Patent Publication Number: US-2021190203-A1

Title: Transmission hydraulic control system

Description:
INTRODUCTION 
     The present disclosure relates to a hydraulic control system for an automatic transmission in an automotive vehicle. 
     A typical automatic transmission includes a hydraulic control system that, among other functions, is employed 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 automotive vehicles, it is desirable to stop the engine during certain circumstances, such as when stopped at a red light or idling. However, during this automatic stop, the transmission pump is no longer driven by the engine. Accordingly, hydraulic fluid pressure within the hydraulic control system drops. This leads to clutches and/or brakes within the transmission becoming disengaged. As the engine restarts, these clutches and/or brakes may take time to reengage fully, thereby producing slippage and delay between engagement of the accelerator pedal or release of the brake and the movement of the motor vehicle. 
     In some cases, these transmissions have a separate auxiliary electric pump for providing the pressurized hydraulic fluid when the engine is turned off. The auxiliary electric pump maintains hydraulic fluid pressure to keep selected clutches and/or brakes within the transmission engaged when the engine and the transmission pump are not providing hydraulic pressure to the system. As the engine restarts, these clutches and/or brakes are fully engaged, preventing slippage and delay between engagement of the accelerator pedal or release of the brake and the movement of the automotive vehicle. 
     In some cases, these transmissions use an accumulator to remotely store pressurized hydraulic fluid when the engine is turned off. When the engine and the transmission pump are running, the accumulator is charged with pressurized hydraulic fluid from the hydraulic circuit. When the engine and the transmission pump are turned off, a valve holds pressurized hydraulic fluid within the accumulator. As the engine restarts, pressurized hydraulic fluid is released from the accumulator into the hydraulic circuit. This injection of pressurized hydraulic fluid engages clutches and brakes within the transmission, preventing slippage and delay between engagement of the accelerator pedal or release of the brake and the movement of the automotive vehicle as the engine restarts. 
     Thus, while conventional hydraulic control systems are effective, there is a need for an improved hydraulic control circuits that does not rely on an auxiliary electric pump or a remotely located accumulator to provide hydraulic pressure to the hydraulic circuit during engine restart. 
     SUMMARY 
     According to several aspects of the present disclosure, a transmission hydraulic control system for actuating at least one torque transmitting device in a transmission for an automobile includes a hydraulic circuit in fluid communication with the at least one torque transmitting device, a transmission pump in fluid communication with the hydraulic circuit and adapted to provide pressurized hydraulic fluid to the hydraulic circuit, an accumulator including an inner volume in fluid communication with the hydraulic circuit, the inner volume having an annular cylindrical shape concentric with a center-line of the automatic transmission, an annular piston positioned within the inner volume, the piston moveable between a first position and a second position, and a spring adapted to bias the piston to the first position, and a valve mechanism positioned between the hydraulic circuit and the accumulator, the valve mechanism adapted to selectively allow fluid communication between the inner volume of the accumulator and the hydraulic circuit, and to prevent fluid communication between the inner volume of the accumulator and the hydraulic circuit, wherein the valve mechanism allows pressurized hydraulic fluid to enter the inner volume of the accumulator when the transmission pump is running, the valve mechanism holds pressurized hydraulic fluid within the inner volume of the accumulator when the transmission pump is not running, and the valve mechanism selectively releases pressurized hydraulic fluid from the inner volume of the accumulator to the hydraulic circuit. 
     According to another aspect, the valve mechanism includes a first control device and a second control device, the first control device adapted to allow pressurized hydraulic fluid to enter the inner volume of the accumulator from the hydraulic circuit, the second control device adapted to selectively allow pressurized hydraulic fluid to flow from the inner volume of the accumulator to the hydraulic circuit. 
     According to another aspect, the first and second control devices are located within a control valve body of the transmission. 
     According to another aspect, the first control device is a one-way ball check valve that allows fluid communication from the hydraulic circuit to the accumulator and prevents fluid communication from the accumulator to the hydraulic circuit. 
     According to another aspect, the second control device is a selectively actuatable valve having an open condition for allowing fluid communication between the inner volume of the accumulator and the hydraulic circuit and a closed condition for preventing fluid communication between the accumulator and the hydraulic circuit. 
     According to another aspect, the second control device is an on/off solenoid. 
     According to another aspect, the spring biases the piston to the first position with a biasing force, and wherein the pressurized hydraulic fluid within the hydraulic circuit when the transmission pump is running is sufficient to overcome the biasing force of the spring such that when pressurized hydraulic fluid enters the inner volume of the accumulator the piston moves from the first position to the second position. 
     According to another aspect, when the transmission pump is not running and the valve mechanism is selectively actuated to allow fluid communication between the inner volume of the accumulator and the hydraulic circuit, the biasing force of the spring pushes the piston from the second position to the first position and forces hydraulic fluid within the inner volume of the accumulator into the hydraulic circuit. 
     According to another aspect, the valve mechanism is a selectively actuated pressure locking solenoid that is positioned within a control valve body of the transmission. 
     According to another aspect, the hydraulic control system further includes a controller adapted to send a start/stop signal to the valve mechanism to selectively actuate the valve mechanism. 
     According to several aspects of the present disclosure, a transmission hydraulic control system for actuating at least one torque transmitting device in a transmission for an automobile includes a hydraulic circuit in fluid communication with the at least one torque transmitting device, a transmission pump in fluid communication with the hydraulic circuit and adapted to provide pressurized hydraulic fluid to the hydraulic circuit, an accumulator including an inner volume in fluid communication with the hydraulic circuit, the inner volume having an annular cylindrical shape concentric with a center-line of the automatic transmission, an annular piston positioned within the inner volume, the piston moveable between a first position and a second position, and a spring adapted to bias the piston to the first position, and a valve mechanism positioned within a control valve body of the transmission between the hydraulic circuit and the accumulator, the valve mechanism adapted to selectively allow fluid communication between the inner volume of the accumulator and the hydraulic circuit, and to prevent fluid communication between the inner volume of the accumulator and the hydraulic circuit, wherein, when the transmission pump is running and the valve mechanism is selectively actuated to allow fluid communication between the hydraulic circuit and the inner volume of the accumulator, pressurized hydraulic fluid entering the inner volume of the accumulator is sufficient to overcome the biasing force of the spring and move the piston from the first position to the second position, increasing the capacity of the inner volume of the accumulator, and when the transmission pump stops running the valve mechanism is actuated to prevent fluid communication between the hydraulic circuit and the inner volume of the accumulator, and pressurized hydraulic fluid is held within the inner volume of the accumulator, and when the transmission pump is not running and the valve mechanism is selectively actuated to allow fluid communication between the hydraulic circuit and the inner volume of the accumulator, the biasing force of the spring pushes the piston from the second position to the first position and forces pressurized hydraulic fluid within the inner volume of the accumulator into the hydraulic circuit. 
     According to another aspect, the valve mechanism includes a first control device and a second control device, the first control device adapted to allow pressurized hydraulic fluid to enter the inner volume of the accumulator from the hydraulic circuit, the second control device adapted to selectively allow pressurized hydraulic fluid to flow from the inner volume of the accumulator to the hydraulic circuit. 
     According to another aspect, the first and second control devices are located within the control valve body of the transmission. 
     According to another aspect, the first control device is a one-way ball check valve that allows fluid communication from the hydraulic circuit to the accumulator and prevents fluid communication from the accumulator to the hydraulic circuit. 
     According to another aspect, the second control device is a selectively actuatable valve having an open condition for allowing fluid communication between the inner volume of the accumulator and the hydraulic circuit and a closed condition for preventing fluid communication between the accumulator and the hydraulic circuit. 
     According to another aspect, the second control device is an on/off solenoid. 
     According to another aspect, the valve mechanism is a selectively actuated pressure locking solenoid that is positioned within a control valve body of the transmission. 
     According to another aspect, the hydraulic control system further includes a controller adapted to send a start/stop signal to the valve mechanism to selectively actuate the valve mechanism. 
     According to several aspects of the present disclosure, a transmission hydraulic control system for actuating at least one torque transmitting device in a transmission for an automobile includes a hydraulic circuit in fluid communication with the at least one torque transmitting device, a transmission pump in fluid communication with the hydraulic circuit and adapted to provide pressurized hydraulic fluid to the hydraulic circuit, an accumulator including an inner volume in fluid communication with the hydraulic circuit, the inner volume having an annular cylindrical shape concentric with a center-line of the automatic transmission, an annular piston positioned within the inner volume, the piston moveable between a first position and a second position, and a spring adapted to bias the piston to the first position, and a selectively actuated pressure locking solenoid positioned within a control valve body of the transmission between the hydraulic circuit and the accumulator, the pressure locking solenoid adapted to selectively allow fluid communication between the inner volume of the accumulator and the hydraulic circuit, and to prevent fluid communication between the inner volume of the accumulator and the hydraulic circuit, wherein, when the transmission pump is running and the pressure locking solenoid is selectively actuated to allow fluid communication between the hydraulic circuit and the inner volume of the accumulator, pressurized hydraulic fluid entering the inner volume of the accumulator is sufficient to overcome the biasing force of the spring and move the piston from the first position to the second position, increasing the capacity of the inner volume of the accumulator, and when the transmission pump stops running the pressure locking solenoid is actuated to prevent fluid communication between the hydraulic circuit and the inner volume of the accumulator, and pressurized hydraulic fluid is held within the inner volume of the accumulator, and when the transmission pump is not running and the pressure locking solenoid is selectively actuated to allow fluid communication between the hydraulic circuit and the inner volume of the accumulator, the biasing force of the spring pushes the piston from the second position to the first position and forces pressurized hydraulic fluid within the inner volume of the accumulator into the hydraulic circuit. 
     According to another aspect, the hydraulic control system further includes a controller adapted to send a start/stop signal to the pressure locking solenoid to selectively actuate the valve mechanism. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE 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 of a hydraulic control system in accordance with an exemplary embodiment; 
         FIG. 2  is a partial sectional view of a transmission having a hydraulic control system according to an exemplary embodiment; 
         FIG. 3  is a partial sectional view of an accumulator wherein a piston is in a first position; and 
         FIG. 4  is the partial sectional view of  FIG. 3 , wherein the piston is in a second position. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     Referring to  FIG. 1 , a transmission hydraulic control system  10  for actuating at least one torque transmitting device  12  in a transmission  14  for an automobile includes a hydraulic circuit  16  in fluid communication with the at least one torque transmitting device  12 , a transmission pump  18  in fluid communication with the hydraulic circuit  16  and adapted to provide pressurized hydraulic fluid to the hydraulic circuit  16 , and an accumulator  20 . 
     The at least one torque transmitting device  12  is hydraulically actuated by hydraulic fluid. The at least one torque transmitting device  12  may include a plurality of friction clutches and/or brakes, or other types of hydraulically actuated torque transmitting devices  12 . The hydraulic fluid is, by way of non-limiting example, an oil conventionally used in automatic transmission systems. 
     The hydraulic control system  10  includes a reservoir or tank for receiving and storing the hydraulic fluid. The transmission pump  18  may take many forms, such as, by way of non-limiting example, an impeller pump, gear pump, or vane pump, without departing from the scope of the present invention. The transmission pump  18  is driven by an engine (not shown) in the automobile. The transmission pump  18  is operable to provide a flow of hydraulic fluid to the hydraulic circuit  16  of the transmission  14  and to the at least one torque transmitting device  12 . 
     The hydraulic control system  10  further includes a control valve body  22 . The control valve body  22  includes a plurality of passages and valves that control the flow of hydraulic fluid within the transmission  14  and to the torque transmitting devices  12  within the transmission  14 . Selective actuation of the valves within the control valve body  22  controls actuation and de-activation of the torque transmitting devices  12 . 
     Referring to  FIG. 3  and  FIG. 4 , in an exemplary embodiment, the at least one torque transmitting device  12  is a friction clutch that includes a plurality of alternating rotatable plates  24  and non-rotatable plates  26 . The plates  24 ,  26  are generally flat annular shaped rings that extend circumferentially around and are concentric with a center line  28  of the transmission  14 , as is common in automobile transmissions of this type. Actuation of the torque transmitting device  12  is accomplished by feeding pressurized hydraulic fluid from the hydraulic circuit  16  to a chamber  30 . Positioned within the chamber  30  is a clutch piston  32 . The clutch piston  32  is moveable between a first position and a second position within the chamber  30 . A clutch spring  34  biases the clutch piston  32  to the first position, as shown in  FIG. 3 . 
     When pressurized hydraulic fluid is fed into the chamber  30 , the hydraulic fluid overcomes the biasing force of the clutch spring  34  and pushes the clutch piston  32  from the first position toward a second position and toward the plurality of alternating rotatable and non-rotatable plates  24 ,  26 , as indicated by arrow  36 . An actuator  38  engages the stack of alternating rotatable and non-rotatable plates  24 ,  26 , pushing the plates  24 ,  26  against one another. Friction between the rotatable and non-rotatable plates  24 ,  26  prevent the rotatable and non-rotatable plates  24 ,  26  from rotating relative to one another, thereby locking the rotatable plates  24  and engaging the torque transmitting device  12 . To disengage the torque transmitting device  12 , a valve within the control valve body  22  diverts the flow of pressurized hydraulic fluid from the chamber  30  allowing the clutch spring  34  to bias the clutch piston  32  away from the plurality of rotating and non-rotating plates  24 ,  26  and allowing the rotatable plates  24  to rotate relative to the non-rotating plates  26 . 
     The accumulator  20  is an energy storage device in which the non-compressible hydraulic fluid is held under pressure. The accumulator  20  includes an inner volume  38  in fluid communication with the hydraulic circuit  16 . The inner volume  38  has an annular cylindrical shape and is concentric with the center-line  28  of the automatic transmission  14 . Referring to  FIG. 2 , the accumulator  20  is positioned circumferentially around and concentric with the center-line  28  of the transmission  14 , as are other portions of the transmission  14 , such as torque transmitting devices  12  and gear sets  40 . 
     An annular piston  42  is positioned within the inner volume  38 . The inner volume  38  is defined by rigid features  44  of the transmission  14  and a top surface  46  of the annular piston  42 . The annular piston  42  is moveable between a first position, as shown in  FIG. 3 , and a second position, as shown in  FIG. 4 . A spring  48  is positioned to act on a bottom surface  50  of the annular piston  42  to bias the annular piston  42  toward the first position and to provide a compressive force on hydraulic fluid within the inner volume  38 . 
     A branch  52  of the hydraulic circuit  16  within the transmission  14  provides fluid communication between the control valve body  22  and the accumulator  20 . The accumulator  20  includes an inlet/outlet port  54  that allows hydraulic fluid to flow in and out of the accumulator  20 . 
     A valve mechanism  56  controls the flow of hydraulic fluid to and from the accumulator  20 . In an exemplary embodiment, a selectively actuated pressure locking solenoid  58  is positioned within the control valve body  22  of the transmission  14 . The pressure locking solenoid  58  controls the flow of hydraulic fluid from a main line  60  of the hydraulic circuit  16  to the branch  52  that feed the accumulator  20 . The pressure locking solenoid  58  selectively allows fluid communication between the inner volume  38  of the accumulator  20  and the hydraulic circuit  16 , and prevents fluid communication between the inner volume  38  of the accumulator  20  and the hydraulic circuit  16 . 
     In another exemplary embodiment, the valve mechanism  56  includes a first control device  62  and a second control device  64 . The first and second control devices  62 ,  64  are located within the control valve body  22  of the transmission  14 . The first control device  62  is adapted to allow pressurized hydraulic fluid to enter the inner volume  38  of the accumulator  20  from the hydraulic circuit  16 . By way of non-limiting example, the first control device  62  may be a one-way ball check valve that passively allows fluid communication from the hydraulic circuit  16  to the accumulator  20  and prevents fluid communication from the accumulator  20  to the hydraulic circuit  16 . The second control device  64  is adapted to selectively allow pressurized hydraulic fluid to flow from the inner volume  38  of the accumulator  20  to the hydraulic circuit  16 . By way of non-limiting example, the second control device  64  may be a selectively actuatable valve, such as an on/off solenoid, having an open condition for allowing fluid communication between the inner volume  38  of the accumulator  20  and the hydraulic circuit  16  and a closed condition for preventing fluid communication between the accumulator  20  and the hydraulic circuit  16 . 
     The hydraulic control system  10  operates in at least two modes: a first mode, wherein the transmission pump  18  provides pressurized hydraulic fluid to the at least one torque transmitting device  12 , and a second mode, where the accumulator  20  provides pressurized hydraulic fluid to the at least one torque transmitting device  12  in order to engage the at least one torque transmitting device  12  when the motor vehicle engine is stopped. It should be appreciated that both modes of operation may occur simultaneously. 
     Generally, when the motor vehicle stops (i.e., at a red light for example), the engine shuts off and the transmission pump  18  stops rotating, so there is no pressure in the hydraulic circuit  16  providing pressurized hydraulic fluid to the at least one torque transmitting device  12 . To start the motor vehicle without delay, the hydraulic circuit  16  should be filled with pressurized oil very fast. So, when the operator of the motor vehicle releases the brake pedal, or pushes on the accelerator pedal, a controller  66  sends an electric signal to the control valve body  22 . The signal triggers the control valve body  22  to release the pressure locking solenoid  58 , thereby allowing the accumulator  20  to discharge and send pressurized hydraulic fluid to the at least one torque transmitting device  12 . 
     The inner volume  38  if the accumulator  20  volume is limited, and torque transmitting devices  12  have leakages, so the pressure of the hydraulic fluid from the accumulator  20  drops rapidly. A drop in pressure of the hydraulic fluid will cause slippage in torque transmitting devices  12 , and the start of the motor vehicle can be delayed or slowed. Also, torque transmitting devices  12  can burn due to excessive slippage. Therefore, simultaneously with the signal sent to the pressure locking solenoid  58  to discharge the accumulator  20 , another signal is sent to start the engine, which will drive the transmission pump  18 . The transmission pump  18  will start to provide pressurized hydraulic fluid to the hydraulic circuit  16 . In the very beginning, the engine and the transmission pump  18  are rotating relatively slowly, so the amount of pressurized hydraulic fluid going to the hydraulic circuit  16  is low and not sufficient to fully engage the torque transmitting devices  12 . The main function of the accumulator  20  is to provide pressurized hydraulic fluid to the at least one torque transmitting device  12  very fast at high pressure for a short period of time and to minimize the delay of the motor vehicle start. After the engine starts, the transmission pump  18  will provide sufficient pressurized hydraulic fluid to operate the at least one torque transmitting device  12 . 
     When the engine of the automobile is running and the transmission pump  18  is in operation, the pressure locking solenoid  58  is selectively actuated to allow fluid communication between the hydraulic circuit  16  and the inner volume  38  of the accumulator  20 . Pressurized hydraulic fluid entering the inner volume  38  of the accumulator  20  is sufficient to overcome the biasing force of the spring  48  and move the annular piston  42  from the first position toward the second position, increasing the capacity of the inner volume  38  of the accumulator  20 . 
     When the automobile comes to a stop, the start/stop system shuts off the engine of the automobile, and the transmission pump  18  no longer operates. This causes the pressure of the hydraulic fluid within the hydraulic circuit  16  to drop. When the pressure within the main line  60  drops below the pressure of the hydraulic fluid within the accumulator  20 , the pressure locking solenoid the pressure locking solenoid  58  is actuated to prevent fluid communication between the main line  60  of the hydraulic circuit  16  and the branch  52  of the hydraulic circuit that feeds the inner volume  38  of the accumulator  20 . This holds pressurized hydraulic fluid within the inner volume  38  of the accumulator  20  and the branch  52  of the hydraulic circuit  16  that feeds the accumulator  20  after the engine of the automobile is shut off and the transmission pump  18  is no longer operating, during a start/stop event. 
     When the operator of the motor vehicle releases the brake pedal, or pushes on the accelerator pedal, an electric signal is sent to the control valve body  22 . The signal triggers the control valve body  22  to release the pressure locking solenoid  58 , thereby allowing the accumulator  20  to discharge and send pressurized hydraulic fluid to the main line  60  of the hydraulic circuit  16 . When the transmission pump  18  is not running and the pressure locking solenoid  58  is selectively actuated to allow fluid communication between the hydraulic circuit  16  and the inner volume  38  of the accumulator  20 , releasing pressurized hydraulic fluid to the hydraulic circuit  16 . The biasing force of the spring  48  pushes the annular piston  42  from the second position toward the first position and forces the pressurized hydraulic fluid within the inner volume  38  of the accumulator  20  into the hydraulic circuit  16 . 
     A hydraulic control system  10  of the present disclosure offers several advantages. These include providing an accumulator  20  for a start/stop system within the transmission  14  of an automobile wherein the accumulator  20  is positioned internally and concentric with a center-line  28  of the transmission  14 . In addition, the associated valve mechanism  56  that controls the accumulator  20  is positioned within the control valve body  22  of the transmission  14 . 
     The description of the present disclosure is merely exemplary in nature and variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.