Abstract:
A method of controlling an electric oil pump in a hybrid vehicle controls, at an ultra-low temperature, the electric oil pump so that the number of revolutions thereof is not unnecessarily increased, so as to prevent unnecessary power consumption of the battery, thereby contributing to an increase in fuel efficiency, to prevent unnecessary noise, thereby improving the market quality of the vehicle, and to improve the endurance of the electric oil pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority of Korean Patent Application Number 10-2011-0131872 filed Dec. 9, 2011, the entire contents of which application is incorporated herein for all purposes by this reference. 
         [0002]    BACKGROUND OF INVENTION 
         [0003]    1. Field of Invention 
         [0004]    The present invention relates, in general, to a method of controlling an electric oil pump in a hybrid vehicle and, more particularly, to a method of controlling an electric oil pump at an ultra-low temperature. 
         [0005]    2. Description of Related Art 
         [0006]    A hybrid vehicle is provided with an electric oil pump, which can operate irrespective of the operation of an engine, in addition to a mechanical oil pump, which is provided inside a transmission, so that hydraulic pressure necessary for the transmission can be supplied even in a situation in which, for example, the engine does not operate. 
         [0007]    The above-mentioned method of controlling an electric oil pump of the related art is generally carried out as shown in  FIG. 1 . The electric oil pump is controlled following a target number of revolutions that is provided from a transmission control unit (TCU). In order to ensure responsibility at an early stage of the startup of the electric oil pump, the electric oil pump is controlled in an open loop up to a predetermined reference number of revolution, thereby rapidly increasing the number of revolution of the electric oil lamp. Once the number of revolutions exceeds the reference number of revolutions, closed loop control mode is performed by following the target number of revolutions that is provided from the TCU. 
         [0008]    In the control method as described above, the reference number of revolutions is set in consideration of the viscosity of oil of the transmission, so that an intended oil pressure can be rapidly built up. 
         [0009]    However, in an ultra-low-temperature state, such as at −10° C. or less, the viscosity of the oil is relatively greater than that of the oil at room temperature, a sufficient amount of oil pressure can be built up even if the electric oil pump is rotated at a relatively small number of revolutions. 
         [0010]    Therefore, in the ultra-low-temperature state, it may be inappropriate to control the electric oil pump, which is set to the room temperature state, in an open loop up to a reference number of revolutions. 
         [0011]    As shown in  FIG. 2 , when the reference number of revolutions that is appropriately set to the room temperature state is 500 RPM, even if the target number of revolutions provided from the TCU is merely 300 RPM at an early stage, the electric oil pump is controlled in an open loop up to the reference number of revolutions of 500 RPM by the same method as that of the related art. Only after the number of revolutions has reached the reference number of revolutions, performed is a closed loop control mode, which follows the target number of revolutions. This consequently leads to a situation in which the number of revolutions of the electric oil pump is unnecessarily increased, as indicated by “A” in  FIG. 2 . 
         [0012]    When the number of revolutions of the electric oil pump is needlessly increased like this, the battery unnecessarily consumes electrical power, resulting in an adverse effect on fuel efficiency. In particular, this unnecessarily causes noise, thereby reducing the market quality of a vehicle, and is undesirable for the endurance of the vehicle, which is problematic. 
         [0013]    An exemplar of the related art is Korean Patent Application No. KR 10-2009-0045990 A. 
         [0014]    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. 
       SUMMARY OF INVENTION 
       [0015]    Various aspects of the present invention provide for a method of controlling an electric oil pump in a hybrid vehicle, in which the electric oil pump is controlled so that the number of revolutions thereof is not unnecessarily increased at an ultra-low temperature, so as to prevent unnecessary power consumption of the battery, thereby contributing to an increase in fuel efficiency, to prevent unnecessary noise, thereby improving the market quality of the vehicle, and to improve the endurance of the electric oil pump. 
         [0016]    Various aspects of the present invention provide for a method of controlling an electric oil pump in a hydraulic vehicle. The method includes the steps of: measuring an oil temperature of a transmission; determining whether or not the oil temperature of the transmission is an ultra-low temperature that does not exceed a predetermined reference temperature; controlling the electric oil pump in an open loop up to a target number of revolutions when the oil temperature of the transmission is the ultra-low temperature as a result of the step of determining whether or not the oil temperature of the transmission is an ultra-low temperature; and controlling the electric oil pump in a closed loop in order to follow the target number of revolutions after the step of controlling the electric oil pump in the open loop is ended. 
         [0017]    At an ultra-low temperature, the electric oil pump of the hybrid vehicle may be controlled so that the number of revolutions thereof is not unnecessarily increased, so as to prevent unnecessary power consumption of the battery, thereby contributing to an increase in fuel efficiency, to prevent unnecessary noise, thereby improving the market quality of the vehicle, and to improve the endurance of the electric oil pump. 
         [0018]    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 
         [0019]      FIG. 1  is a graph showing a process of the related art, which controls an electric depicting pump at room temperature. 
           [0020]      FIG. 2  is a graph depicting a process of the related art, which controls an electric depicting pump at ultra-low temperature. 
           [0021]      FIG. 3  is a process view depicting an exemplary method of controlling an electric oil pump in a hybrid vehicle according to the present invention. 
           [0022]      FIG. 4  is a graph depicting an exemplary process of controlling an electric oil pump at ultra-low temperature according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    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. 
         [0024]    Referring to  FIG. 3 , a method of controlling an electric oil pump in a hybrid vehicle according to various embodiments of the invention includes oil temperature-measuring step S 10  of measuring the oil temperature of a transmission, ultra-low temperature determination step S 20  of determining whether or not the oil temperature of the transmission is an ultra-low temperature that does not exceed a predetermined reference temperature, first open loop control step S 30  of controlling the electric oil pump in an open loop up to the target number of revolutions, and closed loop control step S 40  of controlling the electric oil pump in a closed loop in order to follow the target number of revolutions. 
         [0025]    When the operation of the electric oil pump is started at an ultra-low-temperature state, the electric oil pump is not unconditionally controlled in an open loop up to a predetermined reference number of revolutions unlike the related art. Rather, the electric oil pump is controlled in the open loop up to a target number of revolutions that is provided from a transmission control unit (TCU), and after that, is controlled in a closed loop. This consequently excludes an excessive initial operation, which exceeds the target number of revolutions, from the electric oil pump, thereby increasing fuel efficiency by preventing unnecessary energy consumption, decreasing noise, and helping to improve the durability of the electric oil pump. 
         [0026]    The predetermined reference temperature in the ultra-low temperature determination step S 20  is set in consideration of the effect that a change in the viscosity of oil in the transmission takes on the formation of oil pressure in response to the operation of the electric oil pump. In various embodiments, the reference temperature may be set in the range of at least −10° C. or less. 
         [0027]    As a result of the ultra-low temperature determination step S 20 , when it is not the ultra-low-temperature state, the second open loop control step S 50  is performed to control the electric oil pump in an open loop up to the predetermined reference number of revolutions, and then the closed loop control step S 40  is performed after the second open loop control step S 50 . 
         [0028]    That is, the second open loop control step S 50  is the same as a control method of the related art in a common situation. 
         [0029]    Therefore, the reference number of revolutions in the second open loop control step S 50  is set in consideration of the responsibility of the electric oil pump based on the room temperature state, and is a number of revolutions that is higher than the target number of revolutions in the first open loop control step S 30 . 
         [0030]    That is, for example, as shown in  FIG. 4 , when the reference number of revolutions is set at 500 RPM in consideration of the viscosity of the transmission oil at room temperature and in consideration of the responsibility following the start-up of the electric oil pump, the target number of revolutions that is calculated and presented by the TCU at the first open loop control step S 30  is a number of revolutions that is of course smaller than the reference number of revolutions. The relatively high target number of revolutions at the early stage of the startup of the electric oil pump is 300 RPM that is smaller than the reference number of revolutions 500 RPM. This conversely means that the reference number of revolutions is set to be greater than the target number of revolutions in the first open loop control step S 30 . 
         [0031]    The open loop control can be performed in duty control mode in which only a duty value is provided to the motor of the electric oil pump, whereas the closed loop control can be performed in proportional integration (PI) control mode in which the target number of revolutions is followed by feeding back the number of revolutions of the electric oil pump. Of course, in addition to the above, proportional/integral/derivative control (PID) mode or the like may be used as a particular method of closed loop control. 
         [0032]    When comparing  FIG. 4  with  FIG. 2 , it can be appreciated that an overshoot at the early stage of the operation of the electric oil pump is solved, and that the number of revolutions of the electric oil pump is not unnecessarily increased. Accordingly, it is of course possible to increase the fuel efficiency of a vehicle, reduce noise in the vehicle, and increase the durability of the electric oil pump. 
         [0033]    For convenience in explanation and accurate definition in the appended claims, the terms upper or lower, front or rear, inside or outside, and etc. are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
         [0034]    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.