Patent Publication Number: US-2013232962-A1

Title: Hydraulic control for a vehicle powertrain

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/607,152, filed Mar. 6, 2012, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a system and method for providing fluid to a vehicle powertrain, and more specifically, a system and method for providing fluid to a vehicle powertrain through an accumulator. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     A typical automatic transmission includes a hydraulic control system that is employed to lubricate the transmission&#39;s moving parts and/or to actuate a plurality of torque transmitting devices. These torque transmitting devices may be, for example, friction clutches and brakes. The conventional hydraulic control system typically includes a main pump that provides a pressurized fluid, such as oil, to a plurality of valves and solenoids within a valve body. The main pump is driven by the engine of the motor vehicle. The valves and solenoids are operable to direct the pressurized hydraulic fluid through a hydraulic fluid circuit to the plurality of torque transmitting devices within the transmission. The pressurized hydraulic fluid delivered to the torque transmitting devices is used to engage or disengage the devices in order to obtain different gear ratios. 
     In order to increase the fuel economy of motor vehicles, it may be desirable to stop the engine during certain circumstances, such as when stopped at a red light or idling. However, after the engine has been shut down and has remained off for an extended period of time, the fluid generally tends to drain down from the passages into a transmission sump under the force of gravity. Upon engine restart, the transmission may take an appreciable amount of time to establish pressure before full transmission operation may resume. 
     Therefore, there is a need for a system for accurately controlling the pressure of the hydraulic fluid located within the accumulator to enable proper use of engine start/stop techniques. 
     SUMMARY 
     In some forms of the present disclosure, a vehicle powertrain is provided having an engine capable of being selectively turned on and turned off, and a transmission operatively connected to the engine. The powertrain additionally includes a hydraulic control system with a pump arranged relative to the transmission in fluid communication with the transmission via a structure forming a fluid passage. The pump is operatively connected to the engine for supplying fluid to the transmission when the engine is on, and for being idle when the engine is off. The hydraulic control system also has an accumulator arranged relative to the transmission in fluid communication with the fluid passage. The accumulator is configured to actively accumulate fluid when the engine is on, and in some embodiments, to also passively accumulate fluid when the engine is on. The accumulator is configured to retain the fluid when the engine is turned off and to actively discharge the fluid to the fluid passage when the engine is restarted. 
     In accordance with another aspect of the present disclosure, which may be combined with or separate from other aspects described herein, a method for controlling a hydraulic system for a vehicle powertrain having an engine and a transmission is also provided. The method includes providing a fluid line pressure via a fluid passage to the transmission by a pump operatively connected to the engine when the engine is turned on, wherein the pump is idle when the engine is off. The method further includes actively accumulating fluid within an accumulator. The method may include passively accumulating fluid when the line pressure in the transmission exceeds the pressure from an accumulated fluid. The method may also include retaining the accumulated fluid when the engine is turned off and discharging the fluid to the fluid passage when the engine is restarted. 
     In accordance with yet another aspect of the present disclosure, which may be combined with or separate from other aspects described herein, a method of controlling a hydraulic system of a vehicle powertrain having an engine and a transmission is provided. The method includes providing a fluid line pressure to the transmission by opening a fluid passage when the engine is turned on; opening a valve via an electronic controller to actively accumulate fluid from the fluid line pressure into an accumulator when the engine is turned on; closing the valve via the electronic controller to retain the fluid in the accumulator when the engine is turned off; and discharging the fluid from the accumulator to the fluid passage when the engine is restarted such that full transmission operation is afforded substantially without delay. 
     In accordance with still another aspect of the present disclosure, which may be combined with or separate from other aspects described herein, a method of controlling a hydraulic system of a vehicle powertrain having an engine and a transmission is provided. The method includes providing a fluid line pressure to the transmission by opening a fluid passage when the engine is turned on; opening a solenoid valve to actively accumulate fluid from the fluid line pressure into an accumulator when the engine is turned on; closing the solenoid valve to retain the fluid in the accumulator when the engine is turned off; and discharging the fluid from the accumulator to the fluid passage when the engine is restarted such that full transmission operation is afforded substantially without delay. 
     In accordance with still another aspect of the present disclosure, which may be combined with or separate from other aspects described herein, a method of controlling a hydraulic system of a vehicle powertrain having an engine and a transmission is provided. The method providing a fluid line pressure to the transmission from a pump by opening a tranmisssion fluid passage when the engine is turned on. The method also includes opening a solenoid valve via an electronic controller to actively accumulate fluid from the fluid line pressure into an accumulator through an active channel when the engine is turned on. Further, the method includes passively accumulating the fluid into the accumulator through a passive channel and a ball check-valve when the fluid line pressure is greater than pressure from the fluid in the accumulator. Further yet, the method includes closing the solenoid valve via the electronic controller to retain the fluid in the accumulator when the engine is turned off. Additionally, the method includes discharging the fluid from the accumulator to the transmission fluid passage through the active channel when the engine is restarted such that full transmission operation is afforded substantially without delay. 
     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 diagram of a portion of an exemplary hydraulic control system, illustrating an accumulator accumulating fluid, in accordance with the principles of the present invention; 
         FIG. 2  is a schematic diagram of the portion of the exemplary hydraulic control system of  FIG. 1 , illustrating the accumulator retaining fluid, according to the principles of the present invention; 
         FIG. 3  is a schematic diagram of the portion of the exemplary hydraulic control system of  FIGS. 1-2 , illustrating the accumulator discharging fluid, in accordance with the principles of the present invention; 
         FIG. 4  is a schematic diagram of a portion of another exemplary hydraulic control system, illustrating an accumulator accumulating fluid, in accordance with the principles of the present invention; 
         FIG. 5  is a schematic diagram of the portion of the exemplary hydraulic control system of  FIG. 4 , illustrating the accumulator retaining fluid, according to the principles of the present invention; 
         FIG. 6  is a schematic diagram of the portion of the exemplary hydraulic control system of  FIGS. 4-5 , illustrating the accumulator discharging fluid, in accordance with the principles of the present invention; and 
         FIG. 7  is a block diagram illustrating a method for controlling a hydraulic system of a vehicle powertrain, according to the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIGS. 1-6  show a hydraulic control system  10  for a transmission  11  that is connected to an engine  13  in a vehicle powertrain. Generally, a viscous, largely incompressible fluid is utilized in transmissions for cooling and lubrication of moving components, such as gears and bearings. Additionally, in automatic transmissions such a working fluid is also commonly employed for actuating various components that affect gear ratio changes, such as clutches and brakes. The hydraulic control system  10  may be operable to selectively engage the clutches or brakes by selectively communicating a hydraulic fluid, such as automatic transmission fluid, from a sump to a clutch actuation circuit. In  FIGS. 1-6 , direction of the working fluid flow is represented by arrows. 
       FIGS. 1-3  show the hydraulic control system  10  utilizing a fluid pump  12  to provide pressurized fluid via a fluid passage  14  to the transmission  11 , e.g., to establish transmission line pressure, and via a fluid passage  16  to an accumulator  18 . The hydraulic fluid is forced from the sump and communicated throughout the hydraulic control system  10  via the pump  12 . The pump  12  may be, for example, a gear pump, a vane pump, a gerotor pump, or any other positive displacement pump. The hydraulic fluid line  16  may include various optional features including, for example, a spring biased blow-off safety valve, a pressure side filter, or a spring biased check valve. Various other components (not illustrated) may be included in the hydraulic control system  10 , as is understood in the art. 
     Fluid passages  14  and  16  may be formed by structures such as a transmission casing, a tube external to the transmission, or otherwise. Fluid pump  12  is operatively connected to the engine  13 , i.e., the pump  12  is driven directly by the engine  13  when the engine  13  is on, and is therefore idle when the engine  13  is off. 
     The accumulator  18  is an energy storage device in which the non-compressible hydraulic fluid is held under pressure by an external source. The accumulator  18  has an internal piston  20  that has a seal  22  that slides along a bore of the accumulator housing, by way of example. The seal  22  may be a hermetic o-ring seal  22  that seals off a pressure cavity  24  from a cavity  26  housing a piston return spring  28 . The seal  22  may alternatively have any other configuration suitable for sealing off the working fluid. 
     On one side of the piston  20  there is hydraulic fluid in a hydraulic cavity  24 , and on the other side of the piston  20 , there is one or more springs  28  and air, in this embodiment. The accumulator  18  uses a combination of spring(s)  28  and air to generate the force on one side of the piston  20  that reacts against the hydraulic fluid pressure on the opposite side of the piston  20 . 
     Accordingly, the accumulator  18  is operable to supply pressurized fluid back to the hydraulic circuit line  16 . The accumulator  18 , when charged, effectively replaces the pump  12  as the source of pressurized hydraulic fluid, thereby eliminating the need for the pump  12  to run continuously. Hydraulic fluid is stored in the accumulator  18  at a set volume and pressure while the engine  12  is off. 
     The spring  28  is used to counterbalance a force  30  (shown in  FIG. 1 ) due to the fluid line pressure, and to provide gradual movement of the piston  20  into the cavity  26  when the accumulator  18  is accumulating fluid, i.e. is being filled. The spring  28  is also utilized to provide a piston return force  32  (shown in  FIG. 3 ) when the accumulator  18  is being discharged. Although the accumulator  18  is shown with the piston  20  being supported by the spring  28 , other mechanisms may be employed to perform such a function. For example, a compressed gas may be utilized in cavity  26  to pressurize the piston  20  in order to provide the return force  32  for affecting the discharge of the fluid (shown in  FIGS. 4-6 ). 
       FIG. 1  illustrates the filling of the accumulator  18 . In  FIG. 1 , the fluid flows through the passage  16 , to a passive-fill channel  50  and an active-fill channel  52 . Through the passive-fill channel  50 , the fluid flows past a ball check-valve  34  into a passive accumulator fill channel  36 , then into the accumulator passage  56 , and from there, into a cavity  24  in the accumulator  18 . (In  FIG. 2 , the check ball  34  is seated, thereby preventing fluid from flowing from the passive accumulator channel  36  and into the passive-fill channel  50 , which will be described in further detail below). The ball check-valve  34  is utilized to achieve a passive accumulator  18  fill during transmission operation, in particular when fluid line pressure supplied by the pump  12  is greater than the pressure of the fluid already accumulated in cavity  24 . 
     The filling of the accumulator  18  past the ball check-valve  34  is termed “passive” due to the fact that it takes place automatically, without any outside intervention or support, solely through the unseating of the ball check-valve  34  based on relative pressures on either side of the ball check-valve  34 . In other words, when the pressure on the transmission side  11  in line  16  exceeds the pressure in the accumulator  18  and in line  56 , the ball check-valve  34  will unseat and allow fluid to flow past the ball check-valve  34  from the passive-fill channel  50  to the passive channel  36 . When the fluid pressure is greater in the accumulator cavity  24  and line  56  than in the transmission line  16 , however, the ball check-valve  34  will remain seated as shown in  FIG. 2 . As understood by those skilled in the art, any appropriate mechanism may be utilized in place of the shown ball check-valve  34  to affect a passive accumulator fluid fill in the hydraulic control system  10 . 
     The accumulator  18  may also be filled via the active-fill channel  52 . In other words, the accumulator  18  may be filled via the active-fill channel  52 , the passive-fill channel  50 , or both. If both active and passive filling of the accumulator  18  are used, the active and passive filling may be accomplished simultaneously or serially. 
     To fill the accumulator  18  through the active-fill channel  52 , a latching solenoid  38  opens a poppet valve  40  to cause fluid to flow from the active-fill channel  52  to a channel  54  on the accumulator  18  side of the solenoid  38 . The latching solenoid  38  could alternatively be any other suitable type of solenoid or valve, without or without the poppet valve  40 . Fluid then flows from the channel  54  to the accumulator channel  56  and into the accumulator cavity  24 . As such, the latching solenoid  38  is used to actively fill the accumulator cavity  24 , and at the same time, the ball check-valve  34  may be used to passively fill the accumulator cavity  24 . Filling of the accumulator cavity  24  is termed “active” because the poppet valve  40  of the latching solenoid  38  is actively controlled to fill the accumulator cavity  24 . The poppet valve  40  of the latching solenoid  38  is controlled via an algorithm programmed into an electronic controller  44 . The controller  44  governs, i.e. actuates, the latching solenoid  38  to open the poppet valve  40  and introduce fluid from the active-fill passage  52  into the passage  54 , thereby feeding the fluid to the accumulator cavity  24 . 
     The passive-fill channel  50  has an orifice that is smaller than both the orifice of the active-fill channel  52  and the orifice of the cavity  42  around the poppet valve  40 . This allows the controller  44  to actively fill the accumulator cavity  24 . In some embodiments, the passive-fill channel  50 , the ball check-valve  34 , and the passive accumulator passage  36  could be eliminated so that the accumulator cavity  24  is filled solely by the latching solenoid  38 . 
     In the illustrated embodiment, wherein both active and passive filling of the accumulator cavity  24  are employed, a) the ball check-valve  34  unseats under a pressure differential that is higher in the transmission line  16  than in the accumulator line  56 , and b) the poppet valve  40  is moved to allow fluid to flow from the transmission line  16  and the active-fill channel  52 , into the poppet valve cavity  42  and past the poppet valve  40 . Thus, the fluid from the passage  16  enters the passages  36  and  54  for filling the accumulator  18 . 
     When the line pressure supplied by the pump  12  is not greater than the pressure of the fluid already accumulated in cavity  24 , the ball check-valve  34  seats, thus restricting fluid flow to the accumulator  18  (shown in  FIG. 2 ). In addition, when the poppet valve  40  of the latching solenoid  38  is closed (as shown in  FIG. 2 ), the latching solenoid  38  prevents fluid within the accumulator  18  from flowing through the poppet valve cavity  42  and past the poppet valve  40 . Fluid cannot flow in either direction past the poppet valve  40  when it is closed. Typically, the line pressure supplied by the pump  12  is less than the fluid pressure inside the cavity  24  either when the pump  12  is off, i.e. when the engine  13  is not powering the pump  12 , or when the pressure due to the spring  28  being compressed has risen to the point of being equal to or greater than the line pressure. 
     To return fluid from the actuator cavity  24  to the transmission line  16 , an algorithm causes the controller  44  to actuate the latching solenoid  38  to open the poppet valve  40  and introduce fluid from the accumulator  18  into passage  16 , thereby feeding the fluid to various transmission components (not shown) via passage  14 . The poppet valve  40  is generally directed to open following a prolonged engine shut down, which typically leads to a transmission fluid drain into a sump (not shown), and a subsequent engine restart. Providing pressurized fluid to the transmission components from the accumulator  18  immediately after an engine restart thereby affords full transmission operation without an otherwise likely delay. 
     Thus, the latching solenoid  38  is used both for actively filling the accumulator cavity  24  of the accumulator  18  and for discharging fluid from the cavity  24  of the accumulator  18 . In other embodiments, separate solenoids can be used to fill and discharge the accumulator  18  respectively, instead of having both functions performed by the same latching solenoid  38  as shown. Additionally, various types of actively actuated devices may be used in place of the latching solenoid  38  to fill and/or discharge the accumulator  18 . For example, a two-way valve  46  may be used as shown in  FIGS. 4-6 . 
     In some variations, while the solenoid  38  is off, it will block hydraulic fluid from bypassing it, excluding the minute amount of leakage that weeps past the clearances in the parts of the solenoid valve. In this example, when the solenoid  38  is energized electrically, the solenoid  38  opens. The decision to energize the solenoid  38  may be determined based on an engine start command in order to have the clutches/brakes ready for vehicle launch, or it may be based on another command. The hydraulic control system  10  controls the pressure and flow rate to the clutches/brakes to control clutch capacity during the engine start up event to eliminate torque bumps. Once pressure within the main line pressure circuit rises due to the activation of the pump  12 , the solenoid  38  is closed electrically, for example, by turning off power to the solenoid  38 . The accumulator  18  charge process can start over again to allow for another engine off event or other desired reason for actuation. 
       FIGS. 4-6  show an alternate hydraulic control system  10 A utilizing a two-way, i.e. bi-directional, solenoid valve  46  in place of the latching solenoid  38 , and a compressed gas to pressurize the piston  20 A and provide the return force  32 A. In all other respects, the hydraulic control system  10 A shown in  FIGS. 4-6  is structured and operates identically to the system  10  shown in  FIGS. 1-3 , including both a passive-fill channel  50 A to fill the accumulator cavity  24 A via the ball check-valve  34 A and an active-fill channel  52 A to fill the accumulator cavity  24 A via the bi-directional solenoid valve  46 . In addition, like the control system  10  described above, the hydraulic control system  10 A has a transmission (not shown) including a pump  12 A to provide pressurized fluid via a fluid passage  14 A to the transmission and via a fluid passage  16 A to the accumulator  18 A. The accumulator  18 A has an internal piston  20 A with a hermetic o-ring seal  22 A to seal off the pressure cavity  24 A from the cavity  26 A housing the compressed gas. 
     Similar to the system  10 , in the system  10 A, the bi-directional solenoid valve  46  operates to actively fill the accumulator  18 A via the active fill passages  52 A,  54 A, and the ball check-valve  34 A operates to passively fill the accumulator via the passive-fill channels  50 A,  36 A. The channels  36 A and  54 A are connected to the accumulator fill channel  56 A, which is connected to the accumulator cavity  24 A. Fluid is discharged from the accumulator  18 A through the two-way valve  46  back to the transmission line  16 A. Thus, upon discharge of the accumulator  18 A, fluid travels from the accumulator cavity  24 A to the accumulator line  56 A to the passage  54 A, through the valve  46 , then to the passage  52 A and to the transmission line  16 A. 
     The solenoid or valve device  38 ,  38 A may be an open/close type wherein the valve  40 ,  38 A is either opened or closed, but it is not restricted to this type. In other variations, the displacement of the valve  40 ,  38 A may be varied, so that it may be less than completely open. In other words, the valve  40 ,  38 A may be moved along a continuum from closed to open, such that it has a plurality or continuum of partially open positions. As such, the displacement of the valve  40 ,  38 A may be varied to control the flow rate to or from the accumulator  18 ,  18 A. Thus, the accumulator  18 ,  18 A may be actively filled by varying the displacement of the valve  40 ,  38 A. In some embodiments, the accumulator  18 ,  18 A could simultaneously be filled passively, for example via the ball check-valve  34 ,  34 A, as described above. 
     In another alternative, the accumulator  18 ,  18 A could be provided with a piston  20 ,  20 A that is loaded both by a spring and by a compressed gas to provide the return force  32 ,  32 A. 
     A method (shown in  FIG. 7 ) for controlling a hydraulic system of a vehicle powertrain having an engine and a transmission is provided and described with respect to the elements of the hydraulic control system  10  of  FIGS. 1-3  or the hydraulic control system  10 A of  FIGS. 4-6 . The method commences in block  100 . In block  102  the method includes providing fluid line pressure to the transmission  11  by opening a fluid passage when the engine is on, while no fluid pressure is provided when the engine  13  is off. The fluid pressure may be provided by the pump  12 ,  12 A via fluid passage  14 ,  14 A. As described in relation to  FIGS. 1-3 , the pump  12 ,  12 A is connected to the engine  13  for being operative when the engine  13  is on, and being inoperative, i.e. idle, when the engine  13  is off. 
     Proceeding to block  104 , according to the method, the fluid is actively accumulated via the accumulator  18 ,  18 A. As described in connection with  FIGS. 1-6 , the accumulator  18 ,  18 A being in fluid communication with passage  14 ,  14 A via the fluid passage  16 ,  16 A, is filled actively via the latching solenoid  38  or two-way valve  46  through the active-fill channel  52 ,  54 . Thus, the accumulation step  104  includes opening a valve  38 ,  46  via an electronic controller  44  to actively accumulate fluid from the fluid line pressure into the accumulator  18 ,  18 A when the engine is turned on. In addition, the step  104  may include passively filling the accumulator  18 ,  18 A when the ball check-valve  34 ,  34 A becomes unseated due to the line pressure being greater than the pressure due to the fluid accumulated, i.e. contained, by the accumulator  18 ,  18 A. The accumulator  18 ,  18 A is passively filled through the passive-fill channel  50 ,  36 . 
     In block  106 , the fluid is retained via the accumulator  18 ,  18 A when the engine  13  is turned off due to the latching solenoid  38  or two-way valve  46  remaining closed. Accordingly, the step  106  includes closing the valve  38 ,  46  via the electronic controller  44  to retain the fluid in the accumulator  18 ,  18 A when the engine is turned off. 
     In block  108 , the fluid is discharged via the accumulator  18 ,  18 A to the fluid passage  16 ,  16 A when the engine  13  is restarted by opening the latching solenoid  38  or two-way solenoid  46  via the controller  44 ,  44 A. The accumulator  18 ,  18 A is discharged when the engine is restarted such a full transmission operation is afforded substantially without delay. The fluid is discharged from the accumulator  18 ,  18 A through the active-fill channel  52 ,  54 . 
     Subsequent to the engine  13  having been restarted, and the accumulator  18 ,  18 A having discharged its fluid content to the transmission  11 , the accumulator  18 ,  18 A is again ready to accumulate fluid to the level dictated by the spring  28  or the gas in the chamber  26 A. Accordingly, after block  108 , the method returns to block  104  to again accumulate fluid via the accumulator  18 ,  18 A. 
     Elements of the hydraulic control system  10  of  FIGS. 1-3  may be mixed with hydraulic control system  10 A of  FIG. 4-6 , and vice versa. For example, an accumulator  18 A having a compressed gas that pressures a piston  20 A may be used in a system utilizing a latching solenoid  38 ; or an accumulator  18  having a spring  28  biasing a piston  20  may be used in a system utilizing a two-way valve  46 . 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist 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. In addition, it should be understand that the system and method disclosed herein could incorporate various elements and features that are described throughout the present disclosure, as well as equivalents, without departing from the spirit and scope of the present invention.