Abstract:
In order to improve precision and reliability of a hydraulic pressure control apparatus for a brake system of a vehicle, this invention provides a hydraulic pressure control apparatus for a brake system of a vehicle including a control unit for controlling operation of the hydraulic pressure control apparatus, a pressurized fluid generating unit for pressurizing brake fluid and supplying the pressurized fluid, and a hydraulic pressure distributing unit for mechanically selecting and transmitting at least one of hydraulic pressure of the pressurized fluid supplied from the pressurized fluid generating unit and hydraulic pressure supplied from a master cylinder of the brake system to a wheel brake cylinder of the brake system.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a brake system of a vehicle, and more particularly, to a hydraulic pressure control apparatus for a brake system of a vehicle. 
     BACKGROUND OF THE INVENTION 
     Recent progress in the field has provided vehicles with a distance control system for automatically controlling a distance to a vehicle ahead. Such a distance control system must include an apparatus, that is, a brake system, for reducing the speed of a vehicle, and a variety of brake systems have been investigated. 
     Typically, a brake system for a distance control system utilizes a hydro-vacuum apparatus, where the hydro-vacuum apparatus generates, or more specifically amplifies, hydraulic pressure for braking owing to pressure difference between a surge tank and atmosphere. A solenoid valve is adopted to control a consequent deceleration of the vehicle according to control of an electronic control unit. Such a brake system using a hydro-vacuum apparatus usually shows slow response and bad precision because the surge tank pressure depends on various circumstantial factors. 
     Another type of brake system provided with a hydraulic control apparatus between a master cylinder and a brake cylinder of a wheel has also been developed. 
     However, such a type of brake system has an excessively complicated hydraulic line structure because of many electrically controlled solenoid valves and check valves, and therefore its control logic is also much too complicated. 
     SUMMARY OF THE INVENTION 
     The present invention provides a hydraulic pressure control apparatus for a brake system of a vehicle where hydraulic pressure supplied to a brake cylinder of a wheel is more mechanically controlled, such that reliability of hydraulic pressure control is improved and cost of manufacturing the brake system is reduced. According to one embodiment of the present invention, a hydraulic pressure control apparatus for a brake system of a vehicle includes a control unit for controlling operation of the hydraulic pressure control apparatus, a pressurized fluid generating unit for pressurizing brake fluid and supplying the pressurized fluid, and a hydraulic pressure distributing unit for mechanically selecting and transmitting at least one of hydraulic pressure of the pressurized fluid supplied from the pressurized fluid generating unit and hydraulic pressure supplied from a master cylinder of the brake system to a wheel brake cylinder of the brake system. 
     The hydraulic pressure distributing unit preferably includes a pressure chamber for receiving pressurized fluid from the pressurized fluid generating unit; a distributing chamber adjoining the pressure chamber, to which a master cylinder is connected by a first port and a brake cylinder is connected by a second port; and a spool disposed in the distributing chamber for transmitting hydraulic pressures of the pressure chamber and the master cylinder to the second port. 
     The spool is operated by pressure of the pressure chamber and an elastic force of a first elastic member abutted against an inside portion of the distributing chamber. A first hole communicating with the first port and a second hole selectively communicating with the second port are formed at the spool. A check valve is disposed at the second hole such that the selective communication between the second hole and the second port is controlled by the check valve. 
     The check valve may be realized by including a second spring abutted against an inside portion of the distributing chamber, a valve seat connected to the second spring for selectively opening the second hole, and a valve stem connected to the valve seat and penetrating the second hole. A hollow space is formed inside the spool, and a stopper is disposed in the hollow space for limiting a moving distance of the check valve. 
     The pressurized fluid generating unit may be realized by including a pressurized fluid generator for pressurizing fluid supplied from the master cylinder under control of the control unit, and a hydraulic-input control valve unit for controlling supply of the pressurized fluid of the pressurized fluid generator to the hydraulic pressure distributing unit through a hydraulic input line. 
     The pressurized fluid generator may include a motor driven by control of the control unit and a hydraulic pump driven by the motor. 
     The pressurized fluid generating unit preferably includes an accumulator for accumulating the pressurized fluid supplied from the pressurized fluid generator, a first pressure detector for detecting hydraulic pressure of the pressurized fluid supplied from the pressurized fluid generator to the hydraulic-input control valve unit, and a second pressure detector for detecting hydraulic pressure of the pressurized fluid supplied from the hydraulic-input control valve unit to the hydraulic pressure distributing unit. 
     The hydraulic-input control valve unit preferably includes a first hydraulic-input control valve and a second hydraulic-input control valve, where the first hydraulic-input control valve is disposed in the hydraulic pressure distributing unit on a hydraulic input line, the hydraulic input line communicating the pressurized fluid generator and the hydraulic pressure distributing unit, and the second hydraulic-input control valve is disposed in the pressurized fluid generator on the hydraulic input line. The first hydraulic-input control valve is preferably normally open and the second hydraulic-input control valve is preferably normally closed. The pressurized fluid generator unit further includes a hydraulic exhaust control valve for controlling exhaust of brake fluid from the hydraulic input line, and the hydraulic exhaust control valve is preferable normally open. 
     According to an alternative preferred embodiment, a brake system of the invention includes a master cylinder actuated in response to driver manipulation of a brake pedal. A plurality of wheel cylinders communicate with the master cylinder. A hydraulic pressure generating unit is provided separate from and in addition to the master cylinder. A control unit communicates with the hydraulic pressure generating unit to signal the generating unit to generate hydraulic pressure. A distributing unit communicates with the master cylinder, the hydraulic pressure generating unit and the wheel cylinders to distribute fluid there between. The wheel cylinders communicate with the master cylinder through the distributing unit and the distributing unit selectively provides hydraulic pressure to the wheel cylinders from one or both of the master cylinder and hydraulic pressure generating unit in response to user manipulation of the brake pedal and signals from the control unit. 
     In a further preferred embodiment, the distributing unit comprises a body defining a cavity. At least one piston member is disposed in the cavity to define a pressure chamber at one side of the piston member and a distributing chamber at an opposite side of said piston member. The hydraulic pressure generating unit communicates with the pressure chamber to provide pressurized hydraulic fluid thereto and the master cylinder communicates with the wheel cylinders through the distributing chamber. Additionally, an elastic member is disposed in the distributing chamber acting on the piston member in opposition to hydraulic pressure in the pressure chamber supplied by the generating unit. By this arrangement, hydraulic pressure to the wheel cylinders from the distributing chamber may be varied by changing pressure in the pressure chamber with the hydraulic pressure generating unit. 
     Further, the at least one piston member preferably defines an internal space through which the master cylinder communicates with the distributing chamber. A check valve is then preferably disposed between this internal space and the distributing chamber to control hydraulic fluid flow there between in response to the piston member position in the distributing chamber. More preferably, the distributing unit includes first and second piston members, distributing chambers and check valves disposed symmetrically around a central pressure chamber. 
     According to another preferred embodiment the pressure generating unit comprises a hydraulic pump with an inlet and an outlet. A first fluid line from the outlet communicates with the distributing unit. At least one supply control valve is disposed in the first fluid line to control fluid flow from the pump to the distributing unit. A second fluid line communicates between the distributing unit, the pump inlet and a fluid reservoir associated with the master cylinder. Preferably, at least one exhaust control valve is disposed in the second fluid line to control fluid flow from the distributing unit. More preferably, the second fluid line comprises a fluid exhaust line and a pump supply line. The fluid exhaust line communicates with the first fluid line between the at least one supply control valve and the distributing unit. The pump supply line communicates between the exhaust line and the pump inlet. Preferably, the at least one exhaust control valve is disposed in the fluid exhaust line between the first fluid line and the pump supply line. Also preferably, two fluid control vales are disposed in the first fluid line between the pump and the distributing unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention: 
     FIG. 1 is a schematic diagram of a hydraulic pressure control apparatus for a brake system of a vehicle according to a preferred embodiment of the present invention; and 
     FIG. 2 is a schematic diagram showing operation of a hydraulic pressure control apparatus for a brake system of a vehicle according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
     As shown in FIG. 1, the hydraulic pressure control apparatus for a brake system of a vehicle according to a preferred embodiment of the present invention includes hydraulic pressure distributing unit  10  and a pressurized fluid generating unit  50 . Generating unit  50  pressurizes brake fluid for brake cylinders  110 ,  111 ,  112 , and  113  of wheels according to control by electronic control unit (referred to as “ECU” hereinafter)  150 . Hydraulic pressure distributing unit  10 , disposed between the pressurized fluid generating unit  50  and the master cylinder  100 , supplies hydraulic pressure of brake fluid to the brake cylinders  110 - 113  selectively from the pressurized fluid generating unit  50  and the master cylinder  100 . 
     The pressurized fluid generating unit  50  includes a pressurized fluid generator comprising a motor  52  activated by control of the ECU  150 , a hydraulic pump  51  activated by the motor  52 . Accumulator  53  accumulates pressurized fluid supplied from the hydraulic pumps  51 . A hydraulic-input control valve unit including a first and a second hydraulic-input control valve  55  and  54 , disposed on a hydraulic input line  56  providing communication between the accumulator  53  and the pressurized fluid generator with the hydraulic pressure distributing unit  10 , controls hydraulic pressure input to the hydraulic pressure distributing unit  10 . A hydraulic exhaust control valve  57 , disposed on a hydraulic exhaust line  58  branched from the hydraulic input line  56  to a reservoir  101 , controls hydraulic pressure exhausted to the reservoir  101 . 
     The hydraulic exhaust line  58  is also connected to the hydraulic pumps  51  through a hydraulic supply line  59  to supply brake fluid thereto. A check valve  60  is disposed at each of the hydraulic input line  56  and the hydraulic supply line  59  such that the brake fluid flows in only one direction. 
     As shown in FIG. 1, the first hydraulic-input control valve  55  is normally open, that is, open when not activated, while second hydraulic-input control valve  54  is normally closed. The hydraulic exhaust control valve  57  is normally open. 
     Hydraulic pressure supplied to the second hydraulic-input control valve  54  is detected by a first pressure detector  71  and the detected value is provided to the ECU  150 . Hydraulic pressure supplied from the first hydraulic-input control valve  55  to the hydraulic pressure distributing unit  10  is detected by a second pressure detector  72  and the detected value is also provided to the ECU  150 . 
     The hydraulic pressure distributing unit  10  includes a body  11  forming the housing of the hydraulic pressure distributing unit  10 ; a pressure chamber  12  disposed inside the body  10  and connected, through a first port  13 , to the hydraulic input line  56  of the pressurized fluid generating unit  50 . Distributing chambers  14 , formed at both sides of the pressure chamber  12 , are connected to the brake cylinders  110 - 113  and the master cylinder  100  through second and third ports  15  and  16 , respectively. A spool  20  is slidably located in each distributing chamber  14  such that the first, second, and third ports  13 ,  15 , and  16  are separated by the spools  20 . 
     Distributing unit  10  further includes first springs  17 , each located between an exterior surface of one spool  20  and an interior surface of the associated distributing chamber  14  such that each first spring  17  forces the associated spool  20  toward the pressure chamber  12 . A first hole  21  and a second hole  22  are formed on a circumference and an end surface of each spool  20 , respectively, such that the second and third ports  15  and  16  can communicate with each other through the first and second holes  21  and  22 . 
     A check valve  30  is disposed at the second hole  22  of each spool  20  such that communication between the second hole  22  and the second port  15  is controlled by the check valve  30 . Check valve  30  functions as a one-way valve to permit hydraulic pressure to be supplied only in the direction of the master cylinder  100  to the brake cylinders  110 - 113 . 
     A hollow space  23  is formed inside the spool  20 , and a sealing ring  24  is provided around each circumferential end of the spool  20  such that each distributing chamber  14  is divided into two portions, one toward the brake cylinders  110 -  113  and the other toward the master cylinder  100 . Furthermore, first hole  21  is formed at the spool  20  such that the hollow space  23  always communicates with the third port  16 , and the hollow space  23  selectively communicates with the second port  15  according to the operation of the check valve  30 . 
     Second springs  31  abutted against an interior surface of each distributing chamber  14  forces a valve seat  29  of the associated check valve  30  toward the second hole  22 , and a valve stem  32  connected to the valve seat  29  penetrates the second hole  22 . A stopper  33 , disposed in the hollow space  23 , limits a moving distance of the check valve  30  such that the second hole  22  is opened when each spool  20  is fully displaced toward the pressure chamber  12 . 
     The operation of the hydraulic pressure control apparatus according to the preferred embodiment of this invention is hereinafter described in detail. 
     When a distance control system is not operating, that is, when the hydraulic pressure control apparatus of the present embodiment is not operating, the ECU  150  closes the first and second hydraulic-input control valves  55  and  54  and opens the hydraulic exhaust control valve  57  as shown in FIG.  1 . 
     Therefore, the pressurized fluid in the pressure chamber  12  is exhausted to the reservoir  101  through the hydraulic exhaust line  58  and spools  20  slide toward the pressure chamber  12  by the elastic force of first springs  17 . Check valves  30  also move by the elastic force of second springs  31 , however movement is limited by stopper  33 , and therefore second holes  22  are opened even if initially closed. 
     When a brake pedal (not shown) is operated, hydraulic pressure from brake fluid in the master cylinder  100  is transmitted into the hollow space  23  of each spool  20  through third ports  16  and first holes  21 . Pressure is subsequently transmitted into each distributing chamber  14  through opened second holes  22 , and is therefore supplied to brake cylinders  110 - 113  through second ports  15  such that the vehicle equipped with the hydraulic pressure control apparatus decelerates. 
     When the ECU  150  activates the motor  52  and accordingly the hydraulic pump  51  is operated, pressurized fluid expelled from the hydraulic pump  51  is accumulated in the accumulator  53  to a predetermined pressure, and is also supplied toward the pressure chamber  12  through the first port  13 . The ECU  150  also closes the hydraulic exhaust line  58  by activating the hydraulic exhaust control valve  57 , and opens the hydraulic input line  56  by sequentially opening the second and first hydraulic-input control valves  55  and  54 . Therefore the pressurized brake fluid flows into the pressure chamber  12 . 
     As the pressurized fluid flows into the pressure chamber  12 , spools  20  are forced to symmetrically move against the elastic force of first springs  17 . As this happens, each check valve  30  closes each second hole  22 . Brake fluid in each distributing chamber  14  is therefore pressurized and expelled toward the brake cylinders  110 - 113  through the second port  15 . Thus, the brake cylinders  110 - 113  are operated and the vehicle decelerates. 
     When the hydraulic pressure of the brake cylinders  110 - 113  is to be reduced, the ECU  150  activates the first hydraulic-input control valve  55  to close the hydraulic input line  56  and opens the hydraulic exhaust control valve  57  on the hydraulic exhaust line  58 . 
     Because the pressurized fluid flowing from the accumulator  53  into the pressure chamber  12  is accordingly stopped and the pressure chamber  12  communicates with the reservoir  101  through the hydraulic exhaust line  58 , the spools  20  are forced by first springs  17  to move toward the pressure chamber  12 . Accordingly, pressurized fluid in the brake cylinders  110 - 113  flows into distributing chambers  14  through the second ports  15 , and the fluid in the pressure chamber  12  is exhausted to the reservoir  101  through the hydraulic exhaust line  58 . 
     When the brake pedal (not shown) is operated while the hydraulic pressure is being controlled, the resultant hydraulic pressure of the brake pedal operation can also be transmitted to the brake cylinders. That is, when the brake pedal is operated, the resultant hydraulic pressure is transmitted into hollow spaces  23  of spools  20  through third ports  16  and first holes  21  such that the resultant hydraulic pressure applies a force on check valves  30 . Therefore,if the resultant hydraulic pressure exceeds a predetermined level (an elastic force level of the second spring  31  forcing the valve seat  29  toward spools  20 ), check valves  30 , and accordingly second holes  22  are opened. Because third ports  16  and second ports  15  consequently communicate with each other through hollow spaces  23  and distributing chambers  14 , the pressurized fluid inflow from the master cylinder  100  is expelled toward the brake cylinders  110 - 113  through the second port  15 . 
     As described above, the driver does not lose control of the brake system because the hydraulic pressure resulting from operation of the brake pedal is still transmitted to the brake cylinders. Thus, according to the invention, the structure of the hydraulic control system is simplified and mechanicalized such that reliability and precision of its operation is improved, and further, the cost for manufacturing the system is reduced. 
     While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, 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.