Abstract:
Disclosed is a creep control system and method for a hybrid vehicle, which controls the driving of a motor according to the distance to a preceding vehicle in order to provide creep driving when the hybrid vehicle has come to a complete stop. In particular, driving information is detected and a determination is made as to whether the hybrid vehicle is in an idle stop and completely stationary state. Then when the hybrid vehicle is in the idle stop and completely stationary state, a determination is made as to whether a distance from a preceding vehicle is more than a predetermined distance. When the distance to the preceding vehicle is more than the predetermined distance, a motor is driven to perform creep driving.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0107148 filed in the Korean Intellectual Property Office on Oct. 19, 2011, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to a hybrid vehicle, and more particularly, to a creep control device and method for a hybrid vehicle, which control the driving of a motor according to the distance to a preceding vehicle in order to provide creep driving once the hybrid vehicle has come to a complete stop. 
         [0004]    (b) Description of the Related Art 
         [0005]    An automatic transmission installed in a typical internal combustion engine vehicle transmits power from an engine through a torque converter, and provides creep driving so that the vehicle moves slightly even when the accelerator pedal is not pressed, while operating in lower speeds and the vehicle is in Drive (D) or reverse (R). This allows a vehicle to get take off smoothly, and may help the vehicle avoid rolling backward when the vehicle is very slowly moving or temporarily stopping and then starting up an inclined road. 
         [0006]    In order to reduce costs and minimize the loss of torque transmitted to an automatic transmission, a hybrid vehicle has an engine clutch installed between an engine and a motor instead of a torque converter. Such a hybrid vehicle that does not have a torque converter installed typically includes an engine that enters an idle stop state when stationary, performs motor-driven creep driving to reduce the dissimilarity to typical passenger vehicles and provide comfortable drivability. 
         [0007]    In a hybrid vehicle, creep torque may vary depending on whether the brake pedal is deployed and whether the vehicle is stationary. For example, when the brake pedal is deployed and the vehicle is stationary, torque output is not required so that creep torque is controlled to a minimum value—but not to “0” in consideration of the vehicle&#39;s off-the-line responsiveness. 
         [0008]    Such a hybrid vehicle typically generates creep torque even at a standstill, in view of take off responsiveness, whereby unnecessary driving of the motor occurs, causing draining of the battery. Accordingly, repeated charging and discharging of the battery by the engine may occur, causing deteriorated fuel efficiency, and the repeated charging and discharging may cause a reduction in battery efficiency. 
         [0009]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention has been made in an effort to provide a creep control device and method for a hybrid vehicle having the advantages of providing active creep control by controlling the driving of a motor according to the distance to a preceding vehicle, when the hybrid vehicle is completely stationary. 
         [0011]    An exemplary embodiment of the present invention provides a creep control device for a hybrid vehicle having an engine and a motor, including: a vehicle speed detecting unit detecting a vehicle speed; an inter-vehicle distance detecting unit detecting a distance to preceding vehicle; a motor controller configured to control driving of a motor with the voltage from a battery; and a hybrid controller configured to analyze the distance to a preceding vehicle provided by the inter-vehicle distance detecting unit when information from the vehicle speed detecting unit is detected as a complete stop during driving, and performing creep driving by controlling the driving of the motor through the motor controller when the distance to the preceding vehicle exceeds a predetermined distance. 
         [0012]    The hybrid controller may stop the driving of the motor when the distance to the preceding vehicle becomes equal to or less than the predetermined distance in a state in which creep driving is being performed through the driving of the motor. The inter-vehicle distance detecting unit may be configured as a distance measurement sensor, and may be installed at a predetermined position on a cabin rearview mirror or a front bumper. 
         [0013]    Another exemplary embodiment of the present invention provides a creep control method for a hybrid vehicle, including: detecting driving information and determining whether the hybrid vehicle is in an idle stop and completely stationary state; determining, when the hybrid vehicle is in the idle stop and completely stationary state, whether a distance from a preceding vehicle is more than a predetermined distance; and driving a motor to perform creep driving when the distance to the preceding vehicle exceeds a predetermined distance. The driving information may include vehicle speed, engine rpm, brake pedal displacement, and accelerator pedal displacement information. When the distance to the preceding vehicle is equal to or less than the predetermined distance while the creep driving is being performed by driving the motor, the creep driving may be stopped. 
         [0014]    Such a hybrid vehicle according to an exemplary embodiment of the present invention performs creep driving by driving a motor according to an inter-vehicle distance, and does not drive the motor in a stationary state and in a low-speed range when creep torque is not needed, thus minimizing battery drainage, and allowing for driving stability in electric vehicle (EV) mode. Further, because unnecessary battery drainage does not occur, enhancement of fuel efficiency may be ultimately provided, and battery efficiency may be stabilized and maintained. In addition, since the present invention may stably maintain an inter-vehicle distance required by a driver, driving convenience and stability may be provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  a drawing schematically illustrating a creep control device for a hybrid vehicle according to an exemplary embodiment of the present invention. 
           [0016]      FIG. 2  is a flowchart illustrating a creep control process for a hybrid vehicle according to an exemplary embodiment of the present invention. 
         DESCRIPTION OF SYMBOLS 
         [0000]    
         
           
             
                 10 : Inter-vehicle distance detecting unit 
                 11 : Vehicle speed detecting unit 
                 20 : HCU 
                 30 : MCU 
                 70 : Motor 
             
           
         
       
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0022]    The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. The drawings and description are to be regarded as illustrative in nature and not restrictive. 
         [0023]    It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, combustion, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). 
         [0024]    Furthermore, the control logic of the present invention may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller or the like. Examples of the computer readable mediums include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable recording medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a server or a network. Additionally, although the exemplary embodiment is described as using one control unit to perform the above process, it is understood that the above processes may also be performed by a plurality of control units, controllers, processors or the like. 
         [0025]    The present invention relates to a technology for creep control of a hybrid vehicle, and because the driving operation of the hybrid vehicle is performed in the same way as a typical operation a detailed description thereof will not be provided. 
         [0026]      FIG. 1  a drawing schematically illustrating a creep control device for a hybrid vehicle according to an exemplary embodiment of the present invention. As illustrated in  FIG. 1 , the present invention may include an inter-vehicle distance detecting unit  10 , a vehicle speed detecting unit  11 , an hybrid control unit (HCU)  20 , an motor control unit (MCU)  30 , a battery  40 , a battery management system (BMS)  50 , an engine control unit (ECU)  60 , a motor  70 , an engine  80 , an hybrid start and generator (HSG)  81 , a clutch  90 , and a transmission  100 . 
         [0027]    More specifically, the inter-vehicle distance detecting unit  10  may be configured to detect the distance to a preceding vehicle and provide information thereon to the HCU  20 . The inter-vehicle distance detecting unit  10  may be a distance measurement sensor, and may be installed at a predetermined position on a cabin rearview minor or a front bumper. 
         [0028]    The vehicle speed detecting unit  11 , on the other hand, may be configured to detect the vehicle speed from the output shaft of the transmission and provides information thereon to the HCU  20 . The HCU  20  controls output torque through integrated control of each controller through a network according to driving requirements and the vehicle state, and controls the clutch  90  according to driving conditions, to provide EV mode and HEV mode driving. 
         [0029]    Further, when information provided from the vehicle speed detecting unit  11  shows that the vehicle is completely stationary during driving, the HCU  20  analyzes the distance to the preceding vehicle provided by the inter-vehicle distance detecting unit  10 , and determines, when it is determined that the distance between the present vehicle and the preceding vehicle exceeds a predetermined distance, that the two vehicles are more than the predetermined distance apart, and controls the driving of the motor  70  through the MCU  30  to perform creep driving. The HCU  20  stops the driving of the motor  70  to prevent unnecessary draining of the battery  40 , when the distance to the preceding vehicle provided by the inter-vehicle distance detecting unit  10  is equal to or less than the predetermined distance, while performing creep driving through driving of the motor  70  by the MCU  30 . 
         [0030]    In the above, the HCU  20  may further include information on the acceleration pedal and the brake pedal, in addition to the vehicle speed and inter-vehicle distance information. 
         [0031]    The MCU  30  performs creep driving by controlling the driving of the motor  70  through converting the DC voltage from the battery  40  to a 3-phase AC voltage, according to a control signal provided by the HCU  20  through a network. The motor  70  is operated by the 3-phase AC voltage applied from the MCU  30  to generate creep torque. The MCU  30  may include an inverter configured with a plurality of power switching devices, and the power switching devices may be configured with any one of an IGBT (Insulated Gate Bipolar Transistor), a metal-oxide-semiconductor field-effect transistor (MOSFET), or a transistor. 
         [0000]    The battery  40  is formed of a plurality of unit cells, and stores a high voltage of DC 350V, for example. The BMS  50  detects the current, the voltage, and the temperature of each cell within the operating range of the battery  40 , controls the SOC (State Of Charge) thereof, and controls charging and discharging voltages of the battery  40  to prevent shortened battery life due to over-discharging to below a threshold voltage or overcharging to above a threshold voltage. 
         [0032]    The ECU  60  drives the HSG  81  according to a control signal applied from the HCU  20  through a network, and performs ignition “on” of the engine  80  to provide charging of the battery  40  and driving in HEV (hybrid) mode. The engine  80  has engine ignition on/off functions and the output thereof controlled by the ECU  60 , and has intake air quantity thereof controlled through an ETC (Electric Throttle Control) (not illustrated). The HSG  81  operates as a starter and a generator, and performs ignition on of the engine  80  and generates a voltage to provide a charge for the battery  40 . In addition, the clutch  90  may be disposed between the engine  80  and the motor  70  and controls the connecting of power between the engine  80  and the motor  70  according to the driving mode. 
         [0033]    A creep control process for a hybrid vehicle according to the present invention including the above-described functions is implemented as follows. 
         [0034]    With a hybrid vehicle to which the present invention is applied in a driven state in step S 101 , the HCU  20  detects the distance to the preceding vehicle provided by the inter-vehicle distance detecting unit  10 , and the vehicle speed detecting unit  11  detects the vehicle speed in step S 102 . In addition information on engine rpm, the accelerator pedal, and the brake pedal is detected. 
         [0035]    In step S 103 , the HCU  20  analyzes the detected information to determine whether the engine ignition is off and the information from the vehicle speed detecting unit  11  shows that the vehicle is completely stationary. In step S 103 , when the HCU  20  determines that the engine ignition is off and the vehicle is completely stationary, the distance to the preceding vehicle provided by the inter-vehicle distance detecting unit  10  is analyzed in step S 104 , and it is determined in step S 105  whether the distance between the present vehicle and the preceding vehicle is greater than a predetermined distance. 
         [0036]    In step S 105 , when the HCU  20  determines that the present vehicle is completely stationary and is a distance between the preceding vehicle is more than the predetermined distance, the driving of the motor  70  is controlled through the MCU  30  and creep driving is performed in steps S 106  and S 107 . Creep driving speed through driving of the motor  70  may be maintained at about 1-3 KPH, for example. 
         [0037]    As described above, with the HCU  20  performing creep driving by controlling the driving of the motor  70  through the MCU  30 , the distance to the preceding vehicle provided by the inter-vehicle distance determining unit  10  is analyzed, and when the distance becomes equal to or less than the predetermined distance, the driving of the motor  70  is stopped in step S 108  to prevent unnecessary draining of the battery  40 . 
         [0038]    Accordingly, an example has been described above of where creep driving is automatically/dynamically controlled with the vehicle completely stationary, according to the distance to the vehicle in front. Moreover, creep driving may be performed according to the selection of a separate switch that is installed for selecting creep driving, and all similar techniques besides the selecting of a switch that are the same or similar to the above-described operations will fall within the scope of the present invention. 
         [0039]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.