Abstract:
Disclosed is a hybrid brake system equipped with a pedal simulator having a parallel structure. The hybrid brake system includes an input shaft connected to a brake pedal, a pedal simulator provided therein with a control plunger connected with the input shaft, a master cylinder communicating with the pedal simulator and provided therein with first and second pistons, an oil supply part supplying oil to the pedal simulator and the master cylinder, and a boosting part communicating with the pedal simulator and forming repulsive force when the brake pedal is stepped on.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2009-0117615, filed on Dec. 1, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The disclosure relates to a hybrid brake system, and more particularly to a hybrid brake system capable of improving brake pedal feeling by employing a pedal simulator having a parallel structure. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, when a driver steps on a brake pedal, a hydraulic active booster (HAB) detects displacement of the brake pedal from a pedal displacement sensor and closes a shut-off valve to close a fluid path between a master cylinder of a pedal simulator and a wheel, and an electronic control unit (ECU) calculates wheel pressure according to a pressure signal of a pressure sensor to control pressure of each wheel through an independent feedback control. 
         [0006]    When the HAB fails, the shut-off valve is switched into a normally open (NO) state, so liquid pressure of the master cylinder corresponding to pedal force of the driver is transferred to a wheel cylinder so that the minimum braking operation can be performed upon the system failure. 
         [0007]    In such a HAB, if the driver steps on the brake pedal, an input shaft is moved and the ECU detects the movement of the input shaft, so fluid stored in an accumulator is transferred to the master cylinder to generate the liquid pressure in the master cylinder. However, if the pressure of the master cylinder is changed during the regenerative braking operation, the pressure variation may be transferred to the brake pedal, thereby deteriorating the pedal feeling. 
       SUMMARY 
       [0008]    Accordingly, it is an aspect of the disclosure to provide a hybrid brake system equipped with a pedal simulator having a parallel structure capable of increasing the brake pedal feeling. 
         [0009]    Additional aspects and/or advantages of the disclosure will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the disclosure. 
         [0010]    The foregoing and/or other aspects of the disclosure are achieved by providing a hybrid brake system. The hybrid brake system includes an input shaft connected to a brake pedal, a pedal simulator provided therein with a control plunger connected with the input shaft, a master cylinder communicating with the pedal simulator and provided therein with first and second pistons, an oil supply part supplying oil to the pedal simulator and the master cylinder, and a boosting part communicating with the pedal simulator and forming repulsive force when the brake pedal is pressed. 
         [0011]    The pedal simulator includes a simulator housing having a chamber for receiving the control plunger, and wherein the boosting part is provided at a lower portion of the simulator housing and has a parallel structure. 
         [0012]    The boosting part includes a cylinder communicating the pedal cylinder, a spring retainer, which slides upward or downward in the cylinder, a compression spring compressed by the spring retainer, and a housing cap supporting the compression spring. 
         [0013]    The simulator housing is provided therein a first oil port for supporting oil into the cylinder. 
         [0014]    The master cylinder includes a second oil port for supplying oil to a space between the second piston and an internal surface of the master cylinder. 
         [0015]    The second piston is a booster piston to move the first piston while moving forward by oil received therein through the second oil port. 
         [0016]    The first piston has a recess part recessed inward from a rear end of the first piston, a front end portion of the control plunger is inserted into the recess part, and a gap is formed between the recess part and the control plunger. 
         [0017]    As described above, according to the hybrid brake system of the disclosure, hydraulic pressure can be independently controlled by the pedal simulator having a parallel structure, so that brake pedal feeling can be improved. 
         [0018]    Since the pedal simulator is installed separately from the housing, the pedal simulator can be freely designed, and can be easily tuned. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0020]      FIG. 1  is a schematic perspective view showing a hybrid brake system according to the disclosure; 
           [0021]      FIG. 2  is a schematic sectional view showing the hybrid brake system according to the disclosure; 
           [0022]      FIG. 3  is a partial sectional view of  FIG. 2 ; and 
           [0023]      FIG. 4  is a schematic view showing the operation of the hybrid brake system according to the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the disclosure by referring to the figures. 
         [0025]    As shown in  FIGS. 1 to 2 , a hybrid brake system  1  according to the disclosure includes a brake pedal  10  manipulated by a driver in braking, an input shaft  11  connected to the brake pedal  10 , a pedal simulator  20  providing repulsive force against the brake pedal  10 , a master cylinder  30  connected to the pedal simulator  20  to transfer braking pressure to a wheel brake (not shown) as the braking pressure is generated by the brake pedal  10 , an oil reservoir  40  storing oil, and an oil supply part  50  supplying the oil of the oil reservoir  40  to the master cylinder  30  and the pedal simulator  20 . 
         [0026]    The input shaft  11  is linked with the brake pedal  10  and inserted into a rear end of a control plunger  21 , which will be described later, so that the control plunger  21  can be moved toward the direction of the input shaft  11  in a simulator housing  20   a.    
         [0027]    The master cylinder  30  includes a cylinder housing  31  having a space to store oil therein, and an oil reservoir  40  is coupled with the upper portion of the cylinder housing  31 . 
         [0028]    One end surface of the cylinder housing  31  is open and coupled with the pedal simulator  20  to be described later. 
         [0029]    The cylinder housing  31  of the master cylinder  30  includes a second piston  33  into which the control plunger  21  is inserted, a first piston  32  slidably provided by the second piston  33 , and an elastic spring  34  interposed between an inner wall of the cylinder housing  31  and the first piston  32  to elastically support the cylinder housing  31  and the first piston  31 . 
         [0030]    A second oil port  35  is provided at an upper portion of the master cylinder  30  to supply oil into the first chamber  36  between the second piston  33  and the inner surface of the master cylinder  30 . 
         [0031]    The second piston  33  is inserted into a front end portion  21   a  of the control plunger  21 , and a sealing member  33   b  is provided between the second piston  33  and the control plunger  21 . 
         [0032]    A recess part  32   a  is formed inward from one end portion of the first piston  32 , and a gap G is formed between the recess part  32   a  and the front end portion  21   a  of the control plunger  21 . 
         [0033]    In the normal operation, force applied by the input shaft  11  connected to the brake pedal  10  does not deliver to the control plunger  21  and the first piston  32  due to the gap G. 
         [0034]    In other words, in the case of the regenerative braking, even if the first piston  32  moves backward, since the control plunger  21  does not make direct contact with the first piston  32 , the pedal feeling of the brake pedal  10  is not deteriorated. 
         [0035]    Sealing members  33   a  and  21   b  are provided at an outer portion of the control plunger  21  to seal the gap with the first piston  32  and the gap with the internal lateral surface of the simulator housing  20   a.    
         [0036]    The pedal simulator  20  includes the simulator housing  20   a  coupled with the open end of the cylinder housing  31 , and a second chamber  23  is formed in the simulator housing  20   a  into which the control plunger  21  slidably moves. 
         [0037]    A first oil port  22  is formed at an upper portion of the simulator housing  20   a  to supply oil from the oil supply part  50  to the second chamber  23 . 
         [0038]    A boosting part  25  having a parallel structure is provided at a lower portion of the simulator housing  20   a.    
         [0039]    The boosting part  25  is provided at one side thereof with a first boosting part  25   a  and provided at an opposite side thereof with a second boosting part  25   b , in which the first and second boosting parts  25   a  and  25   b  are provided in parallel to each other. Pressure control is independently achieved by the first and second boosting parts  25   a  and  25   b , so that braking force can be independently controlled. 
         [0040]    The first boosting part  25   a  includes a cylinder  25   a ′ communicating with the second chamber  23  of the simulator housing  20   a , a spring retainer  26  that can be slid upward or downward in the cylinder  25   a ′, a compression spring  27  compressed by the spring retainer  26 , and a housing cap  28  supporting the spring retainer  26 . 
         [0041]    A third chamber  25 ″ is formed inside the cylinder  25   a ′, that is, in a space between a top surface of the inside of the cylinder  25   a ′ and the upper end of the spring retainer  26 , and oil introduced through the first oil port  22  is supplied to the third chamber  25 ″ through the second chamber  23 . 
         [0042]    The oil supply part  50  includes a motor M controlled by an ECU (electronic control unit) (not shown), a pump operated by the motor M, and an accumulator to temporarily store high-pressure oil generated by the pump. 
         [0043]    The motor M is controlled by the ECU (not shown), and the ECU adjusts a pressure corresponding to the pedal force of a driver according to the pressing degree of the brake pedal  10  detected by the pedal displacement sensor  51  by controlling the motor M. 
         [0044]    A pressure sensor (not shown) is provided at an outlet of the accumulator to measure the oil pressure of the accumulator, so that the oil pressure measured through the pressure sensor is compared with the preset pressure. If the measured oil pressure is lower than the present pressure, the pump is driven so that the accumulator can be filled with oil. 
         [0045]    In addition, the ECU transfers oil filled in the accumulator into the first to third chambers  36 ,  23 , and  25   b  through the first and second oil ports  22  and  25  to make hydraulic pressure corresponding to the pedal force of the driver. 
         [0046]    As shown in  FIGS. 3 to 4 , the spring retainer  26  moves upward or downward inside the cylinder  25 ′ by oil supplied from the oil supply part  50  through the first oil port  22  in normal operation. 
         [0047]    The spring retainer  26  includes a body  26 ′ having a cylindrical shape, a flange part  26 ″ provided at an upper portion of the body  26 ′, and a guide groove  26 ″ recessed inward from a lower end of the spring retainer  26 . 
         [0048]    Sealing members  29  are provided between the upper portion of the spring retainer  26  and the cylinder  25 ′. 
         [0049]    The body  26 ′ of the spring retainer  26  has an inner diameter less than that of the cylinder  25 ′, and the flange part  26 ″ has a size corresponding to the inner diameter of the cylinder  25 ′ to support the compression spring  27 . 
         [0050]    The housing cap  28  is provided at an open lower end of the cylinder  25 ′. The housing cap  28  includes a support part  28 ″ having a diameter corresponding to an inner diameter of the cylinder  25 ′ and a guide  28 ′ protruding upward from the central portion of the support part  28 ″ and inserted into a guide groove  26 ″ of the spring retainer  26 . 
         [0051]    The compression spring  27  is installed at a rear end of the cylinder  25 ′ and interposed between the support part  28 ″ of the housing cap  28  and the flange part  26   a ″ of the spring retainer  26 . 
         [0052]    The spring constant, the acting area, and mounting load of the compression spring  27  are variable. 
         [0053]    Accordingly, oil supplied through the first oil port  22  of the simulator housing  20   a  is introduced into the third chamber  25 ″ through the second chamber  23 , and the spring retainer  26  is moved downward by the oil introduced into the third chamber  25 ″. 
         [0054]    If the compression spring  27  is compressed by the movement of the spring retainer  26 , the compression spring  27  has repulsive force, so that the driver may have brake pedal feeling. 
         [0055]    In this case, since the boosting part  25  includes the first and second boosting parts  25   a  and  25   b  installed in parallel to each other, pressure can be independently supplied to each chamber, so that braking force can be independently controlled. 
         [0056]    Since the first and second boosting parts  25   a  and  25   b  have the same structure and operation, the details thereof will be omitted. 
         [0057]    Although few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.