Abstract:
An oil pump system and method of a hybrid vehicle stably supplies an operating hydraulic pressure to an automatic transmission using only an electric oil pump. The oil pump system of the hybrid vehicle, which supplies an operating hydraulic pressure to an automatic transmission of the hybrid vehicle, includes: an automatic transmission control unit controlling operation of the automatic transmission; an electric oil pump pumping oil to generate an operating hydraulic pressure which is to be supplied to the automatic transmission; and an oil pump control unit receiving information on a state of the automatic transmission from the automatic transmission control unit and controlling operation of the electric oil pump. The operating hydraulic pressure supplied to the automatic transmission may be generated solely through the electric oil pump which is electrically operated.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority of Korean Patent Application Number 10-2013-0066783 filed Jun. 11, 2013, the entire contents of which application is incorporated herein for all purposes by this reference. 
       BACKGROUND OF INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to an oil pump system of a hybrid vehicle and a method for controlling the same, and more particularly, to an oil pump system of a hybrid vehicle, which is provided to supply a hydraulic pressure to an automatic transmission using only an electric oil pump, and a method for controlling the same. 
         [0004]    2. Description of Related Art 
         [0005]    In general, an automatic transmission is connected to an oil pump system for supplying an operating hydraulic pressure to the automatic transmission. The oil pump system includes one or more oil pumps. 
         [0006]    Conventionally, an oil pump system which supplies an operating hydraulic pressure to an automatic transmission using a mechanical oil pump and an electric oil pump together has been mainly used. In particular, hybrid vehicles have mainly employed a control method of an oil pump system, which divides a running state of a vehicle into a stoppage section, a low-speed section, and a high-speed section, and selectively operates a mechanical oil pump and an electric oil pump. According to the control method of the oil pump system, only the electric oil pump may be operated during the stoppage section, the mechanical oil pump and the electric oil pump may be simultaneously operated during the low-velocity section, and only the mechanical oil pump may be operated during the high-velocity section. 
         [0007]    However, when two or more oil pumps such as the mechanical oil pump and the electric oil pump are used, the production cost may excessively increase. Furthermore, the mechanical oil pump operated by driving torque of an engine may serve as a factor having a bad influence on the fuel efficiency of the vehicle. When one of the mechanical oil pump and the electric oil pump is omitted, an operating hydraulic pressure may not be stably supplied to the automatic transmission. In particular, when only the electric oil pump is used, it is not easy to perform a control operation for dealing with a defect which may occur in supplying a hydraulic pressure to the automatic transmission, due to a trouble of a solenoid or the like. Furthermore, when a hydraulic pressure required for the electric oil pump is set to be fixed to an excessively high hydraulic pressure at the time at which a hydraulic pressure supply defect occurs, power may be wasted to drive the electric oil pump, and parts may be damaged by over-current. 
         [0008]    The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
       BRIEF SUMMARY 
       [0009]    Various aspects of the present invention provide for an oil pump system of a hybrid vehicle, which is capable of stably supplying an operating hydraulic pressure to an automatic transmission using only an electric oil pump, and a method for controlling the same. 
         [0010]    The present invention has also been made in an effort to provide an oil pump system of a hybrid vehicle, which is capable of minimizing power waste even when a defect occurs in supplying a hydraulic pressure to an automatic transmission, and a method for controlling the same. 
         [0011]    Various aspects of the present invention provide for an oil pump system of a hybrid vehicle, which supplies an operating hydraulic pressure to an automatic transmission of the hybrid vehicle. The oil pump system includes: an automatic transmission control unit controlling operation of the automatic transmission; an electric oil pump pumping oil to generate an operating hydraulic pressure which is to be supplied to the automatic transmission; and an oil pump control unit receiving information on a state of the automatic transmission from the automatic transmission control unit and controlling operation of the electric oil pump. 
         [0012]    The operating hydraulic pressure supplied to the automatic transmission may be generated only through the electric oil pump which is electrically operated. 
         [0013]    When a hydraulic pressure supply defect occurs in the automatic transmission, the oil pump control unit may perform control to constantly fix the operating hydraulic pressure of the automatic transmission, which is generated through the electric oil pump. 
         [0014]    The constantly-fixed operating hydraulic pressure may be set to be equal to or more than an operating hydraulic pressure generated through a normal operation of the electric oil pump. 
         [0015]    When the operating hydraulic pressure of the automatic transmission is controlled to be constantly fixed, the automatic transmission control unit may perform control to reduce output torque required for the automatic transmission. 
         [0016]    The electric oil pump may be controlled to an RPM corresponding to a required operating hydraulic pressure of the automatic transmission, which is reduced according to the reduced output torque of the automatic transmission. 
         [0017]    The RPM of the electric oil pump may be set by a map on relationship among oil temperature, hydraulic pressure, and the RPM of the electric oil pump, which is stored in the oil pump control unit. 
         [0018]    Various aspects of the present invention provide for a method for controlling an oil pump system which supplies an operating hydraulic pressure to an automatic transmission of a hybrid vehicle using an electric oil pump. The method includes: determining whether or not a hydraulic pressure supply defect occurred in the automatic transmission; fixing the operating hydraulic pressure supplied to the automatic transmission; reducing output torque required for the automatic transmission; and controlling an RPM of the electric oil pump. 
         [0019]    When it is determined that no hydraulic pressure supply defect occurred in the automatic transmission, the electric oil pump may be normally operated. 
         [0020]    When it is determined that a hydraulic pressure supply defect occurred in the automatic transmission, the operating hydraulic pressure supplied to the automatic transmission may be fixed. 
         [0021]    When the operating hydraulic pressure supplied to the automatic transmission is fixed, the output torque required for the automatic transmission may be reduced. 
         [0022]    A required operating hydraulic pressure of the automatic transmission may decrease according to the reduced output torque of the automatic transmission, and the RPM of the electric oil pump may be controlled as the required operating hydraulic pressure of the automatic transmission decreases. 
         [0023]    The RPM of the electric oil pump may be controlled to an RPM set by a map on relationship among the electric oil pump, oil temperature, and hydraulic pressure. 
         [0024]    The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a schematic diagram of an exemplary oil pump system of a hybrid vehicle according to the present invention. 
           [0026]      FIG. 2  is a flow chart for explaining an exemplary method for controlling the oil pump system of the hybrid vehicle according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0028]      FIG. 1  is a schematic diagram of an oil pump system of a hybrid vehicle according to various embodiments of the present invention. 
         [0029]    As illustrated in  FIG. 1 , the oil pump system of the hybrid vehicle according to various embodiments of the present invention includes an automatic transmission  50 , a transmission control unit (TCU)  90 , an electric oil pump (EOP)  60 , and an electric oil pump unit (OPU)  70 . Furthermore, a power train system of the hybrid vehicle includes an engine  20 , a hybrid starter and generator (HSG)  22 , a motor  40 , a battery  10 , an engine clutch  30 , an automatic transmission  50 , and an axle  80 . 
         [0030]    Power transmission of the hybrid vehicle is performed as follows. Power generated from the engine  20  or the motor  40  is selectively transmitted to an input shaft  52  of the automatic transmission  50 , and power output to an output stage  54  of the automatic transmission  50  is transmitted to the axle  80  through a final reduction device  84  and a differential gear device  86 . Furthermore, as the axle  80  rotates wheels  82 , the hybrid vehicle is operated through the power generated from the engine  20  or the motor  40 . 
         [0031]    The battery  10  supplies a driving voltage to the motor  40 . That is, the battery  10  stores a high voltage. Furthermore, the HSG  22  operates as a motor to start the engine  20  or operates as a generator in a state where the engine  20  is driven, thereby charging the battery  10 . The battery  10  may also be charged through energy regenerated by the motor  40  during a coasting operation of the hybrid vehicle. Furthermore, the engine clutch  30  selectively connects the engine  20  and the motor  40 . That is, the powers of the engine  20  and the motor  40  are connected or blocked by the engine clutch  30 . 
         [0032]    The power transmission and regenerative braking of the hybrid vehicle and a fluid clutch (not illustrated) for selectively blocking power transmitted to the automatic transmission  50  are obvious to a person of an ordinary skill in the art. Thus, the detailed descriptions thereof are omitted herein. 
         [0033]    The automatic transmission  50  serves to change speed by changing a gear ratio of the input shaft  52  to the output stage  54 . Furthermore, the automatic transmission  50  changes speed according to operations of a plurality of friction elements including one or more brakes (not illustrated) and one or more clutches (not illustrated). The plurality of friction elements are operated to be coupled or decoupled by an operating hydraulic pressure supplied to the automatic transmission  50 . 
         [0034]    The TCU  90  serves to control torque of the automatic transmission  50  and the operation of the friction elements. Since the operations of the TCU  90  and the automatic transmission  50  are obvious to a person of an ordinary skill in the art, the detailed descriptions thereof are omitted herein. 
         [0035]    The oil pump system of the hybrid vehicle may properly supply an operating hydraulic pressure for operating the friction elements of the automatic transmission  50 , in order to smoothly perform the power transmission of the hybrid vehicle. 
         [0036]    The electric oil pump  60  is connected to the automatic transmission  50 . Furthermore, the electric oil pump  60  may be embedded in the automatic transmission  50 . The electric oil pump  60  pumps oil to supply an operating hydraulic pressure to the automatic transmission  50 . In the oil pump system of the hybrid vehicle according to various embodiments of the present invention, only the electric oil pump  60  generates an operating hydraulic pressure, and supplies the generated operating hydraulic pressure to the automatic transmission  50 . 
         [0037]    The OPU  70  is connected to the electric oil pump  60 , and controls the drive of the electric oil pump  60 . Furthermore, the OPU  70  is connected to the TCU  90 , and controls the drive of the electric oil pump  60  according to information on the state of the automatic transmission  50 , which is received from the TCU  90 . 
         [0038]    Hereafter, referring to  FIG. 2 , a method for controlling the oil pump system of the hybrid vehicle according to various embodiments of the present invention will be described. 
         [0039]      FIG. 2  is a flow chart for explaining the method for controlling the oil pump system of the hybrid vehicle according to various embodiments of the present invention. 
         [0040]    When the oil pump system of the hybrid vehicle is operated (S 100 ), the TCU  90  determines whether or not a hydraulic pressure supply defect occurred in the automatic transmission  50  (S 110 ). For example, the hydraulic pressure supply defect may include a trouble of a solenoid (not illustrated) which supplies a hydraulic pressure to the friction elements. 
         [0041]    When it is determined that no hydraulic pressure supply defect occurred in the automatic transmission  50 , the TCU  90  transmits information on the normal state of the automatic transmission  50  to the OPU  70 . Furthermore, the OPU  70  controls the electric oil pump  60  to normally operate (S 130 ). The normal operation of the electric oil pump  60  may be set by a person of an ordinary skill in the art, based on the generated operating hydraulic pressure. 
         [0042]    When it is determined that a hydraulic pressure supply defect occurred in the automatic transmission  50 , the TCU  90  transfers information on the hydraulic pressure supply defect state of the automatic transmission  50  to the OPU  70 . Furthermore, the OPU  70  controls the drive of the electric oil pump  60  to constantly fix the operating hydraulic pressure supplied to the automatic transmission  50  from the electric oil pump  60  (S 120 ). The constantly-fixed operating hydraulic pressure is set to be equal to or more than an operating hydraulic pressure generated through the normal operation of the electric oil pump  60 . For example, when the operating hydraulic pressure generated through the normal operation of the electric oil pump  60  varies in the range of 11 bar to 16 bar, the operating hydraulic pressure in the hydraulic pressure supply defect state of the automatic transmission  50  may be fixed to 16 bar or more. 
         [0043]    However, when the operating hydraulic pressure is continuously fixed to more than the operating hydraulic pressure generated through the normal operation of the electric oil pump  60  for a predetermined time, an operating hydraulic pressure higher than needed may be supplied, power may be wasted to drive the electric oil pump  60 , and parts may be damaged by over-current. 
         [0044]    Thus, when the operating hydraulic pressure supplied to the automatic transmission  50  is constantly fixed (S 120 ), the TCU  90  performs control to reduce output torque of the automatic transmission  50  (S 140 ). When the output torque of the automatic transmission  50  is reduced, the operating hydraulic pressure required from the automatic transmission  50  may be reduced. The reduced output torque and the reduced required operating hydraulic pressure are set by a person of an ordinary skill in the art. 
         [0045]    Hereinafter, the reduced output torque will be referred to as a limit torque, and the reduced required operating hydraulic pressure will be referred to as a limit hydraulic pressure. The limit torque is set in a range where the power transmission of the automatic transmission  50  is smoothly performed. Furthermore, the limit hydraulic pressure set according to the limit torque is set in a range where the electric oil pump  60  is smoothly driven. 
         [0046]    When the output torque of the automatic transmission  50  is reduced (S 140 ) and the limit torque and the limit hydraulic pressure are set, the OPU  70  extracts information from a map (S 150 ). The OPU  70  controls the RPM of the electric oil pump  60  according to the information extracted from the map (S 160 ). The map stores information on the relationship among oil temperature, hydraulic pressure, and the RPM of the electric oil pump  60 . That is, when the information of the map is used, the RPM of the electric oil pump  60  may be set according to the limit hydraulic pressure and the current oil temperature. 
         [0047]    When the RPM of the electric oil pump  60  is controlled (S 160 ), the hybrid vehicle is operated in a limp-home mode (S 170 ), and the control for the oil pump system of the hybrid vehicle is ended (S 180 ). 
         [0048]    According to the embodiment of the present invention, as only the electric oil pump  60  is used, the production cost may be reduced, and the fuel efficiency may be improved. Furthermore, as the map about oil temperature, hydraulic pressure, and the RPM of the electric oil pump  60  is used, the hydraulic pressure may be stably supplied even when a defect occurs in supplying the hydraulic pressure to the automatic transmission  50 , and the waste of power may be minimized. 
         [0049]    The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.