Abstract:
A brake booster wherein second and third pistons are separated within a bore of a master cylinder to define second and third chambers. Compensation valves control the flow fluid from a reservoir to the bore while a passage in the second piston connects the second chamber with the third chamber that is connected to the reservoir through an tilt valve that is held opened by pressurized fluid acting on a fourth piston. A control valve responds to a resiliently applied force from an input rod carried by the third piston to supply pressurized fluid to the brake system. In an event pressurized fluid is unavailable, a spring moves the fourth piston and a sixth spring to moves the tilt valve against a seat to seal the third chamber and create a hydraulic lock. Further movement of the third piston correspondingly moves the second piston to effect a manual brake application.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a blended brake booster having a hydraulic lock during a manual brake application. 
     2. Description of the Related Art 
     The present invention is of a type hydraulic brake boosters referred to as a “full-power” brake booster, of which the following U.S. Pat. Nos. are considered to be typical: 4,441,319; 4,490,977; 4,514,981; 4,665,701; 4,685,297; 4,704,867; 4,724,674; 5,526,731, 5,927,074, 6,606,859 and 7,354,116. In such brake boosters, an accumulator is charged with fluid pressure and selectively activated through movement of a control valve by an input member to present pressurized fluid to an actuation chamber that acts on an actuation piston and is directly supplied to a first set of wheel brakes. The pressurized fluid acts on the actuation piston in to develop a force for moving a power piston in a master cylinder that pressurizes operational fluid that is presented to a second set of wheel brakes to effect a brake application. The operational pressure that is developed in the master cylinder is proportional to the force applied to the actuation piston and inversely proportional to the cross-sectional area of the power piston in the master cylinder for a given force applied to an input member by an operator to move the control valve. The resulting travel of the input member and brake pedal is proportional to the travel of the actuation piston in the master cylinder. Conversely, the travel of the power piston in the master cylinder is also proportional to the displacement of the fluid in the brake system at any given pressure and inversely proportional to the cross-sectional area of the actuation piston. Thus, the travel of the input member and brake pedal is inversely proportional to the cross-sectional area of the actuation piston. Given these facts, when brake blending is implemented during a brake application with such prior art structure, a pulsation may be felt by an operator on the input pedal. 
     SUMMARY OF THE INVENTION 
     The present invention provides structure for a brake booster in a brake system wherein an input pedal is not affected by the opening and closing of build and decay valves to effect traction control during a power brake application and wherein a hydraulic lock is produced during a manual brake application. 
     In more particular detail the brake booster has a housing with a first axial bore therein for receiving a first piston that is separated from the bottom of the axial bore by a first spring to define a first chamber, a second piston that is separated from the first piston by a second spring that holds the second piston against a first stop to define a second chamber and a third piston that is separated from the second piston by a third spring that urges the third piston against a second stop to define a third chamber. The first chamber is connected to a reservoir through a first inlet port and to a first set of wheel brakes through a first outlet port while the second chamber is connected to a second set of wheel brakes through a second outlet port and the third chamber that is connected to the reservoir through a second inlet port and to the second chamber through a passage in the second piston. The second piston has a second axial bore therein that is connected to a supply port source to receive pressurized fluid from a source, the second axial bore a control valve for controlling communication of the pressurized fluid presented to the supply port to the first passage as a function to an input force supplied by an actuator rod. The actuator rod is resiliently connected to the third piston and moves in response to a manual brake force applied to a pedal by an operator. During a brake application should a brake blending traction function be implemented, additional pressurized fluid may be added and subtracted to the pressurized fluid supplied to the first and second set of brakes, this adding and subtracting is compensated by the balancing of the force from the resiliently positioned input rod. Fluid communication with the reservoir is controlled by a poppet valve associated with the first inlet port and by a tilt valve associated with the second inlet port. The tilt valve is characterized by being held in an opened state by the position of the third piston in a rest position or by the pressurized fluid from the source acting on a compensation piston such that the third chamber remains connected to the reservoir during a power brake application resulting from the presentation of pressurized fluid to the second chamber while in an absence of pressurized fluid from the source the, a first compensation spring moves the compensation piston and a second compensation spring closes the tilt valve on movement of the third piston. When the tilt valve closes, the third chamber is sealed and a hydraulic lock is created such the fluid pressure developed by movement of the third piston by the manual brake force moves the second piston away from the first stop and correspondingly pressurizes fluid in the second chamber to effect a manual brake application. 
     An object of this invention is to provide blending of pressurized fluid developed in a master cylinder with additional pressurized fluid supplied by a traction control source during a power brake application without causing movement of an input brake pedal. 
     A further object of this invention resides in the development of a hydraulic lock in a master cylinder such that a manual brake application moves a control piston to develop pressurized fluid to effect a brake application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a brake system with a sectional view of a brake booster according to the present invention a position of rest; 
         FIG. 2  is an enlarged sectional view of the circumscribed area  2  of  FIG. 1 ; 
         FIG. 3  is a sectional view of the brake booster of  FIG. 1  in a actuation mode of operation wherein pressurized fluid available to the brake booster is supplied to the brake system to effect a brake application in response to an operator input force; 
         FIG. 4  is an enlarged sectional view of the circumscribed area  4  of  FIG. 4 ; 
         FIG. 5  is a sectional view of the brake booster of  FIG. 1  in a manual mode of operation to effect a brake application in response to an operator input force; and 
         FIG. 6  is an enlarged sectional view of the circumscribed area  6  of  FIG. 5 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several drawing views and may be identified by the same reference number. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and particularly to  FIG. 1 , there is shown a brake system  12  with a brake booster  14  that responds to an input force applied to a pedal  16  by an operator to supply pressurized fluid from a first source  18  of pressurized fluid to a first set of wheel brakes  22 ,  22 ′ and a second set of wheel brakes  24 ,  24 ′ to effect a brake application. Each of the wheel brakes  22 ,  22 ′,  24 ,  24 ′ include a wheel speed sensor  26 , a build valve  30  and a decay valve  32  that provides information to an ECU  28  that controls the presentation of an additional pressurized fluid from a second source  36  of pressurized fluid to the first  22 ,  22 ′ and second  24 ,  24  set of wheel brakes if needed during a brake application. The presentation of pressurized fluid from the second source  36  to a wheel brake  22 ,  22 ′,  24 ,  24 ′ may cause a fluid pressure osculation that could be felt on the brake booster  14 ; however, the present invention prevents such osculation from being presented to the brake pedal  16 . 
     In more particular detail, as best illustrated in  FIG. 1 , the brake booster  14  has a housing  40  with a first axial bore  42  therein for receiving a first piston  44  that is separated from the bottom  41  of the axial bore  42  by a first spring  46  to define a first chamber  48 , a second piston  50  that is separated from the first piston  44  by a second spring  52  that holds the second piston  50  against a first stop  54  to define a second chamber  56  and a third piston  58  that is separated from the second piston  50  by a third spring  60  that urges the third piston  58  toward a second stop  62  to define a third chamber  64 . 
     The first chamber  48  is connected to a reservoir  66  through a first inlet port  68  and to the first set of wheel brakes  22 ,  22 ′ through a first outlet port  70  while the second chamber  56  is connected to the second set of wheel brakes  24 ,  24 ′ through a second outlet port  72  and the third chamber  64  that is connected to the reservoir  66  through a second inlet port  74  and to the second chamber  56  by way of a passage  76  in the second piston  50 . 
     The second axial bore  78  is connected to a supply port  80  through a cross bore  82  and a groove  84  in the second piston  50  to receive pressurized fluid from the first source  18 . A check valve  86  defined by a ball  88  and spring  90  is associated with the supply port  80  to prevent the flow of fluid from the second chamber  56  toward the first source  18  of pressurized fluid. The second axial bore  78  opens at one end to the second chamber  56  and is fluidly connected to the passage  76  at the other end. Communication of pressurized fluid from the second axial bore  78  to the passage  76  is under the control of a control valve  92  as a function of an input force supplied by an actuator rod  104  resiliently connected to the third piston  58 . 
     The control valve  92  includes a stem  94  located in the second axial bore  78  with a ball  98  attached thereto that is urged toward a seat  100  by a spring  102  to isolate the fluid under pressure from the first source  18  from the passage  76  in the second piston  50 . 
     The third piston  58  is defined by a cylindrical body  120  that is located in the axial bore  42  and urged by spring  60  toward the third stop  62  to define a false travel or the third chamber  64 . The cylindrical body  120  has an extension  121  that projects into the third chamber  64  with an annular rib  106  thereon that engages a stem  200  on a tilt valve  202  located in a second inlet port  74 . The cylindrical body  120  has an axial bore  122  that receives a solid end  107  of the actuator rod  104 . 
     The solid end  107  of the actuator rod  104  extends to an annular spring retainer  108  from which a hollow stem  103  extends toward the valve seat  100 . The hollow stem  103  has a cross bore  109  therein to connect the third chamber  64  with the second axial bore  78  and passage  76  in the second piston  50 . An actuation spring  110  is located between the spring retainer  108  and the third piston while a return spring  112  is located between the spring retainer  108  and the second piston  6   50 . In a position of rest as illustrated in  FIGS. 1 and 2 , return spring  112  positions the actuator rod  104  such that the end  105  of the hollow stem  103  is adjacent ball  98  and passage  76  is opened to the third chamber  64  via the hollow stem  103  and reservoir  66  via the inlet port  74 . 
     Communication from reservoir  66  to the first axial bore  42  through the first inlet port  68  and second inlet port  74  are respectively under the control of a first compensation valve  220  that is in axial alignment with axial bore  42  and a second compensation valve  240  that is in radial alignment with the axial bore  42 . 
     The first compensation valve  220  includes a poppet  222  that is attached to a shaft  224  to cage the first spring  46  and a closure spring  226  located between poppet  222  and a retainer  228 . 
     The second compensation valve  240  includes tilt valve  202  located in the second inlet port  74  and a piston  242  located in chamber  77  of control port  73 . The tilt valve  202  has a head  244  with a first stem  200  that extends there from into the first axial bore  42 , a spring  246  urges the head  244  toward a seat  248 . The second inlet port  74  is connected to reservoir  66  by passage  250  such that the third chamber  64  is in communication to receive fluid from reservoir  66  and dispel fluid from chamber  64  to the reservoir  66 . The piston  242  which is located in control port  73  is connected by passage  75  to the first source  18  of pressurized fluid, has a second stem  252  that extends there from and engages head  244  on the tilt valve  202  to hold head  244  off seat  248  as long as pressurized fluid is available from the first source  18 . A spring  254  is located in the control port  73  to urge the piston  242  away from head  244  whenever pressurized fluid is not available from the first source  18  in chamber  77 . 
     MODE OF OPERATION 
     The brake system  12  as illustrated in  FIGS. 1 and 2  the brake booster  14  is in a position of rest with the first chamber  48  and third chamber  64  in communication with reservoir  66 . The first source  18  of pressurized fluid is available at a level determined by a pressure switch that is in communication with the Electronic Control unit (ECU)  28  that controls the activation of a pump and motor that supplied pressurized fluid to an accumulator, the supply port  80  and passage  75  of control chamber  77  in brake booster  14 . The pressurized fluid in the supply port  80  is communicated to axial bore  78  in the second piston  50  and acts on ball  98  of control valve  92  to urge the ball  98  toward seat  100  and seal the supply port  80  from the axial bore  42  of the brake booster  14  while the pressurized fluid in control chamber  77  acts on and moves piston  242  such that stem  252  engages head  244  of tilt valve  202  to hold head  244  off seat  248  and provide a flow path between chamber  64  and reservoir  66 . 
     When an operator desires to effect a brake application, an input force is applied to pedal  16  that moves the third piston  58  within axial bore  42  as illustrated in  FIGS. 3 and 4  by overcoming spring  60  however the second piston  50  remains stationary against the first stop  54 . The initial movement of piston  58  provides a force that is applied through actuation spring  110  to move the end  105  of hollow stem  103  on actuation rod  104  into engagement with ball  98  and close communication from passage  76  to chamber  64  and even though rib  106  moves away from stem  200  the tilt valve  202  remains open as it is under the control of piston  242 . Once end  105  engages ball  98 , further movement by the actuation rod  104  moves ball  98  off seat  100  and pressurized fluid from the first source  18  is allowed to flow past stem  94  and ball  98  and is communicated to the second chamber  56  by way of passage  76  to the second set of wheel brakes  24 , 24 ′ by way of outlet port  72  and the various conduits illustrated in  FIG. 1 . The pressurized fluid in the second chamber acts on and moves piston  44  to overcome spring  46  and allow spring  226  to move poppet  224  and close inlet port  68  and pressurize fluid in chamber  46  that is supplied to the first set of wheel brakes  22 , 22 ′ to effect a brake application corresponding to the input force applied to pedal  16 . When the fluid pressure in the second chamber corresponds to the desired brake application, the fluid pressure acts on stem  94  to move ball  98  into engagement with seat  100  and sustain the brake application. During a brake application, each individual wheel sensor  26  supplies the ECU with input signals relating to a current functional operation of the vehicle, in addition to other inputs and data relating to the vehicle including but not limited to: the 8 operation of the motor pump; the pressure of the pressurized supply fluid; dynamic forces experienced by the vehicle; accumulator fluid supply pressure, the level of fluid in a reservoir and etc., all such inputs and data may effect a brake application. Should the ECU determine that an individual brake  22 , 22 ′,  24 ,  24 ′ be functioning in a manner different from a desired standard, fluid pressure from a second source  36  developed by a second motor and pump may be added or subtracted from the pressurized fluid presented to an individual brake  22 , 22 ′,  24 ,  24 ′. The adding and subtraction of pressurized fluid to the brake system may be transmitted back to chamber  48  or chamber  56  of the brake booster  14  provided, however, the end  105  of the hollow stem  103  of the actuation rod  104  may be moved away from ball  98  and pressurized fluid dispelled into chamber  64  while the actuation spring  110  absorbs any such change and as a result the pedal  16  does not oscillate or feel any change in the braking application. 
     When a brake application is completed, return spring  60  moves piston  58  against stop  62  and rib  106  engages stem  200  of tilt valve  202  which is already off seat  248  to assure chamber  64  is in communication with reservoir  66 . On termination of the input force on the third piston  58 , return spring  112  moves end  105  of the hollow stem  103  of the actuation rod  104  away from ball  98  and opens communication from the second chamber  56  to the reservoir  66  by way of passage  76 , hollow stem  103 , cross bore  109  and chamber  64 . 
     In an event pressurized fluid is not available from the first source  18 , spring  254  moves piston  242  away from head  244  and brings the tilt valve  202  under the control of the position of the third piston  58 . Thereafter should an operator desire to effect a brake application, an input force applied to pedal  16  moves piston  58  within bore  42  such that projection or rib  106  on extension moves away from stem  200  on tilt valve  202  and spring  246  moves head  244  against seat  248  to seal chamber  64  from reservoir  66  and create a hydraulic lock. The hydraulic lock transmits an actuation force corresponding to the force applied to the third piston  58  by the pedal  16  to move the second piston  50  away from stop  54  and pressurize fluid in chamber  56  that is communicated through outlet port  72  to the set of wheel brakes  24 , 24 ′ to initiate a brake application. The build up of fluid pressure in chamber  56  acts on and moves piston  44  to close the communication through port  68  and pressurize fluid in chamber  48  that is communicated through outlet port  70  to the set of wheel brakes  22 , 22 ′ to complete the manual brake application.