Abstract:
A brake apparatus for a vehicle includes a housing including a bore formed therein. A piston is slidably positioned in the bore, the piston and bore defining a fluid chamber therebetween. A screw member is operatively engaged with the piston. The piston and screw member are movable based on fluid pressure in the fluid chamber and movable in a linear direction based on the rotational movement of the screw member.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to automotive braking systems. More particularly, the brake assembly of the present invention includes a combined hydraulic service brake and electric park brake feature, which eliminates the need for a separate parking brake and associated structure.  
         BACKGROUND OF THE INVENTION  
         [0002]    In conventional automotive braking systems the service brake and the parking/emergency brake are separate systems. The service brake is used for normal braking function during operation of the vehicle. The service brake typically includes a master cylinder that converts a manual exertion of force on a brake pedal into an increase of hydraulic pressure. The hydraulic pressure acts on a remote wheel cylinder or slave cylinder causing a brake pad to be applied to an associated rotor connected to a wheel of the vehicle, thus slowing the vehicle. Conventional park brakes are typically engaged when the vehicle operator pulls a lever or depresses a pedal connected to the park brake by a steel cable.  
           [0003]    Hydraulic brakes are generally not used as parking brakes because hydraulic fluid under constant pressure has a tendency to leak past seals of a hydraulic brake system over time resulting in a decrease in fluid pressure, which would cause the brake to release its hold on the rotor. Therefore, this inadequacy of the hydraulic brake for use as a parking brake has required the existence of two separate braking systems to fulfill the needs of a vehicle operator.  
           [0004]    It would be desirable to have a brake system that would improve on the existing brake system.  
         SUMMARY OF THE INVENTION  
         [0005]    One aspect of the invention provides a brake apparatus including a housing including a bore formed therein. A piston is slidably positioned in the bore. The piston and bore define a fluid chamber therebetween. A screw member is operably engaged with the piston, wherein the piston and screw member are movable based on fluid pressure in the fluid chamber and wherein the piston is movable in a linear direction based on the rotational movement of the screw member.  
           [0006]    Other aspects of the invention provide the brake apparatus with a driving member positioned in the bore and operatively engaged with the screw member. A motor may be operatively engaged with the driving member. A transmission may be operatively engaged with the driving member and a motor may be operatively connected to the transmission. The screw member may include a first helically shaped groove formed into an outer surface of the screw member and the piston may include a second helically shaped groove formed into an inner surface of the piston, the first and second grooves positioned to engage a plurality of rolling elements disposed therebetween. The screw member may include a first threaded portion on an outer surface thereof, and the piston includes a second threaded portion on an inner surface thereof, the first and second threaded portions being threadably engaged. The driving member may include an extending portion operatively connected to the screw member. The brake apparatus may include a first seal disposed between the housing and the driving member, a second seal disposed between the housing and the piston and a third seal disposed within the piston.  
           [0007]    Another aspect of the invention may provide a first seal disposed between the housing and the driving member, a second seal disposed between the housing and the piston and a third seal disposed within the piston, wherein the screw member includes a first helically shaped groove formed into an outer surface of the screw member, and the piston includes a second helically shaped groove formed into an inner surface of the piston, the first and second grooves positioned to engage a plurality of rolling elements disposed therebetween, the driving member including a driving portion operatively connected to the screw member.  
           [0008]    Another aspect of the present invention provides a method of applying an electric park brake for a hydraulic apply brake system including rotating a screw member engaged with a piston and linearly advancing the piston into contact with a brake pad responsive to the rotation of the screw member.  
           [0009]    Another aspects of the method of the present invention include activating a motor to rotate the screw member. The method may include activating a motor to engage a transmission and activating the transmission to rotate the screw member.  
           [0010]    Another aspect of the present invention provides a brake apparatus including a means for rotating a screw member operatively engaged with a piston and a means for linearly advancing the piston into contact with a brake pad responsive to the rotation of the screw member. Other aspects of the invention provide a brake apparatus including a means for activating a motor to engage a transmission and a means for activating the transmission to rotate the screw member.  
           [0011]    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  
       [0012]    [0012]FIG. 1 illustrates a cross-sectional view of one embodiment of a brake assembly in accordance with the present invention.  
         [0013]    [0013]FIG. 2 illustrates a cross-sectional view of another embodiment of a brake assembly in accordance with the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    Referring to FIG. 1, one embodiment of an exemplary brake assembly  20  is shown for use as a normal hydraulic service brake during vehicle operation including an electric brake feature or assembly for use during parking and emergency situations.  
         [0015]    In the embodiment shown, the brake assembly  20  may include a brake caliper  30 , a caliper housing  32 , a transmission  74  and a motor  70 . The caliper housing  32  may be suitably connected to a plate  82  with fasteners  86  and  88 . Fasteners  86  and  88  may be flat screws. A transmission  74 , which may be a non-backdrivable transmission, can be connected to plate  82  by fastener  76 . Fastener  76  may be a cap screw. The motor  70  may be connected to the plate  82  by fastener  72 . Fastener  72  may be a cap screw. In an alternative embodiment of the present invention, the plate structure can be an integral portion of the caliper housing to which the transmission and motor are operably connected.  
         [0016]    Brake caliper  30  can be slidably connected to the caliper housing  32  in a known manner. The caliper housing  32  can include a central bore  33 . A ball screw assembly  34 , can be slidably positioned within the bore  33  of the caliper housing  32  so that a hydraulic fluid chamber  38  is defined.  
         [0017]    The ball screw assembly  34  can include a screw member  42  and a piston  36 , which can be hollow, defining the nut portion of the ball screw assembly  34 . The hollow piston  36  may have, for example, a cylindrical shape. In one embodiment, the hollow piston  36  may include a grooved inside wall portion  40 . The screw member  42  can be generally H-shaped having an axial opening  44  and a grooved outer wall portion  46 . The grooved inner wall portion  40  of hollow piston  36  can be positioned adjacent to or along the grooved outer wall portion  46  of screw member  42  to form, in one embodiment, a ball race, including ball bearings  48 .  
         [0018]    Ball screw assembly  34  may have an anti-rotation feature (not shown) that prevents rotation of the hollow piston  36  thereby allowing the hollow piston  36  to maintain a linear motion. In one embodiment the anti-rotation feature may be positioned between the hollow piston  36  and brake pad (not shown) and may comprise an anti-rotation clip attached to the back of the brake pad which fits into an axial groove in the hollow piston.  
         [0019]    In a second embodiment, illustrated in FIG. 2, there can be a threaded engagement between hollow piston  136  and screw member  142 . In one embodiment, the inner wall  140  of hollow piston  136  can be threaded and the outer wall  146  of the screw member  142  can be similarly threaded and engaged with the inner wall threads so that the threads cooperate in such a manner that the rotation of the screw member  142  linearly moves the hollow piston  136 . An axial opening of the screw member  142  is shown at  144 .  
         [0020]    Returning to FIG. 1, a driving member  50  can be positioned centrally within the caliper housing  32 . The driving member  50  can be positioned within the caliper housing  32  through an axial opening  64  in the closed end  66  of the caliper housing  32  and through an axial opening (not shown) of plate  82 . Driving member  50  may include a driving extension or extending portion  52  that extends through the axial opening  44  of screw member  42 . In one embodiment, the driving portion  52  may have a square cross-section. Alternatively, the driving portion may have a non-square cross-section such as, for example, a rectangular, oval, or splined configuration with a corresponding complimentary axial opening of screw member  42 .  
         [0021]    The driving member  50  can include a central bore  78  opposite the driving portion  52 . A drive shaft (not shown) of transmission  74  can be inserted into the central bore  78  of driving member  50  and can be suitably connected to driving member  50  by fastener  56 . Fastener  56  can be a setscrew.  
         [0022]    A bearing  54  with an axial opening can be positioned adjacent to the inside wall  92  of the closed end  66  of caliper housing  32  so that the axial opening of the bearing  54  corresponds with the axial opening  64  of the closed end  66  of the caliper housing  32  and through which the driving member  50  can be inserted. The bearing  54  may be a thrust needle bearing. The invention contemplates any sort of suitable arrangement of bushings and/or bearings that reduces the friction between the screw member and the inside wall of the caliper housing.  
         [0023]    A first seal  58  can be positioned between the driving member  50  and the caliper housing  32 . The first seal  58  may be an O-ring made of suitable material such as rubber. This first seal may be positioned to prevent the loss of hydraulic fluid from the fluid chamber between the driving member and the caliper housing.  
         [0024]    A second seal  60  can be positioned between the caliper housing  32  and the hollow piston  36 . The second seal  60  may be an O-ring made of suitable material such as rubber. The second seal  60  may be positioned to prevent the loss of hydraulic fluid from the fluid chamber between the hollow piston and the caliper housing.  
         [0025]    A third seal  62  can be positioned within the hollow piston  36  to prevent the loss of hydraulic fluid from the fluid chamber between the hollow piston and the screw member. The third seal can be held in place within the hollow piston using a ring  100 . The ring  100  may be a snap ring fitted within a groove  102  cut into the inner wall  40  of hollow piston  36 . In one embodiment, the third seal may be a seal disc composed of a tool steel to suit.  
         [0026]    In operation of the hydraulic brake during normal driving conditions, the vehicle operator actuates the brake system in a known manner resulting in an increase of hydraulic fluid pressure in one or more brake lines leading to the assembly  20 . The increase in pressure of the hydraulic fluid in the brake line results in an increase of fluid in the fluid chamber  38  of the brake assembly  20 . The increase of hydraulic fluid in the fluid chamber  38  can cause the ball screw assembly  34  and piston  36  to move linearly (laterally in FIG. 1) within the caliper housing  32 . The lateral movement of the ball screw assembly  34  causes the hollow piston  36  portion of the ball screw assembly  34  to engage a rotor (not shown) in a known manner to slow the vehicle. Conversely, the release of the brake pedal by the vehicle operator decreases the hydraulic fluid pressure within the fluid chamber  38  resulting in release of an associated rotor, allowing the rotor to move.  
         [0027]    In operation of the electric park brake portion of the brake assembly  20 , the vehicle operator can engage the park brake (not shown) by some suitable means such as by a switch, lever, button or remote control. Alternatively, a control device, such as an electronic brake control module or computer of the vehicle can engage the park brake automatically when the vehicle is turned off or put into park. The electric motor  70  is activated, rotating the transmission  74  to rotate a transmission drive shaft or the like (not shown) that can be connected to the driving member  50 . It will be understood that transmission  74  can be any suitable device for transmitting output from the motor  70 , such as, for example, a set of meshed gears, chains and sprockets, pulleys and belts and the like. The rotation of the transmission  74  can rotate the driving member  50 . The rotation of the driving member  50  can result in the rotation of screw member  42  of the ball screw assembly  34 . The ball groove connection between the screw member  42  and the hollow piston  36  translates the rotational movement of the screw member  42  into linear movement of the hollow piston  36 . The linear movement of the hollow piston  36  causes the hollow piston to move associated brake pads to engage a rotor in a similar manner as that via the hydraulic brake system described above. The brake pads remain held against the rotor until such time when the non-backdriveable transmission is reversed by the motor.  
         [0028]    As described above, the assembly  20  provides a number of advantages, some of which have been described above and others of which are inherent in the invention. Also modifications may be proposed without departing from the teachings herein. Accordingly the scope of the invention is only to be limited as necessitated by the accompanying claims.  
         [0029]    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.