Patent Publication Number: US-2007116586-A1

Title: Pump for brake system

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the benefit of Korean Patent Application No. 2005-0112256, filed on Nov. 23, 2005 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a pump for a brake system, and, more particularly, to a pump for a brake system for achieving an improvement in oil pumping performance and pump assembling efficiency.  
      2. Description of the Related Art  
      Generally, a brake system has the purpose of efficiently preventing a wheel slip caused upon braking, quick start, or sudden acceleration of a vehicle. The brake system includes a plurality of solenoid valves to control a braking hydraulic pressure to be transmitted to hydraulic brakes of vehicle wheels, a pair of low-pressure and high-pressure accumulators to temporarily store an oil discharged from the hydraulic brakes, a pair of pumps provided between the low-pressure and high-pressure accumulators, the pumps being operated by a motor, and an ECU to control operations of the solenoid valves and motor. All the above elements are received in a modulator block made of aluminum.  
      In particular, the pumps of the brake system serve to forcibly pump the oil stored in the low-pressure accumulator or master cylinder to the high-pressure accumulator, so as to transfer the oil to the hydraulic brakes or master cylinder.  
      Many patents, including Korean Patent Laid-open No. 10-2005-0050168 and Korean Patent Registration No. 10-0381592 filed by the applicant of the present invention, disclose conventional pumps for a conventional electronically controlled brake system.  
      Explaining the conventional electronically controlled brake system in brief, it includes a booster and master cylinder associated with a brake pedal, a plurality of solenoid valves to control a braking hydraulic pressure to be transmitted to hydraulic brakes installed at front and rear vehicle wheels, a low-pressure accumulator to temporarily store oil discharged from the hydraulic brakes, a pair of pumps to pump the oil in the low-pressure accumulator or master cylinder, a motor to drive the pair of pumps simultaneously, and a high-pressure accumulator having an orifice disposed at an exit side thereof to reduce a pressure pulsation of the oil compressed and discharged by operation of the pumps. All the above elements are received in a modulator block made of aluminum. The pair of pumps are operated by the single motor to have a predetermined phase difference, thereby compressing the oil in the low-pressure accumulator or master cylinder and pumping the compressed oil to the high-pressure accumulator. Herein, further detailed description of the brake system will be omitted because it is fully disclosed in the above mentioned patent documents related to the prior art.  
       FIG. 1  illustrates a conventional pump for a brake system. The conventional brake system comprises a motor  10 , a spindle  11  to be rotated by the motor  10 , an eccentric shaft  12  to be eccentrically rotated by the spindle  11 , a bearing  13  installed around the eccentric shaft  12 , a piston  30  installed in a bore  21  formed in a modulator block  20  to perform reciprocating motions under the assistance of the bearing  13 , the piston  30  having an inner oil flow path  31 , an inlet valve  40  to open and close an exit side of the oil flow path  31  based on a position of the piston  30 , and an outlet valve  60  provided at an open end of the bore  21 , operations of the inlet and outlet valves  40  and  60  being contrary to each other.  
      The modulator block  20  is formed with a suction port  22  and a discharge port  23 . The suction port  22  is used to connect an entrance side of the oil flow path  31  defined in the piston  30  to a low-pressure accumulator (not shown) or master cylinder (not shown), and the discharge port  23  is used to connect the an entrance side of a high-pressure accumulator (not shown) to an exit side of the outlet valve  60 . The discharge port  23  communicates with the bore  21 .  
      The inlet valve  40  for opening and closing the oil flow path  31  includes a valve opening/closing member  42  installed at an exit-side end of the oil flow path  31 , a valve spring  43  to elastically push the valve opening/closing member  42  toward the exit side of the oil flow path  31 , and a holder  44  configured to receive the valve opening/closing member  42  and valve spring  43 . Also, a conical valve seat  41  is formed at an end of the piston  30  in the exit side of the oil flow path  31 . The valve seat  41  is adapted to come into contact with or be spaced apart from the valve opening/closing member  42 .  
      A valve cover  50  is also installed in the bore  21 . The piston  30  assembled, at one end thereof, with the inlet valve  40  is inserted in the valve cover  50 . The outlet valve  60  is also inserted in the valve cover  50 . The valve cover  50  defines a compression chamber  51  with the end of the piston  30  in accordance with the reciprocating motions of the piston  30 .  
      In the conventional pump having the above described configuration, if the motor  10  operates, the spindle  11  is rotated and thus, the eccentric shaft  12  is eccentrically rotated, causing rectilinear reciprocating motions of the piston  30 . Thereby, as the inlet and outlet valves  40  and  60  perform opening and closing operations contrary to each other by a pressure variation in the bore  21 , oil is compressed and pumped to the high-pressure accumulator (not-shown).  
      Specifically, if the piston  30  moves toward the outlet valve  60 , a pressure of the oil between the piston  30  and the outlet valve  60  rises, causing the inlet valve  40  to be closed and the outlet valve  60  to be opened. Thereby, the oil is pumped to the high-pressure accumulator (not shown) through the discharge port  23 .  
      On the other hand, if the piston  30  moves toward the bearing  13 , the pressure of the oil between the end of the piston  30  and the outlet valve  60  falls, causing the inlet valve  40  to be opened and the outlet valve  60  to be closed. Thereby, the oil stored in the low-pressure accumulator (not shown) or master cylinder (not shown) is suctioned into a space between the piston  30  and the outlet valve  60 , i.e. compression chamber  51 , through the suction port  22  and oil flow path  31 .  
      In addition to the above described configuration, seal members  32  are provided to prevent any possible leakage of the oil from a gap between the piston  30  and the bore  21  during operation of the piston  30 .  
      However, the above described conventional brake system has many problems as follows. Firstly, since the bore  21  guides the reciprocating motions of the piston  30  and the seal members  32  move together with the piston  30 , there is a problem in that the piston and bore may cause a gap therebetween due to their friction contact, and the gap may result in serious deterioration in sealing performance by the seal members. Secondly, the seal members have a limit in sealing effect because they are secured to the piston and adapted to move together with the piston. Thirdly, the conventional brake system suffers from low durability thereof due to wear of an inner portion of the bore, an outer portion of the piston, seal members, etc. Fourthly, the piston may be easily separated from the bore in a state wherein the motor, spindle, eccentric shaft, bearing, etc. are removed from the modulator block for the assembling or disassembling of the pump, and reassembling the piston into the bore is a very difficult and troublesome work.  
     SUMMARY OF THE INVENTION  
      The present invention has been made in order to solve the above problems. It is an aspect of the invention to provide a pump for a brake system which can achieve an increase in sealing performance between a piston and a bore as well as motion performance and durability of the piston, and can guarantee easy assembling of the piston into the bore.  
      Consistent with one aspect, an exemplary embodiment of the present invention provides a pump for a brake system comprising: a bore formed in a modulator block and connected to a suction port and discharge port; a piston installed in the bore to perform rectilinear reciprocating motions, the piston comprising an oil flow path to move an oil suctioned through the suction port toward the discharge port; an inlet valve to open and close the oil flow path in accordance with the motions of the piston and an outlet valve to selectively allow the discharge of the compressed oil; and a fixing unit comprising a guide member provided around the piston to be coupled to the bore and adapted to guide the motions of the piston and a sealing member provided around the piston to be coupled to the bore and adapted to keep between the bore and the piston in an air-tightness state.  
      The guide member and sealing member may be integrally formed with each other to constitute the fixing unit.  
      The piston may have a protruding portion to be caught by the fixing unit, so as to prevent the piston from extending out of the bore beyond a predetermined length.  
      The inlet valve may comprise a valve seat formed at an end of the oil flow path, a valve opening/closing member to open and close the valve seat, a valve spring to elastically support the valve opening/closing member, and a holder to hold the valve spring at a fixed position, the holder having an end configured to be caught by the fixing unit, so as to prevent the piston from extending out of the bore beyond a predetermined length.  
      The pump may further comprise: a guide bush provided between the piston and the bore to guide the motions of the piston; and a sliding seal member adapted to slide between the guide bush and the fixing unit so as to keep between the piston and the bore in an air-tightness state, and the fixing unit may be extended from the inlet valve of the piston and adapted to support the sliding seal member to thereby prevent the sliding seal member from sliding beyond a predetermined distance.  
      The pump may further comprise: a valve seat coupled to the piston, the valve seat defining an exit of the oil flow path to be opened and closed by the inlet valve, and the valve seat may have a protruding portion to be caught by the fixing unit, so as to prevent the piston from extending out of the bore beyond a predetermined length.  
      The piston may have a stepped portion defined between different outer-diameter portions thereof, and the fixing unit has a holding portion defined between different inner-diameter portions thereof, the stepped portion being caught by the holding portion to prevent the piston from extending out of the bore beyond a predetermined length.  
      Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and/or other aspects and advantages of the exemplary embodiments of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, of which:  
       FIG. 1  is a sectional view showing a conventional pump for a brake system;  
       FIG. 2  is a sectional view showing a pump for a brake system consistent with a first embodiment of the present invention;  
       FIG. 3  is a sectional view showing a pump for a brake system consistent with a third embodiment of the present invention;  
       FIG. 4  is a sectional view showing a pump for a brake system consistent with a fifth embodiment of the present invention; and  
       FIG. 5  is a sectional view showing a pump for a brake system consistent with a seventh embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below to explain a pump for a brake system consistent with the present invention by referring to the figures.  
     First Embodiment  
       FIG. 2  is a sectional view showing a pump for a brake system consistent with a first embodiment of the present invention.  
      As shown in  FIG. 2 , the pump for a brake system consistent with the present invention comprises a motor  100 , a spindle  110 , an eccentric shaft  120  and a bearing  130 , which are installed in a modulator block  200 . A bore  210  is formed in the modulator block  200 , and a piston  300  is inserted in the bore  210  to perform rectilinear reciprocating motions using a force transmitted from the bearing  130 . The modulator block  200  is also formed with a suction port  211  and a discharge port  212 . If oil from a low-pressure accumulator (not shown) or master cylinder (not shown) is introduced into the pump through the suction port  211 , the oil is compressed in the pump and discharged to a high-pressure accumulator (not shown) through the discharge port  212 .  
      A fixing unit  400  is located between an inner circumference of the bore  210  and an outer circumference of the piston  300  and coupled to the bore  210 . The fixing unit  400  includes a guide member  401  to guide the rectilinear reciprocating motions of the piston  300  and a sealing member  402  to seal a gap between the bore  210  and piston  300  in an air-tightness state, so as to eliminate the risk of oil leakage.  
      The piston  300  has an oil flow path  310  formed therein for the movement of the oil suctioned from the suction port  211 . A valve seat member  560  is installed at an exit side of the oil flow path  310 , i.e. at a leading end of the piston  300 , and in turn, an inlet valve  500  is installed at a leading end of the valve seat member  560 . The inlet valve  500  is adapted to open and close the oil flow path  310  for controlling introduction or discharge of the oil into or from the oil flow path  310 .  
      The inlet valve  500  includes a valve seat  510  formed at the leading end of the valve seat member  560 , a valve opening/closing member  520  to come into contact with or be spaced apart from the valve seat  510 , a valve spring  530  to elastically support the valve opening/closing member  520 , and a holder  540  configured to receive and support all the above elements.  
      The inlet valve  500  installed at the leading end of the piston  300  defines a compression chamber  610  with a valve cover  600  fixedly installed in the bore  210 . Both the valve seat member  560  and holder  540  formed at the leading end of the piston  300  are elastically supported by a return spring  550  crossing the compression chamber  610 . Thereby, when the piston  300  is moved forward to compress the oil, the piston  300  is able to be moved rearward by the return spring  550 .  
      An outlet valve  700  is installed in the valve cover  600  and adapted to control the discharge of the oil compressed in the compression chamber  610 . The outlet valve  700  includes an outlet valve seat  710  defining an orifice  620  for the movement of the compressed oil, an outlet valve opening/closing member  720  to open and close the outlet valve seat  710 , and a valve spring  730  to elastically support the outlet valve opening/closing member  720 .  
      To prevent the piston  300  from extending out of the bore  210  beyond a predetermined length, the valve seat member  560  has a protruding portion  561  to be caught by the fixing unit  400 .  
      Independently of the fixing unit  400 , the piston  300  is externally provided with a guide bush  420  and a sliding seal member  410 . The guide bush  420  is coupled to the bore  210  at a trailing end of the piston  300  and adapted to guide the reciprocating motions of the piston  300 . The sliding seal member  410  is slidable between the guide bush  420  and the fixing unit  400 , to seal a gap between the piston  300  and the bore  210 .  
      The fixing unit  400  is extended by a predetermined length to limit a movement range of the sliding seal member  410 . Consequently, the fixing unit  400  has the function of preventing excessive sliding movement of the sliding seal member  410 .  
      Herein, a series of courses for introducing the oil into the suction port  211  and discharging the oil from the discharge port  212  will not be described because they are similar to the prior art.  
     Second Embodiment  
      Although a pump for a brake system consistent with a second embodiment of the present invention is not shown in the drawing, it is noted that the present embodiment is similar to the above described first embodiment except for the fact that the guide member  401  and sealing member  402  of the fixing unit  400  are integrally formed with each other.  
      Specifically, in the second embodiment of the present invention, the guide member  401  and sealing member  402  are made of the same elastic material as each other to form the single fixing unit  400 , so as to perform both piston guiding and sealing functions together.  
     Third Embodiment  
       FIG. 3  is a sectional view showing a pump for a brake system consistent with a third embodiment of the present invention.  
      As shown in  FIG. 3 , the pump of the present embodiment is basically the same as that of the above described first embodiment in several ways, such as, the piston  300  is arranged to perform the rectilinear reciprocating motions in the bore  210  formed in the modulator block  200 , the guide member  401  and sealing member  402  are provided between the inner circumference of the bore  210  and the outer circumference of the piston  300 , and the like.  
      However, the third embodiment of the present invention as shown in  FIG. 3  has a feature in that the valve seat  510  is formed by processing the piston  300 , instead of installing the valve seat member  560  at the leading end of the piston  300  as described in relation with the first embodiment of the present invention, and a stopper  301  is formed around the valve seat  510 . The stopper  301  is configured to be caught by the fixing unit  400 , and serves to prevent the piston  300  from extending out of the bore  210  beyond a predetermined length. The stopper  310  has the effect of facilitating the assembling or disassembling of the piston  300  into or from the bore  210  formed in the modulator block  200 .  
      The function and operation of other elements shown in  FIG. 3  are the same as those of the above described first embodiment of the present invention shown in  FIG. 2 .  
     Fourth Embodiment  
      Although a pump for a brake system consistent with a fourth embodiment of the present invention is not shown in the drawing, it is noted that the present embodiment is similar to the above described third embodiment except for the fact that the guide member  401  and sealing member  402  of the fixing unit  400  are integrally formed with each other.  
      Specifically, in the fourth embodiment of the present invention, the guide member  401  and sealing member  402  are made of the same elastic material as each other to form the single fixing unit  400 , so as to perform both piston guiding and sealing functions together.  
     Fifth Embodiment  
       FIG. 4  is a sectional view showing a pump for a brake system consistent with a fifth embodiment of the present invention.  
      As shown in  FIG. 4 , the pump of the present embodiment is basically the same as that of the above described third embodiment in several ways, such as, the piston  300  performs the rectilinear reciprocating motions in the bore  210  formed in the modulator block  200 , the guide member  401  and sealing member  402  are provided between the inner circumference of the bore  210  and the outer circumference of the piston  300 , and the like.  
      However, the fifth embodiment of the present invention as shown in  FIG. 4  has a feature in that, instead of forming a stopper at the piston, an end portion of the holder  540  is bent outward to form a flange portion  541 . Thereby, as the flange portion  541  is caught by the fixing unit  400 , it is possible to prevent the piston  300  from extending out of the bore  210  by a predetermined length, and this enables easy assembling of the piston  300 .  
      The function and operation of other elements shown in  FIG. 4  are the same as those of the above described third embodiment of the present invention shown in  FIG. 3 .  
     Sixth Embodiment  
      Although a pump for a brake system consistent with a sixth embodiment of the present invention is not shown in the drawing, it is noted that the present embodiment is similar to the above described fifth embodiment except for the fact that the guide member  401  and sealing member  402  of the fixing unit  400  are integrally formed with each other.  
      Specifically, in the sixth embodiment of the present invention, the guide member  401  and sealing member  402  are made of the same elastic material as each other to form the single fixing unit  400 , so as to perform both piston guiding and sealing functions together.  
     Seventh Embodiment  
       FIG. 5  is a sectional view showing a pump for a brake system consistent with a seventh embodiment of the present invention.  
      As shown in  FIG. 5 , the pump of the present embodiment is basically the same as that of the above described fifth embodiment in several ways, such as, the piston  300  performs the rectilinear reciprocating motions in the bore  210  formed in the modulator block  200 , the guide member  401  and sealing member  402  are provided between the inner circumference of the bore  210  and the outer circumference of the piston  300 , and the like.  
      However, the seventh embodiment of the present invention as shown in  FIG. 5  has a feature in that the piston  300  is provided with a stepped portion  302 , rather than providing the holder with the flange portion. Specifically, the piston  300  consists of two parts having different outer-diameters from each other, and thus, the stepped portion  302  is formed between the large-diameter part and the small-diameter part. Also, the fixing unit  400  consists of two parts having different inner-diameters from each other, and thus, a stepped holding portion  403  is formed between the small-diameter part and the large-diameter part. With this configuration, the stepped portion  302  is caught by the holding portion  403 , to prevent the piston  300  from extending out of the bore  210  beyond a predetermined length. This has the effect of facilitating the assembling or disassembling of the piston  300  into or from the modulator block  200 .  
      The function and operation of other elements shown in  FIG. 5  are the same as those of the above described fifth embodiment of the present invention shown in  FIG. 4 .  
     Eighth Embodiment  
      Although a pump for a brake system consistent with an eighth embodiment of the present invention is not shown in the drawing, it is noted that the present embodiment is similar to the above described seventh embodiment except for the fact that the guide member  401  and sealing member  402  of the fixing unit  400  are integrally formed with each other.  
      Specifically, in the eighth embodiment of the present invention, the guide member  401  and sealing member  402  are made of the same elastic material as each other to form the single fixing unit  400 , so as to perform both piston guiding and sealing functions together.  
      As apparent from the above description, the present invention provides a pump for a brake system having the following several effects. Firstly, the pump can safely and efficiently guide reciprocating motions of a piston, and achieve an increase in sealing performance in accordance with the compression of oil in a bore. Further, the pump can enhance durability thereof by reducing wear between the piston and the bore, and facilitate the assembling or disassembling of the piston, etc. into or from a modulator block.  
      Although embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.