Abstract:
Disclosed is a system for controlling a hybrid vehicle when the state of charge of a high voltage battery is sufficiently low. In particular, a motor unit is connected to an engine via a rotation element, a high voltage battery is electrically connected to the motor unit to provide power thereto, and a low voltage battery is electrically connected to the high voltage battery through a two-way converter. Advantageously, a control portion is configured to boost voltage of the low voltage battery to supply the high voltage battery with high voltage through the two-way converter when the state of charge of the high voltage battery falls below a first predetermined value.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0079055 filed in the Korean Intellectual Property Office on Aug. 9, 2011, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention The present invention relates to a hybrid vehicle in which the output from an engine and a motor are independently controlled according to driving conditions so as to reduce fuel and improve power efficiency of the hybrid vehicle overall. 
         [0003]    (b) Description of the Related Art 
         [0004]    A hybrid vehicle efficiently combines different types of power sources to in order to power a vehicle. Typically, hybrid vehicles combines an engine which generates torque through fuel combustion (gasoline, fossil fuel) and an electric motor that generates torque through battery power. 
         [0005]    Hybrid vehicles can run in either an EV (electric vehicle) mode that uses only torque from the electric motor, an HEV (hybrid electric vehicle) mode that uses torque from the engine as the main source of power and torque from the electric motor as auxiliary power, or a regenerative braking (Regenerative Braking, RB) mode energy retrieved from braking and inertia energy are used to charge a battery. 
         [0006]    Hybrid vehicles, as stated above, (1) use mechanical energy from the engine and electrical energy from a battery installed therein, (2) utilize an optimized operating region within the engine and the drive motor, and (3) simultaneously retrieve the braking energy through the drive motor so that the fuel consumption efficiency is improved. 
         [0007]    Currently, hybrid vehicles may chose from various types of power delivery systems in order to implement their intended design. These various types of power delivery systems are chosen based on the orientation and structure of the overall system and power provide from the engine and motor respectively. However, most hybrid vehicle manufactures utilize either a parallel type power delivery system or an in-line/series type power delivery system. 
         [0008]    In a series or in-line type power delivery system, the engine and the motor are connected in series to have a simple structure and a simple control logic compared to a parallel power delivery system. However, the energy transformation in the series/in-line power delivery system is problematic, because the mechanical energy from the engine/generator is stored in the battery and then the motor uses the stored energy to drive the vehicle thereof. 
         [0009]    The parallel type power delivery system has a more complex structure and control logic in comparison to the series power delivery system, but the mechanical energy of the engine and the battery are simultaneously used to improve energy efficiency and therefore the parallel system has been widely adopted for use in passenger vehicles. 
         [0010]    In a hybrid vehicle, driving torque is generated by the electric/drive motor when the vehicle initially starts to move or is moving at slow speeds, because this is when the engine efficiency is deteriorated in comparison to the motor efficiency. That is, the drive motor rather than the engine is used to initially move the vehicle in the parallel type hybrid vehicle, thus increase the engines overall fuel efficiency. 
         [0011]    Further, after the vehicle begins to move at a sufficient speed due to torque provided by the drive motor, a motor/generator (ISG: integrated starting and generating) starts the engine so that the engine can now output a torque along with the motor to provide a simultaneous drive force to the vehicle. 
         [0012]    However, when a high voltage battery used to provide power to the drive motor or the motor/generator is dead or is operated at a low temperature, there is no way to start the engine in the vehicle and thus the driver is stranded. Further, although the electricity from the high voltage battery is supplied only to the engine, when the SOC (state of charge) is low, a problem may occur where the there is not enough energy to start the engine when it is required by the power delivery system, thus eventually stranding the consumer if he or she cannot get a charging station before the high voltage battery is completely dead. 
         [0013]    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 
       [0014]    The present invention has been made in an effort to provide a hybrid vehicle which temporally starts an engine to charge a high voltage battery, when the engine is not started by the drive motor or the motor/generator when a SOC of a high voltage battery is low or a temperature thereof is low. 
         [0015]    A hybrid vehicle according to an exemplary embodiment of the present invention may include a motor unit connected to an engine through a rotation element, a high voltage battery electrically connected to operate the motor unit, a low voltage battery electrically connected to the high voltage battery through a two-way converter, and a control portion configured to boost voltage of the low voltage battery to supply the high voltage battery with high voltage through the two-way converter. 
         [0016]    A detecting portion is configured to detect a state of charge of the high voltage battery. The control portion boosts the voltage of the low voltage battery through the two-way converter, supplies the high voltage battery with high voltage, and controls the motor unit to start the engine, when it is determined that the state of charge of the high voltage battery is lower than a predetermined value. 
         [0017]    The motor unit may include a first motor that one side thereof is connected to the engine and the other side thereof is connected to the transmission, and a second motor that starts the engine or uses the torque of the engine to generate electricity. The control portion then the first motor or the second motor to start the engine. 
         [0018]    The high voltage battery may operate the first motor through the first inverter and the high voltage battery may operate the second motor through the second inverter. The control portion may make the high voltage battery charge the low battery through the two-way convertor, if the state of charge that is detected by the detecting portion is larger than a predetermined value. The control portion may generate an emergency signal for activating an emergency charging mode, if the state of charge that is detected by the detecting portion is lower than a predetermined value. The motor unit may use the torque of the engine to charge the high voltage battery and the control portion generates a release signal for releasing the emergency charging mode, when the state of charge that is detected by the detecting portion is larger than a predetermined value. 
         [0019]    The two-way converter may be a two-way DC/DC converter that transforms a DC low voltage to a DC high voltage or a DC high voltage to a DC low voltage, and the hybrid vehicle may further include a temperature detecting portion that detects a temperature of the high voltage battery. The control portion then boosts the voltage of the low voltage battery and operates the motor unit to start the engine, when the temperature detected by the temperature detecting portion is less than a predetermined value. 
         [0020]    As stated above, a two-way DC/DC converter that is disposed between a high voltage battery and a low voltage battery is used to make the low voltage battery charge the high voltage battery so that the engine can be instantly started and to charge the high voltage battery above a predetermine value when the state of charge or a temperature of a high voltage battery is lower than a predetermined value in the hybrid vehicle according to an exemplary embodiment of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic diagram of a hybrid vehicle according to an exemplary embodiment of the present invention. 
           [0022]      FIG. 2  is a schematic diagram showing a situation in which the state of charge of a high voltage battery is lower than a predetermined value according to an exemplary embodiment of the present invention. 
           [0023]      FIG. 3  is a schematic diagram showing a power flow in a condition that a low voltage battery charges a high voltage battery in a hybrid vehicle according to an exemplary embodiment of the present invention. 
           [0024]      FIG. 4  is a schematic diagram showing a power flow in a condition that an engine charges a high voltage battery in a hybrid vehicle according to an exemplary embodiment of the present invention hybrid vehicle. 
           [0025]      FIG. 5  is a schematic diagram showing a power flow in a condition that a high voltage battery operates a first motor and charges a low voltage battery in a hybrid vehicle according to an exemplary embodiment of the present invention. 
           [0026]      FIG. 6  is a flowchart for controlling a hybrid vehicle according to an exemplary embodiment of the present invention hybrid vehicle. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0027]    An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
         [0028]      FIG. 1  is a schematic diagram of a hybrid vehicle according to an exemplary embodiment of the present invention. Referring to  FIG. 1 , a hybrid vehicle includes an engine  100 , a clutch  110 , a first motor  120 , a transmission  130 , a second motor  140 , a first inverter  150 , a second inverter  160 , a high voltage battery  170 , a two-way converter  180 , a low voltage battery  190 , a control portion  200 , and a drive wheel  210 . 
         [0029]    The first and second motor  120  and  140  can be classified as a motor unit. The first motor is referred to herein also as a main drive motor and the second motor is referred to herein also as a motor/generator. The engine  100 , the clutch  110 , the first motor  120 , and the transmission  130  are sequentially disposed in series. An output shaft of the engine  100  transfers torque to the first motor  120  through the clutch  110 , and the first motor  120  adds the motor torque to the engine torque that is transferred by the clutch  110  to input the combinational torque to the transmission  130 . The transmission  130  then transfers the torque to the drive wheel through a power delivery assembly. 
         [0030]    The second motor  140  is connected to the engine  100  via a torque transmit device such as a belt. The second motor  140  may be embodied as a motor/generator (ISG; integrated starting and generating) which is configured to start the engine  100  or receive the torque from the engine  100  to generate electricity and charge the high voltage and low voltage batteries  170  and  190 , respectively. 
         [0031]    The first inverter  150  is connected to the first motor  120 , and the second inverter  160  is connected to the second motor  140 . The high voltage battery  170  is electrically connected to the first inverter  150  and the second inverter  160  so that the high voltage battery  170  can supply the first inverter  150  and the second inverter  160  with electricity. The electrical energy that is charged in the high voltage battery  170  is transferred to the first inverter  150  or the second inverter  160  to operate the first motor  120  or the second motor  140 . 
         [0032]    The high voltage battery  170  is connected to the low voltage battery  190  through the two-way converter ( 180 , DC/DC). The low voltage battery  190  may be a 12 V battery in an exemplary embodiment of the present invention, but various kinds including 24 volt batteries can also be applied thereto. 
         [0033]    The control portion  200  is configured to control the first inverter  150 , the second inverter  160 , and the two-way converter  180  and constituent elements of the transmission  130  so as to control the engine  100 , the first motor  120 , and the second motor  140  therefrom. Furthermore, the control portion  200  may be embodied as a controller or computer device which is capable of controlling multiple devices within an automotive structure. 
         [0034]    A method that the control portion  200  controls a hybrid vehicle refers to techniques well known in the art and thus, the detailed descriptions thereof has been omitted in the exemplary embodiment of the present invention. 
         [0035]      FIG. 2  is a schematic diagram showing a situation in which the state of charge of a high voltage battery is lower than a predetermined value in a hybrid vehicle according to an exemplary embodiment of the present invention. Referring to  FIG. 2 , detailed descriptions for a state of charge detecting portion that detects SOC (state of charge) of the high voltage battery  170  are omitted. 
         [0036]    More specifically, the state of charge detecting portion is configured to detect a state of charge of the high voltage battery  170  and the control portion  200  is configured to determine whether the state of charge of the high voltage battery  170  detected by the state of charge detecting portion is less than a predetermined value. 
         [0037]    When the engine  100  stops operating, the engine  100  cannot be started by the second motor  140  or the first motor  120 , because the state of charge of the high voltage battery  170  is too low in this situation. Accordingly, the engine  100  cannot be operated, because the charging rate of the high voltage battery  170  is less than a predetermined value. 
         [0038]    To rectify the above problem,  FIG. 3  shows a schematic diagram with a power flow that is provided to allow a low voltage battery to charge a high voltage battery in a hybrid vehicle according to an exemplary embodiment of the present invention. Referring to  FIG. 3 , the control portion  200  controls the two-way converter  180  to boost voltage of the low voltage battery  190  so that the electrical energy of the low voltage battery  190  is able to charge the high voltage battery  170 . 
         [0039]    In most cases, the voltage of the high voltage battery  170  is reduced by the converter  180  to charge the low voltage battery  190 . However, as described above, when the charging rate of the high voltage battery  170  is less than a predetermined value, the two-way converter  180  charges the high voltage battery  170  by boosting the voltage of the low voltage battery  190 . Accordingly, the high voltage battery  170  is charged by the low voltage battery  190  through the two-way converter  180  and the first motor  120  or the second motor  140  may then be used to start the engine  100 . 
         [0040]      FIG. 4  is a schematic diagram showing a power flow for a situation in which an engine charges a high voltage battery in a hybrid vehicle according to an exemplary embodiment of the present invention. As described in  FIG. 3 , the engine is started. Referring to  FIG. 4 , the engine  100  securely charges the high voltage battery  170  through the second motor  140  and the second inverter  160 . 
         [0041]      FIG. 5  is a schematic diagram showing a power flow for a situation in which a high voltage battery operates a first motor and charges a low voltage battery in a hybrid vehicle according to an exemplary embodiment of the present invention. As described in  FIG. 4 , the high voltage battery is charged at this time. Referring to  FIG. 5 , while the high voltage battery  170  is charged above a predetermined charging rate, the first motor  120  is operated through the first inverter  150  to start the engine  100 . Further, the high voltage battery  170  charges the low voltage battery  190  through the two-way converter  180 . 
         [0042]    If the state of charge of the high voltage battery  170  becomes greater than a predetermined value in an exemplary embodiment of the present invention, the engine  100  is operated by the second motor  140  and the high voltage battery  170  is charged again through the second motor  140 . The predetermined value of the state of charge of the high voltage battery  170  can be varied depending on test data or design specifications in an exemplary embodiment of the present invention. 
         [0043]      FIG. 6  is a flowchart for controlling a hybrid vehicle according to an exemplary embodiment of the present invention hybrid vehicle. Referring to  FIG. 6 , a control starts at S 600  determining whether the state of charge of the high voltage battery  170  is greater than a predetermined value, which is able to start the engine, in a S 610 . If it is determined that the state of charge of the high voltage battery  170  is greater than the predetermined value in the S 610 , the engine  100  is started via the first motor  120  in a S 680 . 
         [0044]    If it is determined that the state of charge of the high voltage battery  170  is less than the predetermined value in the S 610 , the control portion  200  generates an emergency signal to notify the driver of an emergency charging mode. Then, the two-way converter ( 180 , DC/DC converter) boosts the voltage of the low voltage battery  190  to charge the high voltage battery, accordingly. Once the state of charge of the high voltage battery  170  exceeds the predetermined value in a S 630 , the second motor  140  is operated to start the engine  100 . 
         [0045]    Once it is determined that the engine  100  is operational, the voltage boosting of the two-way converter  180  is stopped in a S 640 , and the engine  100  charges the high voltage battery  170  through the second motor  140 . The state of charge of the high voltage battery  170  is then monitored by the controller until it is determined that the state of charge of the high voltage battery is greater than a predetermined value in a S 650 . Here, the predetermined value can be varied depending on the design specification. 
         [0046]    The control portion  200  then generates an emergency release signal to notify the driver of an emergency charging mode release in a S 660  and reduces the voltage of the two-way converter  180  so that the high voltage battery  170  can charge the low voltage battery  190 . Further, when the engine  100  is not being operated, the first motor  120  configured to start the engine  100 . 
         [0047]    Thus, when the engine  100  cannot be started, because the state of charge of the high voltage battery or the temperature of the high voltage battery  170  is less than a predetermined value, the low voltage battery  190  is used to charge the high voltage battery  170  in the exemplary embodiment of the present invention. 
         [0048]    Further, as described above, when the temperature of the high voltage battery  170  is less than a predetermined value, the low voltage battery  190  is used to charge the high voltage battery  170  so that the battery performance can be promoted. Also, the temperature detecting portion (not shown) can be further included to detect the temperature of the high voltage battery. 
         [0049]    As described above, when the charging state of the high voltage battery  170  or the temperature thereof is less than a predetermined value, a two-way DC/DC converter is employed to utilize a low voltage battery  190  to charge the high voltage battery  170 , and thereby the engine  100  is instantly started and the engine  100  can securely charge the high voltage battery  170  without stranding the driver. 
         [0050]    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. 
       DESCRIPTION OF SYMBOLS 
       [0000]    
       
         
           
               100 : engine 
               110 : clutch 
               120 : first motor 
               130 : transmission 
               140 : second motor 
               150 : first inverter 
               160 : second inverter 
               170 : high voltage battery 
               180 : two-way converter 
               190 : low voltage battery 
               200 : control portion 
               210 : drive wheel