Abstract:
A system and method for controlling automatic stop-start of a motor vehicle is provided. The system and method is configured to enable an automatic stop-start mode of operation that minimizes clutch fill during engine restart.

Description:
CROSS-REFERENCE 
     This application claims the benefit of U.S. Provisional Application No. 61/392,161, filed Oct. 12, 2010. The entire contents of the above application are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a system and method for controlling an automatic engine restart, and more particularly to a system and method for controlling an automatic engine restart that minimizes how many torque transmitting mechanisms are filled with hydraulic fluid. 
     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, 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 motor 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 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 to be fully 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. 
     Therefore, there is a need in the art for a system and method for controlling automatic engine restarts based on motor vehicle operating conditions as well as providing controllability of the motor vehicle during engine restart. 
     SUMMARY 
     A system and method for controlling automatic restart of a motor vehicle is provided. The system and method is configured to enable an automatic restart that allows a minimum number of torque transmitting devices to fill with hydraulic fluid. 
     In one example, the system and method uses a position of an accelerator pedal to determine whether a single clutch is filled. In another example, the system and method uses a position of an accelerator pedal to determine whether a minimum number of clutches are filled. 
     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 an exemplary powertrain in a motor vehicle; 
         FIG. 2  is a schematic diagram of a portion of an exemplary hydraulic control system; and 
         FIG. 3  is a flow chart illustrating a method of operating the motor vehicle of  FIGS. 1-2  according to the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     With reference to  FIG. 1 , a motor vehicle is shown and generally indicated by reference number  5 . The motor vehicle  5  is illustrated as a passenger car, but it should be appreciated that the motor vehicle  5  may be any type of vehicle, such as a truck, van, etc. The motor vehicle  5  includes an exemplary powertrain  10 . It should be appreciated at the outset that while a rear-wheel drive powertrain has been illustrated, the motor vehicle  5  may have a front-wheel drive powertrain without departing from the scope of the present invention. The powertrain  10  generally includes an engine  12  interconnected with a transmission  14 . 
     The engine  12  may be a conventional internal combustion engine or an electric engine, or any other type of prime mover, without departing from the scope of the present disclosure. The engine  12  supplies a driving torque to the transmission  14  through a flexplate  15  or other connecting device that is connected to a starting device  16 . The starter device  16  may be a hydrodynamic device, such as a fluid coupling or torque converter, a wet dual clutch, or an electric motor. It should be appreciated that any starting device between the engine  12  and the transmission  14  may be employed. 
     The transmission  14  includes a typically cast, metal housing  18  which encloses and protects the various components of the transmission  14 . The housing  18  includes a variety of apertures, passageways, shoulders and flanges which position and support these components. Generally speaking, the transmission  14  includes a transmission input shaft  20  and a transmission output shaft  22 . Disposed between the transmission input shaft  20  and the transmission output shaft  22  is a gear and clutch arrangement  24 . The transmission input shaft  20  is functionally interconnected with the engine  12  via the starting device  16  and receives input torque or power from the engine  12 . Accordingly, the transmission input shaft  20  may be a turbine shaft in the case where the starting device  16  is a hydrodynamic device, dual input shafts where the starting device  16  is dual clutch, or a drive shaft where the starting device  16  is an electric motor. The transmission output shaft  22  is preferably connected with a final drive unit  26  which includes, for example, propshaft  28 , differential assembly  30 , and drive axles  32  connected to wheels  33 . The transmission input shaft  20  is coupled to and provides drive torque to the gear and clutch arrangement  24 . 
     The gear and clutch arrangement  24  includes a plurality of gear sets, a plurality of clutches and/or brakes, and a plurality of shafts. The plurality of gear sets may include individual intermeshing gears, such as planetary gear sets, that are connected to or selectively connectable to the plurality of shafts through the selective actuation of the plurality of clutches/brakes. The plurality of shafts may include layshafts or countershafts, sleeve and center shafts, reverse or idle shafts, or combinations thereof. The clutches/brakes, indicated schematically by reference number  34 , are selectively engageable to initiate at least one of a plurality of gear or speed ratios by selectively coupling individual gears within the plurality of gear sets to the plurality of shafts. It should be appreciated that the specific arrangement and number of the gear sets, clutches/brakes  34 , and shafts within the transmission  14  may vary without departing from the scope of the present disclosure. 
     The motor vehicle  5  includes a control module  36 . The control module  36  may be a transmission control module, an engine control module, or both, or any other type of controller. The control module  36  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 control module  36  controls the actuation of the clutches/brakes  34  via a hydraulic control system  38 . The hydraulic control system  38  is operable to selectively engage the clutches/brakes  34  by selectively communicating a hydraulic fluid to the clutches/brakes  34  that engages the clutches/brakes  34 . The control module  36  is also in communication with a plurality of sensors located throughout the motor vehicle  5 . For example, the control module  36  communicates with engine speed and temperature sensors  37 A and  37 B, an accelerator pedal position sensor  37 C, an ignition key sensor  37 D, a vehicle speed sensor  37 E, to name but a few. 
     Turning to  FIG. 2 , a portion of the hydraulic control system  38  is illustrated. At the outset it should be appreciated that the portion of the hydraulic control system  38  shown in  FIG. 2  is exemplary and that other configurations may be employed. The hydraulic control system  38  is operable to selectively engage the clutches/brakes  34  by selectively communicating a hydraulic fluid  44  from a sump  46  to a plurality of shift actuating devices  48 . The hydraulic fluid  44  is communicated to the shift actuating devices  48  under pressure from either an engine driven pump  50  or an accumulator  52 . 
     The sump  46  is a tank or reservoir to which the hydraulic fluid  44  returns and collects from various components and regions of the automatic transmission  14 . The hydraulic fluid  44  is forced from the sump  46  and communicated throughout the hydraulic control system  38  via the pump  50 . The pump  50  may be, for example, a gear pump, a vane pump, a gerotor pump, or any other positive displacement pump. The pump  50  includes an inlet port  54  and an outlet port  56 . The inlet port  54  communicates with the sump  46  via a suction line  58 . The outlet port  56  communicates pressurized hydraulic fluid  44  to a supply line  60 . The supply line  60  is in communication with a spring biased blow-off safety valve  62 , an optional pressure side filter  64 , and an optional spring biased check valve  66 . The spring biased blow-off safety valve  62  communicates with the sump  46 . The spring biased blow-off safety valve  62  is set at a relatively high predetermined pressure and if the pressure of the hydraulic fluid  44  in the supply line  60  exceeds this pressure, the safety valve  62  opens momentarily to relieve and reduce the pressure of the hydraulic fluid  44 . The pressure side filter  64  is disposed in parallel with the spring biased check valve  66 . If the pressure side filter  64  becomes blocked or partially blocked, pressure within supply line  60  increases and opens the spring biased check valve  66  in order to allow the hydraulic fluid  44  to bypass the pressure side filter  64 . 
     The pressure side filter  64  and the spring biased check valve  66  each communicate with an outlet line  68 . The outlet line  68  is in communication with a second check valve  70 . The second check valve  70  is in communication with a main supply line  72  and is configured to maintain hydraulic pressure within the main supply line  72 . The main supply line  72  supplies pressurized hydraulic fluid to a control device  76 . The control device  76  is electrically controlled by the control module  36  and is operable to control whether the accumulator  52  is charged or discharged. When the control device  76  is open, the accumulator  52  may discharge. When the control device  76  is closed, the accumulator  52  may charge and remain charged. The control device  76  may be an on/off solenoid or a pressure or flow control solenoid. 
     The main supply line  72  communicates through a hydraulic circuit that may include other control devices, valves, etc., to the plurality of actuating devices  48 . The actuating devices  48  may be, for example, piston assemblies that when engaged in turn engage the clutches/brakes  34 . 
     The control device  76  communicates with the accumulator  52  and a pressure sensor  74 . The accumulator  52  is an energy storage device in which the non-compressible hydraulic fluid  44  is held under pressure by an external source. In the example provided, the accumulator  52  is a spring type or gas filled type accumulator having a spring or compressible gas that provides a compressive force on the hydraulic fluid  44  within the accumulator  52 . However, it should be appreciated that the accumulator  52  may be of other types, such as a gas-charged type, without departing from the scope of the present invention. Accordingly, the accumulator  52  is operable to supply pressurized hydraulic fluid  44  back to the main supply line  72 . However, upon discharge of the accumulator  52 , the second check valve  70  prevents the pressurized hydraulic fluid  44  from returning to the pump  50 . The accumulator  52 , when charged, effectively replaces the pump  50  as the source of pressurized hydraulic fluid  44 , thereby eliminating the need for the pump  50  to run continuously. The pressure sensor  74  reads the pressure of the hydraulic fluid  44  within the main supply line  72  or the accumulator  52  in real time and provides this data to the control module  36 . Other types of sensors, such as volume or position sensors, may also be included. 
     With reference to  FIG. 3 , and with continued reference to  FIGS. 1 and 2 , a method  100  for operating the motor vehicle  5  will now be described. The method  100  is configured to override a commanded shift during an automatic engine stop and at the beginning of an automatic engine restart such that a minimum number of torque transferring devices (clutches, brakes, free wheelers, etc.) is primed during restart. For example, the method  100  begins at step  102  where the control module  36  determines whether the accumulator  52  is being used and whether the transmission  14  is in a forward drive state. If the transmission  14  is not using the accumulator  52  or the transmission is not in a forward drive state, the method  100  ends. If the transmission  14  is using the accumulator  52  and the transmission is in a forward drive state, the method  100  proceeds to step  104  where the control module  36  determines whether the motor vehicle  5  is currently in an automatic engine stop condition. If the engine  12  is in an automatic stop mode the method proceeds to step  106 . At step  106 , the commanded shift is overridden such that a minimum number of the clutches  34  required for a first forward gear will be engaged during the automatic engine restart and the method  100  ends. 
     If the engine  12  is not in an automatic stop mode, i.e. the engine  12  has begun to restart after an automatic engine stop, the method  100  proceeds from step  104  to step  108 . At step  108  the control module  36  determines if the engine  12  has been restarted. If the engine has not been restarted, the method  100  proceeds to step  110 . If the engine  12  has been restarted, the method proceeds to step  112  where an engine timer is set to a zero value. The engine timer is the time since the engine  12  has been restarted. The method  100  then proceeds to step  110 . 
     At step  110  determines whether to override the commanded shift such that a minimum number of clutch/brakes  34  are engaged. If the override of the commanded shift is not performed, the method  100  ends. If the override is performed, the method proceeds to step  114 . 
     At step  114 , the control module  36  calculates a time threshold for holding the minimum number of clutches/brakes override based on a power request from a driver to the powertrain, for example using the accelerator pedal position. The accelerator pedal position is communicated to the control module  36  via the sensor  37 C. A low power request (for example, a low application of the accelerator pedal) indicates less time in the override state. A high power request (for example, a higher application of the accelerator pedal) indicates more time in the override state. At step  116  the control module  36  compares the calculated time threshold to a time since the engine  12  has restarted. If the time since the engine  12  has been running exceeds the threshold, the method proceeds to step  118  and the commanded shift override is disabled and the method  100  ends. If the time since the engine  12  has been running does not exceed the threshold, the method proceeds to step  120 . 
     At step  120  the control module  36  determines whether the transmission  14  has shifted to a higher gear. If the transmission  14  has shifted to a higher gear, the method proceeds to step  118 . If the transmission  14  has not yet shifted to a higher gear, the method  100  proceeds to step  122  where the commanded shift is overridden such that a minimum of the clutches  34  required for a first forward gear will be engaged during the automatic engine restart. 
     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.