Patent Application
20070227837
The present invention relates to a brake assembly and more particularly relates to a variable ratio coupling mechanism that may be engaged by an apply mechanism at a plurality of orientations to engage a brake mechanism.
Typically, a brake assembly includes a parking brake assembly that can engage a brake mechanism when a parking lever, pedal, etc. is engaged. The brake mechanism extends a piston against brake pads to clamp the brake pads against a rotor. With the parking brake engaged, a vehicle may park on a hill, etc. Two typical parking brake assembly designs include what may be commonly referred to as a cam-strut mechanism and a ball-ramp mechanism.
Briefly, a ball ramp mechanism includes, for example, a ball that is disposed between two plates. A ramp is formed on the first plate and a pocket that holds the ball is formed on the second plate. As the ball travels up the ramp due to the relative motion between the two plates, the plates move away from each other. In this regard, a portion of the ball-ramp mechanism extends to engage the brake mechanism.
The cam-strut mechanism includes a strut that extends to engage the brake mechanism and a cam that engages an opposite end of the strut. Movement of the cam urges the strut toward the piston to engage the brake mechanism. Specifically, the cam may be configured to cup the end of the strut. When the cam is moved relative to the strut, the strut travels up a wall of the cam to urge the strut toward the piston and engage the brake mechanism.
In some instances, the ball-ramp mechanism may be more efficient than the cam-strut mechanism. For example, while exerting a clamping force, there tends to be less friction when rolling a ball up a ramp (in the ball-ramp mechanism) than sliding a strut within a pocket of the cam (in the cam-strut mechanism). The ball-ramp mechanism may also include a varying mechanical ratio. For example, an initial low mechanical ratio permits a fast take-up to quickly remove clearance between the brake pads and the rotor. A subsequent high ratio can provide more clamping force for less travel of the brake cable relative to the initial low mechanical ratio. In this regard, the parking brake lever initially travels quickly, when the clamp force is lower. The parking brake lever then travels relatively less quickly with the higher mechanical ratio, when the clamp force is higher.
Notwithstanding efficiency, the cam-strut mechanism may be oriented at almost any direction that allows for connection of the brake cable and travel of the strut and an engaging member. In contrast, the ball-ramp mechanism must be rotated (i.e., rotation that causes it to extend) on the same axis on which the mechanism extends, thus limiting orientation of the engaging member and routing paths of the brake cable.
The cam-strut mechanism is typically configured so that the cam and the strut are outside of the caliper body and thus not within the hydraulic fluid chamber. In contrast, the ball-ramp mechanism is configured so that the ball-ramp mechanism is inside the caliper body and inside the hydraulic chamber. Additional mechanisms inside the fluid chamber may increase the propensity for air entrapment within the fluid chamber and may make it more difficult to bleed air from the fluid chamber.
The present teachings generally include a parking brake assembly that includes a brake mechanism, a coupling mechanism and an apply mechanism. The brake mechanism includes a piston that clamps brake pads against a rotor. The coupling mechanism couples the apply mechanism to the brake mechanism. The coupling mechanism includes a first member having a first end and a second end. The first end is configured to engage the piston. The second end includes a pocket. The coupling mechanism includes a second member having a first end and a second end. The first end of the second member defines a roller surface. The roller surface has a ramp portion. The coupling mechanism includes a rolling member held by the pocket and disposed between the pocket and the roller surface. The rolling member travels along the roller surface when the first member moves a first distance increment along a first axis and the second member moves a second distance increment along a second axis. The first and second axes are not collinear and a ratio based on the first distance increment and the second distance increment varies based on a position of the rolling member along the roller surface.
Further areas of applicability of the present teachings will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating various embodiments of the present teachings, are intended for purposes of illustration only and are not intended to limit the scope of the teachings.
The present teachings will become more fully understood from the detailed description, the appended claims and the accompanying drawings, wherein:
The following description of the various embodiments is merely exemplary in nature and is in no way intended to limit the teachings, their application, or uses.
With reference to
In accordance with the present teachings, the coupling mechanism 2 may provide a variable mechanical ratio between the apply mechanism 3 and the brake mechanism 1. In addition, the coupling mechanism 2 may permit the apply mechanism 3 to be coupled to the brake mechanism 1 so that the coupling mechanism 2 may be engaged (to engage the brake mechanism 1) at a plurality of orientations by the apply mechanism 3. It will be appreciated that portions of the brake mechanism 1, the coupling mechanism 2, the apply mechanism 3 and/or combinations thereof may be integral to one another or separate components.
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Briefly, the adjuster mechanism 30 allows for wear of the brake pads 20 (
The adjuster mechanism 30 includes, among other things, a rod member 32 having a first end 34 and a second end 36. In addition, the adjuster mechanism 30 includes a sleeve nut 38 having a flange 40. The second end 36 of the rod member 32 is received by the sleeve nut 38. The coupling mechanism 2 of the parking apply mechanism 12 includes a first member 42 that engages the sleeve nut flange 40. The parking apply mechanism 12 also includes a second member 44 that engages the first member 42 via a rolling member 46.
A lever 48 may couple to the caliper body 14 and to the second member 44. The first member 42 travels generally along a piston axis 50 when urged by the second member 44 as the second member 44 travels along a second axis 52. The piston axis 50 may generally not be collinear with the second axis 52 along which the second member 44 travels.
In one example, the first member 42 or the post member 42 may include a first end 54 that may engage the flange 40 of the sleeve nut 38. The first end 54 of the post member 42 may include a suitable gasket 56. The post member 42 may also include a second end 58 that may include a pocket 60. The pocket 60 may hold the rolling member 46. The gasket 56 may seal the fluid chamber 24 around the post member 42 and may permit the first end 54 of the post member 42 to travel relative to the fluid chamber housing 57. It will be appreciated that the sleeve nut 38 and a relatively small portion of the first end 54 of the post member 42 may be within the fluid chamber 22, while the remaining portion of the post member 42 is outside of the fluid chamber 22. A portion of the post member 42 may be held by a portion of the fluid chamber housing 57 of the caliper body 14 and thus may restrict the travel of the post member 42 to generally travel along the piston axis 50.
The second member 44 or the wedge member 44 may include a first end 62 and a second end 64. The first end 62 may include a roller surface 66. The second end 64 may define an aperture 68. The rolling member 46 may be contained between the pocket 60 formed on the second end 58 of the post member 42 and the roller surface 66. In this regard, the rolling member 46 rolls along the roller surface 66 while held in the pocket 60. As illustrated in
With reference to
A pin 80 may be disposed in the channel 76 and may connect the lever 48 to the wedge member 44. Specifically, the pin 80 may be received by the apertures 68 formed in dual opposed flanges 64a that extend from the second end 64. In this configuration, movement of the lever 48 may cause movement of the wedge member 44, along the second axis 52 because the pin 80 may travel through the channel 76. When the wedge member 44 travels along the second axis 52, the wedge member 44 may urge the post member 42 along the piston axis 50 via the rolling member 46 and thus engage the brake mechanism 1.
The roller surface 66 formed on the wedge member 44 may have at least the two following regions. A first region may include a recess 82. A second region may include a ramp 84. The recess 82 may include a bottom 86 and walls 88. The rolling member 46 may initially reside in the recess 82 but then travel out of the recess 82 (i.e., up the walls 88) and then along the ramp 84, while held in the pocket 66. Based on a slope of the walls 88 relative to a slope of the ramp 84, the motion of the rolling member 46 in the first region may cause the post member 42 to move away from the wedge member 44 at a rate of travel. The rate of travel at which the post member 42 moves away from the wedge member 44, while the rolling member 46 is in the first region, may be greater than the rate of travel at which the post member 42 moves away from the wedge member 44, when the rolling member 46 is in the second region. More specifically, the rolling member 46 may quickly move up the walls 88 of the recess 82, which may, for example, quickly remove the clearance between the brake pads 20 and the rotor 22 (i.e., the initial increment of travel to move the brake pads 20 into contact with the rotor 22).
As the rolling member 46 quickly moves up the walls 88, the mechanical ratio of coupling mechanism changes. Because the rolling member 46 has to initially travel up the walls 88 (or jump up and out) of the recess 82 and then travel up the ramp 84, it may be shown that the ratio of distances traveled by the post member 42 relative to the wedge member 44 varies based on a position of the rolling member 46 relative to the roller surface 66 and the aforesaid regions. It may further be shown that as the rolling member 46 travels out of the recess 82 and up the ramp 84, the distance the post member 42 travels for a given amount of travel of the wedge member 44 changes in accordance with the predetermined mechanical ratio. For example, one increment of travel for the wedge member 44 with the rolling member in the first region will produce a first resulting increment of travel for the post member 42. The same increment of travel for the wedge member 44 but with the rolling member 46 in the second region will produce a second resulting increment of travel that may be less than the first resulting increment of travel.
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While specific examples have been described in the specification and illustrated in the drawings, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present teachings as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various examples may be expressly contemplated herein so that one skilled in the art would appreciate from the present teachings that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise above. Moreover, many modifications may be made to adapt a particular situation or material to the present teachings without departing from the essential scope thereof. Therefore, it may be intended that the present teachings not be limited to the particular examples illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the scope of the present disclosure will include any embodiments falling within the foregoing description and the appended claims.
