Patent Publication Number: US-11655867-B2

Title: Disc brake system

Description:
PRIORITY 
     This application claims priority to and the benefit of: U.S. Ser. No. 16/545,367 filed Aug. 20, 2019; U.S. 62/720,280 filed Aug. 21, 2018; and U.S. 62/724,808 filed Aug. 30, 2018, all of which are incorporated by reference herein for all purposes. 
    
    
     FIELD 
     These teachings relate to a brake system, and more particularly to a brake system brake having a first pad section and a second pad section. 
     BACKGROUND 
     Brake systems can be used to slow, stop, or prevent movement of a brake rotor or road wheel. 
     One type of brake system is an opposed piston brake system, which includes one or more brake pistons that oppose each other (i.e., the brake pistons are supported on both sides of the brake rotor). During a braking event, whether for service braking or for park braking, a pair of pads are pushed against a corresponding side of the brake rotor by the opposed brake pistons. 
     Improvements in brake systems, including opposed piston brake systems, may be desired. 
     SUMMARY 
     These teachings provide an improved disc brake system; an improved parking brake system; and an improved combined disc brake system and parking brake system. 
     These teaching provide a disc brake system comprising a brake caliper; a first brake pad supported by the brake caliper, and a second brake pad supported by the brake caliper; and a pin connected to both the first brake pad and the second brake pad. One or both of the brake pads move or slide along the pin during a brake apply. In some configurations, the brake system may be free of any pins for supporting the brake pads. The brake caliper comprises an inboard side and an outboard side. The bolt that is configured to connect together the inboard side and the outboard side. 
     These teaching provide a disc brake system comprising a brake caliper; a first brake pad supported by the brake caliper, and a second brake pad supported by the brake caliper; and a pin connected to both the first brake pad and the second brake pad. One or both of the brake pads move or slide along the pin during a brake apply. A cross sectional shape of the pin is other than a circle. 
     These teaching provide a disc brake system comprising a brake caliper comprising a leading end and an opposing trailing end, and a first side and an opposing second side; and a parking brake system comprising a bridge extending across the first side and the second side. The first side may be an inboard side, and the second side may be an outboard side, or vice versa. The bridge is centered between the leading end and the trailing end such that the disc brake system is symmetrical between the leading end and the trailing end. In some configurations, the bridge may be offset towards either the front or leading end or the rear or trailing end. 
     These teaching provide a disc brake system comprising: a brake caliper comprising a leading end and an opposing trailing end, and a first or inboard side and an opposing second or outboard side; and a parking brake system. The first side and the second side are separate pieces that are joined together with one or more fasteners. 
     These teaching provide a disc brake system comprising: a brake caliper; a brake pad supported by the brake caliper; and a parking brake system comprising a bridge extending across a first side and a second side of the brake caliper. The bridge may comprise fingers, and the fingers and the brake pad may be integrated, which means the fingers and the brake pad are connected together by way of one or more mechanical fasteners, or the fingers and the pressure plate are made from a single common material. 
     These teaching provide an opposed piston disc brake system comprising: a brake caliper comprising two or more brake pistons supported at an inboard side of the brake caliper and two or more brake pistons supported at an outboard side of the brake caliper; and a parking brake system. The parking brake system is configured to move two or more of the brake pistons at the outboard side of the brake caliper during a parking brake apply. 
     These teachings provide a brake system that includes a brake caliper having an inboard side and an outboard side. The inboard side of the brake caliper is configured to support more brake pistons than the outboard side of the brake caliper. 
     These teachings also provide an opposed piston brake system that includes a brake caliper having an inboard side and an outboard side. The outboard side is configured to support only one brake piston, while the inboard side is configured to support more than one brake piston. The outboard side is free of a brake piston that is located directly across from the brake piston supported at the inboard side. 
     These teachings further provide an opposed piston brake system that includes a brake caliper having an inboard side and an outboard side. The outboard side is configured to support only one brake piston, while the inboard side is configured to support only two brake pistons. 
     By having a brake system with less brake pistons supported at the inboard side of the brake caliper or at the outboard side of the brake caliper, the brake system is lighter, less costly, and may be easier and faster to assemble and/or service. 
     An opposed piston brake system comprising: a brake caliper comprising an inboard side and an outboard side, wherein the inboard side is configured to support more than one brake piston, and the outboard side is configured to support only one brake piston. 
     The outboard side may be free of a brake piston that is located directly across from the brake piston supported at the inboard side. 
     An opposed piston brake system comprising: a brake caliper comprising an inboard side and an outboard side, wherein the inboard side is configured to support more than one brake pistons, and wherein the outboard side is configured to support only one brake piston. 
     A disc brake system comprising: a brake caliper; a first brake pad supported by the brake caliper, and a second brake pad supported by the brake caliper; and wherein the brake caliper comprises an inboard side and an outboard side, and wherein a bolt is configured to connect together the inboard side and the outboard side. 
     A disc brake system comprising: a brake caliper comprising a leading end and an opposing trailing end, and a first side and an opposing second side; and a parking brake system comprising a bridge extending across the first side and the second side; wherein the bridge is centered between the leading end and the trailing end such that the disc brake system is symmetrical between the leading end and the trailing end. 
     An opposed piston disc brake system comprising a brake caliper that is free of a middle bridge that extends between the first side and the second side of the brake caliper. 
     A brake system comprising: a brake caliper; and a brake pad supported by the brake caliper, the brake pad comprises a plurality of brake pad sections, and wherein the brake system comprises a plurality of pins configured to support the brake pad sections. The brake system comprises three pad sections and four pins. 
     An opposed piston disc brake system comprising a ball nut assembly configured to move a brake piston during the parking brake apply. 
     An opposed piston brake system comprising: a brake caliper; and a parking brake system, the parking brake system comprising a bridge with fingers, wherein the fingers are configured to surround two brake pistons. At two pins (or one pin, or more than two pins) are provided for supporting brake pistons between the fingers. 
     An opposed piston brake system comprising: a brake caliper; and a parking brake system, the parking brake system comprises a spot caliper located at a leading end of the brake caliper or a trailing end of the brake caliper. 
     A disc brake system comprising: a brake caliper; a brake pad supported by the brake caliper; and a parking brake system comprising a bridge extending across a first side and a second side of the brake caliper, the bridge comprises fingers; wherein the fingers and the brake pad are integrated. 
     A brake system comprising a brake caliper; and a shaft configured to extend above a brake rotor; the shaft is connected to an outboard brake pad. 
     A brake system comprising: a brake caliper; and a shaft configured to above a brake rotor; the shaft is connected to an outboard brake pad. During a brake apply or a parking brake apply, rotation of the shaft causes the outboard brake pad to move towards the brake rotor to create a clamping force. Rotation of the shaft causes an inboard brake pad to move towards the brake rotor to create the clamping force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a perspective view of a brake system. 
         FIG.  1 B  is a perspective view of a brake system. 
         FIG.  1 C  is a front view of a brake pad. 
         FIG.  2    is a side view of a brake system. 
         FIG.  3    is a perspective view of another caliper body of the brake system. 
         FIG.  4    is a perspective view of a brake system. 
         FIG.  5    is an exploded view of a brake piston assembly. 
         FIG.  6 A  is a cross-sectional view of a brake system. 
         FIG.  6 B  is a cross-sectional view of a brake system. 
         FIG.  7    is a perspective view of a brake system. 
         FIG.  8    is a perspective view of a brake system. 
         FIG.  9    is a perspective view of a portion of a parking brake system and brake pad. 
         FIG.  10    is a perspective view of a brake system. 
         FIG.  11    is a perspective view of a portion of a parking brake system and brake pad. 
         FIG.  12    is a cross-sectional view of a brake system. 
         FIG.  13    is a top view of a brake system. 
         FIG.  14    a bottom view of the brake system of  FIG.  13   . 
         FIG.  15    is a perspective view of a portion of a parking brake system and brake pad. 
         FIG.  16    is a front view of a brake pad. 
     
    
    
     DETAILED DESCRIPTION 
     The teachings herein provide a brake system. The brake system may function to create a clamp force to slow, stop, and/or maintain a vehicle in a stopped or parked position. The brake system may be an opposing brake system (i.e., a fixed caliper brake system). These teachings provide a combined fixed caliper portion and a floating caliper portion. While these teachings provide for the fixed caliper portion to be used for service braking and the floating caliper portion to be used for parking braking, in some configurations the fixed caliper portion can be used for parking braking and/or the floating brake portion may be used for service braking. 
     The parking brake system may include one or more rotary to linear stage mechanisms. The rotary to linear stage mechanism may function to receive a rotary force or torque and then transfer the rotary force or torque into an axial or linear force. The rotary to linear stage mechanism may move a brake piston so that the brake piston moves a brake pad. 
     The rotary to linear stage mechanism may include a spindle and a nut. The rotary to linear stage mechanism may be at least partially located within a brake piston of the brake system. The rotary to linear stage mechanism may include a ball screw, roller screw. The rotary to linear stage mechanism may be a self-locking spindle and nut. 
     Exemplary ball screws may utilize ball bearings as load transfer elements between the nut and spindle or screw. During movement of the ball screw, the ball bearings may circulate along races or grooves between the spindle and the nut. A roller screw or planetary screw may be similar to a ball screw except that roller screws use rollers as the load transfer elements between nut and screw. The load on a ball screw, the roller screw, or both is distributed over a large number of ball bearings or rollers, via roller threads, respectively, so that each ball bearing or roller, when subjected to force, may roll, and therefore, friction is reduced, which may equate to high efficiency. Accordingly, less force or torque may be required to move a spindle and nut in a ball screw or roller screw in an apply direction, a release direction, or both. 
     The torque generating mechanism may be any suitable motor for creating a force or torque. For example, the motor may be a DC motor, a brushless motor, a series-wound motor, a shunt wound motor, a compound wound motor, a separately excited motor, a servomotor, a stepping motor, or a permanent magnet motor. 
     The torque generating mechanism may include a motor gear unit (MGU), which may include one or more gears or gear trains that may function to transfer, increase, and/or decrease a power output or torque of the motor. 
     The torque generating mechanism may be an actuator that may be moved to provide torque to the rotary to linear stage mechanism. The actuator may be moved to provide torque to rotate the rotary to linear stage mechanism. Movement or rotation of the actuator may function to move the rotary to linear stage mechanism, a spindle, a shaft, one or more brake pistons, one or more brake pads, the fingers, or a combination thereof to create and/or release the clamp force. The actuator may be moved or rotated by a cable pull. Preferably, the actuator may be moved or rotated by a user manually manipulating a cable or a lever. 
     The clamp force or clamping force may be any force that, when coupled with a brake pad coefficient of friction, functions to create drag to decelerate, slow, stop, and/or prevent movement or rotation of a brake rotor and/or a vehicle. The clamp force may be created during a standard or service brake apply (i.e., a brake apply force). The clamp force may be created during a parking brake apply (i.e., a parking brake force). One or more brake pads may be used to create the clamp force. The same one or more brake pads are used to create the clamp force during application of the service brake and during application of the parking brake. The clamp force generates friction which generates heat. 
     The one or more brake pads may include a friction material and a pressure plate. The one or more brake pads may be supported on the brake caliper so that the friction material faces a side of the brake rotor. The pressure plate may oppose the friction surface. 
     One or more brake pistons, one or more grasping members fingers, or both may face and/or may be in communication with the pressure plates of a corresponding brake pad. For example, one or more brake pistons may be in contact with the pressure plate of an inboard brake pad, one or more brake pistons may be in contact with the pressure plate of an outboard brake pad, one or more fingers may be in contact with the pressure plate of an outboard brake pad, or a combination thereof. During a standard brake apply, or while applying the parking brake, the one or more brake pistons and/or the one or more fingers may push, pull, or otherwise move all or an end of a corresponding brake pad so that the corresponding friction material engages a corresponding side of the brake rotor to create the clamping force. 
     The brake caliper may have one or more caliper bores. Each caliper bore may define a hollow region in the brake caliper. The caliper bore may be adapted to receive and support a corresponding brake piston. One or more caliper bores can be located on each side of the brake rotor (e.g., inboard side and outboard side). A brake piston supported within a caliper bore may be moved along an axis of the caliper bore to create or release a clamp force during application of the service brake, the parking brake, or both. 
     The one or more brake pistons may function to move a brake pad, or a corresponding end of brake pad, towards the brake rotor to create the clamp force. During a brake apply to decelerate or stop a vehicle, the brake pistons may be moved by pressurizing a fluid, such as brake fluid. To release the clamp force or the brake apply, the brake piston can be moved by depressurizing the fluid. During a parking brake apply, to create clamp force, the same brake piston used during a brake apply may be moved by moving a corresponding rotary to linear stage mechanism in an apply direction. To release the clamp force or the parking brake, the brake piston can be moved by moving the corresponding rotary to linear stage mechanism in an opposing release direction. During both a parking brake apply and a standard brake apply, the brake piston may be moved along a brake piston axis, which may be collinear or essentially collinear with the piston bore axis. The brake piston may include a closed end selectively engaging the pressure plate of a brake pad, and an open end defining an opening into a piston bore. 
     The piston bore may function to receive at least a portion of the parking brake system. The piston bore may receive at least a portion of the rotary to linear stage mechanism. One or more of the brake pistons may include a piston bore. 
     The piston bore may be a cup or recess formed into an end of a brake piston. The piston bore may include a surface at or near a bottom wall or end of the piston bore. A gap may be defined between a corresponding surface on the nut and the surface at the bottom wall. During a parking brake apply, the gap may be taken up by moving the rotary to linear stage mechanism in an apply direction towards the inboard brake pad. Once the gap is taken up, further movement of the rotary to linear stage mechanism or nut sleeve may cause the rotary to linear stage mechanism to press against the bottom wall and then move the brake piston and the brake pad against the brake rotor to create the clamp force. 
       FIGS.  1 A and  1 B  illustrate a brake system  10 . The brake system  10  comprises a brake caliper  12 . The brake caliper  12  comprises a first side  14  and a second side  16 . The first side  14  is the inboard side of the brake caliper  12 , and the second side  16  is the outboard side of the brake caliper  12 . The brake system  10  is an opposed piston brake system. This means one or more brake pistons are supported in the first side  14  of the brake caliper  12 , and one or more brake pistons are supported in the second side  16  of the brake caliper  12 . 
     A first brake pad  18  is supported at the first side  14  of the brake caliper  12 , and a second brake pad  20  is supported at the second side  16  of the brake caliper  12 . The brake pads  18 ,  20  may be supported on pins  22 ,  24  that are supported at each of the sides  14 ,  16  of the brake caliper  12 . One or both of the pins  22 ,  24  may extend through hooks or loops or ears or flanges  3  extending from a top end, a bottom end, and/or side end (leading/trailing end) of the brake pad or pressure plate. The hooks or loops or ears or flanges  3  extending from a top end of the pad sections A, B, and/or C may be omitted, move to a bottom end of the pad section, or eliminated. Additionally, or alternatively, one or more of the pins may be provided through bores or apertures defined in the pressure plate in between pad or friction material sections, like illustrated in  FIG.  1 C  and/or  FIG.  16   . During a brake apply, the one or more brake pistons supported on the first side  14  of the brake caliper  12  are configured to be moved, causing the first brake pad  18  to move towards and against a brake rotor located between the sides  14 ,  16  of the caliper  12  to create clamping force. The one or more brake pistons supported on the second side  16  of the brake caliper  12  are also configured to be moved, causing the second brake pad  20  to be moved towards and against the opposing side of the brake rotor to create clamping force. 
     While the brake system  10  of  FIGS.  1 A and  1 B  includes two pins  22 ,  24 , the system  10  may include more than two pins. For example, the brake system  10  may include three or more pins, four or more pins, five or more pins, etc. The pins  22 ,  24  may be used to support the brake pads  18 ,  20  and assist in servicing or changing or replacing the brake pads  18 ,  20 . 
     For example, referring to  FIG.  1 C , the system may include four pins  22 ,  24 ,  25 ,  27 . Such a configuration may be used, for example, when the brake pad  18 ,  20  comprises three individual or discrete brake pad sections A, B, C, where each brake pad section comprises a pressure plate and friction material. One or more of the brake pad sections A, B, C may be used during application of the service brake, and one or more of the brake pad sections A, B, C may be used during application of the parking brake. In other words, some or all of the brake pad sections A, B, C may be used during a brake apply and some or all of the brake pad sections A, B, C may be used during a parking brake apply. The pins  22 ,  24 ,  27 ,  29  may be used to support the pad sections A, B, C. 
     In some configurations, five or more pins, six or more pins, three or more, etc. may be used. For example, brake pads that have two brake pad sections may have three pins, brake pads with four brake pad sections may have five pins, etc. 
     Alternatively, the brake system  10  may include two pins. Referring to  FIG.  16   , a brake pad  18 ,  20  may include two pins  27 ,  27  provided between three pad sections A, B, C. Each pad section A, B, C, may have a separate and discrete pressure plate and friction material. For example, pad section A or the pressure plate thereof may include an abutment  23  at one end there of a pin  24  at the other end. Pad section B may include two pins  24 ,  27 . And pad section C may include a pin  27  at one end and a pressure plate having an abutment  23  at the other end. The abutments  23  may be configured to engage corresponding slots or recesses in the caliper body and/or clips supported by the caliper body. 
     For example, in some configurations, the brake system may include less than two pins. For example, the brake system  10  may include only one pin. The one pin may be generally centered between the ends of the brake pads  18 ,  20 . The one pin may be offset or biased towards one of the ends of the brake pads  18 ,  20 . Having less than two pins may reduce weight, cost, and/or assembly or service complexities of the brake system  10 . Having less than two pins may also reduce or prevent chances of one or both of the brake pads  18 ,  20  cocking or jamming while moving towards and away from the brake rotor. In some configurations, the brake system  10  may be free of any pins for supporting the brake pads  18 ,  20 . 
     Referring back to  FIGS.  1 A and  1 B , at one end of the brake caliper  12 , a first wall or bridge  26  extends between and connects the first side  14  and the second side  16 . At the opposing end of the brake caliper  12 , a second wall or bridge  28  extends between and connects the first side  14  and the second side  16 . 
     The brake caliper  12  in  FIG.  1 A  includes a third wall or bridge  30  that extends between and connects the first side  14  and the second side  16 . The third wall or bridge  30  may be located at a center location of the brake caliper  12 , for example centered between a first end  32  and an opposing second end  34  of the brake caliper  12 . For example,  FIG.  3    illustrates a wall or bridge  30  that is generally centered between the ends  32 ,  34  of the caliper  12 . Alternatively, the third wall or bridge  30  may be offset towards one end  32 ,  34  or the other end  32 ,  34  of the caliper  12 . 
     The brake caliper  12  in  FIG.  1 B  does not include, or is free of, a wall or bridge like wall or bridge  30  in  FIG.  1 A . Instead, the center area between walls or bridges  26 ,  28  is substantially free of any walls or bridges or connecting structures extending between the first and second sides  14 ,  16  of the caliper  12 . This may advantageously reduce material cost of the brake caliper  12 ; may reduce a weight of the caliper  12  and brake system  10 ; may reduce manufacturing and/or assembly complexities of the caliper  12  or system  10 ; or a combination thereof. 
     In the above description, first end  32  may be a leading end of the brake caliper  12 , and the second end  34  may be the trailing end of the brake caliper  12 , or vice versa. In the above description, side  14  may be the outboard side of the brake caliper  12 , and side  16  may be the inboard side of the brake caliper  12 , or vice versa. 
     With continued reference to  FIG.  1 C , each pad section A, B, C, has a friction material F 1 , F 2 , F 3 . The friction material F 1 , F 2 , F 3  of each of the pad sections A, B, C, (or on two or more of the pad sections A, B, C) may be the same or have the same coefficient of friction. For example, the coefficient of friction may be 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, etc. 
     Alternatively, the material of the friction material F 1 , F 2 , F 3  on each of the pad sections A, B, C (or on two or more of the pad sections A, B, C) may be different and/or or have a different coefficient of friction. For example, it may be desirable for the friction material F 1 , F 2  F 3 , of one or more of the pad sections A, B, C that is associated with a parking brake application to have a higher coefficient of friction than the friction material F 1 , F 2 , F 3  of one or more of the pad sections A, B, C that is associated with a service brake application. This difference in friction material may advantageously reduce NVH issues (Noise, Vibration and Harshness) during a brake application (service and/or parking brake application) and/or advantageously reduce clamp load applied on one or more components of the brake system, such as the actuator, spindle, nut, motor, etc. 
     To compensate for the different friction materials F 1 , F 2 , F 3  on the pad sections, the pressure applied onto the pad sections A, B, C (via the brake piston and/or fingers and/or actuators) may be different on each pad section. In other words, the pressure applied by a brake piston or actuator onto pad section A may be different (higher or lower) than the pressure applied by a brake piston or actuator onto pad section B and/or C. This difference in applied pressure may be accomplished by having different sized brake pistons (i.e., piston on pad section A is larger than the brake piston on pad section B and/or C, or vice versa), a larger actuator, timing one actuator to start before or after another actuator starts moving, etc. 
     For example, assuming the friction material F 1  is used for both a parking brake application and a service brake and has a friction coefficient as μ 1  and the friction material B and/or C is used for only a service brake apply and has a friction coefficient as μ 2 , then the friction coefficient may be μ2&gt;μ1. In some configurations, the ratio may be μ 1 =2μ 2 . Such a ratio may be beneficial for the parking brake system since the same torque output could be achieved, while reducing load or clamp force on the actuator, spindle, nut, motor, etc. However, if the same hydraulic pressure is applied onto the friction materials F 1 , F 2 , F 3 , then the torque generated from friction material F 1  may be greater, for example, 2× the torque generated from the friction material F 2  and/or F 3 , assuming the effective radii are same. This could result in the tangential force (which is the force to generate torque) being higher (i.e., twice as high) under friction material F 1 . The more tangential excitation force may mean more propensity to have an NVH issue, such as a squeal. Thus, to achieve a similar level tangential force during a service brake application, it may be desirable to have lower hydraulic area or pressure acting on the friction material F 1  or pad section A. To obtain a lower hydraulic area, the brake piston associated with the pad section A may be smaller than brake piston associated with pad section B and/or C. To obtain a lower hydraulic pressure applied to the brake piston associated with pad section A associated the friction material F 1 , a proportioning valve, or use different master cylinder may be used. 
     Alternatively, in some configurations, it may be advantageous for two or more of the friction materials F 1 , F 2 , F 3  to be the same or to have the same coefficient of friction. 
     The size or surface area of the friction material F 1 , F 2 , F 3  of each pad section A, B, C may be generally the same. Or, the size or surface area of the friction material F 1 , F 2  F 3  of the pad section A, B, C configured for service brake application may be larger than the surface area of the friction material F 1 , F 2  F 3 , of the pad section A, B, C configured for parking brake application, or vice versa. 
       FIG.  2    illustrates a brake system  10 , that may include one or more of the features described above in either or both of  FIGS.  1 A and  1 B  or in any of other brake systems included, described, or illustrated herein. Therefore, in the interest of brevity, like features will not be described again. 
     The brake system  10  comprises a parking brake system  36 . The parking brake system  36  is a slider-type of brake system. The parking brake system  36  may function and/or include features that are disclosed in Applicant&#39;s previously-filed U.S. patent application Ser. No. 15/248,134, filed on Aug. 26, 2016, which is expressly incorporated by reference herein for all purposes. The parking brake system  36  may function and/or includes features of the parking brake system identified by reference numeral 12 in Applicant&#39;s aforementioned U.S. patent application Ser. No. 15/248,134. 
     The parking brake system  36  comprises a bridge  38  that extends over a gap defined between the first and second sides  14 ,  16  (See  FIGS.  1 A,  1 B  for the sides  14 ,  16 ) of the caliper  12 . As illustrated, the bridge  38  is offset relative to a center plane  40  of the brake system  10 . The center plane  40  may be centered between the ends  32 ,  34  of the brake caliper  12 . The parking brake system  36  comprises fingers  42   a ,  42   b  that surround pin  24 . 
     Alternatively, the brake system  10  may have a parking brake system  36  that is symmetrically located on the brake system  10 . This means that the parking brake system  36  is symmetric about plane  40 , for example. This means that the parking brake system  36  and/or bridge  38  is centered about plane  40 . More specifically, a center plane or portion  44  of bridge  38  may be aligned with or the same as plane  40 . This may mean that the bridge  38  is moved towards end  34  of the brake caliper  12 . This may mean that the bridge  38  is configured such that finger  42   b  remains in substantially the same spot, but finger  42   a  is moved towards end  34  so that the plane  44  is aligned with or the same as plane  40 . This may mean that the bridge  38  is moved or translated towards end  34 , and openings or passages are provided in the fingers  42   a ,  42   b  for the corresponding pins  22 ,  24  to pass through the fingers  42   a ,  42   b . This may also mean that the parking brake system  36  is configured to move more than one brake piston that is supported at the second side (e.g., side  16  of  FIGS.  1 A,  1 B ) during a parking brake apply, which is described further in  FIG.  3   . An example of a symmetrical parking brake system  36  is also illustrated at  FIG.  8 B . 
       FIG.  3    illustrates a brake system  10 , that may include features substantially similar to those described above in one or more of  FIGS.  1 A- 2    or in any of other brake systems included, described, or illustrated herein. Therefore, in the interest of brevity, like features will not be described again. 
     The brake system  10  of  FIG.  3    comprises a brake caliper  12  that includes a first and second side  14 ,  16 . Each side  14 ,  16  comprises one or more caliper bores. For example, side  16  comprises three caliper bores  46   a ,  46   b ,  46   c . Side  16  can have more or less than three caliper bores. Side  14  can have any number of caliper bores, for example, more or even less than three caliper bores. The brake system  10  comprises a brake piston inside each of the caliper bores. Each side  14 ,  16  may have the same number of caliper bores and brake pistons, or a different number of caliper bores and brake pistons. 
     During a standard brake apply (e.g., service brake) one or more of the brake pistons supported at side  14  of the caliper  12  may be moved and/or one or more of the brake pistons supported at the opposing side  16  of the caliper  12  may be moved. The brake pistons may be moved by pressuring hydraulic fluid and/or with an electromechanical system that comprises an electric motor, spindle, and nut system. Movement of one or more of the brake pistons may result in movement of the corresponding brake pad towards and against a brake rotor. 
     Referring to  FIG.  4   , the brake system  10  comprises a parking brake system  36 , that may be similar to the one illustrated and described in  FIG.  2    at reference numeral  36 . The parking brake system  36  may be configured to move one or more of the brake pistons. For example, the parking brake system  36  may be a sliding caliper system like the one illustrated at  FIG.  2    that is configured to move one or more brake pistons supported at side  14  of the caliper  12  and/or one or more brake pistons supported at side  16  of the caliper  12 . The parking brake system  36  may be configured to move adjacent brake pistons, for example the brake pistons supported in bores  46   a  and  46   b  and/or  46   b  and  46   c  in  FIG.  3   . Alternatively, the parking brake system  36  may be configured to move spaced apart brake pistons, for example, the brake pistons supported in bores  46   a  and  46   c  in  FIG.  3   . 
     In another configuration, the parking brake system  36  may be configured to move brake pistons located at opposing sides  14 ,  16  of the caliper  12 . For example, the parking brake system  36  may include two parking brake systems, each one of which is configured to move one or more brake pistons on each side  14 ,  16  of the caliper  12 . The parking brake systems  36  can have fingers configured to pull opposing brake pads. For example, one of the parking brake systems can be configured to move one or more brake pistons supported in bores on side  14  of the caliper  12  and fingers configured to pull the brake pad supported at side  16  of the caliper  12 . The other parking brake system is configured to move one or more brake pistons supported in bores on side  16  of the caliper  12  and fingers configured to pull the brake pad supported at side  14  of the caliper  12 . Such a system may ensure that both brake pads are moved against the brake caliper to create clamping force. 
     Referring back to  FIG.  1 A , the brake system  10  comprises pins  22 ,  24  that are configured to extend between the sides  14 ,  16  of the brake caliper  12 , and support the brake pistons  18 ,  20 . The brake system  10  may comprise any number of pins  22 ,  24 . For example, the system  10  may comprise two pins  22 ,  24  like shown in  FIG.  1 A . For example, the system  10  may comprise one pin, or more than 2 pins (e.g.,  3  of more pins, 4 or more pins, 5 or more pins, etc.). A cross-section of one or more of the pins  22 ,  24  may be circular. 
     In leu of the brake pads moving sliding one or more of the pins  22 ,  24  during a brake apply or release (whether for service braking or parking braking), the brake pads  18 ,  20  may be configured to move or slide within the notches or grooves that are configured to support the ears or end so the pressure plate of the brake pads. In other words, one or more of the pins  22 ,  24  may be eliminated. In such a configuration, the notches or grooves are defined in the first side and the opposing second side of the brake caliper. Each of the brake pads have ears or projections that engage the corresponding grooves. The fit between the ears or projections and the corresponding grooves enables the brake pads to move or slide towards and away from the brake rotor without the need for the pins to support the brake pads during such movement. Advantageously, this may provide for a cost-effective brake system by eliminating the overhead pins and/or may ease or reduce manufacturing and/or assembly complexities. 
       FIG.  5    illustrates a brake piston assembly  48  that comprises a piston body  72  which extends along a longitudinal axis  74 ; a spindle  54 ; a piston seal  76 ; a thrust bearing assembly  60 ; a spindle O-ring  78 ; and a retaining clip  80 . The brake piston assembly  48  may be configured for use during a standard braking operation (e.g., service brake) or during a parking brake operation. Accordingly, the brake piston assembly  48  may be inserted into one or more of the caliper bores  46  illustrated in  FIG.  3   , for example, described in any of other brake systems included, described, or illustrated herein. 
     An outer surface  82  of the piston body  72  comprises an optional pair of anti-rotation features  84  that generally oppose one another. Stated another way, the anti-rotation features  84  are located on opposing sides of the piston body  72 . The outer surface  82  of the piston body  72  is generally circular, and the anti-rotation features  84  are generally flat sections relative to the generally circular outer surface  82 . The anti-rotation features  84  of the brake piston  48  are adapted to engage or be engaged by corresponding anti-rotation features defined in a caliper bore  46  ( FIGS.  3 ,  6   , etc.) of the caliper  12 . The anti-rotation features cooperate to restrict or prevent the brake piston  48  from rotating inside the caliper bore  46  about the axis  74 . 
     The piston body  72  comprises a piston pocket  86 . The piston pocket  86  is a bore defined in the piston body  72 . The piston pocket  86  comprises a threaded portion  88  that is defined or formed directly in the annular wall or side wall defining the piston pocket  86 . Alternatively, the threaded portion  88  may be a sleeve or insert that is fit into the piston pocket  86 . The threaded portion  88  is adapted to threadably engage a corresponding threaded portion  90  of the spindle  54 . Alternatively, the threaded portion  88  may be a groove or track that is configured to cooperate with a corresponding groove or track in the spindle  90  to house or support ball bearings, for example, like a ball nut assembly. The spindle  54  comprises an input portion  66 . The input portion  66  of the spindle  54  is adapted to engage a motor or MGU or other source of rotary force or torque so that the spindle  54  can be rotated. Rotation of the spindle  54  about the longitudinal axis  72  causes the brake piston  48  to move axially along the longitudinal axis  40 . 
     The piston seal  76  is a generally annular structure that is adapted to fit around and surround the outer surface  82  of the piston body  82 . The piston seal  76  comprises anti-rotation features  92  disposed around an inner diameter thereof. The ant-rotation features  92  generally correspond to and are adapted to engage the corresponding ant-rotation features  84  located on the outer surface  82  of the piston body  72 . 
       FIGS.  6 A and  6 B  illustrate a cross section of the brake system  10  of  FIGS.  1 A- 2   . The brake system  10  may include one or more of the features described above or below in any of the figures included herewith. Therefore, similar or like features will not be described again. 
     The brake system  10  comprises a parking brake system  36 . The parking brake system  36  is a slider-type of brake system. The parking brake system  36  may function and/or include features that are disclosed in Applicant&#39;s previously-filed U.S. patent application Ser. No. 15/248,134, filed on Aug. 26, 2016, which is expressly incorporated by reference herein for all purposes. More specifically, the parking brake system  36  may function and/or includes features of the parking brake system identified by reference numeral 12 in Applicant&#39;s aforementioned U.S. patent application Ser. No. 15/248,134. 
     Referring to  FIG.  6 A , the parking brake system  36  comprises a bridge  38  that extends over a gap defined between the first and second sides  14 ,  16  of the caliper  12 . The parking brake system  36  comprises fingers  42   a ,  42   b . The fingers  42   a ,  42   b  are configured to surround pin  24  and brake piston  48   a  that is located or supported in caliper bore  46   a.    
     Referring to  FIG.  6 B , the fingers  42   a ,  42   b  are configured to surround both pins  22 ,  24  and both brake pistons  48   a ,  48   b . More specifically, finger  42   a  is located at one side of pin  22  and brake piston  48   b , and pin  42   b  is located at another side of pin  24  and brake piston  48   a . a center portion, which may be a finger  42   c  extends between pins  22 ,  24  and brake pistons  48   a ,  48   b  supported in corresponding caliper bores  46   a ,  46   b.    
     With continued reference to  FIG.  6 B , the parking brake system  36  is generally centered on the brake caliper  12 . That is, a center portion or plane of the parking brake system  36  is generally centered between the ends of the brake caliper  12 . 
       FIG.  7    illustrates a brake system  10 . The brake system  10  may include one or more of the features described above or below in any of the figures. Therefore, in the interest of brevity, like features will not be described again. 
     The brake system  10  comprises a brake caliper  12 . The brake caliper may be formed as a single, integral component. This means that the brake caliper  12  is manufactured from a single piece that does not need to be subsequently joined together afterwards. 
     Alternatively, the brake caliper may be made of two or more pieces. For example, the brake caliper may be made of two or more halves or pieces, which are then joined together at a parting line  94 . The two sides  14 ,  16  may be joined together with suitable fasteners like bolts, screws, welding, etc. For example, the first side  14  and the second side  16  may be separate discrete pieces, which are then joined together. The first and second sides  14 ,  16  may be mirror images of each other. Alternatively, the first and second sides  14 ,  16  may be different from each other. Different means that the first side  14  may be thicker or thinner than the other side and/or may have geometry that is different than the second side  16  (e.g., not mirror image). Additionally, or alternatively, the brake caliper may comprise two or more sections or pieces that are joined together at a parting line that is angled relative to the line illustrated at  94 . For example, the line may be perpendicular to line  94 , or the line may be at an angle that is acute or obtuse to line  94 . A brake caliper  12  that is made of two or more sections or portions that are subsequently joined together may be advantageous in that the sections may be made of different materials; manufacturing complexities may be reduced or eliminated; or both. 
     With continued reference to  FIG.  7   , if the caliper body  12  comprises two halves or sides  14 ,  16  that are separated at parting line  94 , the two halves  14 ,  16  may be joined together with one or more bolts  94 ,  96  (two bolts shown). In addition to connecting the two halves together  14 ,  16 , one or more of the bolts  94 ,  96  may also function as sliding pins  22 ,  24  for the inboard and outboard brake pads  18 ,  20  to move or slide along. The brake system  10  may include one or more of the features described above or below in any of the figures. Therefore, in the interest of brevity, like features will not be described again. 
     Having a caliper body  12  comprises of two or more halves may be advantageous in that complex geometries can be manufactured, which may be difficult or costly to form if the caliper body  12  is constructed of a single construction. Moreover, scrap in the manufacturing process may be reduced by being able to salvage and join together halves of the caliper body  12 . In some configurations, the caliper body  12  may be strengthened via the bolts holding the halves of the caliper body  12  together. 
       FIG.  8    illustrates a brake system  10 . The brake system  10  may include one or more of the features described above or below in any of the figures. Therefore, in the interest of brevity, like features will not be described again. 
     The brake system  10  comprises a brake caliper  12  that includes a first side  14  and an opposing second side  16 . The brake system  10  is an opposed piston brake system. This means one or more brake pistons are supported in the first side  14  of the brake caliper  12 , and one or more brake pistons are supported in the second side  16  of the brake caliper  12 . 
     A first brake pad  18  is supported at the first side  14  or inboard side of the brake caliper  12 , and a second brake pad  20  is supported at the second side  16  or outboard side of the brake caliper  12 . During a brake apply, the one or more brake pistons supported on the first side  14  of the brake caliper  12  are configured to be moved, causing the first brake pad  18  to move towards and against a brake rotor located between the sides  14 ,  16  of the caliper  12  to create clamping force. At the same time, the one or more brake pistons supported on the second side  16  of the brake caliper  12  are configured to be moved, causing the second brake pad  20  to be moved towards and against the opposing side of the brake rotor to create clamping force. 
     The brake system comprises a parking brake system  36 . The parking brake system  36  may be a spot caliper that includes a bridge  38  and fingers  42 . The bridge  38  may be connected to the brake caliper  12 . For example, the bridge  38  may be connected to the first side  14 , the second side  16  of the brake caliper  12 , or both sides  14 ,  16  of the caliper  12 . When the brake system  10  is mounted to a vehicle, the bridge  38  is configured to straddle or at least partially surround a brake rotor (not illustrated) just like how the sides  14 ,  16  of the brake caliper  12  are configured to straddle or at least partially surround the brake rotor. The parking brake system  36  may extend from a leading end of the brake caliper  12  or the training end of the brake caliper. For example, the parking brake system  36  may be configured to move one or more brake pad sections A, B, C, illustrated in  FIG.  1 C . Alternatively, while not illustrated, a parking brake system  36  may be located at both ends of the brake caliper  12  (i.e., the brake system comprises a parking brake system at both ends of the brake caliper). The parking brake system  36  may be located in the middle of the caliper, between the leading and trailing ends of the brake caliper and configured to move one or more pad sections of the brake pad, like brake pad section B illustrated in  FIG.  1 C , for example. An outboard brake pad  96  located adjacent the fingers  42 , and an inboard brake pad  98  is located adjacent a brake piston (not illustrated). The parking brake system  36  may be configured such that the fingers pull or draw the outboard brake pad  96  against the rotor to create the clamping force, or the parking brake system  36  may flipped such that the fingers  42  are configured to pull the inboard brake pad  98  against the brake rotor to create the clamping force. 
     The parking brake system  36  may be used to create a clamping force during a parking brake application, and the brake system  10  may be used to create a clamping force during application of the service brake, or vice versa. 
       FIG.  9    illustrates a portion of the parking brake system  36  that may be used with any of the brake calipers  12  disclosed herein. The parking brake system  36  comprises a bridge  38  and  42   a ,  42   b . The fingers  42   a ,  42   b  are configured to surround pin  24 . In some configurations, the fingers  42   a ,  42   b  may surround only pin  22 , or may surround both pins  22 ,  24 , like in  FIG.  8 B . 
     The fingers  42   a ,  42   b  are in contact with a brake pad  100 . More specifically, the fingers  42   a ,  42   b  are in contact with a pressure plate  102  of the brake pad  100 . The fingers  42   a ,  42   b  may be integrally-formed with the pressure plate,  102  or attached to the pressure plate  102  with mechanical fasteners like screws, bolts, an adhesive, or a combination thereof. 
     In some configurations, the bridge  38  may be free of fingers  42   a ,  42   b , and instead, the brake pad  100  may be connected directly to the bridge  38 . 
       FIG.  10    illustrates a brake system  10 . The brake system  10  comprises a brake caliper  12  and a parking brake system  36 . The brake caliper  12  and the parking brake system  36  may be like one or more of the systems described herein. Therefore, in the interest of brevity like components or elements will not be described. 
     The brake caliper  12  including the bridge  30  may be made of a suitable material like steel or aluminum. Additionally, or alternatively, the brake caliper  12  and/or the bridge  30  may be made of a phenolic plastic, aluminum or steel. Use of a phenolic material may be advantageous to reduce heat transfer and corrosion, while reducing an overall weight of the system  10 . Some non-load bearing portions of the brake caliper  12  may be made of a carbon fiber material. 
     Similarly, the parking brake system  36  including the bridge  48  and/or fingers  42   a ,  42   b  may be made of a suitable material like steel or aluminum. Additionally, or alternatively, the parking brake system  36 , the bridge  48 , and/or fingers  42   a ,  42   b  may be made of a phenolic plastic, aluminum or steel. Use of a phenolic material may be advantageous to reduce heat transfer and corrosion, while reducing an overall weight of the system  36 . Some non-load bearing portions of the parking brake system  36  may be made of a carbon fiber material. 
     The parking brake system may also comprise a motor gear unit (MGU hereafter). The MGU may comprise an electric motor and optionally one or more gears that are configured to increase or decrease a torque output from the motor. The MGU may be configured to move the one or more brake pistons and thus brake pads during a braking event, whether for parking or service, or both. One MGU may be configured to produce sufficient torque to move one or more of the brake pistons. Alternatively, the parking brake system may comprise multiple MGU. For example, it may be advantageous to have a parking brake system that includes a dedicated MGU for each brake piston. Such a configuration would ensure all of the brake pistons are sufficiently moved to create the clamping force. Because the parking brake system in these configurations is a sliding-type of system, the MGU may be attached to a top of the bridge, or even to an end of the bridge. In such a configuration, the MGU may be configured to move or slide with the bridge or fingers during a braking event. 
       FIG.  11    illustrates a portion of the parking brake system  36 . The parking brake system comprises a bridge  38  and fingers  42   a ,  42   b . The fingers  42   a ,  42   b  are in contact with a brake pad  100 . The brake pad  100  is a two-piece brake pad, comprising a first piece or pad section  104  and a second piece or pad section  106 . The fingers  42   a ,  42   b  are in contact with the pressure plate of the first piece  104  of the brake pad  100 . During a brake apply, both pistons  48   a ,  48   b  may move both of the pad sections  104 ,  106  against a brake rotor to create the clamping force. With additional reference to  FIG.  15   , during a parking brake apply, the fingers  42   a ,  42   b  may pull only the pad section  104  against the brake rotor to create the clamping force. 
     With continued reference to  FIGS.  11  and  15   , the material of the friction material F 1 , F 2 , on each of the two pad sections  104 ,  106  may be the same or have the same coefficient of friction. For example, the coefficient of friction may be 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, etc. 
     Alternatively, the material of the friction material F 1 , F 2 , on each of the two pad sections  104 ,  106  may be different and/or or have a different coefficient of friction. For example, it may be desirable for the friction material F 1 , F 2  of the pad section  104 ,  106  that is associated with a parking brake application to have a higher coefficient of friction than the friction material F 1  or F 2  of the pad section  104 ,  106  that is associated with a service brake application. This difference in friction material may advantageously reduce NVH issues (Noise, Vibration and Harshness) during a brake application (service and/or parking brake application) and/or advantageously reduce clamp load applied on one or more components of the brake system, such as the actuator, spindle, nut, motor, etc. 
     To compensate for the different friction materials F 1 , F 2 , pressure applied onto the pad sections  104 ,  106  (via the brake piston  48   b ,  48   a , and/or fingers  42   a,b ) may be different. In other words, the pressure applied by brake piston  48   b  onto pad section  106  may be different (higher or lower) than the pressure applied by brake piston  48   a  and/or fingers  42   a , 42   b  onto pad section  104 . This difference in applied pressure may be accomplished by having different sized brake pistons (i.e., piston  48   b  is larger than brake piston  48   a , or vice versa). For example, if the coefficient of friction of the frication material F 1  is 0.6 and the other friction material F 2  is 0.3, then the size of brake piston  48   a  may be 50% smaller than the size of brake piston  48   b . In certain configurations, the size of brake piston  48   a  may be 10% smaller than the size of brake piston  48   b,  20% smaller than the size of brake piston  48   b,  30% smaller than the size of brake piston  48   b,  40% smaller than the size of brake piston  48   b,  50% smaller than the size of brake piston  48   b,  60% smaller than the size of brake piston  48   b,  70% smaller than the size of brake piston  48   b,  80% smaller than the size of brake piston  48   b,  90% smaller than the size of brake piston  48   b , etc. Of course, the opposite also applies, where the size of brake piston  48   b  may be smaller than the brake piston  48   a  via the aforementioned percentages. 
     Assuming the friction material F 1  is used for both a parking brake application and a service brake and has a friction coefficient as μ 1  and the friction material F 2  is used for only a service brake apply and has a friction coefficient as μ 2 , then the friction coefficient may be μ2&gt;μ1. In some configurations, the ratio may be μ 1 =2μ 2 . Such ratios may be beneficial for the parking brake system since the same torque output could be achieved, while reducing load or clamp force on the actuator, spindle, nut, motor, etc. However, if the same hydraulic pressure is applied onto the friction materials F 1 , F 2  via the brake pistons  48   a ,  48   b , then the torque generated from friction material F 1  may be greater than the torque generated from the friction material F 2 , assuming the effective radii are same, for example twice as much, or more. This could result in the tangential force (which is the force to generate torque) being higher (for example twice as high) under friction material F 1 . The more tangential excitation force may mean more propensity to have an NVH issue, such as a squeal. Thus, to achieve a similar level tangential force at both brake pistons  48   a ,  48   b  during a service brake application, it may be desirable to have lower hydraulic area or pressure acting on the friction material F 1  or pad section  106 . To obtain a lower hydraulic area, the brake piston  48  may be smaller than brake piston  48   a . To obtain a lower hydraulic pressure applied to the brake piston  48   b  associated the friction material F 1 , a proportioning valve, or use different master cylinder may be used. 
     Alternatively, in some configurations, it may be advantageous for both friction materials F 1 , F 2  to be the same or to have the same coefficient of friction. 
     The size or surface area of the friction material F 1 , F 2  of each pad section  104 ,  106  may be generally the same. Or, the size or surface area of the friction material F 1 , F 2  of the pad section  104 ,  106  configured for service brake application may be larger than the surface area of the friction material F 1 , F 2  of the pad section  104 ,  106  configured for parking brake application, or vice versa.  FIG.  12    illustrates a top section view of a brake system  10 . The brake system  10  comprises an inboard brake pad  18 , an outboard brake pad  20 , a rotor R between the two brake pads  18 ,  20 . The brake system  10  comprises a parking brake system  36  that includes a shaft  108 . The shaft  108  extends either through the brake rotor R, or above the brake rotor R and is connected to the outboard brake pad  20 . During a brake apply or a parking brake apply, rotation of the shaft  108 , by way of a motor or MGU, causes the outboard brake pad  20  to move towards the brake rotor R to create the clamping force. The inboard brake pad  18  may be moved toward the opposing side of the brake rotor R by way of the same shaft  108 . This means that the end or portion of the shaft  108  that connects to the outboard brake pad  20  is treaded in reverse or opposite the end of portion of the shaft  108  that connects to the inboard brake pad  18 . 
       FIG.  13    illustrates a brake system  10 . The brake system  10  comprises a brake caliper  12  that includes an inboard side  14  and an opposing outboard side  16 . The brake caliper  12  is configured to support an inboard brake pad  18  and an opposing outboard brake pad  20 . The inboard and outboard brake pads  18 ,  20  are configured to be supported on opposite sides of a brake rotor. The brake caliper  12  comprises mounting features  22  for attaching the brake caliper  12  to a fixed portion of a vehicle, like a knuckle. The brake system  10  comprises a parking brake system  24 . 
     Referring now to  FIG.  14   , the brake system  10  comprises more brake pistons located or supported at the inboard side  14  of the brake caliper  12  than at the outboard side  16  of the brake caliper. For example, the brake system  10  may include two inboard brake pistons  26   a ,  26   b  supported in corresponding caliper bores defined in the inboard side  14  of the brake caliper  12 . The brake system  10  may comprise one outboard brake piston  28  supported in a caliper bore defined in the outboard side  16  of the brake caliper  12 . The brake system  10  is free of an outboard brake piston supported on the outboard side  16  of the brake caliper  12  that is located directly across from the inboard brake piston  26   a  supported on the inboard side  14  of the brake caliper  12 . 
     While the outboard brake piston  28  is illustrated to be exactly across from the inboard brake piston  26   b , the outboard brake piston  28  may be moved or shifted towards either the leading or trailing edge of the brake caliper  12 . In some configurations, the outboard brake piston  28  may be located exactly in between the leading and trailing edge of the brake caliper  12 . In some configurations, the outboard brake piston  28  may be centered on the outboard brake pad  20 . 
     During a service brake apply to create a clamping force to slow, stop, or prevent movement of the brake rotor, brake fluid is pressurized and then supplied to the inboard brake pistons  26   a ,  26   b , which causes the inboard brake pistons  26   a ,  26   b  to move out of their corresponding caliper bores and move the inboard brake pad  18  against the corresponding side of the brake rotor to generate friction. The pressurized brake fluid is also supplied to the outboard brake piston  28 , which causes the outboard brake piston  28  to move out of its corresponding caliper bores and move the outboard brake pad  20  against the corresponding side of the brake rotor to generate friction. The pressurized fluid will also act on the bottom of the sliding caliper or bridge  30  and push the fingers  32  against the outboard brake pad  20  and against the outboard side of the brake rotor. The friction generated by the inboard and outboard brake pads  18 ,  20  pressed against the side of the brake rotor is the clamping force that functions to slow, stop, or prevent movement of the brake rotor and thus the vehicle wheel. 
     To release clamping force to allow movement of the brake rotor and vehicle, the brake fluid is depressurized so that the inboard brake pistons  26   a ,  26   b  move back into their corresponding caliper bores thus allowing the inboard brake pad  18  to move away from and thus out of contact with and the corresponding side of the brake rotor. Depressurized the brake fluid also allows the outboard brake piston  28  to back into its corresponding caliper bore thus allowing the outboard brake pad  20  to move out away from and out of contact with the corresponding side of the brake rotor. Depressurizing the brake fluid also allows the fingers  32  of the sliding caliper or bridge  30  to move away from the outboard brake pad  20  so that the outboard brake pad  20  can move away from and out of contact with the outboard side of the brake rotor. 
     Referring to both  FIGS.  13  and  14   , the parking brake system  12  comprises a bridge  30  that spans or extends over the inboard and outboard sides  14 ,  16  of the brake caliper  12 . A grasping member of finger  32  extends from the bridge and is configured to engage the outboard brake pad  20 . 
     The parking brake system  24  comprises a rotary to linear stage mechanism  34  that comprises a spindle and nut. The spindle comprises an outer threaded portion that is configured to engage an inner threaded portion of the nut. The spindle and nut are received inside a pocket of the inboard brake piston  26   a . The spindle comprises an input portion  36  that is in communication with a torque generating feature  38  that is configured to generate torque. The torque from the torque generating feature  38  is configured to rotate the spindle, which causes the nut to move axially within the pocket of the inboard brake piston  26   a . The torque generating feature may be a motor, a motor gear unit (MGU), or a cable pull that is configured to rotate a shaft or actuator. 
     During a parking brake apply to create clamping force to prevent movement of the brake rotor and vehicle, the torque generating feature  38  is configured to generate torque in an apply direction, which causes the spindle to rotate in an apply direction. The nut is restricted or prevented from rotating inside the pocket of the inboard brake piston  26   a . Instead, when the spindle is rotated, the nut is configured to axially move. When the spindle is rotated in an apply direction, the nut is configured to axially move in an apply direction until the nut contacts a bottom wall or surface of the piston pocket of the inboard brake piston  26   a . Continued rotation of the spindle in the apply direction and thus movement of the nut in the apply direction causes the nut to move or push the inboard brake piston  26   a  and ultimately the inboard brake pad  18  into contact with the side of the brake rotor to generate friction. A reacting force is generated by this pressing of the inboard brake pad  18  against the brake rotor, which is transmitted through the bridge  30  such that the grasping member of finger  32  is moved, which thus moves the outboard brake pad  20  into contact with the opposite side of the brake rotor to generate friction. The friction generated by the inboard and outboard brake pads  18 ,  20  pressed against the side of the brake rotor is the clamping force that functions to prevent movement of the brake rotor and thus the vehicle wheel. 
     To release the clamping force that was generated by the parking brake apply, the torque generating feature  38  is configured to generate torque in a release direction, which causes the spindle to rotate in a release direction. When the spindle is rotated in the release direction, the nut is configured to axially move in a release direction until the nut is out of contact with the bottom wall or surface of the piston pocket of the inboard brake piston  26   a , which thus allows the inboard brake piston  26   a  to move back into its corresponding caliper bore so that the inboard brake pad  16  can move away from and out of contact with the corresponding side of the brake rotor. The reacting force that was generated by the pressing of the inboard brake pad  18  against the brake rotor is reduced or eliminated, which is transmitted through the bridge  30  such that the grasping member of finger  32  is moved in an opposite direction, which thus moves the outboard brake pad  20  out of contact with the opposite side of the brake rotor to release the friction or clamping force. 
     In the aforementioned brake system  10 , the inboard brake piston  26   a  functions as a dual use brake piston—for creating clamping force during application of the service brake and for creating the clamping force during application of the parking brake. The other brake pistons  26   b ,  28  are used for creating clamping force during application of the service brake. 
     While the brake system  10  is illustrated and described as having more brake pistons located or supported on the inboard side than on the outboard side, in some configurations it may be advantageous and/or desirable to have more brake pistons located or supported on the outboard side than on the inboard side of the brake caliper. 
     Moreover, while the brake system  10  is illustrated and described as having one more inboard brake piston than outboard brake pistons, in some configurations the brake system may have two more inboard brake pistons than outboard brake pistons, or even three or more, four or more, or even five or more inboard brake pistons than outboard brake pistons. For example, while a ratio of inboard brake pistons to outboard brake pistons in the brake system illustrated and described above is 2:1, in some configurations, the ratio may be 3:1, 4:1, or even 5:1. 
     The brake system  10  may have more than one inboard brake piston, but the number of inboard brake pistons is less than the number of outboard brake pistons. 
     While the brake system  10  is illustrated and described as having the inboard brake piston  26   a  function as the dual use brake piston, it is understood that the other inboard brake piston  26   b  may instead be the dual use brake piston and the inboard brake piston  26   a  may be used for creating clamping force during application of the service brake. 
     While the brake system  10  is illustrated and described as having the inboard brake piston  26   a  function the dual use brake piston, it is understood that both of the brake pistons  26   a ,  26   b  may be dual use brake pistons. In such an alternative brake system, each of the brake pistons  26   a ,  26   b  include a corresponding rotary to linear stage mechanism for moving the brake piston  26   a ,  26   b  and thus the inboard brake pad  18  against the brake rotor to crate the clamping force. The spindles may be rotated by individual motors or by a single motor with a torque distribution assembly or differential, as has been disclosed by Applicant in various other commonly owned patent applications. 
     While the brake system  10  is illustrated and described as not having a brake piston located across from the dual use inboard brake piston, it is understood that in some configurations, the outboard brake piston may be located across from the dual use inboard brake piston and no brake piston may be located across from the other inboard brake piston. For example, referring to  FIG.  2   , in some configurations the outboard brake piston  28  may be located across from the dual use inboard brake piston  26   a , and no brake piston may be located across from the other inboard brake piston  26   b.    
     One or more of the features illustrated and/or described in any of the brake systems disclosed herein can be combined, duplicated, substituted, and/or omitted to form one or more brake systems. This means that one or more features from any of the brake and/or parking brake systems disclosed herein can be combined with one or more features or elements from any of the other brake and/or parking brake systems disclosed herein. 
     The explanations and illustrations presented herein are intended to acquaint others skilled in the art with the invention, its principles, and its practical application. The above description is intended to be illustrative and not restrictive. Those skilled in the art may adapt and apply the invention in its numerous forms, as may be best suited to the requirements of a particular use. 
     Accordingly, the specific embodiments of the present invention as set forth are not intended as being exhaustive or limiting of the teachings. The scope of the teachings should, therefore, be determined not with reference to this description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The omission in the following claims of any aspect of subject matter that is disclosed herein is not a disclaimer of such subject matter, nor should it be regarded that the inventors did not consider such subject matter to be part of the disclosed inventive subject matter. 
     Plural elements or steps can be provided by a single integrated element or step. Alternatively, a single element or step might be divided into separate plural elements or steps. 
     The disclosure of “a” or “one” to describe an element or step is not intended to foreclose additional elements or steps. 
     While the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. Other combinations are also possible as will be gleaned from the following claims, which are also hereby incorporated by reference into this written description.