Patent Application
20080000731
Further features and other objects and advantages will become apparent from the following detailed description in which:
On rail vehicles, brake discs are normally fixed relative to the axle of a wheeled vehicle. They may be pressed onto the axle or supported from the wheel. The axle is journaled in a truck supporting the wheels and axle from the vehicle chassis. Normally, the truck comprises side frames spaced apart and supported by a bolster which, in turn, is rotatably attached to the vehicle chassis. The present invention relates to a disc brake caliper assembly for moving brake pads against each side of the brake disc.
Referring now to the drawings, a hinge plate 10 has openings for bolts enabling the hinge plate to be mounted onto a supporting structure, such as the side frames of the truck. The hinge plate 10 has a journaled hinge pin 12 with an axis lying in a plane embraced by the brake disc. In this way, the caliper assembly is generally aligned with edges of the brake disc. A frame 14 is pivotably supported from the hinge plate 10 by the journaled hinge pin 12. Normally, rotation of the frame 14 about the hinge pin is very slight. This movement allows for adjustments needed because of flexing of the axle as it rolls down the track. The frame 14 supports two spaced apart parallel journaled tong pins 16, 18 having axes lying in a plane perpendicular to hinge pin 12. Two tongs 20, 22 are pivotably supported from the frame 14 by respective tong pins. The tongs are generally symmetrical and having brake head pins 24, 26 journaled at one end and power nut support pins 28, 30 journaled in forked extension at the other end.
Brake heads 32, 33 and pads 34, 35 are pivotally supported from the brake pins 24, 26. Brake pads 34, 35 have friction faces for abutting the brake disc.
Power nuts 36, 38 are pivotally supported between the forked extensions by the power nut support pins 28, 30. The power nuts have internal threads; one has right-hand threads and the other has left-hand threads. A power screw 40 extends generally perpendicular to the tongs and has external threaded ends turned into the power nuts. Thus, rotation of the power screw moves the forked ends of the tongs away or together depending on the direction of rotation.
A lever arm 42 is operatively attached to the power screw 40 via slack adjuster mechanism 50 for imparting rotation of the power screw. A pneumatic cylinder 44 and piston 46 are positioned between the frame 14 and lever arm 42 for causing rotation of the lever arm 42 and the power screw 40. The power screw 40 multiplies the force output of the pneumatic piston and cylinder to levels necessary for stopping a train while using air cylinders designed for automotive applications. In the embodiment described here, the pitch of the power screw and normal positioning of the pads are such that the power screw will not rotate more than about one-half turn to fully apply the brakes.
A slack adjuster mechanism 50 between the lever arm 42 and power screw 40 adjusts the angular orientation between the lever arm 42 and power screw 40 as the brake shoes wear. The slack adjuster permits relative angular movement between the lever arm 42 and the power screw 40 only when the lever arm is returning to its near normal starting position, thus taking up slack that has developed as a result of the wear of the brake pads. In this way, the braking response does not change significantly as the pads wear.
According to a preferred embodiment of this invention, the slack adjuster is provided in a chamber in the lever arm that has the worm of a worm gear journaled therein. The worm gear pinion is fixed to the power screw between the right- and left-hand threads. Worm gears have the property of having a large gear ratio resulting in a large force amplification going from the pinion to the worm. Also, while it is easy for the worm to turn the pinion, the opposite is not the case. These properties are especially useful in this application making it possible to use less powerful pneumatic cylinders and piston combinations. Moreover, during brake applications resulting from rotation of the lever arm to spread the ends of the tongs, the worm must not turn in a direction to reduce the spread of the tongs.
Slack adjusters based upon worm gears are known in the brake art but, so far as known to the inventors, not in caliper-type disc brakes with pivoted tongs straddling the brake disc. A mechanism for driving the worm to take up slack includes apparatus for allowing the worm to turn only in the direction to take up slack and a clutch for disengaging the driving mechanism upon retraction of the brake pads. In some cases, the drive mechanism includes a rack for driving a pinion fixed to rotate the worm to take up slack. The rack is displaced by a lever or other connection that is responsive to the position of the lever or connection relative to the brake pad. The slack adjuster allows the piston to return to the same position relative to the cylinder as the brake pads wear while maintaining the same piston stroke to engage the brake pads. See, for example, U.S. Pat. No. 3,507,369 entitled “Adjuster for Cam Brake.” Worm gear slack adjusters are available commercially of the Euclid/Haldex type and Crewson Brenner type from Euclid Industries, L.L.C. an ArvinMeritor, Inc. company.
Having thus defined our invention in the detail and particularity required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.
