Balanced bridge bleeder brake with HLA

A valvetrain assembly configured to selectively perform a bleeder brake operation includes a rocker arm configured to rotate about a rocker shaft, a camshaft having a lobe configured to impart motion to the rocker arm through a pushrod, and a valve bridge assembly operably associated with the rocker arm and configured to be selectively engaged by the rocker arm to open at least one of a first and second engine valve. An engine brake capsule is operably associated with the valve bridge assembly and configured to operate in a drive mode where the engine brake capsule does not cause the valve bridge assembly to open the first or second engine valves, and a brake mode where the engine brake capsule engages the valve bridge assembly to partially open the first engine valve to perform the bleeder brake operation.

FIELD

The present disclosure generally relates to valvetrain assemblies for internal combustion engines and, more particularly, to a valvetrain assembly for bleeder braking.

BACKGROUND

Engine braking can be used to retard forces within an engine to ultimately slow a vehicle down. In a typical valve train assembly used with an engine brake, an exhaust valve is actuated by a rocker arm which engages the exhaust valve by means of a valve bridge. The rocker arm rocks in response to a cam on a rotating cam shaft and presses down on the valve bridge which itself presses down on the exhaust valve to open it.

One form of engine braking includes a bleeder brake. Bleeder brakes can be used as auxiliary brakes, in addition to wheel brakes, on relatively large vehicles, for example trucks, powered by heavy or medium duty diesel engines. A bleeder brake typically includes a piston that selectively extends to a full stroke. In the full stroke, the piston can maintain an exhaust valve open a fixed amount throughout an engine cycle. As a result, a mechanical gap can be generated in the valve train. In many instances, such a gap can be incompatible with a common hydraulic lash adjuster (HLA). A hydraulic lash adjuster may also be provided in the valve train assembly to remove any lash or gap that develops between the components in the valve train assembly. The mechanical gap can allow the HLA to unfavorably pump-up preventing the exhaust valves to close once the bleeder brake is deactivated.

SUMMARY

According to various aspects of the present disclosure, a valvetrain assembly configured to selectively perform a bleeder brake operation is provided. In one example the valvetrain assembly includes a rocker arm configured to rotate about a rocker shaft, a camshaft having a lobe configured to impart motion to the rocker arm through a pushrod, and a valve bridge assembly operably associated with the rocker arm and configured to be selectively engaged by the rocker arm to open at least one of a first and second engine valve. An engine brake capsule is operably associated with the valve bridge assembly and configured to operate in a drive mode where the engine brake capsule does not cause the valve bridge assembly to open the first or second engine valves, and a brake mode where the engine brake capsule engages the valve bridge assembly to partially open the first engine valve to perform the bleeder brake operation.

In addition to the foregoing, the described valvetrain assembly may include one or more of the following features: a hydraulic lash adjustment (HLA) lifter disposed between the camshaft and the pushrod; wherein the HLA lifter is a deactivating HLA lifter; wherein the HLA lifter is a roller lifter; wherein the valve bridge assembly includes a lever assembly disposed within a bridge main body; wherein the lever assembly includes a lever pivotably coupled to the bridge main body by a bridge pin, the lever configured to engage the first engine valve; wherein the lever assembly further includes a valve shoe pivotably coupled to the lever by a valve shoe pin; wherein the valve shoe pin is limited in upward movement by a pair of stop arms extending from the bridge main body; and wherein in the brake mode, the lever is selectively engaged by the engine brake capsule, thereby causing rotation about the bridge pin and upward movement of the bridge main body, the upward movement causing rotation of the rocker arm and a downward reaction force into a hydraulic lash adjuster (HLA) lifter to prevent pump-up thereof.

In addition to the foregoing, the described valvetrain assembly may include one or more of the following features: wherein valve bridge assembly is a pass-through bridge assembly having a pin assembly disposed within a bridge main body; wherein the pin assembly is disposed within a bore formed in the bridge main body and includes a contact pin and a valve shoe, the contact pin configured to be engaged by the engine brake capsule in the brake mode to impart movement to the valve shoe to thereby engage the first engine valve; and wherein the contact pin extends through an aperture formed in the bridge main body, and wherein a shoulder that at least partially defines the bore and the aperture is configured to limit upward movement of the valve shoe.

In addition to the foregoing, the described valvetrain assembly may include one or more of the following features: wherein the valve bridge assembly is a solid bridge assembly having a first end configured to engage and pivot on the first engine valve, and a second end configured to engage and pivot on the second engine valve; wherein the engine brake capsule comprises an outer body defining an upper chamber and a lower chamber; wherein the engine brake capsule further comprises a pin and a biasing mechanism disposed in the upper chamber, the biasing mechanism configured to bias the pin downward toward the lower chamber; wherein the engine brake capsule further comprises a plunger and check ball assembly disposed in the lower chamber, the plunger configured to slide along the lower chamber between a retracted position and an extended position; and wherein the check ball assembly comprises a check ball, a seat, and a biasing mechanism configured to bias the check ball toward the upper chamber to seal a passage.

In another aspect, a method of operating a valvetrain assembly having a rocker arm configured to rotate about a rocker shaft, a camshaft having a lobe configured to impart motion to the rocker arm through a pushrod, a valve bridge assembly operably associated with the rocker arm and configured to be selectively engaged by the rocker arm to open at least one of a first and second engine valve, and an engine brake capsule operably associated with the valve bridge assembly is provided. In one example, the method includes operating in a drive mode where the engine brake capsule does not cause the valve bridge assembly to open the first or second engine valves, and operating in a brake mode where the engine brake capsule engages the valve bridge assembly to partially open the first engine valve to perform a bleeder brake operation.

In addition to the foregoing, the described method may include one or more of the following features: wherein operating in the brake mode comprises supplying pressurized fluid to the engine brake capsule; and wherein operating in the drive mode comprises not supplying pressurized fluid to the engine brake capsule.

DETAILED DESCRIPTION

Described herein are systems and methods incorporating a bleeder brake with a hydraulic lash adjuster (HLA) by utilizing a balanced valve bridge with a pivot arm in a diesel engine valvetrain. A bleeder brake, which holds an exhaust valve open to generate brake power, can cause a valvetrain with an HLA to “pump-up” and prevent the exhaust valve from closing during normal drive mode operation. The systems described herein utilizes a fixed brake capsule with oil control to hold open one exhaust valve during engine braking operations, which is commonly referred to as a “bleeder brake.” The additional use of a balanced valve bridge featuring an offset pivot arm can generate a reaction load when acted upon by the fixed brake capsule. This reaction force is translated back into the normal valvetrain to facilitate preventing the HLA pump-up (e.g., expansion).

During bleeder engine braking, in addition to the main exhaust valve event, one or more exhaust valves are held open throughout the remaining engine cycles (i.e., the intake, compression, and expansion cycles) for a full-cycle bleeder brake or during a portion of the remaining cycles (e.g., the compression and expansion cycles) for a partial-cycle bleeder brake.

With initial reference toFIG. 1, an exemplary valve train assembly constructed in accordance to one example of the present disclosure is shown and generally identified at reference10. The valve train assembly10can generally include a cam shaft12with one or more lobes configured to indirectly drive a first end of a rocker arm14via a pushrod16.

In some examples, a hydraulic lash adjuster (HLA) lifter18is implemented between the cam lobe12and the pushrod16. In other examples, HLA lifter18is a deactivating HLA roller lifter configured to operate between an activated mode and a deactivated mode. In the activated mode, HLA roller lifter18transfers motion of the cam lobe12to the pushrod16to cause rotational movement of rocker arm14. In the deactivated mode, HLA roller lifter18absorbs the motion of cam lobe12such that lifter18does not impart motion to pushrod16and cause rotation of rocker arm14.

In operation, as the cam lobe12rotates, the rocker arm14pivots about a fixed rocker shaft20and the opposite second end of the rocker arm14actuates one or more engine valves22,24via a balanced valve bridge assembly26.

A brake capsule28is fixed to a cylinder head of the engine (not shown) and is configured to selectively extend to hold valve22open during a predetermined time (e.g., during all engine strokes creating brake power). When activated, brake capsule28moves from a retracted position to an extended position to contact the valve bridge assembly26. This causes the valve bridge assembly26to generate a reaction force ‘F1’ into the rocker arm14, which is then translated to HLA lifter18to prevent pump-up when braking is activated.

With reference now toFIG. 2, the valve bridge assembly26will be described in more detail. As illustrated, the valve bridge assembly26includes a lever assembly40disposed within a bridge main body42. The bridge main body42includes a first end44and a second end46. The first end44can be configured to engage valve24, and the lever assembly40can be pivotably coupled to the second end46.

In the example embodiment, the lever assembly40generally includes a pivot arm or lever48, a pivot axle or bridge pin50, an e-foot or valve shoe52, and an e-foot axle or valve shoe pin54. The lever48, which is shown transparent inFIG. 2, can be pivotably coupled to the bridge main body42by the bridge pin50, which extends through opposed apertures56formed in the bridge main body42.

In the illustrated example, the lever48generally includes an engagement surface58and opposed openings60. The engagement surface58is configured to be selectively engaged by brake capsule28, as described herein in more detail, and the opposed openings60are configured receive the valve shoe pin54, which is limited in upward movement by stop arms62of the bridge main body42.

In the example embodiment, the valve shoe52can include a main body64having an aperture66formed therein. The main body64is configured to receive a portion of the valve22, and the aperture66is configured to receive the valve shoe pin54therethrough.

Accordingly, lever48can be selectively engaged at the engagement surface58, which can cause rotation about bridge pin50and upward movement of an opposed end68of the lever that is opposite surface58. This upward movement of lever end68is transferred via bridge pin50to cause upward movement of bridge main body42, which in turn causes rotation of the rocker arm14and a downward reaction force into HLA lifter18to prevent pump-up.

Although described as a balanced valve bridge assembly26, it will be appreciated that other arrangements and valve bridge assemblies may be utilized with the systems described herein. For example,FIG. 5illustrates an alternative embodiment utilizing a pass-through bridge assembly126, andFIG. 6illustrates an alternative embodiment utilizing a solid bridge assembly226.

With reference now toFIGS. 3 and 4, the engine brake capsule28will be described in more detail. In the example embodiment, the brake capsule28generally includes an outer body70defining an upper chamber72and a lower chamber74. A cap76seals an upper end of the upper chamber72, and a pin78and a biasing mechanism80(e.g., a spring) are disposed in the upper chamber72. The biasing mechanism80is configured to bias the pin78downward toward the lower chamber74.

In the illustrated example, a plunger82and check ball assembly84are disposed in the lower chamber74. The plunger82is configured to slide along lower chamber74between a retracted position (FIG. 3) and an extended position (FIG. 4). A clip or stop86is configured to limit downward movement of plunger82. Check ball assembly84can include a check ball88, a seat90, and a biasing mechanism92(e.g., a spring). The biasing mechanism92is configured to bias the check ball88toward the upper chamber72to seal a passage94.

In the example implementation, engine brake capsule28is operable in a drive mode (FIG. 3) and a brake mode (FIG. 4). In the drive mode, pressurized fluid is not supplied to engine brake capsule28, in particular to the lower chamber74such that plunger82is collapsed or retracted into the lower chamber74. In brake mode, pressurized fluid (e.g., oil) is supplied to engine brake capsule28via one or more ports96. The pressurized fluid enters and fills lower chamber74via passage94as pin78biases check ball88downward. This forces plunger82downward into the extended position to contact engagement surface58to facilitate performing a bleeder brake operation.

With reference now toFIG. 5, valve train assembly10is shown with balanced valve bridge assembly26replaced by the pass-through bridge assembly126. In the example embodiment, pass-through bridge assembly126generally includes a pin assembly140disposed within a bridge main body142. The bridge main body142includes a first end144and a second end146. The first end144can be configured to engage valve24, and the pin assembly140is slidingly disposed within the second end146.

In the example embodiment, the pin assembly140is disposed within a cutout or bore148formed in the bridge second end146and generally includes a contact pin150and a valve shoe152. The contact pin150extends through an aperture154formed in the bridge second end146, and the valve shoe152is limited in upward movement by stops or shoulders156that partially define the bore148and aperture154. The contact pin150includes an engagement surface158, and the valve shoe152is configured to receive a portion of the valve22.

Accordingly, in the drive mode, pressurized fluid is not supplied to engine brake capsule28, and plunger82is retracted into the lower chamber74and does not engage contact pin150. In the brake mode, pressurized fluid is supplied to engine brake capsule28to force plunger82downward into the extended position to contact the engagement surface158, thereby opening valve22to facilitate performing a bleeder brake operation.

With reference now toFIG. 6, valve train assembly10is shown with balanced valve bridge assembly26replaced by the solid bridge assembly226. In the example embodiment, solid bridge assembly226generally includes a bridge main body242having a first end244and a second end246. The first end244can be configured to engage and pivot on valve24, the second end246can be configured to engage and pivot on valve22.

Accordingly, in the drive mode, pressurized fluid is not supplied to engine brake capsule28, and plunger82is retracted into the lower chamber74and does not engage bridge second end246. In the brake mode, pressurized fluid is supplied to engine brake capsule28to force plunger82downward into the extended position to contact an engagement surface258of the second end246, thereby opening valve22to facilitate performing a bleeder brake operation.

Described herein are systems and methods for incorporating a bleeder brake with a hydraulic lash adjuster (HLA) by utilizing a valve bridge assembly. A brake capsule is movable between a retracted position and an extended position, which is configured to engage a portion of the valve bridge assembly and open an exhaust valve a predetermined distance to perform a bleeder brake operation.

The foregoing description of the examples has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular example are generally not limited to that particular example, but, where applicable, are interchangeable and can be used in a selected example, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.