HYDRAULICALLY-ADJUSTABLE ROTARY TO LINEAR STAGE MECHANISM

Abstract

A brake system that includes a brake piston that includes a piston pocket. A nut is located inside the piston pocket. During a brake apply, the brake piston is adapted to move a brake pad against a brake rotor to create a clamping force. During the brake apply, the nut is moved with the brake piston.

Claims

1) A brake system comprising: a) a brake caliper; b) a brake piston supported in the brake caliper, the brake piston comprising a piston pocket; and c) a rotary to linear stage mechanism, the rotary to linear stage mechanism comprises a nut located in the piston pocket; wherein during a brake apply, the brake piston is moved in an apply direction, and movement of the brake piston in the apply direction during the brake apply causes a brake pad to be moved against a brake rotor to create a clamping force, and wherein during the brake apply, the rotary to linear stage mechanism moves with the brake piston so that a position of the nut relative to the brake piston is adjusted.

2) The brake system of claim 1, wherein a clip engages a wall of the piston pocket, and wherein the clip traps the nut inside the piston pocket so that during the brake apply, the nut is moved with the brake piston when the brake piston is moved in the apply direction.

3) The brake system of claim 1, wherein the rotary to linear stage mechanism comprises a spindle; and wherein during a parking brake apply, the spindle is rotated with an MGU, which causes the nut to move the brake piston and the brake pad against the brake rotor.

4) The brake system of claim 3, wherein during the brake apply, the brake piston is moved by pressuring hydraulic fluid.

5) The brake system of claim 3, wherein the piston pocket comprises at least one rib, and the nut comprises an O-ring that frictionally engages a wall of the piston pocket and/or the at least one rib so that the nut is restricted from rotating when the nut is moved during the parking brake apply.

6) The brake system of claim 5, wherein the nut rotates when the nut is moved during the brake apply.

7) The brake system of claim 3, wherein the brake system comprises: d) a second brake piston; e) a rotary to linear stage mechanism that includes a second nut and a second spindle; f) a first gear in communication with the spindle; and g) a second gear in communication with the second spindle, wherein during the parking brake apply, torque provided by an MGU is applied to the first gear, which causes the spindle to rotate in the apply direction, which causes the nut to move in the apply direction and move the brake piston and the brake pad against the brake rotor, and wherein the second gear is connected to the first gear so that rotation of the first gear in the apply direction causes the second gear to rotate in the apply direction, which causes the second spindle to rotate in the apply direction, which causes the second nut to move in the apply direction and move the second brake piston and the brake pad against the brake rotor.

8) The brake system of claim 7, wherein a second clip engages a wall of a piston pocket of the second brake piston, wherein the second clip traps the second nut inside the piston pocket of the second brake piston so that during the brake apply, the second nut is moved with the second brake piston when the second brake piston is moved in the apply direction.

9) A brake system, comprising: a first brake piston, the first brake piston comprising a first piston pocket; a second brake piston, the second brake piston comprising a second piston pocket; a first nut located inside the first brake piston, and a second nut located inside the second brake piston; wherein during a brake apply, the first brake piston and the second brake piston are adapted to move a brake pad against a brake rotor to create a clamping force, and during the brake apply the first nut is moved with the first brake piston and the second nut is moved with the second piston.

10) The brake system of claim 9, wherein a first clip is fixed to a wall of the first piston pocket, the first clip maintains the first nut within the piston pocket so that the first nut moves with the first brake piston during the brake apply; wherein during the brake apply, the first nut rotates while moving with the first brake piston.

11) The brake system of claim 10, wherein the brake system comprises a first spindle; wherein during a parking brake apply, the first spindle is rotated, which causes the first nut to move axially against a bottom pocket wall of the first piston pocket to move the first brake piston and the brake pad against the brake rotor; and wherein during the parking brake apply the first nut is restricted from rotating.

12) The brake system of claim 11, wherein an O-ring surrounding the first nut frictionally engages a wall of the piston pocket so that the first nut is restricted from rotating during the parking brake apply.

13) The brake system of claim 12, wherein the piston pocket comprises a wall having one or more projections that extend from the wall towards a center of the piston pocket, and wherein the O-ring surrounding the first nut frictionally engages the one or more projections to prevent the nut from rotating during the parking brake apply but allows for bleeding hydraulic fluid.

14) The brake system of claim 11, wherein during the parking brake apply, first the spindle is rotated with torque supplied by an MGU; and wherein during the brake apply, the first brake piston is moved by pressuring hydraulic fluid.

15) The brake system of claim 11, wherein a second clip is fixed to a wall of the second piston pocket, the second clip maintains the second nut within the piston pocket so that the second nut moves with the second brake piston during the brake apply; wherein during the brake apply, the second nut rotates while moving with the second brake piston.

16) The brake system of claim 15, wherein the brake system comprises a second spindle; wherein during the parking brake apply, the second spindle is rotated, which causes the second nut to move axially against a bottom pocket wall of the second piston pocket to move the second brake piston and the brake pad against the brake rotor; and wherein during the parking brake apply the second nut is restricted from rotating.

17) The brake system of claim 16, wherein the brake system comprises a first gear in communication with the first spindle, and a second gear in communication with the second spindle, wherein during the parking brake apply, torque provided by an MGU is applied to the first gear, which causes the first spindle to rotate in the apply direction, which causes the first nut to move in the apply direction and move the first brake piston and the brake pad against the brake rotor, and wherein the second gear is connected to the first gear so that rotation of the first gear in the apply direction also causes the second gear to rotate in the apply direction, which causes the second spindle to rotate in the apply direction, which causes the second nut to move in the apply direction and move the second brake piston and the brake pad against the brake rotor.

18) A brake system, comprising: a) a brake caliper; b) a first brake piston supported in the brake caliper, the first brake piston comprises a first piston pocket; c) a second brake piston supported in the brake caliper, the second brake piston comprises a second piston pocket; d) a parking brake system comprising a first rotary to linear stage mechanism and a second rotary to linear stage mechanism; the first rotary to linear stage mechanism includes a first nut, and the second rotary to linear stage mechanism includes a second nut; wherein the first nut is received in the first piston pocket and the second nut is received in the second piston pocket; wherein during a brake apply, the first brake piston and the second brake piston are adapted to be moved in an apply direction, and movement of the first brake piston and the second brake piston during the brake apply cause a brake pad to be moved against a brake rotor to create a clamping force; and wherein during the brake apply, the first nut moves along with the first brake piston in the apply direction, and the second nut moves along with the second brake piston in the apply direction.

19) The brake system of claim 18, wherein the parking brake system comprises: a) first spindle in communication with the first nut; b) a first gear in communication with the first spindle; c) a second spindle in communication with the second nut; and d) a second gear in communication with the second spindle; wherein during a parking brake apply, the first brake piston is moved in the apply direction by rotating the first gear with an MGU in the apply direction, which causes the first spindle to rotate in the apply direction, which causes the first nut to move the first brake piston and the brake pad against the brake rotor; wherein during the parking brake apply, the second brake piston is moved in the apply direction by rotating the second gear in the apply direction, which causes the second spindle to rotate in the apply direction, which causes the second nut to move the second brake piston and the brake pad against the brake rotor; and wherein the first gear and the second gear are connected together with a belt so that rotation of the first gear causes the second gear to rotate.

20) The brake system of claim 18, wherein during the brake apply, the first nut moves in the apply direction while rotating about an axis of the first spindle, and the second nut moves in the apply direction while rotating about an axis of the second spindle; wherein during a parking brake apply, the first nut is moved axially along the axis of the first spindle and is restricted from rotating about the axis of the first spindle; and wherein during the parking brake apply, the second nut is moved axially along the axis of the second spindle and is restricted from rotating about the axis of the second spindle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 is a perspective view of a brake system.

[0045] FIG. 2 is another perspective view of the brake system of FIG. 1, with the cover removed.

[0046] FIG. 3 is a partial, cross-sectional view of the brake system taken along line III-III of FIG. 2.

[0047] FIG. 4 is an exploded, perspective view of a brake piston assembly that includes the hydraulically-adjustable rotary to linear stage mechanism.

[0048] FIG. 5A is a cross-sectional view of a brake piston and the hydraulically-adjustable rotary to linear stage mechanism relative to the inboard brake pad.

[0049] FIG. 5B is a cross-sectional view of a brake piston and the hydraulically-adjustable rotary to linear stage mechanism relative to the inboard brake pad.

DETAILED DESCRIPTION

[0050] FIG. 1 is a perspective view of the brake system 10. The brake system 10 includes a brake caliper 12 that, supports a leading brake piston assembly 14 and a trailing brake piston assembly 16. The brake system 10 includes a support bracket 18 that supports an inboard brake pad 20 and an outboard brake pad 22. The brake caliper 12 includes a bridge 24 with fingers 26. The fingers 26 are in contact with a pressure plate 28 of the outboard brake pad 22. The brake system 10 also includes a parking brake system 30. The parking brake system 30 includes a motor gear unit (MGU) 32 located within a cover 34. The MGU 32 generally includes a motor and a gear train that functions to increase a torque output of the motor.

[0051] FIG. 2 is a perspective view of the brake system 10, with the cover 34 and the MGU 32 removed for clarity. Relative to a rotational direction R of a brake rotor, the parking brake system 30 includes a leading gear 36 in communication with the leading brake piston assembly 14, and a trailing gear 38 in communication with the trailing brake piston assembly 16. The gears 36, 38 are connected together with a belt 40. The leading gear 36 includes an input area 42 by which torque from the 32 is transmitted to the leading gear 36. By way of the belt 40, rotation of the leading gear 36 via the MGU 32 causes the trailing gear 38 to also rotate.

[0052] FIG. 3 is a partial cross-sectional view of the brake system 10 taken along line III-III of FIG. 2. The leading brake piston assembly 14 includes a leading brake piston 44 that is supported in a caliper bore 46 defined in the brake caliper 12. The leading brake piston 44 includes a cup-shaped piston pocket 48. Received in the piston pocket 48 is a hydraulically-adjustable rotary to linear stage mechanism 50. The hydraulically-adjustable rotary to linear stage mechanism 50 is a high efficiency mechanism that includes a spindle 52 and a nut 54. The spindle 52 is in rotational communication with the leading gear 36 so that when torque is applied to the input portion 42 of the leading gear 36 by the MGU 32 (FIG. 1), the spindle 52 rotates. As will be described further below, when the spindle 52 is rotated, the nut 54 moves axially along a longitudinal axis 80 of the spindle 52 either towards or away from a bottom pocket wall 82 of the piston pocket 48. The direction that the nut 54 is moved depends on the direction that the leading gear 36 is rotated by the MGU 32. That is, during a parking brake apply, the spindle 52 is rotated in an apply direction so that the nut 54 is moved along axis 80 in direction 108. When the parking brake is released, the spindle 52 is rotated in an opposing release direction so that the nut 54 is moved in an opposite direction of direction 108.

[0053] The leading brake piston assembly 14 includes a thrust bearing 56 located adjacent the nut 54, and a clip 58 that is attached to the inner wall 106 of the piston pocket 48 (See FIG. 4). The clip 58 functions to trap and maintain both of the nut 54 and the thrust bearing 56 inside the piston pocket 48 so that during a standard brake apply or application of the service brake, the nut 54 and the thrust bearing 56 are pushed or moved with the brake piston 44 in direction 108. An O-ring 60 surrounds the nut 54 and is in contact with the inner wall 106 of the piston pocket 48 so that the nut 54 is restricted from rotating about axis 80 during a parking brake apply. Another thrust bearing 62 is sandwiched between a flange 94 of the spindle 52 and the brake caliper 12.

[0054] A piston boot 64 is attached to the brake caliper 12 and surrounds the outside surface of the leading brake piston 44. The piston boot 64 prevents dust and debris from entering between the outside surface of the brake piston 44 and the bore 46. A piston seal 66 is received in a groove defined in the brake caliper 12 and surrounds the outside surface of the leading brake piston 44 so that the brake piston 44 is restricted from rotating about axis 80; dust and other debris are restricted from entering the caliper bore 46; and/or hydraulic fluid is prevented from leaking.

[0055] The trailing brake piston assembly 16 includes generally the same components as the leading brake piston assembly 14. The leading brake piston assembly 16 includes a leading brake piston 44 that is supported in a caliper bore 46 defined in the brake caliper 12. The leading brake piston 44 includes a cup-shaped piston pocket 48. Received in the piston pocket 48 is a hydraulically-adjustable rotary to linear stage mechanism 50 that is part of the parking brake system 30. The hydraulically-adjustable rotary to linear stage mechanism 50 is a high efficiency mechanism that includes a spindle 52 and a nut 54. The spindle 52 is in rotational communication with the trailing gear 38 so that when torque is applied to the input portion 42 of the leading gear 36 by the MGU 32 (FIG. 1) and the trailing gear 38 is rotated by way of the belt 40, the spindle 52 is rotated. When the spindle 52 is rotated, the nut 54 moves axially along a longitudinal axis 80 of the spindle 52 either towards or away from a bottom pocket wall 82 of the piston pocket 48. The direction that the nut 54 is moved depends on the direction that the leading gear 36 is rotated by the MGU 32. That is, during a parking brake apply, the spindle 52 is rotated in an apply direction so that the nut 54 is moved along axis 80 in direction 108. When the parking, brake is released, the spindle 52 is rotated in an opposing release direction so that the nut 54 is moved in an opposite direction of direction 108.

[0056] Like the leading brake piston assembly 14, the trailing brake piston assembly 16 includes a thrust bearing 56 located adjacent the nut 54, and a clip 58 that is attached to the inner wall of the piston pocket 48. The clip 58 functions to trap and maintain the nut 54 and the thrust bearing 56 inside the piston pocket 48 so that during a standard brake apply or application of the service brake, the nut 54 and the thrust bearing 56 are pushed or moved with the brake piston 44 in direction 108. An O-ring 60 surrounds the nut 54 and is in contact with the inner wall of the piston pocket 48 to restrict the nut 54 from rotating about axis 80 during a parking brake apply. Another thrust bearing 62 is sandwiched between a flange 94 of the spindle 52 and the brake caliper 12.

[0057] A piston boot 64 is attached to the brake caliper 12 and surrounds the outside surface of the leading brake piston 44. The piston boot 64 prevents dust and debris from entering between the outside surface of the brake piston 44 and the bore 46. A piston seal 66 is received in a groove defined in the brake caliper 12 and surrounds the outside surface of the leading brake piston 44 so that the brake piston 44 is restricted from rotating about axis 80; dust and other debris are restricted from entering the caliper bore 46; and/or hydraulic fluid is prevented from leaking.

[0058] FIG. 4 illustrates an exploded, perspective view of the leading brake piston assembly 14. Because the trailing brake piston assembly 16 includes generally the same components as the leading brake piston assembly 14, it is understood that FIG. 4 also illustrates may if not all of the features of the trailing brake piston assembly 16. The leading brake piston assembly 14 includes the leading brake piston 44, which includes a piston pocket 48. One or more projections 86 project inwardly from the wall 106 of the piston pocket 48 towards the center axis 80 so that when the nut 54 is installed in the piston pocket 48, fluid bubbles can be evacuated during hydraulic fluid bleeding. It is also contemplated, however, that instead of the projections 86 extending from the wall 106 of the piston pocket 48, the wall 106 may be substantially smooth, and, the O-ring 60 surrounding the nut 54 may include one or more projections that contact the wall 106 when the nut 54 is installed in the brake piston 44. This alternative configuration may also allow for fluid bubbles to be evacuated during hydraulic fluid bleeding. It is understood, however, that in some configurations, projections 86 on the wall 106 and projections on the O-ring 60 may be used. Some configurations of O-ring seals and their engagement with the wall of the piston pocket are found in Applicant's currently pending U.S. patent application Ser. No. 15/275,791 filed on Sep. 26, 2016, which is hereby incorporated by reference herein for all purposes.

[0059] The piston pocket 48 and/or projections 86 include grooves 88 for receiving the clip 58 after the nut 54 and the thrust bearing 56 have been installed in the piston pocket 48. After the clip 58 has been installed in the grooves 88, the nut 54 and the thrust bearing 56 are trapped or maintained inside the piston pocket 48 in an assembled state (i.e., FIG. 3), the thrust bearing 56 is sandwiched between the clip 58 and a face 90 of the nut 54. The other thrust bearing 62 is sandwiched between the flange 94 of the spindle 52 and the brake caliper 12.

[0060] The nut 54 is received in the piston pocket 48. An O-ring 60 surrounding the nut 54 is in contact with and frictionally engages the projections 86 and/or wall 106 of the piston pocket 48 so that fluid bubbles can be evacuated during hydraulic fluid bleeding. The O-ring 60 also restricts or prevents rotation of the nut 54 during a parking brake apply, but allows for the nut 54 to rotate during application of the service brake or during a brake apply as will be discussed further below.

[0061] Operation of the service brake or the brake system 10 will now be described with reference to the figures, including FIGS. 5A and 5B. It is understood that these method steps can be performed in virtually any order, and one or more of the steps described herein may be combined, omitted, or repeated.

[0062] While FIGS. 5A and 5B show the inboard brake piston 44 and the components of the hydraulically-adjustable rotary to linear stage mechanism 50, these Figures may also represent the outboard brake piston 44 and the corresponding components of the hydraulically-adjustable rotary to linear stage mechanism 50.

[0063] It is also understood that while the following description refers to both of the inboard and outboard brake pistons 44, 44 and both of the corresponding hydraulically-adjustable rotary to linear stage mechanisms 50, 50, the operation of the service brake or brake system 10 may occur with only one of the brake pistons 44, 44 and only one of the corresponding hydraulically-adjustable rotary to linear stage mechanisms 50, 50.

[0064] First, during application of the service brake or during a standard brake apply to slow or stop a moving vehicle, when a driver depresses the brake pedal, hydraulic fluid is pressurized, which causes the brake pistons 44, 44 to move in the direction 108 towards the pressure plate 98 of the inboard brake pad 20 and take up any gap G defined between the brake piston 11, 44 and the pressure plate 98 (See Gap G at FIG. 5A).

[0065] Once in contact with the pressure plate 98, the pressurized hydraulic fluid causes the brake pistons 44, 44 to move the brake pad 20 in direction 108 towards the brake rotor so that the friction material 100 of the brake pad 20 contacts a face of the brake rotor to create the clamping force to slow or stop the vehicle.

[0066] As was discussed above at FIGS. 3 and 4, each of the brake pistons 44, 44 include a groove 88, 88 that retains the respective clip 58, 58, which functions to trap or retain the nut 54, 54 and the thrust bearing 56, 56 inside the respective piston pocket 48, 48. Therefore, during application the service brake or during a brake apply, as the respective brake piston 44, 44 is moved out of the piston boot 64, 64 in direction 108 to create the clamping force, the clips 58, 58 move with the corresponding brake piston 44, 44 and contact the corresponding thrust bearing 56, 56 which therefore pushes the corresponding nut 54, 54 in direction 108 so that the respective nut 54, 54 remains in close proximity to the corresponding bottom pocket wall 82, 82 and the spacing S between the bottom pocket wall 82, 82 of the piston pocket 48, 48 and the corresponding facing surface 110 the remains generally the same during movement of the brake piston 44, 44. The spacing S may be on the order of about 1 mm, for example. During this movement, torque is developed between the nut 54, 54 and the corresponding piston 44, 44, which causes the nut 54, 54 to rotate about the axis 108, 108, while the spindle 52, 52 is restricted from rotating by way of a brake in the MGU 32, for example. Accordingly, the nut 54, 54 unscrews and moves in direction 108 away from the flange 94, 94 of the spindle 52, 52, thus following the brake piston 44, 44.

[0067] After release of the service brake or release of the brake apply, or after the hydraulic fluid is at least partially depressurized, the brake piston 44, 44 may move partially back into the piston boot 64, 64 and caliper bore 46, 46 (i.e., in a direction opposite 108). However, the brake piston 44, 44 does fully retract in direction 108 or return to its pre-brake apply position in the piston boot 64, 64 and caliper bore 46, 46. Instead, the brake piston 44, 44 remains at least some distance closer to the brake pad 20 than before the brake apply. Of course, the nut 54, 54, which is trapped in the piston pocket 48, 48 by way of the clip 58, 58, also does not return to its pre-brake apply position on the spindle 52, 52, but instead remains in close proximity to the bottom pocket wall 82, 82. Accordingly, the hydraulically-adjustable rotary to linear stage mechanism 50, 50 automatically adjusts the position of the nut 54, 54 relative to the brake piston 44, 44 during every application of the service brake or during a standard brake apply so that when the parking brake system is applied (discussed below), a sufficient clamping force can be quickly created.

[0068] The distance that each nut 54, 54 is adjusted may be primarily based on the distance that the corresponding brake piston 44, 44 moves when the service brake is applied and after the brake apply, which may be primary based on how much of the friction material 100 located at the corresponding end of the brake pad 20 is worn. In other words, the amount that each nut 54, 54 moves during the adjustment may be the same if the wear of the friction material 100 is generally the same between the leading end and the trailing end of the brake pad 20 (i.e., little to no taper wear). Alternatively, when there is a lot of taper wear between the leading and trailing end of the brake pad 20, the amount that each nut 54, 54 moves during the adjustment may be the different or vary.

[0069] Operation of the parking brake system 30 will now be described. It is understood that these method steps can be performed in virtually any order, and one or more of the steps described herein may be combined, omitted or repeated.

[0070] A signal may be transmitted by the controller 112 to the MGU 32 to apply the parking brake. By way of the motor and gear train in the MGU 32, torque is supplied to the input portion 42 of the leading gear 36, which causes the leading gear 36 to rotate in an apply direction. The spindle 52 is fixed to the leading gear 36 so that rotation of the leading gear 36 in the apply direction causes the spindle 52 to also rotate in the apply direction. Rotation of the spindle 52 in the apply direction causes the nut 54 to move axially along axis 80 in the apply direction 108 until the facing surface 110 of the nut 54 contacts the bottom pocket wall 82 of the brake piston 44. Continued rotation of the gear 36 and thus movement of the nut 54 causes the nut 54 to move the brake piston 44 and the brake pad 20 against the brake rotor to generate the clamping force necessary to prevent movement of the vehicle.

[0071] By way of belt 40, rotation of gear 36 causes gear 38 to also rotate. The spindle 52 is fixed to the trailing gear 38 so that rotation of the trailing gear 38 in the apply direction causes the spindle 52 to also rotate in the apply direction. Rotation of the spindle 52 in the apply direction causes the nut 54 to move axially along axis 80 in the apply direction 108 until the nut 54 contacts the bottom pocket wall 82 of the brake piston 44. Continued rotation of the gear 38 and thus movement of the nut 54 causes the nut 54 to move the brake piston 44 and the brake pad 20 against the brake rotor to generate the clamping force necessary to prevent movement of the vehicle.

[0072] While the following description relates to the leading brake piston assembly 14, because the trailing brake piston assembly 16 includes similar components as the leading brake piston assembly 14, the following description may likewise be applicable to the trailing brake piston assembly 16.

[0073] Without adjusting the nut 54 during application of the service brake (i.e., without the clip 58 trapping or retaining the nut 54 and the thrust bearing 56 in the brake piston 44), when the brake piston 44 is moved during the brake apply, the nut 54 would not move with or follow the brake piston 44. Instead, the spacing S between the bottom pocket wall 82, of the piston pocket 48, and the corresponding facing surface 110 of the nut 54 would increase as the brake piston 44 is moved from its position in FIG. 5A relative to the brake pad 20 to its position in FIG. 5B relative to the brake pad 20. Accordingly, in such a configuration, when the parking brake system 30 is activated, more time would be required to move the nut 54 in direction 108 to cover the increased spacing before the facing surface 110 of the nut 54 contacts the bottom pocket wall 82 and begins to move the brake piston 44 in direction 108 to create the clamping force. This spacing S may increase over time as the brake pad continues to wear and the brake piston 44 moves and adjusts its position relative to the brake pad without the nut 54 moving with the brake piston 44.

[0074] Because the gap between the other nut 54 and its corresponding bottom pocket wall 82 is smaller (because that end of die brake pad 20 wears less so that the brake piston 44 does not move or adjust out of the caliper bore 46 as far) the nut 54 at the other brake piston assembly 16 may contact the corresponding bottom pocket wall 82 first and begin generating clamping force while the nut 54 is still being moved to cover the gap between the nut 54 and its bottom pocket wall 82. This may lead to an undesirable condition where uneven clamping force is developed between the two ends of the brake pad 20 or more time being required to develop the clamping force.

[0075] To release the parking brake, the MGU 32 rotates the gears 36, 38 in an opposing direction or release direction, which causes the corresponding spindles 52, 52 to rotate in an opposing or release direction, which causes the corresponding nuts 54, 54 to move axially in a release direction (in a direction opposite 108) and out of contact with the corresponding bottom pocket walls 82, 82. The brake pistons 41, 44 are then free to relax and move away from the inboard brake pad 20 so that the inboard brake pad 20 can move away from the brake rotor to release the clamping force.