Abstract:
A regenerative braking system for a vehicle improves accuracy of a control. The regenerative braking system for a vehicle is operated by hydraulic pressure. The regenerative braking system may include a first cylinder adapted to directly generate hydraulic pressure by a driver&#39;s maneuver; a second cylinder adapted to generate hydraulic pressure necessary for braking of the vehicle and to deliver the hydraulic pressure to a wheel; a hydraulic pressure generator adapted to recognize braking force demanded by the driver and to generate hydraulic pressure; and a first valve interposed between the first cylinder and the second cylinder and adapted to selectively supply the hydraulic pressure generated by the first cylinder to the second cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0068107 filed Jul. 8, 2011, 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 a regenerative braking system for a vehicle. More particularly, the present invention relates to a regenerative braking system for a vehicle that improves accuracy of a control. 
         [0004]    2. Description of Related Art 
         [0005]    Generally, braking of a vehicle is performed by converting kinetic energy of the running vehicle into other types of energy. 
         [0006]    One of the braking of the vehicle is regenerative braking. According to the regenerative braking, a generator is driven or a motor is operated as a generator by the kinetic energy of the vehicle so as to generate electric energy, and a battery is charged by the electric energy. That is, the braking is performed by converting the kinetic energy of the vehicle into the electrical energy. Such regenerative braking is mainly used in an electric vehicle. 
         [0007]    Meanwhile, braking force demanded by a driver is sum of braking force of hydraulic pressure catching a wheel and regenerative braking force charging the battery in the regenerative braking. That is, a regenerative braking system generates the braking force of hydraulic pressure and the regenerative braking force respectively based on the braking force demanded by the driver. Herein, a hydraulic pressure corresponding to the braking force of hydraulic pressure is generated by a master cylinder. However, a target hydraulic pressure corresponding to the braking force of hydraulic pressure is not the same as an actual hydraulic pressure of the master cylinder. If a difference between the target hydraulic pressure and the actual hydraulic pressure is large, accuracy of a braking control may be deteriorated. 
         [0008]    For example, pistons used in a conventional master cylinder are provided with a seal. Herein, resistance of the seal is applied to a direction opposite to a moving direction of the piston, that is a direction to which the braking force of hydraulic pressure is applied. Therefore, as the resistance of the seal becomes large, the difference between the target hydraulic pressure and the actual hydraulic pressure becomes also large. That is, if a plurality of pistons is used in the master cylinder, it is difficult to reduce the number of seals or the resistance of the seals. 
         [0009]    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 
       [0010]    Various aspects of the present invention provide for a regenerative braking system for a vehicle having advantages of improving accuracy of a braking control. 
         [0011]    The present invention has been made in an effort to provide a regenerative braking system for a vehicle having further advantages of reducing product cost and improving operating efficiency by simplifying structures thereof. 
         [0012]    A regenerative braking system for a vehicle according to various aspects of the present invention is operated by hydraulic pressure and may include a first cylinder adapted to directly generate hydraulic pressure by a driver&#39;s maneuver; a second cylinder adapted to generate hydraulic pressure necessary for braking of the vehicle and to deliver the hydraulic pressure to a wheel; a hydraulic pressure generator adapted to recognize braking force demanded by the driver and to generate hydraulic pressure; and a first valve interposed between the first cylinder and the second cylinder and adapted to selectively supply the hydraulic pressure generated by the first cylinder to the second cylinder. 
         [0013]    The second cylinder may be adapted to generate the hydraulic pressure necessary for the braking of the vehicle by receiving the hydraulic pressure from the hydraulic pressure generator or receiving the hydraulic pressure from the first cylinder. 
         [0014]    The first cylinder may have a first piston and the second cylinder may have a second piston, wherein the second cylinder may further have an elastic member. 
         [0015]    One end of the first piston may contact with a push rod moved by the driver&#39;s maneuver. 
         [0016]    The push rod may push the one end of the first piston by the driver&#39;s maneuver and the first piston moves to a length direction thereof and applies pressure to fluid so as to generate the hydraulic pressure. 
         [0017]    The second cylinder may be divided into a first pressure chamber and a second pressure chamber by the second piston provided with a seal. 
         [0018]    The elastic member may be disposed in the second pressure chamber and may be adapted to elastically support the second piston. 
         [0019]    The first pressure chamber and the second pressure chamber may be respectively provided with hydraulic pressure lines connected to different wheels. 
         [0020]    The first cylinder may be connected to the first pressure chamber through a first hydraulic pressure line, and a first valve may be provided at the first hydraulic pressure line. 
         [0021]    The first hydraulic pressure line may be divaricated between the first valve and the first cylinder and may be connected to a reaction force generator, wherein a second valve may be provided at the divaricated hydraulic pressure line. 
         [0022]    The reaction force generator may be adapted to generate reaction force against force by which the push rod pushes the first piston when the first valve is closed and the second valve is open. 
         [0023]    The hydraulic pressure may be delivered to the first pressure chamber when the first valve is open. 
         [0024]    The first pressure chamber may be connected to the hydraulic pressure generator through a second hydraulic pressure line. 
         [0025]    The hydraulic pressure generator may be adapted to deliver the hydraulic pressure to the first pressure chamber or to receive the hydraulic pressure from the first pressure chamber. 
         [0026]    The hydraulic pressure generator may be connected to a reservoir tank through a third hydraulic pressure line. 
         [0027]    One end of a fourth hydraulic pressure line may be connected to the reservoir tank, and the other end thereof may be divaricated and connected to the first and second cylinders. 
         [0028]    The second pressure chamber may be connected to the hydraulic pressure generator through a fifth hydraulic pressure line such that the first pressure chamber and the second pressure chamber are controlled independently. 
         [0029]    The hydraulic pressure generator may be adapted to deliver the hydraulic pressure to the second pressure chamber or to receive the hydraulic pressure from the second pressure chamber. 
         [0030]    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 
         [0031]      FIG. 1  is a schematic diagram of an exemplary regenerative braking system for a vehicle according to the present invention. 
           [0032]      FIG. 2  is a schematic diagram of another exemplary regenerative braking system for a vehicle according to the present invention. 
           [0033]      FIG. 3  is a detailed view of a hydraulic pressure generator shown in  FIG. 1 . 
           [0034]      FIG. 4  is a detailed view of a hydraulic pressure generator shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    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. 
         [0036]    In a regenerative braking system for a vehicle according to various embodiments of the present invention, the number of pistons provided in a master cylinder is reduced, and two cylinders are disposed in parallel. Hereinafter, a regenerative braking system for a vehicle according to various embodiments of the present invention will be described in detail with reference to  FIGS. 1 to 4 . 
         [0037]      FIG. 1  is a schematic diagram of a regenerative braking system for a vehicle according to various embodiments of the present invention. 
         [0038]    As shown in  FIG. 1 , a regenerative braking system for a vehicle according to various embodiments of the present invention includes a first cylinder  100 , a second cylinder  200 , a reaction force generator  300 , a hydraulic pressure generator  400 , a reservoir tank  500 , and a plurality of hydraulic pressure lines. 
         [0039]    The first cylinder  100  generates hydraulic pressure by driver&#39;s maneuver. In addition, the first cylinder  100  is provide with a first piston  110  and a push rod  120 . 
         [0040]    The first piston  110  is provided in the first cylinder  100 . One end of the push rod  120  is connected to a pedal maneuverable by a driver and the other end of the push rod  120  contacts with the first piston  110 . Therefore, if the driver manipulates the pedal, the push rod  120  is moved and pushes the first piston  110 . The piston applies pressure to fluid filled in the first cylinder  100  and generates the hydraulic pressure. 
         [0041]    In this specification, it is exemplified that the push rod  120  is moved by the pedal manipulated by the driver. However, movement of the push rod  120  can be achieved by other means. 
         [0042]    The second cylinder  200  receives hydraulic pressure from the hydraulic pressure generator  400  and generates hydraulic pressure necessary for braking. In various embodiments, an accumulator is disposed between the hydraulic pressure generator  400  and the second cylinder  200 . 
         [0043]    Herein, the second cylinder  200  is a master cylinder generating the hydraulic pressure corresponding to braking force demanded by the driver. In addition, the accumulator accumulates and supplies the hydraulic pressure when needed. 
         [0044]    For example, if the driver presses down the pedal, a pedal stroke sensor detects a displacement of the pedal and delivers an electrical signal corresponding to the displacement to the hydraulic pressure generator  400 . In addition, the hydraulic pressure generator  400  receiving the signal delivers the hydraulic pressure corresponding to the braking force of hydraulic pressure demanded by the driver to the second cylinder  200  through the accumulator. Herein, the braking force of hydraulic pressure demanded by the driver, as described above, is braking force calculated by subtracting regenerative braking force from braking force demanded by the driver. 
         [0045]    The accumulator applied to a hydraulic pressure braking system is well known to a person skilled in the art, and thus detailed description thereof will be omitted. In this specification, the accumulator may be a high-pressure tank  430  (referring to  FIG. 3  and  FIG. 4 ). 
         [0046]    A second piston  210  is provided in the second cylinder  200 . In addition, the second cylinder  200  is divided into a first pressure chamber  220  and a second pressure chamber  230  by the second piston  210 . 
         [0047]    A seal  240  is provided at an exterior circumference of the second piston  210  and blocks fluid flow between the first pressure chamber  220  and the second pressure chamber  230 . 
         [0048]    The first pressure chamber  220  receives the hydraulic pressure from the accumulator. In addition, the hydraulic pressure necessary for the braking is generated by the first pressure chamber  220  and is delivered to a wheel  610 . Further, the second piston  210  is pushed by the hydraulic pressure generated at the first pressure chamber  220  and applies pressure to fluid filled in the second pressure chamber  230 . Therefore, hydraulic pressure is generated at the second pressure chamber  230 . 
         [0049]    The second pressure chamber  230  delivers the hydraulic pressure to a wheel  600 . In addition, an elastic member for elastically supporting the second piston  210  is provided in the second pressure chamber  230 . The elastic member moves the second piston  210  to an original position when the hydraulic pressure of the first pressure chamber  220  decreases. 
         [0050]    It is exemplified in  FIG. 1  and  FIG. 2  that a spring is used as the elastic member, but the elastic member is not limited to the spring. Any means for supplying restoring force to the second piston  210  can be used as the elastic member. 
         [0051]    The hydraulic pressures supplied to the wheels  600  and  610  operate a wheel cylinder and perform the braking of the vehicle. Herein, the wheel  600  connected to the second pressure chamber is different from that  610  connected to the first pressure chamber. For example, the wheels  600  are a front left wheel and a rear right wheel, and the wheels  610  are a front right wheel and a rear left wheel in various embodiments. In various embodiments, the wheels  600  are front left and right wheels, and the wheels  610  are rear left and right wheels. 
         [0052]    The hydraulic pressure generator  400  controls hydraulic pressure and flow of fluid in the regenerative braking system for a vehicle. In addition, the hydraulic pressure generator  400  calculates a target braking force of the vehicle and calculates a regenerative braking force and a braking force of hydraulic pressure according to the target braking force. Therefore, the hydraulic pressure generator  400  controls the hydraulic pressure and the flow of the fluid. 
         [0053]    The reservoir tank  500  prepares a volumetric change of the fluid according to pressure and temperature thereof That is, the reservoir tank  500  supplies the fluid when the regenerative braking system lacks the fluid and stores the fluid when excessive fluid is in the regenerative braking system. 
         [0054]    The hydraulic pressure lines includes a first hydraulic pressure line  710 , a second hydraulic pressure line  720 , a third hydraulic pressure line  730 , and a fourth hydraulic pressure line  740 , and further includes hydraulic pressure lines connecting the wheels  600  and  610  with the pressure chambers  220  and  230 . 
         [0055]    The first hydraulic pressure line  710  connects the first cylinder  100  with the first pressure chamber  220  of the second cylinder  200 . In addition, a first valve  250  is provided at the first hydraulic pressure line  710 . The first valve  250  is open or closed selectively so as to deliver the hydraulic pressure to the first pressure chamber  220  or not. 
         [0056]    Meanwhile, the first hydraulic pressure line  710  is divaricated between the first cylinder  100  and the first valve  250  and is connected to the reaction force generator  300 . In addition, a second valve  350  is provided at the divaricated the first hydraulic pressure line  710  so as to open or close it. Further, a piston and an elastic member are provided at the reaction force generator  300  such that reaction force against the hydraulic pressure delivered to the reaction force generator  300  can be generated. 
         [0057]    If the push rod  120  moves, the first piston  110  applies pressure to the fluid in the first cylinder  100  and the hydraulic pressure is generated. At this time, if the first valve  250  is closed and the second valve  350  is open, the hydraulic pressure is delivered to the reaction force generator  300  and the reaction force against the hydraulic pressure is generated. Resultantly, the reaction force is a reaction force to manipulation of a pedal done by the driver. 
         [0058]    A method for generating the reaction force by the reaction force generator  300  is not limited to the method described in this specification, and can be achieved variously by a person skilled in the art. 
         [0059]    If the hydraulic pressure is hard to be generated in the first pressure chamber  220  by the hydraulic pressure delivered from the accumulator, the hydraulic pressure generated at the first cylinder  100  is delivered to the first pressure chamber  220 . Such an operation is performed by opening the first valve  250 . That is, if the regenerative braking system operates normally, the first valve  250  is always closed. If the regenerative braking system does not operate normally, the first valve  250  is open. 
         [0060]    The second hydraulic pressure line  720  connects the first pressure chamber  220  with the hydraulic pressure generator  400 . 
         [0061]    If the hydraulic pressure of the first pressure chamber  220  is lowered, the hydraulic pressure of the first pressure chamber  220  is delivered to the hydraulic pressure generator  400  and lowering pressure is performed. If the hydraulic pressure of the first pressure chamber  220  is increased, the first pressure chamber  220  receives the hydraulic pressure from the hydraulic pressure generator  400  and increasing pressure is performed. 
         [0062]    The third hydraulic pressure line  730  connects the hydraulic pressure generator  400  with the reservoir tank  500 . The fluid flowing into the hydraulic pressure generator  400  through the second hydraulic pressure line  720  is discharged through the third hydraulic pressure line  730  and is then stored in the reservoir tank  500 . The reservoir tank  500  supplies the fluid to the regenerative braking system depending on the circumstances. 
         [0063]    The fourth hydraulic pressure line  740  connects the reservoir tank  500  with the first cylinder  100 . In addition, the fourth hydraulic pressure line  740  is divaricated between the reservoir tank  500  and the first cylinder  100 , and is connected to the second pressure chamber  230  of the second cylinder  200 . That is, the fluid stored in the reservoir tank  500  is supplied to the first cylinder  100  and the second pressure chamber  230 . 
         [0064]    The hydraulic pressure lines connecting the wheels  600  and  610  with the pressure chambers  220  and  230 , as described above, connects the first pressure chamber  220  and the second pressure chamber  230  with the different wheels  600  and  610 . 
         [0065]      FIG. 2  is a schematic diagram of a regenerative braking system for a vehicle according to various embodiments of the present invention. 
         [0066]    For convenience of description, the same constituent elements are represented by the same reference numerals, and detailed description thereto will be omitted. 
         [0067]    As shown in  FIG. 2 , a regenerative braking system for a vehicle according to various embodiments of the present invention further includes a fifth hydraulic pressure line  750 . 
         [0068]    The fifth hydraulic pressure line  750  connects the second pressure chamber  230  of the second cylinder  200  with the hydraulic pressure generator  400 . Therefore, the hydraulic pressures of the first pressure chamber  220  and the second pressure chamber  230  can be independently controlled by the hydraulic pressure generator  400 . 
         [0069]      FIG. 3  is a detailed view of a hydraulic pressure generator shown in  FIG. 1 . 
         [0070]    As shown in  FIG. 3 , the hydraulic pressure generator  400  according to various embodiments of the present invention includes a pump  410 , a motor  420 , a high-pressure tank  430 , and a pressure regulator  440 . 
         [0071]    At least one of the pumps  410  and the motors  420  can be provided in the hydraulic pressure generator  400 . 
         [0072]    The pump  410  pumps the fluid by the motor  420  and flows the fluid in the regenerative braking system. 
         [0073]    The high-pressure tank  430  is provided in the hydraulic pressure generator  400  so as to maintain the hydraulic pressure in the hydraulic pressure generator  400  to be higher than a predetermined pressure. That is, the fluid can be stored in the high-pressure tank  430 , and a space in which the fluid is stored is connected to hydraulic pressure lines exterior of the high-pressure tank  430 . In addition, the fluid stored in the high-pressure tank  430  is pressurized so as to maintain the hydraulic pressure in the high-pressure tank  430  to be higher than the predetermined pressure. Therefore, the fluid can flows out from the hydraulic pressure generator  400  smoothly. 
         [0074]    The pressure regulator  440  controls a plurality of pressure control valves and the hydraulic pressure of the regenerative braking system. 
         [0075]    In  FIG. 3  and  FIG. 4 , four pressure control valves  442 ,  444 ,  446 , and  448  are shown, but the number of pressure control valves is not limited to this. 
         [0076]    The second hydraulic pressure line  720  connected to the hydraulic pressure generator  400  has four branches in the pressure regulator  440 , and the four branches are connected respectively to four pressure control valves  442 ,  444 ,  446 , and  448 . In addition, the four pressure control valves  442 ,  444 ,  446 , and  448  are open or closed selectively so as to control the hydraulic pressure of the second cylinder  200  and the regenerative braking system. 
         [0077]    If the first and second pressure control valves  442  and  444  are open, the fluid in the hydraulic pressure generator  400  discharges from the hydraulic pressure generator  400  through the second hydraulic pressure line  720 . In addition, the discharged fluid flows into the first pressure chamber  220  through the second hydraulic pressure line  720 . Therefore, the hydraulic pressure of the first pressure chamber  220  increases and the hydraulic pressure of the second pressure chamber  230  also increases by operation of the second piston  210 . Therefore, the hydraulic pressure of the second pressure chamber  230  becomes the same as that of the first pressure chamber  220 . 
         [0078]    One or both of the first and second pressure control valves  442  and  444  can be open depending on the circumstances. 
         [0079]    If the third and fourth pressure control valves  446  and  448  are open, the fluid from the outside of the hydraulic pressure generator  400  flows in the hydraulic pressure generator  400  through the second hydraulic pressure line  720 . In addition, the inflow fluid passes through the third and fourth pressure control valves  446  and  448 . A portion of the inflow fluid flows in the pump  410  and the other portion of the inflow fluid flows out from the hydraulic pressure generator  400  through the third hydraulic pressure line  730 . Therefore, the hydraulic pressure of the first pressure chamber  220  connected to the hydraulic pressure generator  400  through the second hydraulic pressure line  720  is lowered, and the hydraulic pressure of the second pressure chamber  230  is also lowered by operation of the second piston  210 . Therefore, the hydraulic pressure of the second pressure chamber  230  becomes the same as that of the first pressure chamber  220 . 
         [0080]    One or both the third and fourth pressure control valves  446  and  448  can be open depending on the circumstances. 
         [0081]      FIG. 4  is a detailed view of a hydraulic pressure generator shown in  FIG. 2 . 
         [0082]    As shown in  FIG. 4 , the hydraulic pressure generator  400  according to various embodiments of the present invention further includes a fifth hydraulic pressure line  750 . In addition, the hydraulic pressure of the first pressure chamber  220  and the second pressure chamber  230  can be independently controlled by the fifth hydraulic pressure line  750 . Therefore, the hydraulic pressure can be controlled with more accuracy. 
         [0083]    The second hydraulic pressure line  720  connected to the hydraulic pressure generator  400  is divaricated into two branches in the pressure regulator  440 . One branch is connected to one of the first and second pressure control valves  442  and  444  and the other branch is connected to one of the third and fourth pressure control valves  446  and  448 . In addition, the fifth hydraulic pressure line  750  connected to the hydraulic pressure generator  400  is divaricated into two branches in the pressure regulator  440 . The two branches are connected to two control valves among four pressure control valves  442 ,  444 ,  446 , and  448  that are not connected to the second hydraulic pressure line  720 . 
         [0084]    The four pressure control valves  442 ,  444 ,  446 , and  448  are open or closed selectively so as to control the hydraulic pressure of the second cylinder  200  and the regenerative braking system. 
         [0085]    If the first and second pressure control valves  442  and  444  are open, the fluid in the hydraulic pressure generator  400  discharges from the hydraulic pressure generator  400  through the second hydraulic pressure line  720  and the fifth hydraulic pressure line  750 . In addition, the discharged fluid through the second hydraulic pressure line  720  flows into the first pressure chamber  220 , and the discharged fluid through the fifth hydraulic pressure line  750  flows into the second pressure chamber  230 . Therefore, the hydraulic pressure of the first pressure chamber  220  and the second pressure chamber  230  increases, and the hydraulic pressure of the second pressure chamber  230  becomes the same as that of the first pressure chamber  220  by operation of the second piston  210 . 
         [0086]    If the third and fourth pressure control valves  446  and  448  are open, the fluid from the outside of the hydraulic pressure generator  400  flows into the hydraulic pressure generator  400  through the second hydraulic pressure line  720  and the fifth hydraulic pressure line  750 . In addition, the inflow fluid passes through the third and fourth pressure control valves  446  and  448 . A portion of the inflow fluid flows in the pump  410  and the other portion of the inflow fluid flows out from the hydraulic pressure generator  400  through the third hydraulic pressure line  730 . Therefore, the hydraulic pressure of the first pressure chamber  220  connected to the hydraulic pressure generator  400  through the second hydraulic pressure line  720  is lowered, and the hydraulic pressure of the second pressure chamber  230  connected to the hydraulic pressure generator  400  through the fifth hydraulic pressure line  750  is also lowered. Therefore, the hydraulic pressure of the second pressure chamber  230  becomes the same as that of the first pressure chamber  220  by operation of the second piston  210 . 
         [0087]    The first, second, third, and fourth pressure control valves  442  and  444  can be open or closed independently depending on the circumstances. 
         [0088]    As described above, a difference between braking force of hydraulic pressure demanded by a driver and actual hydraulic pressure generated at a master cylinder may be reduced according to various embodiments of the present invention. Therefore, accuracy of braking control may be improved. 
         [0089]    In addition, structures of the regenerative braking system for a vehicle may be simplified. Therefore, production cost may be curtailed. 
         [0090]    Since a cylinder provided with a push rod is connected to the master cylinder through hydraulic pressure lines, various layouts can be achieved and spatial utility may be improved. 
         [0091]    For convenience in explanation and accurate definition in the appended claims, the terms rear, and etc. are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
         [0092]    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.