Expansible chamber devices – Relatively movable working members – First working member moves second coaxial working member...
Reexamination Certificate
1998-11-09
2001-05-01
Lopez, F. Daniel (Department: 3745)
Expansible chamber devices
Relatively movable working members
First working member moves second coaxial working member...
C092S128000, C029S516000, C403S282000
Reexamination Certificate
active
06223647
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an improved brake actuator, preferably a small envelope tamper-resistant spring brake actuator which prevents rotation of the cover or head relative to the housing with improved sealing and a method of forming the improved spring brake actuator.
BACKGROUND OF THE INVENTION
Spring brake actuators of the type disclosed herein are used in combination with pneumatic brake systems on heavy vehicles including for example trucks, buses and trailers. The considerable inertial mass of these heavy-duty vehicles in combination with the high speeds at which they travel requires a braking system which responds rapidly with substantial braking power. A tandem spring brake actuator of the type disclosed in this application generally includes an H-shaped central housing member or flangecase which defines an emergency chamber on one side and a service or non-pressure chamber on the opposite side, and a power spring located in the emergency chamber which is biased against a piston which drives a push rod operably connected to the vehicle brake. When the pneumatic pressure in the spring chamber falls below a predetermined pressure or where the vehicle pneumatic pressure fails, the power spring drives the push rod to actuate the brakes, thus serving as an emergency brake for the vehicle. When the vehicle is turned off, the spring chamber also acts as a parking brake. The service chamber generally includes a push rod operable connected to the braking system of the vehicle and the push rod in the emergency chamber and the vehicle pneumatic brake system biases a flexible diaphragm in the service chamber to actuate the brakes of the vehicle. Where the spring brake actuator includes both an emergency chamber and a service chamber in tandem, the spring brake actuator is generally referred to as a “piggyback” spring brake actuator. There are generally two types of piggyback spring brake actuators. In the piston-type, the piston in the emergency chamber includes an annular seal at its outer periphery which seals against the inside surface of the cylinder case of the emergency chamber. In a diaphragm-type, commonly referred to as a dual diaphragm spring brake actuator, the emergency chamber includes a flexible diaphragm normally secured between opposed flanges of the central housing member or flangecase and the cover or head.
In certain applications, the emergency chamber is separated physically from the service chamber and the improved brake actuator of this invention may be utilized for piggyback spring brake actuators or brake actuators where the emergency chamber is separated from the service chamber. In a typical dual diaphragm spring brake actuator, the central housing member or flangecase is formed of aluminum, such as SAE 360 aluminum, and the head or cover is formed from steel, typically SAE 1008 or 1010 low carbon steel; however, the central housing member may also be formed of steel.
Because the power spring utilized in spring brake actuators is very powerful, the head of the emergency chamber must be securely attached to the housing member. In the past, the head of a dual diaphragm spring brake actuator was retained to the housing or flangecase by a bolted clamp band. In the piston-type spring brake actuator, the head is secured to the flangecase by a split metal retaining ring. More recently, various tamper-resistant brake actuators have been introduced, by the assignee of the present invention, wherein the head of the emergency chamber is permanently attached to the housing member by inelastically deforming a skirt or lip generally on the head around a radial flange of the housing member as disclosed, for example, in U.S. Pat. No. 4,960,036 assigned to the assignee of this application.
Spring brake actuators are mounted on the underside of a vehicle. Where the space available for mounting the spring brake actuator is at a premium, it is desirable to reduce the overall envelope of the spring brake actuator by eliminating the radial flanges on the housing member and the cup-shaped head. This was accomplished by forming a radial groove in the housing member and deforming the open end of the cover, which is telescopically received over the end of the housing member, into a radial groove in the housing member as disclosed in U.S. Pat. No. 5,676,036, also assigned to the assignee of the present application. The cover is then sealed to the central housing member by an annular resilient seal which is resiliently biased against the inner surface of the cover. If the cover rotates relative to the housing member, the annular seal may tear, resulting in leakage around the seal. It is also important where the brake actuator includes a breather tube to maintain the factory set alignment of the breather tube hole in the head or cover to the ports in the case. Thus, there are specific torque (antirotation) requirements in the specifications for brake actuators. Further, even where the housing is not rotated, leakage may occur around the seal because the annular seal may not be pressed tightly against the interior surface of the cup-shaped cover, particularly under extreme temperature conditions. Thus, a primary object of this invention is to prevent rotation of the cup-shaped cover relative to the housing member and improve sealing of the spring brake actuator.
SUMMARY OF THE INVENTION
As described above, the present invention relates to brake actuators of the type including a metal housing member and a cup-shaped metal cover having a tubular open end portion which is telescopically received over the housing member and retained to the housing member in sealed relation. The housing member, which is generally formed of aluminum, but may also be formed of steel, includes an open end having an external radially projecting annular rib which has a diameter greater than the internal diameter of the tubular end portion of the cover, providing an interference fit between the tubular end portion of the cover and the radial rib on the housing member. The rib includes a plurality of spaced channel-shaped transverse depressions which extend toward the open end of the housing member, each preferably having an open end. The diameter of the rib measured between the bottom wall of the opposed channel-shaped depressions is however less than the inside diameter of the cover, such that when the tubular end portion of the cover is pressed telescopically over the larger radially projecting rib of the housing member, the tubular end portion of the cover is simultaneously deformed radially inwardly into the channel-shaped depressions and stretched or expanded over the rib, thereby preventing rotation of the cover relative to the housing member and an improved seal between the cover and the housing member because the cover cannot rotate relative to the housing. In the preferred embodiment of the brake actuator of this invention, the depressions in the annular radially projecting rib include an open end facing the open end of the housing member and the side walls are tapered toward the open end, such that the depressions channel the tubular end portion of the cover into the depressions. In the most preferred embodiment, the bottom wall of the depressions are arcuate, such that the depressions smoothly channel the tubular end portion of the cover into the depressions and permit stretching or expansion of the tubular end portion of the cover over the larger radially projecting rib. This improved interference fit also solves the problem of differential expansion and retraction of the cover and the housing member under extreme temperature conditions, particularly where the cover and housing member are formed of different materials, such as aluminum and steel. As will be understood by those skilled in the art, the coefficient of expansion of steel is greater than aluminum. Where a steel cover is utilized with an aluminum housing member, the interference fit assures a tight sealed connection between the cover and the housing member under extreme variations in temperature.
As set forth abov
Angeli Duane L.
Choinski Graydon J.
Goates James D.
Jensen Greg W.
Plantan Ronald S.
Howard & Howard
Indian Head Industries Inc.
Lopez F. Daniel
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