches to maintain transmission engagement. A valve controls the hydraulic pressure so that it is provided either solely from the engine-driven pump or solely from the auxiliary pump. Accordingly, the main pump must be sized sufficiently to provide adequate pressure to maintain clutch engagement when the engine is at low speed.  
       SUMMARY OF THE INVENTION  
       [0004]     A powertrain includes a first pump, a second pump, and a conduit defining a passageway. A valve assembly operatively interconnects the first pump, the second pump, and the passageway. The valve assembly is configured for at least three modes of operation. In a first mode, the valve assembly provides fluid communication between the first pump and the passageway and does not permit fluid communication between the second pump and the fluid passageway. In a second mode, the valve assembly provides fluid communication between both of the first and second pumps and the fluid passageway. In a third mode, the valve assembly does not permit fluid communication between the first pump and the passageway and provides fluid communication between the second pump and the passageway.  
         [0005]     The valve assembly thus enables either pump to independently provide pressurized fluid to the passageway, and also enables both pumps to provide pressurized fluid to the passageway concurrently, such that each pump augments the other pump&#39;s output to the passageway. This augmentation enables at least one of the pumps to be smaller than prior art pumps, thus reducing fuel consumption of the pumps. The second mode of the valve also provides a smooth transition between operating with only the first pump and operating with only the second pump, i.e., the second mode reduces or minimizes impact to the pressure in the passageway in the transition from the first mode to the third mode.  
         [0006]     In an exemplary embodiment, the powertrain includes a first power source, such as an electric motor, and a second power source, such as an internal combustion engine, and a transmission. The first and second power sources are in hybrid combination to supply torque to the input shaft of the transmission. The first power source is operatively connected to the first pump to selectively power the first pump, and the second power source is operatively connected to the second pump to selectively power the second pump. The passageway is in fluid communication with the transmission, and more specifically, the passageway is in fluid communication with the hydraulic clutch apply circuit of the transmission.  
         [0007]     In an exemplary embodiment, the valve assembly is configured such that the first, second, and third modes occur automatically as a result of the hydraulic pressure supplied by the first and second pumps. More specifically, in the exemplary embodiment, the first mode automatically occurs when the hydraulic pressure from the first pump is higher than a first predetermined amount, the second mode automatically occurs when the hydraulic pressure from the second pump is higher than a second predetermined amount, and the third mode automatically occurs when the hydraulic pressure from the second pump is higher than a third predetermined amount.  
         [0008]     A corresponding method is also provided.  
         [0009]     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  
       [0010]      FIG. 1  is a schematic depiction of a hybrid drivetrain including a valve assembly shown in a partial cutaway side view in a first mode of operation;  
         [0011]      FIG. 2  is a schematic, partial cutaway side view of the valve assembly of  FIG. 1  in a second mode of operation;  
         [0012]      FIG. 3  is a schematic, partially cutaway side view of the valve assembly of  FIG. 1  in a third mode of operation;  
         [0013]      FIG. 4  is a schematic, partially cutaway side view of the valve assembly of  FIG. 1  in a fourth mode of operation;  
         [0014]      FIG. 5  is a schematic, partially cutaway side view of the valve assembly of  FIG. 1  in a fifth mode of operation; and  
         [0015]      FIG. 6  is another schematic, partially cutaway side view of the valve assembly of  FIG. 1 ; 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     Referring to  FIG. 1 , a hybrid powertrain  10  is schematically depicted. The powertrain  10  includes a first power source and a second power source in hybrid combination. In the embodiment depicted, the first power source is an engine  14  and the second power source is an electric motor  18 . The engine  14  includes a rotatable crankshaft  22 , and the electric motor  18  includes a rotor  26 . A selectively-engageable torque transmitting device  30 , such as a clutch, interconnects the rotor  26  and the crankshaft  22 .  
         [0017]     The rotor  26  is coupled to the input shaft  34  of a transmission  38  as understood by those skilled in the art. A selectively engageable torque transmitting device (not shown) or a hydraulic torque convertor (not shown) may be employed between the input shaft  34  and the rotor  26 . Thus, the crankshaft  22  is also connected to the input shaft  34  of the transmission  38  via the rotor  26  when the torque transmitting device  30  is engaged. Accordingly, the rotor  26  and the crankshaft  22  are operatively connected to the input shaft  34  to selectively supply mechanical power thereto. Those skilled in the art will recognize other hybrid powertrain configurations that may be employed within the scope of the claimed invention.  
         [0018]     A main pump  42  is operatively connected to the crankshaft  22  to be driven thereby, such as via a belt drive or chain drive  46 . An auxiliary pump  50  is operatively connected to the rotor  26  to be driven thereby, such as via a belt drive or chain drive  54 . A conduit  60  defines a passageway  64  that is in fluid communication with the main pump  42 ; the main pump  42  is configured to supply pressurized fluid, i.e., hydraulic pressure, to passageway  64  as understood by those skilled in the art. A conduit  68  defines a passageway  72  that is in fluid communication with the auxiliary pump  50 ; the auxiliary pump  50  is configured to supply pressurized fluid to passageway  72  as understood by those skilled in the art.  
         [0019]     The powertrain  10  further includes a valve assembly  76  that is in fluid communication with passageways  64 ,  72 . The valve assembly  76  includes a valve body  80  that defines a cylindrical chamber  84 . The valve assembly  76  includes first and second shuttles  88 ,  92  that are positioned within the chamber  84  and that are configured for selective translation within the chamber  84 . The chamber  84  is characterized by two ports  96 ,  100  defined by the valve body  80  at opposite ends of the chamber  84 . Port  96  is in fluid communication with the passageway  72  of conduit  68 , and therefore is also in fluid communication with the auxiliary pump  50 . Port  100  is in fluid communication with the passageway  64  of conduit  60 , and therefore is also in fluid communication with the main pump  42 .  
         [0020]     The chamber  84  is also characterized by two ports  104 ,  108  that interconnect the chamber  84  and another chamber  112 . Ports  104 ,  108  extend radially from the chamber  84 . Chamber  112  is in fluid communication with a passageway  116  defined by conduit  120 . Passagway  116  is in fluid communication with a pressure regulator valve  124 , and the pressure regulator valve  124  is in fluid communication with the transmission  38  to supply pressurized fluid to the hydraulic circuit of the transmission, which includes clutch apply chambers (not shown), as understood by those skilled in the art. More specifically, the pressure regulator valve  124  is in fluid communication with the transmission  38  via conduit  128 , which defines passageway  132 . Thus, the ports  104 ,  108  are in fluid communication with the passageway  116 , the pressure regulator valve  124 , and the transmission  38 . An exemplary hydraulic circuit for a transmission is described in U.S. Pat. No. 5,601,506, issued Feb. 11, 1997 to Long et al., and which is hereby incorporated by reference in its entirety.  
         [0021]     Passageway  72  is also in fluid communication with a blow-off valve  136 , and passageway  64  is also in fluid communication with a blow-off valve  140 , as understood by those skilled in the art. Each blow-off valve includes a spring  144  that biases a stopper  148 . When the pressure in passageway  72  exceeds a predetermined amount, the pressure overcomes the bias of the spring  144  so that the stopper  148  does not obstruct the blow-off valve  136  and pressure is then reduced as fluid is released through the blow-off valve  136 . Similarly, when the pressure in passageway  64  exceeds a predetermined amount, the pressure overcomes the bias of the spring  144  so that the stopper  148  does not obstruct the blow-off valve  140  and pressure is then reduced as fluid is released through the blow-off valve  140 . The pressure at which blow-off valve  140  opens is higher than the pressure at which blow-off valve  136  opens.  
         [0022]     Shuttle  88  is characterized by a generally cylindrical surface  152  that sealingly contacts the inner surface of the chamber  84 . Shuttle  88  is also characterized by a surface  156  in fluid communication with the passageway  72  of conduit  68 . Shuttle  88  is further characterized by surface  160  that is exposed to the chamber  84 .  
         [0023]     Similarly, shuttle  92  is characterized by a generally cylindrical surface  164  that sealingly contacts the inner surface of the chamber  84 . Shuttle  92  is also characterized by a surface  168  that is in fluid communication with the passageway  64  of conduit  60 . Shuttle  92  is further characterized by a surface  170  exposed to the chamber  84  and opposing surface  160 . Shuttle  92  also defines a chamber  174  that is in fluid communication with the chamber  112  through port  108  and a feedback orifice  178  that extends radially with respect to the shuttle  92 . Chamber  174  is open in the direction of shuttle  88  so as to be in fluid communication with chamber  84  and the surface  160  of shuttle  88 . Shuttle  92  defines a concavity  182  in surface  164  to ensure that fluid communication between the feedback orifice  178  and the chamber  112  is not obstructed during movement of the shuttle  92 .  
         [0024]     A coil spring  186  is interposed between the shuttles  88 ,  92  within the chamber, and biases the shuttles  88 ,  92  apart from one another as shown in  FIG. 1 . The shuttle  88  is characterized by a protuberance  190  from surface  156 ; the protuberance  190  contacts a wall of conduit  68  to limit the movement of the shuttle  88 . Similarly, member  194  protrudes from surface  168  of shuttle  92 , and contacts a wall of conduit  60  to limit the movement of the shuttle  92 .  
         [0025]     A first mode of valve assembly operation is depicted in  FIG. 1 . More specifically, with the engine  14  and the motor  18  being stopped or off, the pumps  42 ,  50  do not pressurize fluid in the passageways  64 ,  72 , allowing the spring  186  to bias the shuttles  88 ,  92  in respective closed positions as shown. Shuttle  88  obstructs ports  96  and  104  to prevent fluid communication between the passageway  72 , and therefore the auxiliary pump  50 , and the chamber  112 . Shuttle  92  obstructs port  100 , thereby preventing fluid communication between the passageway  64 , and therefore the main pump  42 , and chamber  112 .  
         [0026]     Referring to  FIG. 2 , wherein like reference numbers refer to like components from  FIG. 1 , the valve assembly  76  is shown in a second mode of operation. More specifically, the motor (shown at  18  in  FIG. 1 ) is driving the auxiliary pump (shown at  50  in  FIG. 1 ), which causes the auxiliary pump to supply pressurized fluid  200 A into the passageway  72  of conduit  68 . The pressurized fluid  200 A exerts a force on surface  156  of shuttle  88 . The force on surface  156  overcomes the bias of spring  186  and causes the shuttle  88  to translate toward shuttle  92  and into an open position as shown in which the shuttle  88  does not fully obstruct ports  96  and  104 . Accordingly, when the shuttle  88  is in its open position, fluid communication is permitted between the chamber  112  and the passageway  72  via port  96 , a portion of chamber  84 , and port  104 . Pressurized fluid  200 A from the auxiliary pump thus enters chamber  112 , passageway  116 , and ultimately the clutch apply chambers of the transmission (shown at  38  in  FIG. 1 ). Thus, the second mode of operation occurs automatically when the pressure in passageway  68  is sufficient to cause movement of shuttle  88  to its open position.  
         [0027]     When the valve assembly is in the second mode of operation, the force of the fluid  200 A on shuttle  88  compresses the spring  186  and produces a corresponding increase of force on shuttle  92 ; however, member  194  prevents shuttle  92  from being extended from the chamber  84  beyond its fully closed position shown in  FIGS. 1 and 2  in which the shuttle  92  obstructs a flowpath between ports  100  and  108 , thereby preventing fluid communication between passageway  64  and the chamber  112 . During the first mode of operation, the engine (shown at  14 ) is not running, and thus the main pump (shown at  42  in  FIG. 1 ) is not providing pressurized fluid to passageway  64 .  
         [0028]     Referring to  FIG. 3 , wherein like reference numbers refer to like components from  FIGS. 1 and 2 , the valve assembly  76  is shown in a third mode of operation. More specifically, the engine (shown at  14  in  FIG. 1 ) is running and driving the main pump (shown at  42  in  FIG. 1 ); accordingly, the main pump supplies pressurized fluid  200 B to the passageway  64  of conduit  60 .  
         [0029]     The pressurized fluid  200 B exerts a force on surface  168  of shuttle  92 . The force on surface  168  overcomes the bias of spring  186  and causes the shuttle  92  to translate toward shuttle  88  and into an open position as shown in which the shuttle  92  does not fully obstruct ports  100  and  108 . Accordingly, when the shuttle  92  is in its open position, the chamber  112  is in fluid communication with the passageway  64  via port  100 , a portion of chamber  84 , and port  108 . Pressurized fluid  200 B from the main pump thus enters chamber  112 , passageway  116 , and ultimately the clutch apply chambers of the transmission (shown at  38  in  FIG. 1 ).  
         [0030]     The auxiliary pump also supplies pressurized fluid  200 A during the second mode of operation, and thus, the pressurized fluid  200 A maintains shuttle  88  in the open position, thereby allowing pressurized fluid  200 A from the auxiliary pump to enter chamber  112 . Accordingly, the third mode of operation occurs automatically when the pressure in passageway  64  is sufficient to move the shuttle  92  to its open position.  
         [0031]     Referring to  FIG. 4 , wherein like reference numbers refer to like components from  FIGS. 1-3 , the valve assembly is shown during a fourth mode of operation. The fourth mode of operation is caused automatically when the fluid  200 B, which is pressurized by the main pump, is at a higher pressure than the fluid  200 A, which is pressurized by the auxiliary pump. More specifically, fluid  200 B from the main pump exerts a force on shuttle  92 , including surface  168 , causing movement of the shuttle  92  with a corresponding compression of spring  186 , which in turn exerts a force on shuttle  88 , urging shuttle  88  to its closed position. Furthermore, the orifice  178  causes the pressure in chamber  174 , and correspondingly the pressure in chamber  84  and on surface  160 , to increase to the pressure in the passagway  64 . The force exerted by the spring  186  and by the fluid acting on surface  160  is higher than the force exerted on the surface  156  of shuttle  88  by fluid  200 A from the auxiliary pump, which is at a lower pressure than fluid  200 B from the main pump. Accordingly, the shuttle  88  moves away from shuttle  92  to the position shown in which the shuttle  88  obstructs port  104 , thereby preventing fluid communication between the auxiliary pump and the chamber  112 .  
         [0032]     Referring to  FIG. 5 , wherein like reference numbers refer to like components from  FIGS. 1-4 , the valve assembly  76  is shown in a fifth mode of operation in which the pressure of fluid  200 B is sufficiently greater than the pressure of fluid  200 A so that the force exerted on shuttle  88 , including surface  160 , by the spring  186  and by fluid from the orifice  178  is sufficiently greater than the force exerted by fluid  200 A on surface  156 , thereby causing the shuttle  88  moves to its fully closed position in which the shuttle  88  obstructs both ports  96  and  104 . Because the auxiliary pump is deadheaded, i.e., fluid flow from the auxiliary pump is blocked, the pressure of fluid  200 A in passageway  72  will be sufficiently high such that fluid  200 A will be released through the auxiliary blow-off valve, as shown in  FIG. 5 .  
         [0033]     Referring to  FIG. 6 , wherein like reference numbers refer to like components from  FIG. 5 , the auxiliary pump is shut down because the engine crankshaft has reached a speed sufficient to drive the main pump to produce adequate pressure in fluid  200 B such that augmentation from the auxiliary pump is not needed.  
         [0034]     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.