FIELD 
       [0001]    The invention relates to braking systems, and in particular to an electrically controlled hydraulic booster. 
       BACKGROUND 
       [0002]    A braking system typically includes a master cylinder which is fluidly coupled to downstream braking circuits. Typically the master cylinder is selectively coupled to a fluid reservoir. A seal arrangement allows fluid flow from the reservoir to the master cylinder and also isolates the master cylinder form the reservoir. A master cylinder piston within the master cylinder slidably seals against the seal arrangement in order to pressurize fluid within the master cylinder, and thereby pressurize the downstream braking circuits. 
         [0003]    In modern braking systems a boost system is typically provided to supply a boost function (i.e., assist in moving the master cylinder piston by providing a boosted force to the master cylinder piston in place or in addition to a force provided by the operator to a brake pedal). Typically the boost function is provided by either a vacuum boost system utilizing available vacuum in an engine, or by a hydraulic boost system. In the hydraulic boost system, a high pressure fluid generator, e.g., a pump, provides high fluid pressure to an accumulator which is utilized to provide the desired boost function. 
         [0004]    The hydraulic boost system uses position of an input rod that is mechanically coupled to the brake pedal in order to determine the amount of boost. The amount of boost that is provided to the master cylinder piston is relative to the position of the brake pedal. 
         [0005]    Furthermore, in a failure mode (i.e., when the high pressure system is inoperable), providing a limited braking function remains desirable. 
         [0006]    Therefore, it is highly desirable to provide a hydraulic boost system utilizing a high pressure source which is capable of quickly reacting to movement of the brake pedal and provide a boosted force to the master cylinder piston in response to the position of the input rod coupled to the brake pedal and also provide a limited braking function in a failure mode in which the high pressure source is inoperable. 
       SUMMARY 
       [0007]    According to one embodiment of the present disclosure, there is provided a braking system with an electric hydraulic booster. The braking system with an electric hydraulic booster includes a booster chamber, a booster piston activating chamber, a booster piston located between the booster chamber and the booster activating chamber, and a solenoid valve operably connected to a high pressure source, the booster chamber, and the booster piston activating chamber, the solenoid movable between (i) a first position whereat the booster chamber and the booster piston activating chamber are in fluid communication and fluidly isolated from the high pressure source, (ii) a second position whereat the booster chamber and the booster piston activating chamber are fluidly isolated from each other and from the high pressure source, and (iii) a third position whereat the booster piston activating chamber and the high pressure source are in fluid communication and fluidly isolated from the booster chamber. 
         [0008]    According to one embodiment of the present disclosure, there is provided a braking system with an electric hydraulic booster. The braking system with an electric hydraulic booster includes a high pressure source, a booster chamber, a booster piston rearward of the booster chamber, and a solenoid valve including a first port selectively fluidly coupled with the high pressure source, a second port selectively fluidly coupled with the booster chamber, and a third port in fluid communication with a rear facing portion of the booster piston. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  depicts a partial cross sectional view of a braking system including a high pressure accumulator, a reservoir, a boost piston assembly, a master cylinder assembly, and a pressure regulating assembly, wherein the pressure regulating assembly is positioned in a first position; 
           [0010]      FIG. 2  depicts a partial cross sectional view of the boost piston assembly, depicted in  FIG. 1 ; 
           [0011]      FIG. 3  depicts a partial cross sectional view of the master cylinder assembly, depicted in  FIG. 1 ; 
           [0012]      FIG. 4  depicts a partial cross sectional view of the pressure regulating assembly, depicted in  FIG. 1 ; 
           [0013]      FIG. 5  depicts a partial cross sectional view of the braking system shown in  FIG. 1  in an initial activation position, wherein the pressure regulating assembly is placed in a second position; and 
           [0014]      FIG. 6  depicts a partial cross sectional view of the braking system shown in  FIG. 1  in a subsequent activation position, wherein the pressure regulating assembly is placed in a third position. 
       
    
    
     DESCRIPTION 
       [0015]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one of ordinary skill in the art to which this invention pertains. 
         [0016]    Referring to  FIG. 1 , a partial cross sectional view of a braking system  100  is depicted. The braking system  100  includes a housing  102 , a high pressure accumulator  104 , and a reservoir  106 . The high pressure accumulator  104  is mechanically coupled to the housing  102  and is fluidly coupled to a high pressure generator (not shown), e.g., a pump (typically an electric motor/pump is utilized for this purpose). The high pressure generator (not shown) is fluidly coupled to the reservoir  106  and maintains high pressure within the high pressure accumulator  104  by pumping fluid from the reservoir  106  thereto. 
         [0017]    The braking system  100  further includes a boost piston assembly  108  and a master cylinder assembly  110 . The boost piston assembly  108  is slidably disposed within the housing  102  and is configured to move from right to left with reference to  FIG. 1  in response to application of high pressure fluid from the high pressure accumulator  104 , as described further below. An input rod  112  is partially positioned within the boost piston assembly  108  and is configured to move therein. The input rod  112  is coupled to a brake pedal (not shown) in a manner in which movement of the brake pedal (not shown) is translated into linear movement of the input rod  112 . The input rod  112  includes a collar  114  which interfaces with a washer  166  to limit the rightward travel of the input rod  112 , as described further below with reference to  FIG. 2 . Additionally, a spring  115  is positioned between the collar  114  and the boost piston assembly  108  and is configured to bias the input rod  112  away from the boost piston assembly  108 , and particularly toward the washer  166 . 
         [0018]    Also included in the braking system  100  is a pressure regulating assembly  116 . The pressure regulating assembly  116  is mechanically coupled to the housing  102  and is in fluid communication with the high pressure accumulator  104  and the reservoir  106 . The pressure regulating assembly  116  defines a booster piston activating chamber  118 , an internal chamber  120 , and a fluid channel  124 . 
         [0019]    The interface between the boost piston assembly  108  and the master cylinder assembly  110  defines a boost chamber  126 , while the master cylinder assembly defines a master cylinder chamber  128 . The boost chamber  126  is in selective fluid communication with the reservoir  106  via a fluid channel  208 , a chamber  130  and a fluid channel  132  (see also  FIG. 3 ). The master cylinder chamber  128  is also in selective fluid communication with the reservoir  106  via a fluid channel  206 , and also in continuous fluid communication with a downstream braking circuit (not shown). 
         [0020]    Referring to  FIG. 2 , a partial cross sectional view of the boost piston assembly  108  is depicted. The boost piston assembly  108  includes a rear body portion  152 , a reaction washer assembly  154 , and a front body portion  158 . The front body portion  158  includes a cavity  160  which partially defines the boost chamber  126 . Within the cavity is a spring  210  (depicted in phantom) which biases the front body portion  158  away from a master cylinder piston  205  of the master cylinder assembly  110 , described further below in reference to  FIG. 3 . The front body portion  158  interfaces with the rear body portion  152  via the reaction washer  154 . 
         [0021]    The reaction washer assembly  154  is a composite member which may include a resilient member  155  and a stiff member  156 . Alternatively the reaction washer assembly  154  may be a single stiff member. The reaction washer assembly  154  is positioned within a cavity  157  of the rear body portion  152 . 
         [0022]    The rear body portion  152  also includes a cavity  168  for receiving the input rod  112  and a travel sensor  162 . The input rod  112  (depicted in phantom) is slidably positioned within the cavity  168  and is configured to move leftward within the cavity  168 , but be limited in its rightward by the washer  166 , as described above. The washer  166  is fixedly coupled to the rear body portion  152 . 
         [0023]    The travel sensor  162  is also fixedly coupled to the rear body portion  152  and is configured to generate an electrical signal placed on a cable  164  corresponding to the relative position of the input rod  112  with respect to the travel sensor  162 . The cable  164  may have multiple wires for transmitting and receiving signals thereon. The travel sensor  162  is coupled to an electronic control unit (ECU, not shown) which is configured to the control pressure regulating assembly  116  and the pressure within the boost activating chamber  118  and the boost chamber  126 , as further described below. The ECU (not shown) contains memory including program instructions that may be executed by a processor aboard the EC (not shown). 
         [0024]    The travel sensor  162  may be of a digital type sensor, e.g., a frequency shift keying type, configured to generate a signal with varying frequencies, or an analog type sensor, e.g., an amplitude modulated type sensor configured to generate varying amplitudes in response to position of the input rod  112 . 
         [0025]    As described above, the spring  115  (depicted in phantom) biases the input rod  112  away from a step  170  formed in the rear body portion  152  by providing a biasing force on the collar  114  of the input rod  112 . 
         [0026]    The boost piston assembly  108  also includes seals  172  and  174  for sealing the rear body portion  152  against the housing  102 . 
         [0027]    Referring to  FIG. 3 , a partial cross sectional view of the master cylinder assembly  110  is depicted. The master cylinder assembly  110  includes a cylinder  202  defining an end portion  204 , the master cylinder piston  205  and the fluid channels  206  and  208 . The space between the end portion  204  and the master cylinder piston  205  defines the master cylinder chamber  128  while the space between the master cylinder piston  205  and the front body portion  158  (depicted in phantom) of the boost piston assembly  158  defines the boost chamber  126 . As described above, the spring  210  biases the front body portion  158  away from the master cylinder piston  205 , while a spring  212  biases the master cylinder piston  205  away from the end portion  204 . 
         [0028]    A seal  214  is configured to isolate the boost chamber  126  from the reservoir  106 . For example, as depicted in  FIG. 3 , the front body portion  158  (depicted in phantom) is position beyond the fluid channel  208  but not beyond the seal  214 . Therefore, the boost chamber  126  as depicted in  FIG. 3  remains in fluid communication with the reservoir  106 . 
         [0029]    Two seals  216  and  218  are configured to isolate the master cylinder chamber  128  from the reservoir  106 . For example, as depicted in  FIG. 3 , the position of the master cylinder piston  205  is beyond the seal  216  and the fluid channel  206 , but not beyond the seal  218 . Therefore, the master cylinder chamber  128  as depicted in  FIG. 3  is in fluid communication with the reservoir  106 . 
         [0030]    Referring to  FIG. 4 , a partial cross sectional view of the pressure regulating assembly  116  is depicted. The pressure regulating assembly  116  includes a body portion  252  (depicted in segments) and a bracket  254 . The body portion  252  is sealed with the housing  102  by seals  250  and  251 . 
         [0031]    The pressure regulating assembly  116  also includes a seal member  256  which is sealingly disposed between an inlet member  258  defining an inlet seat  262  and a spring loaded socket  266 . The spring loaded socket  266  is biased away from the body portion  252  and toward the seal member  256  by a spring  268 . The spring loaded socket  266  is configured to interface with the seal member  256  in a sealed manner in which the high pressure accumulator  104  is isolated from the interface between the seal member  256  and the spring loaded socket  266 . 
         [0032]    The pressure regulating assembly  116  also includes a solenoid assembly  270 . The solenoid assembly is biased away from the inlet member  258  by the spring  272 . The solenoid assembly  270  includes a coil  274 , a core  276 , and a core extension  280 . The coil  274  is fixedly coupled to the body portion  252 , while the core  276  and the core extension  280  are slidably disposed between segments of the body portion  252 . The core extension  280  is fixedly coupled to the core  276  and is configured to move in response to movement of the core  276 . The core extension  280  may be integrally formed with the core  276  or may be formed as a separate member coupled to the core  276  with a fastener. The core extension  280  includes a hollow center  282  which is in fluid communication with the chamber  130  and, therefore, with the reservoir  106 . 
         [0033]    The pressure regulating assembly  116  also includes a hollow outlet seat  284  with an inner bore  286 . The outlet seat  284  is aligned with the core extension  280  in a manner in which the inner bore  286  of the outlet seat  284  is substantially aligned with the hollow center  282  of the core extension  280 . 
         [0034]    The outlet seat  284  is fixedly coupled to the core extension  280  at a first end of the outlet seat  284 . The interface between the outlet seat  284  and the core extension  280  may be one of a permanent type, e.g., welded members, or of a fastened type. The outlet seat  284  includes a seat  288  at a second end of the outlet seat  284 . The seat  288  is configured to interface with the seal member  256  and form a seal. 
         [0035]    The operation of the braking system  100  is described with initial reference to  FIG. 1 . The position of the input rod  112  depicted in  FIG. 1  corresponds to the brake pedal (not shown) in a released position. The position of the braking system  100  depicted in  FIG. 1  is hereinafter referred to as the “rest” position. In the rest position, the boost chamber  126  and the master cylinder chamber  128  are in fluid communication with the reservoir  106  via the fluid channels  208  and  206  (see  FIG. 3 ). 
         [0036]    In the rest position, the solenoid assembly  270  is de-energized by the ECU (not shown). Therefore, the spring  272  biases the outlet seat  284  to a location spaced apart from the seal member  256 . Thus, the inner core  286  and the hollow center  282  provide a vent path for the boost activating chamber  118  through the fluid channel  124  to the chamber  130  and the reservoir  106  (see  FIG. 4 ). 
         [0037]    Additionally, the spring  268  acting on the spring loaded socket  266  which is firmly in contact with the seal member  256  (or integrally formed therewith) forces the seal member  256  against the inlet seat  262  of the inlet member  258 , thereby sealing the boost activating chamber  118  from high pressure accumulator  104 . 
         [0038]    Therefore, the boost chamber  126  which is in fluid communication with the chamber  130  in the rest position is in fluid communication with the boost activating chamber  118  and isolated from the high pressure accumulator  104 . 
         [0039]    Referring to  FIG. 5 , the input rod has moved leftward as compared to  FIG. 1 , in response to the operator applying a force to the brake pedal (not shown). The movement of the input rod is particularly exemplified by the separation between the collar  114  and the washer  166 . The spring  115  is compressed in response to the leftward movement of the input rod  112 . 
         [0040]    The travel sensor  162  senses the leftward movement of the input rod  112  and provides a signal on the cable  164  to the ECU (not shown). The ECU (not shown) receives the signal and energizes the coil  274 , e.g., by providing a first voltage level to the coil  274 , which magnetically force the core  276  and the core extension  280  rightward (with reference to  FIG. 5 ). Since the outlet seat  284  is fixedly coupled to the core extension  280 , the outlet seat  284  moves rightward and makes contact with the seal member  256 . 
         [0041]    The position of the braking system depicted in  FIG. 5  is also referred to as the initial activation position. In the initial activation position, the seat  288  of the outlet seat  284  seals against the seal member  256 , thus, the fluid path including the hollow center  282  and the inner core  286  of the outlet seat  284  no longer provides fluid communication between the chamber  130  and the boost activating chamber  118 . Therefore, these chambers are isolated from each other. Since the boost chamber  126  in the rest position depicted in  FIG. 1  or the initial activation position depicted in  FIG. 6  is in fluid communication with the chamber  130 , the boost chamber  126  is also isolated from the boost activating chamber  118 . 
         [0042]    Since the inlet seat  262  of the inlet member  258  remains firmly seated on the seal member  256 , thereby providing a seal, the boost activating chamber  118  and the boost chamber  126  remain isolated from the high pressure accumulator  104 . In the initial activation position, the braking system is in a ready position to provide the desired braking function. 
         [0043]    Referring to  FIG. 6 , the input rod  112  has traveled further leftward. The travel sensor  162  senses the leftward travel of the input rod  112  and places an electrical signal corresponding to the position of the input rod  112  on the cable  164 . The ECU (not shown) receives the signal and further energizes the coil  274 , e.g. by providing a second voltage level which is higher than the first voltage level. In response to the additional energizing of the coil  274 , the core  276  and the core extension  280  travel further rightward with reference to  FIG. 6  which rightward movements cause the outlet seat  284  to further move rightward. The additional rightward movement of the outlet seat  284  moves the seal member  256  off of the inlet seat  262  of the inlet member  258 . The force applied to the seal member  256 , which remains in firm contact with the spring loaded socket  266 , by the outlet seat  284  compresses the spring  268  (see also  FIG. 4 ). In this position, the booster activating chamber  118  and the high pressure accumulator  104  are in fluid communication with each other via the internal chamber  120  and the fluid channel  124 . 
         [0044]    With fluid entering the boost activating chamber  118 , pressure therein begins to rise. In response to the pressure rise, the boost piston assembly  108  moves leftward and thereby moves the front body portion  158 , which is in contact with the reaction washer assembly  154 , leftward (with reference to  FIG. 6 ). The leftward movement of the boost piston assembly  108  causes the front body portion  158  to seal against the seal  214 , and thereby isolates the boost chamber  126  from the chamber  130  and the reservoir  106  (see also  FIG. 3 ). 
         [0045]    Once the boost chamber  126  is isolated from the reservoir  106 , pressure rises in the boost chamber  126 . The pressure rise applies a force to the master cylinder piston  205  which moves it leftward sealing against the seal  218 , which thereby isolates the master cylinder chamber  128  from the reservoir  106 . 
         [0046]    Once the master cylinder chamber  128  is isolated from the reservoir  106 , pressure in the master cylinder chamber  128  rises. Since the master cylinder chamber  128  is in continuous fluid communication with the downstream braking circuit (not shown), the pressure rise provides the desired braking function. 
         [0047]    With the leftward movement of the boost piston assembly  108 , the washer  166  once again comes in contact with the collar  114  (as depicted in  FIG. 6 ). The relative positions of the input rod  112  and the boost piston assembly  108 , and in particular the travel sensor  162 , causes the travel sensor  162  to generate a signal in correspondence thereto. The signal generated by the travel sensor  162 , and placed on the cable  164 , is received by the ECU (not shown). In response thereto, the ECU (not shown) reduces the energy provided to the coil  274 , e.g., by providing a third voltage to the coil  274 , whereby the third voltage is substantially the same as the second voltage. 
         [0048]    In response to receiving the smaller energy, the coil  274  provides a smaller magnetic force. Since the core  276  and the core extension  280  are biased away from the inlet member  258  which is fixedly coupled to the body portion  252 , the core  276  and the core extension  280  move leftward (with reference to  FIG. 6 ). Since the outlet seat  284  is fixedly coupled to the core extension  280 , the outlet seat  284  also moves leftward, which allows the seal member  256  to seal against the inlet seat  262  of the inlet member  258  (see also  FIG. 4 ). Therefore, the solenoid assembly  270  returns to the position depicted in  FIG. 5 . As described above, in the position depicted in  FIG. 5 , the boost activating chamber  118  and the boost chamber  126  are isolated from each other and from the high pressure accumulator  104 . The difference with the position of the boost piston assembly  108  and the master cylinder assembly  110  that is depicted in  FIG. 5 , however, is that the boost chamber  126  in  FIG. 6  is isolated from the reservoir  106 . In this isolated position, the pressure in the boost chamber is raised, as compared to the boost chamber  126  in  FIG. 5 , and thereby maintains a force on the master cylinder piston  205 . 
         [0049]    The ECU (not shown) continues to increase and decrease the energy applied to the coil  274  by switching between the first and second voltage levels. Thereby the seal member  256  moves right and left with respect to  FIG. 6 , in order to provide a modulation of pressure in the boost activating chamber  118 . 
         [0050]    While not shown, the boost chamber  126  may be continuously coupled to another downstream braking circuit, in order to provide a separate braking function. 
         [0051]    Also, while not shown, in the event of a failure of high pressure in the high pressure accumulator  104 , e.g., due to failure of the high pressure generator (not shown), the input rod  112  may in response to movement of the brake pedal (not shown) move leftward and make contact with the reaction washer assembly  154 . The contact between the input rod  112  and the reaction washer assembly  154  provides the capability of moving the front body portion  158  to provide braking without the boost function. Release of the brake pedal (not shown) moves the input rod  112  rightward which moves the reaction washer assembly  154  and the front body portion  158  rightward, to reduce the braking. The rightward movement is partially generated by the biasing force of the spring  115 . 
         [0052]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.
A braking system with an electric hydraulic booster includes a booster chamber, a booster piston activating chamber, a booster piston located between the booster chamber and the booster activating chamber, and a solenoid valve operably connected to a high pressure source, the booster chamber, and the booster piston activating chamber, the solenoid movable between (i) a first position whereat the booster chamber and the booster piston activating chamber are in fluid communication and fluidly isolated from the high pressure source, (ii) a second position whereat the booster chamber and the booster piston activating chamber are fluidly isolated from each other and from the high pressure source, and (iii) a third position whereat the booster piston activating chamber and the high pressure source are in fluid communication and fluidly isolated from the booster chamber.