Patent Description:
The present invention relates generally to the art of braking systems for heavy-duty vehicles. In particular, the present invention relates to braking systems for heavy-duty vehicles utilizing drum brakes. More particularly, the present invention is directed to a slack adjuster assembly for use in heavy-duty vehicle drum braking systems that increases grease flow through the slack adjuster, relieves grease back pressure in the slack adjuster and/or cam tube, and provides a <NUM>-degree seal about the inboard side of the slack adjuster, thereby reducing required maintenance and increasing the service-life of the slack adjuster.

The use of braking systems on heavy-duty vehicles is well-known. For the purposes of clarity and convenience, reference is made to a heavy-duty vehicle with the understanding that such reference includes trucks, tractor-trailers or semi-trailers, trailers, and the like. Common types of braking systems for heavy-duty vehicles typically include disc brake systems and drum brake systems.

Drum brake systems are generally incorporated into an axle/suspension system of the heavy-duty vehicle. Drum brake systems typically include a brake drum mounted on a wheel hub of a wheel end assembly rotatably mounted on an outboard end of an axle. The brake drum typically includes a pair of brake shoes housed within the brake drum. Each brake shoe has a sacrificial, high coefficient of friction brake lining that is mounted on a metal backing plate, or shoe table, and maintained in a radially-spaced relationship from the interior braking surface of the brake drum. An S-cam attached to the outboard end of a camshaft of a cam shaft assembly of the drum brake system engages a pair of rollers, each of which is connected to an end of a respective brake shoe.

Drum brake systems also include a prior art slack adjuster assembly. Prior art slack adjuster assemblies typically include a slack adjuster attached to the inboard splined end of the camshaft. The slack adjuster establishes a rotation reference point, such as a control arm operatively connected to the axle/suspension system, for an automatic adjustment mechanism, as is known. The automatic adjustment mechanism of the prior art slack adjuster assembly indexes the camshaft rotation from the rotation reference point in order to maintain a preset distance or clearance between the brake lining of the brake shoes and the interior braking surface of the brake drum, regulating the stroke and mechanical force necessary to slow or stop the heavy-duty vehicle.

During operation, when the drum brake system is actuated, compressed air is communicated from an air supply source, such as a compressor and/or air tank, through air conduits or lines to a brake chamber, as is known. The brake chamber converts the air pressure into mechanical force and moves a pushrod. The pushrod, in turn, moves the slack adjuster of the prior art slack adjuster assembly, which causes rotation of the camshaft and S-cam, forcing the brake linings against the interior braking surface of the brake drum, thereby creating friction and slowing or stopping the heavy-duty vehicle. The prior art slack adjuster assembly indexes the rotation of the camshaft when the drum brake system is actuated. When the drum brake system is no longer actuated, the camshaft, and thus the S-cam, rotate back, allowing the radially-spaced relationship between the brake lining and interior braking surface of the brake drums to be re-established. The slack adjuster rotates back to a new position based on the indexed rotation of the cam shaft, thereby maintaining the preset distance or clearance between the brake lining and the interior braking surface of the brake drum.

Prior art slack adjuster assemblies, while adequate for the intended purpose, have potential disadvantages, drawbacks, and limitations. For example, prior art slack adjuster assemblies are typically unsealed along the inboard side, exposing the splined interface between the slack adjuster and camshaft. As a result, moisture, corrosive agents, and/or debris can potentially infiltrate between the slack adjuster and camshaft, causing corrosion and rust-locking of the intermeshed spline teeth and/or other components, thereby increasing braking system maintenance and heavy-duty vehicle downtime. Prior art sealing structures, such as boots, faceplates, and the like, have not optimally addressed the problem on slack adjusters. In addition, when utilizing prior art slack adjuster assemblies with cam tube assemblies, injection of pressurized grease through the cam tube and intermeshed splines of the camshaft and slack adjuster may potentially damage prior art sealing structures and/or may potentially be restricted or inhibited, preventing full lubrication of the splines and potentially increasing the occurrence of corrosion and rust-locking.

Thus, there is a need in the art for an improved slack adjuster assembly that increases grease flow through the slack adjuster, relieves grease back pressure in the slack adjuster and/or cam tube to allow for improved lubrication of the splined connection between the camshaft and the slack adjuster, and provides a <NUM>-degree seal about the inboard side of the slack adjuster to prevent infiltration of water, contaminants, and/or other debris, thereby increasing the maintenance interval and service-life of the slack adjuster and reducing heavy-duty vehicle down time.

<CIT> suggests a slack adjuster for rotating an input shaft of a braking system includes a housing having an aperture defining a first axis. The slack adjuster also includes an output member positioned within the aperture. The output member is engageable with the input shaft for rotation therewith about a second axis parallel with and offset from the first axis. The slack adjuster also includes an incremental adjustment mechanism operable to impart cycloidal motion to the output member relative to the housing.

Objectives of the present invention include providing a slack adjuster assembly that increases grease flow through the slack adjuster.

A further objective of the present invention is to provide a slack adjuster assembly that reduces back pressure of grease in the slack adjuster and/or cam tube.

Yet another objective of the present invention is to provide a slack adjuster assembly with a <NUM>-degree seal on the inboard side of the slack adjuster.

These objectives and advantages are obtained by the slack adjuster assembly for heavy-duty vehicles, according to the present invention, the slack adjuster assembly comprising a slack adjuster and an inboard sealing assembly. The slack adjuster is disposed about and has an internal spline for receiving an external spline of an inboard end of a camshaft of a camshaft assembly of the heavy-duty vehicle. The internal spline has a radial clearance from the external spline, and the external spline has an axial length. A ratio of the length to the radial clearance is less than or equal to <NUM>. The inboard sealing assembly is disposed over the inboard end of the camshaft and engages an inboard side of the slack adjuster to form a <NUM>-degree seal about the inboard side.

The exemplary embodiment of the present invention, illustrative of the best mode in which applicants have contemplated applying the principles, is set forth in the following description, shown in the drawings, and particularly and distinctly pointed out and set forth in the appended claims.

Similar reference characters refer to similar parts throughout.

An exemplary embodiment slack adjuster assembly <NUM> (<FIG>), according to the present invention may be incorporated into any drum braking system (not shown). In particular, slack adjuster assembly <NUM> may be incorporated into a drum braking system utilizing a cam shaft assembly (partially shown) with or without a cam tube (not shown). More particularly, slack adjuster assembly <NUM> may be mounted on a camshaft <NUM> of a cam shaft assembly of a drum braking system.

Slack adjuster assembly <NUM> includes a slack adjuster <NUM> and an inboard sealing assembly <NUM>. Slack adjuster <NUM> includes a body <NUM> having a female or internal spline <NUM> for receiving camshaft <NUM>, as is known. More particularly, internal spline <NUM> mechanically engages a male or external spline <NUM> formed on an inboard end <NUM> of camshaft <NUM>. Internal spline <NUM> is formed with an involute profile known in the art and generally meeting the ANSI B <NUM> requirement. In particular, internal spline <NUM> may be a <NUM>-tooth, <NUM>/<NUM> pitch, <NUM>-degree pressure axle spline. Alternatively, internal and external splines <NUM>, <NUM>, respectively, may be any other suitable spline, such as an SAE straight-sided <NUM>-tooth spline, as is known. External spline <NUM> of camshaft <NUM> may include a major diameter or dimension MeD (<FIG>) of about <NUM> (<NUM> inches), as is known.

In accordance with an important aspect of the present invention, internal spline <NUM> includes a modified root or major diameter or dimension MiD. In particular, material is removed from internal spline <NUM> radially outward of the ANSI B <NUM> standard major dimension MiD to increase the major dimension. Major dimension MiD of internal spline <NUM> may be in the range of from about <NUM> (<NUM> inches) to about <NUM> (<NUM> in) more preferably from about <NUM> (<NUM>. 51in) to about <NUM> (<NUM>. It is also contemplated that, under certain conditions, major dimension MiD could be larger than <NUM>. More particularly, the increase in major dimension MiD of internal spline <NUM> provides a relatively greater radial clearance R of about <NUM> (<NUM> in) between the internal spline and external spline <NUM> of camshaft <NUM>, as compared to prior art internal and external splines that provide a radial clearance of only about <NUM> inches. Increasing major dimension MiD also provides a relatively decreased ratio of an axial length L of external spline <NUM> in inches to radial clearance R in inches. More particularly, increasing major diameter MiD allows internal and external splines <NUM>, <NUM>, respectively, to provide a relatively reduced ratio of axial length L of the external spline to radial clearance R of about <NUM> or less, more preferably of about <NUM> or less, as compared to prior art internal and external splines that provide a ratio of about <NUM>. This reduced ratio allows for relatively increased flow and distribution of grease across the splined connection between internal and external splines <NUM>, <NUM>, respectively, of the respective slack adjuster assembly <NUM> and camshaft <NUM> as compared to prior art splined connections. As a result, internal and external splines, <NUM>, <NUM>, respectively, are better lubricated as compared to prior art slack adjuster assemblies and, thus, better resist corrosion, thereby allowing for reduced maintenance and increased service-life of slack adjuster assembly <NUM>.

Inboard sealing assembly <NUM> is sealingly engaged with the inboard side of slack adjuster <NUM>. More specifically, inboard sealing assembly <NUM> may mechanically engage a coverplate (not shown) or body <NUM> of slack adjuster <NUM> on the inboard side of slack adjuster and form a seal to prevent ingress of water, chemicals, and/or debris into the slack adjuster. Inboard sealing assembly <NUM> includes one or more washers <NUM> (<FIG> and <FIG>), an E type snap ring or E-clip <NUM>, a seal <NUM>, and a cap or cover <NUM>. Washers <NUM> may be disposed about the inboard end <NUM> of camshaft <NUM> inboardly of external spline <NUM> and outboardly of a groove <NUM> formed in the camshaft. In accordance with another important aspect of the present invention, washers <NUM> are formed or constructed with a plurality of circumferentially-spaced notches <NUM> formed adjacent to and merging with a central opening <NUM>. More particularly, each one of notches <NUM> is formed with an arc length that is approximately <NUM> times greater than the arc length of opening <NUM> in contact with camshaft <NUM> adjacent the respective notch. More preferably the arc length of each of notches <NUM> is approximately <NUM> times the arc length of opening <NUM> in contact with camshaft <NUM> adjacent the respective notch. As a result, notches <NUM> provide increased flow and distribution of grease and facilitate grease passing through washers <NUM> without restriction even when the washers are utilized without aligning the notches of respective washers, thereby reducing grease back pressure.

E-clip <NUM> of inboard sealing assembly <NUM> is snapped onto, or disposed about, inboard end <NUM> of camshaft <NUM> inboardly of washers <NUM> (<FIG> and <FIG>). More particularly, E-clip <NUM> mechanically engages inboard end <NUM> of camshaft <NUM> such that the E-clip is disposed within groove <NUM>. E-clip <NUM> acts as a retaining ring to limit the amount of axial movement of washers <NUM>, slack adjuster <NUM>, and camshaft <NUM> in order to maintain the intermeshed relationship of internal and external splines <NUM>, <NUM>, respectively. E-clip <NUM> is formed such that it does not fully encircle camshaft <NUM>, providing gaps <NUM> about the camshaft. Moreover, gaps <NUM> overlap with notches <NUM> of washers <NUM>. As a result, notches <NUM> and gaps <NUM> cooperate to provide a relatively unrestricted path for grease, facilitating grease passing through washers <NUM> and increasing flow and distribution of grease across internal and external splines <NUM>, <NUM>, respectively, and reducing grease back pressure.

In accordance with another important aspect of the present invention, seal <NUM> of inboard sealing assembly <NUM> is disposed over inboard end <NUM> of camshaft <NUM> and forms an interface and/or is in contact with body <NUM> of slack adjuster <NUM> to form a <NUM>-degree seal on the inboard side of the slack adjuster. In particular, seal <NUM> is formed from a flexible elastomeric material, such as rubber, as a generally bell- or cup-shaped structure including a recess or concavity <NUM> (<FIG>) and a central inboardly-extending projection <NUM>. More particularly, a large-diameter flap or lip <NUM> may be formed about the edge of concavity <NUM> and may form an interface and/or be in contact with a coverplate (not shown) or body <NUM> of slack adjuster <NUM> to create a <NUM>-degree seal about the inboard side of the slack adjuster. As a result, pressurized grease may pool within concavity <NUM> as it flows through internal and external splines <NUM>, <NUM>, respectively, washers <NUM>; and E-clip <NUM> to form a grease reservoir about and adjacent to components of slack adjuster assembly <NUM> to prevent wear and corrosion, thereby increasing the maintenance interval and service-life of slack adjuster assembly <NUM>.

Furthermore, the large diameter of lip <NUM> combined with the flexible elastomer of seal <NUM> allows the lip to be displaced from concavity <NUM>. More specifically, in the event grease overfills concavity <NUM>, lip <NUM> may deflect radially outwardly and inboardly away from slack adjuster <NUM>, allowing excess grease to be purged from the concavity. The bell- or cup-shape of seal <NUM> combined with the flexible elastomer material of the seal also prevents the seal from pulling a vacuum in concavity <NUM> or pressurizing the concavity in the event axial movement of camshaft <NUM> occurs during braking. More specifically, in the event axial movement of camshaft <NUM> occurs during braking, seal <NUM> may flex, compensating for any volume changes within concavity <NUM>, thereby preventing suction of water, chemicals and/or other debris past lip <NUM> into the concavity. Similarly, flexion of seal <NUM> may also prevent unintentional purging of grease from concavity <NUM> potentially caused by axial movement of camshaft <NUM> increasing pressure within the concavity of the seal.

In accordance with yet another important aspect of the present invention, inboard sealing assembly <NUM> includes cover <NUM>. Cover <NUM> may be formed from any suitable material, such as steel, plastic, or composite, using any suitable process, such as deep drawing, and include a plate or inboard face <NUM> integrally formed with a generally tubular, axially-extending sidewall <NUM>. Cover <NUM> may be directly attached to the inboard side of slack adjuster <NUM>. More specifically, at least a portion of sidewall <NUM> of cover <NUM> may form a threaded connection with a coverplate (not shown) or body <NUM> on the inboard side of slack adjuster <NUM>. It is also contemplated that cover <NUM> may form any other suitable connection, such as press fit, interference fit, or snap fit, with a coverplate or body <NUM> on the inboard side of slack adjuster <NUM>. Inboard face <NUM> may include a central opening <NUM> and a plurality of slots or vents <NUM> radially-spaced from and circumferentially arranged about the central opening and formed through the inboard face. More preferably, vents <NUM> may be formed through inboard face <NUM> and sidewall <NUM> along a radially outer edge or limit of the inboard face of cover <NUM>. Alternatively, vents <NUM> may be formed through and circumferentially-spaced about inboard face <NUM> or sidewall <NUM> adjacent the radially outer edge of inboard face <NUM>. Vents <NUM> are of any suitable size that is sufficient to provide protection to seal <NUM> from damage potentially caused by power washers, and the like, while also allowing the interior and exterior of cover <NUM> to be at atmospheric pressure. Maintaining the interior and exterior of cover <NUM> at atmospheric pressure allows air and/or grease to be purged from concavity <NUM> of seal <NUM> without creating back pressure. It is contemplated that grease purging past lip <NUM> of seal <NUM> may collect between the outside of the seal and within cover <NUM>. Grease may also purge through vents <NUM>, thereby serving as a visual indicator that radial clearance R between internal and external splines <NUM>, <NUM>, respectively; concavity <NUM>; and at least a portion of cover <NUM> have been filled with grease. In addition, the arrangement of vents <NUM> about inboard face <NUM> and/or about sidewall <NUM><NUM> adjacent the radially outer edge of the inboard face allows water, chemicals, and/or debris to drain, preventing collection inside cover <NUM>.

In accordance with an important aspect of the present invention, seal <NUM> may be connected to or engage with cover <NUM>. More specifically, at least a portion of projection <NUM> may insert into or mechanically engage central opening <NUM> of inboard face <NUM> of cover <NUM>. It is also contemplated that any other suitable method may be used to interconnect or engage seal <NUM> with cover <NUM>. Engagement of seal <NUM> with cover <NUM> may facilitate control and adjustment of the contact pressure of lip <NUM> against the inboard side of slack adjuster <NUM>. In particular, utilizing a threaded connection between cover <NUM> and slack adjuster <NUM> facilitates control of axial positioning of the outboard side of inboard face <NUM> of the cover relative to the slack adjuster. More particularly, because seal <NUM> is connected to or mechanically engages with inboard face <NUM> of cover <NUM>, adjustment of the cover relative to slack adjuster <NUM> facilitates control of the positioning of lip <NUM> of the seal relative to the slack adjuster. As a result, the relative distance and contact pressure between lip <NUM> and the inboard side of slack adjuster <NUM> is independent of any axial movement of camshaft <NUM> that may potentially occur during braking, thereby ensuring a <NUM>-degree seal is maintained.

Thus, slack adjuster assembly <NUM>, according to the present invention, provides improved grease flow and distribution through internal and external splines <NUM>, <NUM>, respectively, of slack adjuster <NUM> and camshaft <NUM>, respectively, by increasing the radial clearance R between the splines and utilizing an inboard sealing assembly <NUM> having washers <NUM> with notches <NUM> and E-clip <NUM> with gaps <NUM>. In addition, inboard sealing assembly <NUM> provides a <NUM>-degree seal on the inboard side of slack adjuster <NUM> utilizing bell- or cup-shaped seal <NUM> and cover <NUM> with vents <NUM> to allow for purging of grease from between internal and external splines <NUM>, <NUM>, respectively, while preventing the pulling of a vacuum or formation of back pressure in and about the seal, thereby allowing for improved lubrication of the splines, thereby increasing the maintenance interval and service-life of the slack adjuster and reducing heavy-duty vehicle down time.

It is contemplated that slack adjuster assembly <NUM> of the present invention could be formed from any suitable material, including but not limited to composites, metal, and the like, without changing the overall concept or operation of the present invention. It is also contemplated that slack adjuster assembly <NUM> of the present invention could be utilized in braking systems on heavy-duty vehicles having more than one axle and/or one or more than one wheel per wheel end assembly, without changing the overall concept or operation of the present invention. It is further contemplated that slack adjuster assembly <NUM> of the present invention could be utilized with all types of heavy-duty vehicle drum braking systems without changing the overall concept or operation of the present invention.

It is contemplated that different arrangements and materials of inboard sealing assembly <NUM> other than those shown and described, could be utilized without changing the overall concept or operation of the present invention, so long as they achieve a <NUM>-degree seal on the inboard side of slack adjuster <NUM> that prevents grease back pressure and improves grease distribution through internal and external splines <NUM>, <NUM>, respectively. For example, opening <NUM> and notches <NUM> of washers <NUM> as well as gaps <NUM> and the inner diameter of E-clip <NUM> could have different configurations without changing the overall concept or operation of the present invention. Similarly, inboard sealing assembly <NUM>, including seal <NUM> and cover <NUM>, could have different configurations without changing the overall concept or operation of the present invention. It is also contemplated that any other style retaining ring that does not fully encircle camshaft <NUM>, such as a C-clip style retaining ring, may be used in place of E-clip <NUM>.

Claim 1:
A slack adjuster assembly (<NUM>) for heavy-duty vehicles, said slack adjuster assembly comprising:
a slack adjuster (<NUM>) disposed about and having an internal spline (<NUM>) for receiving an external spline (<NUM>) of an inboard end (<NUM>) of a camshaft (<NUM>) of a camshaft assembly of the heavy-duty vehicle, said internal spline having a radial clearance (R) from said external spline, the external spline having an axial length (L); and
characterized by:
said slack adjuster assembly comprising an inboard sealing assembly (<NUM>) disposed over said inboard end (<NUM>) of said camshaft (<NUM>) and engaging an inboard side of said slack adjuster (<NUM>) to form a <NUM>-degree seal about said inboard side;
wherein a ratio of said length (L) to said radial clearance (R) is less than or equal to <NUM>.