Patent Application
20070181387
This invention relates to a brake assembly, a brake actuator, and a method of making a brake actuator.
Various types of brakes are provided for motor vehicles. For example, airbrakes are typically provided for heavy vehicles. An actuator for an airbrake typically includes a housing defining an air chamber, a piston moveably disposed in the housing, and a pushrod connected to the piston. The pushrod extends to the outside of the housing, and the end of the pushrod outside of the housing is connected to a yoke. An example is described in U.S. Pat. No. 6,253,890.
The yoke is connected to a cam via a linkage. When the air chamber is supplied with compressed air, the piston/pushrod/yoke assembly extends from the chamber and rotates the cam to push brake shoes into contact with a brake drum. When the compressed air is vented from the chamber, the piston/pushrod/yoke assembly retracts into the air chamber and the cam is rotated in a reverse direction so that the brake shoes move clear of the brake drum. Ideally, an optimal clearance is provided between the brake shoes and the brake drum when the brakes are released. This clearance should be uniform for all brakes so that uniform braking forces are applied to the wheels on both sides of the vehicle. The clearance should also be small so that the piston/pushrod/yoke assembly extending from the air chamber need move only a small distance to engage the brakes. However, sufficient clearance must be provided to prevent the brake shoes from dragging on the drum, even when they are hot and experiencing thermal expansion.
An automatic slack adjuster is used to adjust the clearance between the brake shoes and the brake drum when the brake is released. A typical automatic slack adjuster includes a worm gear which is keyed or connected via splines to the cam shaft which moves the brake shoes. A worm shaft mounted to rotate about an axis perpendicular to the cam axis engages the worm gear for establishing the angular position between a housing for the slack adjuster and the cam shaft. A device is provided for rotating the worm gear to automatically change the angular position between the slack adjuster housing and the cam shaft for eliminating slack as the brake shoes become worn. The device includes a toothed conical clutch that can be used to disconnect the adjusting mechanism during the elasticity part of the brake application so as to obtain a slack adjusting function. During the adjustment, which typically occurs at brake release, the clutch is engaged and transmits an angular movement and a torque to effect slack adjustment. A typical automatic slack adjuster is described in U.S. Pat. No. 5,350,043, the disclosure of which is hereby incorporated by reference.
For the automatic slack adjuster to operate properly, the pushrod must be within a certain range of length. In various vehicle configurations, the pushrods of different lengths are used to ensure proper operation of the automatic slack adjuster. The yoke then is permanently attached to an end of the pushrod. Typically, the yoke is permanently attached to the pushrod using welding.
However, welding of the yoke to the pushrod has several disadvantages. For example, welding equipment is relatively expensive. And the heat generating by welding may weaken the yoke or the pushrod.
In accordance with one aspect of the invention, a brake assembly includes a brake, an actuator, and an automatic slack adjuster for adjusting the clearance between the brake shoes and the brake drum. The actuator includes a housing, a piston moveably disposed in the housing, a yoke disposed outside of the housing, and a pushrod extending through the housing. The pushrod is connected to the piston, and an end portion of the pushrod forms a rivet that attaches the yoke to the pushrod.
In accordance with another aspect of the invention, a brake actuator includes a housing, a piston moveably disposed in the housing, a yoke disposed outside of the housing, and a pushrod extending through the housing. The pushrod is connected to the piston, and an end portion of the pushrod forms a rivet that attaches the yoke to the pushrod.
Preferably, the yoke includes a through hole, and the pushrod extends through the through hole of the yoke. The end of the pushrod may be radially greater than the through hole to prevent the yoke from sliding off the end portion of the pushrod. The end portion of the pushrod can include an indentation.
In a preferred embodiment, the end portion of the pushrod is radially smaller than the rest of the pushrod. For example, the end portion of the pushrod may have a first diameter, and the rest of the pushrod has a second diameter that is greater than the first diameter. The through hole can be radially greater than the end portion of the pushrod but radially smaller than the rest of the pushrod. For example, the through hole can have a third diameter that is greater than the first diameter but smaller than the second diameter. As a result, the yoke can be mounted on the end portion of the pushrod but cannot be mounted on the rest of the pushrod. When the yoke is mounted on the end portion of the pushrod, it may rest against an end of the rest of the pushrod, which end forms the interface between the end portion of the pushrod and the rest of the pushrod.
In accordance with a further aspect of the invention, a method of making a brake actuator includes extending an end portion of a pushrod of the brake actuator through a through hole of a yoke of the brake actuator, and radially extending the end of the pushrod to a size that is radially greater than the through hole to prevent the yoke from sliding off the end portion of the pushrod. The method may further include providing an indentation on the end portion of the pushrod.
The present invention has various advantages. For example, when compared with welding equipment, riveting equipment is less expensive. Additionally, riveting does not weaken the yoke or the pushrod.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
a and 3b are before-and-after partial cross section views illustrating assembly of the rivet connection between the pushrod and the yoke of the brake actuator shown in
The brake actuator 10 includes a housing 12, a piston 14 moveably disposed in the housing 12, a yoke 16 disposed outside of the housing 12, and a pushrod 18 extending through the housing 12. The pushrod 18 is connected to the piston 14, and an end portion 20 of the pushrod 18 forms a rivet 22 that attaches the yoke 16 to the pushrod 18.
The housing 12 may have any suitable configuration, although it typically has a generally hollow cylindrical configuration. The piston 14, typically configured as a cylinder or a disk plate, may be placed in the housing 12 so that it can move in the axial direction in the housing 12. Preferably, a seal 24 is provided between the housing 12 and the piston 14. The seal may be a sealing ring or a sealing membrane. The pushrod 18 has a generally elongated configuration. The cross-section of pushrod 18 may have any suitable shape, such as a circle, a triangle, or a square. The yoke 16 has the general configuration of a fork but can be configured in any manner that allows it to connect the piston-pushrod assembly to the rest of the brake assembly.
As illustrated in
In a preferred embodiment, the end portion 20 of the pushrod 18 is radially smaller than the rest of the pushrod 18. For example, the end portion 20 of the pushrod 18 may have a first diameter, and the rest of the pushrod 18 has a second diameter that is greater than the first diameter. The through hole 26 can be radially greater than the end portion 20 of the pushrod 18 but radially smaller than the rest of the pushrod 18. For example, the through hole 26 can have a third diameter that is greater than the first diameter but smaller than the second diameter. As a result, the yoke 16 can be mounted on the end portion 20 of the pushrod 18 but cannot be mounted on the rest of the pushrod 18. When the yoke 16 is mounted on the end portion 20 of the pushrod 18, it may rest against an end 30 of the rest of the pushrod 18, which end 30 forms the interface between the end portion 20 of the pushrod 18 and the rest of the pushrod 18.
In accordance with a further aspect of the invention, a method of making a brake actuator includes first extending an end portion 20 of a pushrod 18 of the brake actuator through a through hole 26 of a yoke 16 of the brake actuator, as shown in
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
