Abstract:
A master cylinder assembly including a boost assembly. The hydraulic master cylinder includes a cylinder defining an elongated bore, a piston slidably positioned in said bore, inlet means in the cylinder for admitting hydraulic fluid into the bore from a reservoir, and an outlet fitting in said cylinder communicating with said bore and operative to convey hydraulic fluid out of the bore for delivery to a brake device in response to linear movement of the piston in the bore. The boost assembly includes an electric motor. A hollow ball nut and screw assembly is operably connected to the motor. A screw of the ball nut and screw assembly is positioned to advance the piston in response to actuation of the motor. An input rod extending through the screw includes a first end positioned to receive a brake input force and a second end positioned to advance the piston independently from the screw. The assembly further includes sensing and control means to sense the brake input force and control the motor responsive to the brake input force.

Description:
TECHNICAL FIELD 
     This invention relates to master cylinder assemblies, and more particularly to a master cylinder assembly in which the master cylinder includes a boost feature. The boost feature includes an electric motor actuated feature forming a part of the master cylinder assembly. 
     BACKGROUND OF THE INVENTION 
     Master cylinders are in wide use in various industries, but particularly in the motor vehicle industry wherein they serve in conjunction with an associated slave or wheel brake cylinder located at each of the wheels of the vehicle. Each wheel brake cylinder is supplied with pressurized fluid when an operator depressing the brake pedal of the vehicle actuates the master cylinder. Although manual actuation of the master cylinder can be effective to produce the desired resultant action at the associated brake cylinder, often it is desirable to provide power-assist operation of the master cylinder. 
     Many current brake systems include such a power-assist feature using engine vacuum to boost the operation of the master cylinder. In a system where engine vacuum is not available, such as in an electric-powered vehicle, it would be desirable to provide a brake boost feature that provides similar functionality as that of vacuum or other boost schemes. It would be further advantageous to provide a master cylinder having a non-vacuum boost feature in combination with a manual actuation feature in order to ensure continuous operation of the brake system in the event the boost feature becomes disabled. 
     SUMMARY OF THE INVENTION 
     The object of this invention is directed to the provision of an improved master cylinder assembly. More particularly, this invention is directed to the provision of a power operated master cylinder assembly especially suitable for use in a braking system of a motor vehicle. 
     In one aspect of the invention, the master cylinder assembly comprises a motor having a housing; a hydraulic master cylinder including a housing rigidly connected with a transmission housing, wherein the master cylinder includes a cylinder defining an elongated bore, a piston movable linearly and slidably in the bore, inlet means in the cylinder for admitting hydraulic fluid into the bore from a reservoir and an outlet fitting in the cylinder communicating with the bore and operative to convey hydraulic fluid out of the bore for delivery to a braking device in response to linear movement of the piston in the bore. An input rod is positioned to effect movement of the piston. In addition to the input rod, a hollow ball screw assembly is separately operative in response to actuation of the input rod by a brake pedal to move the piston linearly in the bore. This arrangement provides a simple and compact drive mechanism with a manual push through especially suitable for any situation requiring a power boosted manual brake master cylinder. 
     Another aspect of the invention provides a master brake cylinder assembly including a hydraulic master cylinder with a piston slidably positioned in a cylinder. A hollow ball screw assembly is positioned to advance the piston in response to actuation of a motor and an input rod extends through the hollow ball screw assembly to apply an input force to the piston independently of the hollow ball screw assembly. 
     Other aspects of the invention provide a hydraulic master brake cylinder assembly wherein the cylinder defines an elongated bore, inlet means in the cylinder for admitting hydraulic fluid into the bore from a reservoir, and an outlet fitting in said cylinder communicating with said bore and operative to convey hydraulic fluid out of the bore for delivery to a brake device in response to linear movement of the piston in the bore. 
     Other aspects of the present invention provide an assembly further including sensing and control devices to sense the input force and control the motor responsive to the brake input force. The sensing device can include a differential force sensing assembly positioned adjacent an output end of the input rod. The differential force sensing assembly can include an elastomeric member positioned at the output end of the input rod. The output end of the input rod can include a position sensor associated therewith. The differential force sensing assembly can include at least one magnet associated with an output button, the output button contacting the piston. Compression of the elastomeric member causes relative movement between the position sensor and the magnet. 
     Other aspects of the present invention provide a transmission to drivingly connect the motor and hollow ball screw assembly. The transmission can include at least two pulleys, one of which is connected to the motor and the other of which is connected to the ball screw assembly, the at least two pulleys being drivingly connected by a belt. The transmission can further include a clutch. The clutch, when activated, couples the transmission to the motor. The clutch, when deactivated, allows the transmission to turn freely. The motor can include a primary motor and a secondary motor. The primary motor and the secondary motor each have a pulley connected thereto, the transmission further comprising an idler pulley positioned between the primary and secondary motor pulleys. The primary motor is a high current/high torque motor for fast response and high load capacity. The secondary motor is a motor requiring lower current and producing lower torque than the primary motor. 
     Other aspects of the invention provide a position sensor positioned adjacent the idler pulley in the transmission adapted to detect rotation of the idler pulley. The idler pulley can include a shaft extending therefrom, the shaft including at least one magnet, the magnet positioned adjacent the transmission position sensor. 
     Another aspect of the present invention provides a boost assembly for a hydraulic master cylinder including an electric motor. The motor rotatably drives a ball nut. A hollow screw is positioned within and threadably engaged to the ball nut, the screw having an end positioned to advance a piston of the hydraulic master cylinder when rotation of the motor linearly advances the screw. An input rod extends through the screw, the input rod including an input end positioned to receive a brake input force and an output end positioned to advance the piston responsive to the brake input force. A sensing and control means is provided to sense the brake input force and control the motor responsive to the brake input force. 
     Another aspect of the present invention provides a method of providing a boost force to a hydraulic master cylinder including compressing a reaction disc. A change in position of the reaction disc based on the extent of compression of the reaction disc is detected. An input force is determined based on the detected change in position and a boost force is applied based on the determined input force. 
     Other aspects of the present invention provide an application of the boost force that includes activating a boost motor based on the determined input force. The determination of the input force can include comparing the detected change in position to a predetermined change in position and activating the boost motor if the detected change meets or exceeds the predetermined change in position. 
     Another aspect of the present invention provides a system for providing a boost force to a hydraulic master cylinder including means for compressing a reaction disc, means for detecting a change in position of the reaction disc based on the extent of compression of the reaction disc, means for determining an input force based on the detected change in position and means for applying a boost force responsive to the determined input force. 
     The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a motor vehicle brake control system employing an embodiment of a master cylinder boost assembly of the present invention; 
     FIG. 2 is a cross-sectional view of another embodiment of the boost assembly of the present invention; 
     FIG. 3A is a cross-sectional view of a portion of the output and of the ball screw shaft and associated elements; 
     FIG. 3B is a top view of the assembly shown in FIG. 3A partially cut away; 
     FIG. 4 is an end view of an embodiment of a master cylinder boost assembly power transmission arrangement; 
     FIG. 5 is a partial cross-sectional view of an embodiment of a portion of a master cylinder boost assembly power transmission shown in FIG. 4; and 
     FIG. 6 is a cross-sectional view of an embodiment of a position sensor assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The master cylinder and boost assembly  10  seen in FIG. 1, broadly considered, includes, an electric motor  12  that can be a DC motor, a master cylinder  14  interconnected to the electric motor by a transmission system  16 . The master cylinder includes a ball screw  18 , which is drivable by the transmission system  16 . An input rod  20  generally provides input of driver apply force to the assembly  10 . The assembly  10  allows brake input force to be applied to the master cylinder from either operation of the ball screw  18  and linear motion of the input rod  20  or both features in combination. 
     Motor  12  can be of the direct current permanent magnet design and can include a motor housing  22 . The motor  12  can be attached to the assembly  10  by known means or can be positioned within a main body housing  24  of the assembly. A shaft or shaft extension  56  can extend from the motor  12  supported by bearing  57 . As shown, the motor  12  can be positioned substantially axially parallel to the master cylinder  14 . However, it will be understood that the orientation of the motor  12  is not critical to the operation of the invention. As such, the motor could be oriented according to space requirements, and so on. In addition, it is contemplated that the motor  12  could be positioned concentrically outside the ball screw  18  in a known manner. The ball screw can thus be rotated, for example, by attachment to an armature of the motor, thus eliminating need for a transmission. 
     Main body housing  24  can be formed of a ferrous or other suitable material by casting or other known methods. In the embodiment shown in FIG. 1, the main body housing  24  is formed of multiple castings. Thus, a first housing portion  26  can be attached to a second and third housing portion  28 ,  29 . The motor housing  22  can be attached to the first housing portion  26  and the ball screw  18  and input rod  20  can be positioned within housing portions  28 ,  29 . The master cylinder  14  generally including a bore  15  and a reservoir  30  (partially shown) can be attached to housing portion  29 . Motor housing  22  can be attached to main body housing  24  by any known method including fasteners  32 . Similarly, housing  29  can be fastened to the master cylinder  14  by fasteners, one of which is shown at  34  or the like. In the alternate, main body housing  24  can be formed as a single structure or unitary housing. 
     Master cylinder  14  can generally include a main body member  40 , a reservoir  30 , a mounting flange  42 , a piston  17  and a return spring  19 . As is conventional, the spring  19  can provide a return bias to the piston  17 . Main body member  40  and flange  42  can be formed as a single integral member. The flange  42  allows attachment of the master cylinder  14  to the main body housing  24 . The main body member  40  can be a generally cylindrical member. As is conventional, main body member  40  defines an elongated axial bore  15  or chamber into which the piston  17  is slidably disposed. 
     The reservoir  30  can be plastic and attached to the body member  40 . As is conventional, the reservoir  30  stores and provides brake fluid. The bore  15  of the body member  40  is in fluid communication with the reservoir  30 . The piston  17  is slidably received in the bore  15  of main body member  40 . Movement (inward advancement) of the piston  17  (in the left direction with respect to FIGS. 1 and 2) within the bore  15  provides brake fluid apply pressure to an associated remote brake assembly as is conventional, through outlet  21 . 
     The transmission system  16  can include a first and second pulley  50 ,  52 . A belt  54  can be wrapped around pulleys  50 ,  52  to transfer power from the motor  12  to the ball screw  18 . The first pulley  50  can be mounted to the motor shaft  56 . It will be understood that any suitable mechanism can be used to transfer power from the motor  12 , e.g., belts, toothed belts, chain belts or gears and the like. Also, the pulleys can be sprockets or the like, which operate in conjunction with a chain. 
     The motor  12  can be activated in the advancing or retracting direction during a brake application or retraction or designed to only activate in the advancing direction. In one embodiment, the motor  12  and transmission  16  is idle until boost is needed. The transmission can “freewheel” or is otherwise allowed to freely rotate until the motor is actuated. 
     The second pulley  52  can be drivingly engaged to a hollow ball screw  18 . In particular, rotation of the second pulley  52  causes rotation of the ball nut  60  portion of the ball screw  18 . Ball nut  60  can be connected or captured by cylinder  62 . Cylinder  62  in connected to pulley  52  and can be supported by a pair of ball bearings  64 ,  66 . In another embodiment, ball bearings  64 ,  66  can be one or more thrust bearings. Rotation of the pulley  52  rotates cylinder  62  and thus, ball nut  60 . Rotation of ball nut  60  causes linear advancement of the screw shaft  68 . In this manner, when actuation of the motor  12  causes rotation of the pulleys  50 ,  52  of the transmission  16 , the ball screw  18  converts the rotational motion to linear motion of the screw shaft  68 . The ball screw assembly  18  can be “back-drivable”. In another embodiment, (FIG. 2) the ball screw assembly can include a hollow ball screw. 
     An input rod  20 , which can be the same element as the screw shaft  68  or a separate element, is positioned to accept input force or brake demand force from the vehicle driver. If the input rod  20  is separate to screw shaft  68  the rod  20  can be connected to the screw shaft  68 . The input rod  20  can be splined, or the like, and is prevented from rotation by linear bearing  70  which includes an anti-rotation feature. The input rod  20  can, in the alternate, extend the full length of main body housing  24  through the nut  60  of the ball screw  18  and include grooves to operatively cooperate with the nut  60  of the ball screw  18  similar to the operation of the screw shaft  68 . 
     An output end of the screw shaft  72  can transfer the force provided by either (or both) the vehicle operator depressing a brake pedal and operation of the motor  12  and ball screw  18  to the piston  17 . In this manner, the driver apply force and the boost force are additive. 
     As will be explained more fully below, conventional position and/or pressure sensors can be used to sense an input force, for example, through the input rod  20  and sense the position of the output end of the screw shaft. Also, an amount of rotation of the transmission can be sensed. The values provided by the various sensors are used by a control device (not shown) to determine when and how much boost to apply to the master cylinder assembly. 
     The master cylinder and boost assembly  111  seen in FIG. 2, broadly considered, includes, an electric motor  113  that can be a DC motor connected to a transmission system  115 . The transmission  115  drivingly connects the motor  113  to a ball screw assembly  117 . An input rod  119  generally provides input of driver apply force to the assembly  111 . The assembly  111  allows brake input force to be applied to a piston of a master cylinder (shown in partial phantom at  121 ) from either operation of the ball screw  117  or linear motion of the input rod  119  or both features additively, in combination. 
     Motor  113  is attached to housing  123 , which can be essentially a one-piece housing. Transmission  115  and ball screw  117  can be positioned within housing  123 . Input rod  119  is positioned in housing  123 , and can be aligned with the axis of piston of hydraulic cylinder  121 . Input rod  119  can extend through ball screw assembly  117  and function as the screw  149  of ball screw assembly  117 . Cap  161  including an axial bearing  163  can be attached to housing  123  adjacent the input rod  119  to hold the input rod. Set screw  165  can be provided to prevent rotation of input shaft  119 . 
     In this embodiment, the motor  113  can be positioned below hydraulic cylinder  121  and fastened to the housing  123 . Shaft  125  of the motor  113  can extend into the housing  123  to engage transmission  115 . 
     A first pulley  127  of transmission  115  can be mounted upon shaft  125  of motor  113 . Shaft  125  can extend to clutch  129 . The clutch  129  can be an electromagnetic clutch or any suitable clutch, such as a spring clutch. Shaft  125  can be supported at the motor end and the clutch end by bearings  131 ,  133 . Clutch  129  operates to couple pulley  127  to shaft  125 . When clutch  129  is engaged, the shaft  125  is operatively coupled to motor  113 . When the clutch is disengaged, the shaft  125  can rotate freely. Belt  135  is wrapped from pulley  127  around second pulley  137 . As above, the means by which motor  113  rotates ball screw  117  can be any suitable device, for example pulleys, gears, sprockets and so on. 
     The second pulley  137  can turn plate  139 . Plate  139  is connected to cup member  141 . Cup member  141  can be supported by roller bearing  143  and thrust bearing  145 . Roller bearing  143  can be positioned between an outer surface of the cup member  141  and an inner surface of the housing  123 . 
     Cup member  141  is connected to ball member  147  of ball screw  117 . Rotation of cup member  141  rotates the ball portion  147  of ball screw  117 . Rotation of ball  147  urges screw shaft  149  (or input rod  119 ) in a linear (axial) direction as is known. As discussed, screw shaft  149  can be attached to input rod  119 . Screw shaft and input rod can be a single shaft. An output end of the screw shaft  149  can contact a portion of a reaction disc  151 . Output end of screw shaft  149 , reaction disc  151 , and additional associated components are shown in more detail in FIG.  3 . 
     Referring to FIGS. 2,  3 A and  3 B, the reaction disc  151  comprises an elastomeric material that allows the disc to compress. Reaction disc  151  is positioned between bracket  167  and bracket  169 . A differential force assembly  153  can be positioned adjacent the disc. The differential force assembly  153  can include a position sensor  155 , such as a Hall effect sensor, which can be mounted on bracket  169 , and at least one magnet  157 , which can be mounted on bracket  167 . Since bracket  167  is mounted on opposite side of reaction disc  151  with respect to bracket  169 , the two brackets move relative to each other when reaction disk  151  is compressed. The assembly  153  can measure the driver input force when the screw shaft  149  compresses the reaction disc  151  during a brake apply. The input force or demand force is a function of a given relative displacement across the disc  151  detected by the assembly  153 . In this manner, the driver input force can be determined. After an input force is detected and determined, the boost assembly advances the screw shaft  149  by activating the motor  113  and clutch  129 , rotating the transmission  115  and ball screw  117  and further advancing the screw shaft  149 . At this time, a further compression of the disc  151  occurs, the effect of which can also be detected by the sensor  155 . The difference between the initial compression (from the driver input) and the secondary compression yields the force generated by the boost assembly, i.e., the boost force generated by the motor  113  through the transmission  115  and ball screw  117  advancing the screw shaft  149 . In this manner, both the driver input force and boost force can be determined. 
     Returning to FIG. 2, the reaction disc  151  can contact an output rod button  159  attached to or in positioned in contact with the piston rod (not shown) of the hydraulic cylinder  121 . Thus, advancement of the screw shaft  149  (in the left direction of FIG. 2) causes the piston to provide increased fluid pressure within the hydraulic cylinder  121  and thus, impart a brake apply force to slave cylinders or remote brake assemblies connected thereto (not shown). 
     As shown in FIGS. 4 and 5, the arrangement of the transmission system  200  can include more than two motors, each having different characteristics. In the illustrated example, power transmission belt  254  is wrapped around a first pulley  250  associated with a first electric motor  263 . The first electric motor  263  can be a high current/high torque type for fast response. The belt  254  wraps around an idler pulley or gear  251 . The idler  251  when provided with a tensioner capability, as is known, can be used to maintain alignment and tension of the belt  254 . Further, the idler pulley  251  output can be provided to a rotational sensor  265 , which will be illustrated further below. 
     Idler/tensioner mechanism  251  can be positioned between the first pulley  250  and a second pulley  253  associated with a second motor  261 . The second motor  261  can be a low current/high speed type. In this manner, the system  200  is capable of combining a good response time with high load capacity. In addition, the system  200  can produce a mid-range output or holding force using relatively low current. It will also be understood that the respective diameters of the first pulley  250  and the second pulley  253  can be sized according to the operating characteristics of each motor  263 ,  261 . In other words, the pulley ratios are adjusted to match the output of each motor. The belt  254  wraps around pulley  252 , which is driveably connected to the ball screw (not shown). 
     Referring to FIG. 6, rotation sensor assembly  265  is shown in detail. The pulley  251  can include the shaft  267  extending therefrom. The distal end of the shaft  267  can include magnets  269 ,  271 . Magnets  269 ,  271  can be a pair over a plurality of magnet portions. A position sensor  273  is held adjacent magnets  269 ,  271 . Thus, as pulley  251  is rotated by the transmission, the shaft  267  causes magnets  269 ,  271  to rotate past position sensor  273 . In this manner, the signal can be generated by position sensor  273  that represents advancement of the transmission. 
     Referring again to FIGS. 3A and 3B, in operation, the vehicle operator, through an associated pedal, applies a brake force to the input rod  119 . At some point in the assembly, for example, between the brake pedal and the output button  159  an input force can be sensed. The force sensor used to determine the input force can be located at any suitable location. However, locating the sensor between the ball screw assembly  117  and the output button  159  is preferred. 
     The signal obtained from the sensor  153  can be used to determine whether a boost is required and the magnitude of boost required. When the control system (not shown) determines that a boost is required an appropriate electrical signal is sent to the motor  113  and clutch  129 . When electricity is provided in known manner to the motor  113 , the transmission  115  is caused to rotate with the result that ball screw  117  produces linear advancement of the output shaft  149 . For example, to move piston to the left as viewed in FIG. 1 in a direction to discharge pressure fluid from outlet fitting, motor  113  is energized in a sense to rotate the transmission  115  in a direction to advance ball screw shaft  149  to the left as seen in FIG.  2 . 
     Conversely, when it is desired to allow piston to be retracted, the electrical current or signal to motor  113  and clutch  129  is discontinued. A position sensor assembly  153  can continuously sense the linear position of the ball screw shaft  149 . For example, the sensor assembly  153  can include a Hall Effect proximity (position) sensor  155  positioned adjacent the output button  159  with an associated permanent magnet  157 . It will be understood that Hall Effect sensor  155  can detect the passage of magnet  157 , which can be a plurality of magnets or magnetic portions, as the ball screw  147  advances shaft  149  and transmits a signal thereby to a suitable counter device (not shown) or the like, so that the linear position of the ball screw shaft  149  and the master cylinder piston are precisely known at all times by the instantaneous reading of the counter device. 
     In this manner, during a brake command operation of the assembly, the screw shaft  149  of the ball screw  117  is caused to contact the reaction disc  151  and output rod button  159  with the effect of advancing the piston into the bore of the hydraulic cylinder and producing a hydraulic apply force to an associated brake cylinder in a brake assembly. When the apply force is reduced or removed, the screw shaft  149  can retract so as to reduce or remove the hydraulic apply force. 
     It will be understood that the ball screw shaft  149  can advance the piston in the master cylinder  121  by either application of a force applied to the shaft  149  by the vehicle operator alone or in combination with a force produced by actuation of the motor/transmission/ballscrew assembly and thus, produce a hydraulic apply force. In this manner, if a brake command fails to produce a boost operation of the boost assembly, the operator of the vehicle can still produce sufficient advancement of the piston through the input rod  119  to bring the vehicle safely to a halt. 
     Advantages of the system or assembly as described herein include the offering of a low-cost and low power-consuming booster for vehicles without the benefit of a vacuum supply. The booster assembly can emulate all aspects of the booster function. Unlike some other brake-by-wire systems the present booster assembly allows continuously variable pedal feel/feedback. Further, the present booster assembly takes up less space than conventional vacuum boosters. 
     While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.