Patent Description:
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.

<CIT> relates to a valvetrain assembly having a rocker arm a rocker arm rotating about a rocker shaft, a camshaft having a lobe for imparting motion to the rocker arm through a pushrod, a valve bridge assembly configured to be selectively engaged by the rocker arm so as to open engine valves, and an engine brake capsule associated with the valve bridge assembly for operating in a drive mode or a brake mode. Similar valvetrain assemblies are known from <CIT> and from <CIT>. <CIT> relates to valvetrain assembly which is not pushrod actuated.

The invention relates to a valvetrain assembly as defined in claim <NUM> configured to selectively perform a bleeder brake operation and to a method of operating a valvetrain assembly as defined in claim <NUM>, respectively.

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 to <FIG> , an exemplary valve train assembly constructed in accordance to one example of the present disclosure is shown and generally identified at reference <NUM>. The valve train assembly <NUM> can generally include a cam shaft <NUM> with one or more lobes configured to indirectly drive a first end of a rocker arm <NUM> via a pushrod <NUM>.

In some examples, a hydraulic lash adjuster (HLA) lifter <NUM> is implemented between the cam lobe <NUM> and the pushrod <NUM>. In other examples, HLA lifter <NUM> is a deactivating HLA roller lifter configured to operate between an activated mode and a deactivated mode. In the activated mode, HLA roller lifter <NUM> transfers motion of the cam lobe <NUM> to the pushrod <NUM> to cause rotational movement of rocker arm <NUM>. In the deactivated mode, HLA roller lifter <NUM> absorbs the motion of cam lobe <NUM> such that lifter <NUM> does not impart motion to pushrod <NUM> and cause rotation of rocker arm <NUM>.

In operation, as the cam lobe <NUM> rotates, the rocker arm <NUM> pivots about a fixed rocker shaft <NUM> and the opposite second end of the rocker arm <NUM> actuates one or more engine valves <NUM>, <NUM> via a balanced valve bridge assembly <NUM>.

A brake capsule <NUM> is fixed to a cylinder head of the engine (not shown) and is configured to selectively extend to hold valve <NUM> open during a predetermined time (e.g., during all engine strokes creating brake power). When activated, brake capsule <NUM> moves from a retracted position to an extended position to contact the valve bridge assembly <NUM>. This causes the valve bridge assembly <NUM> to generate a reaction force 'FT into the rocker arm <NUM>, which is then translated to HLA lifter <NUM> to prevent pump-up when braking is activated.

With reference now to <FIG>, the valve bridge assembly <NUM> will be described in more detaiL As illustrated, the valve bridge assembly <NUM> includes a lever assembly <NUM> disposed within a bridge main body <NUM>. The bridge main body <NUM> includes a first end <NUM> and a second end <NUM>. The first end <NUM> can be configured to engage valve <NUM>, and the lever assembly <NUM> can be pivotably coupled to the second end <NUM>.

In the example embodiment, the lever assembly <NUM> generally includes a pivot arm or lever <NUM>, a pivot axle or bridge pin <NUM>, an e-foot or valve shoe <NUM>, and an e-foot axle or valve shoe pin <NUM>. The lever <NUM>, which is shown transparent in <FIG>, can be pivotably coupled to the bridge main body <NUM> by the bridge pin <NUM>, which extends through opposed apertures <NUM> formed in the bridge main body <NUM>.

In the illustrated example, the lever <NUM> generally includes an engagement surface <NUM> and opposed openings <NUM>. The engagement surface <NUM> is configured to be selectively engaged by brake capsule <NUM>, as described herein in more detail, and the opposed openings <NUM> are configured receive the valve shoe pin <NUM>, which is limited in upward movement by stop arms <NUM> of the bridge main body <NUM>.

In the example embodiment, the valve shoe <NUM> can include a main body <NUM> having an aperture <NUM> formed therein. The main body <NUM> is configured to receive a portion of the valve <NUM>, and the aperture <NUM> is configured to receive the valve shoe pin <NUM> therethrough.

Accordingly, lever <NUM> can be selectively engaged at the engagement surface <NUM>, which can cause rotation about bridge pin <NUM> and upward movement of an opposed end <NUM> of the lever that is opposite surface <NUM>. This upward movement of lever end <NUM> is transferred via bridge pin <NUM> to cause upward movement of bridge main body <NUM>, which in turn causes rotation of the rocker arm <NUM> and a downward reaction force into HLA lifter <NUM> to prevent pump-up.

Although described as a balanced valve bridge assembly <NUM>, it will be appreciated that other arrangements and valve bridge assemblies may be utilized with the systems described herein. For example, <FIG> illustrates an alternative embodiment utilizing a pass-through bridge assembly <NUM>, and <FIG> illustrates an alternative embodiment utilizing a solid bridge assembly <NUM>.

With reference now to <FIG>, the engine brake capsule <NUM> will be described in more detail. In the example embodiment, the brake capsule <NUM> generally includes an outer body <NUM> defining an upper chamber <NUM> and a lower chamber <NUM>. A cap <NUM> seals an upper end of the upper chamber <NUM>, and a pin <NUM> and a biasing mechanism <NUM> (e.g., a spring) are disposed in the upper chamber <NUM>. The biasing mechanism <NUM> is configured to bias the pin <NUM> downward toward the lower chamber <NUM>.

In the illustrated example, a plunger <NUM> and check ball assembly <NUM> are disposed in the lower chamber <NUM>. The plunger <NUM> is configured to slide along lower chamber <NUM> between a retracted position (<FIG>) and an extended position (<FIG>). A clip or stop <NUM> is configured to limit downward movement of plunger <NUM>. Check ball assembly <NUM> can include a check ball <NUM>, a seat <NUM>, and a biasing mechanism <NUM> (e.g., a spring). The biasing mechanism <NUM> is configured to bias the check ball <NUM> toward the upper chamber <NUM> to seal a passage <NUM>.

In the example implementation, engine brake capsule <NUM> is operable in a drive mode (<FIG>) and a brake mode (<FIG>). In the drive mode, pressurized fluid is not supplied to engine brake capsule <NUM>, in particular to the lower chamber <NUM> such that plunger <NUM> is collapsed or retracted into the lower chamber <NUM>. In brake mode, pressurized fluid (e.g., oil) is supplied to engine brake capsule <NUM> via one or more ports <NUM>. The pressurized fluid enters and fills lower chamber <NUM> via passage <NUM> as pin <NUM> biases check ball <NUM> downward. This forces plunger <NUM> downward into the extended position to contact engagement surface <NUM> to facilitate performing a bleeder brake operation.

With reference now to <FIG>, valve train assembly <NUM> is shown with balanced valve bridge assembly <NUM> replaced by the pass-through bridge assembly <NUM>. In the example embodiment, pass-through bridge assembly <NUM> generally includes a pin assembly <NUM> disposed within a bridge main body <NUM>. The bridge main body <NUM> includes a first end <NUM> and a second end <NUM>. The first end <NUM> can be configured to engage valve <NUM>, and the pin assembly <NUM> is slidingly disposed within the second end <NUM>.

In the example embodiment, the pin assembly <NUM> is disposed within a cutout or bore <NUM> formed in the bridge second end <NUM> and generally includes a contact pin <NUM> and a valve shoe <NUM>. The contact pin <NUM> extends through an aperture <NUM> formed in the bridge second end <NUM>, and the valve shoe <NUM> is limited in upward movement by stops or shoulders <NUM> that partially define the bore <NUM> and aperture <NUM>. The contact pin <NUM> includes an engagement surface <NUM>, and the valve shoe <NUM> is configured to receive a portion of the valve <NUM>.

Accordingly, in the drive mode, pressurized fluid is not supplied to engine brake capsule <NUM>, and plunger <NUM> is retracted into the lower chamber <NUM> and does not engage contact pin <NUM>. In the brake mode, pressurized fluid is supplied to engine brake capsule <NUM> to force plunger <NUM> downward into the extended position to contact the engagement surface <NUM>, thereby opening valve <NUM> to facilitate performing a bleeder brake operation.

With reference now to <FIG>, valve train assembly <NUM> is shown with balanced valve bridge assembly <NUM> replaced by the solid bridge assembly <NUM>. In the example embodiment, solid bridge assembly <NUM> generally includes a bridge main body <NUM> having a first end <NUM> and a second end <NUM>. The first end <NUM> can be configured to engage and pivot on valve <NUM>, the second end <NUM> can be configured to engage and pivot on valve <NUM>.

Accordingly, in the drive mode, pressurized fluid is not supplied to engine brake capsule <NUM>, and plunger <NUM> is retracted into the lower chamber <NUM> and does not engage bridge second end <NUM>. In the brake mode, pressurized fluid is supplied to engine brake capsule <NUM> to force plunger <NUM> downward into the extended position to contact an engagement surface <NUM> of the second end <NUM>, thereby opening valve <NUM> to 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.

Claim 1:
A valvetrain assembly (<NUM>) configured to selectively perform a bleeder brake operation, the assembly comprising:
a rocker arm (<NUM>) configured to rotate about a rocker shaft (<NUM>);
a camshaft (<NUM>) having a lobe configured to impart motion to the rocker arm through a pushrod (<NUM>);
a valve bridge assembly (<NUM>, <NUM>, <NUM>) operably associated with a first engine valve (<NUM>) and a second engine valve (<NUM>), the valve bridge assembly configured to be selectively engaged by the rocker arm so as to open at least one engine valve of the first and second engine valves, wherein the valve bridge assembly includes a lever assembly (<NUM>) disposed within a bridge main body (<NUM>), and wherein the lever assembly includes a lever (<NUM>) pivotably coupled to the bridge main body by a bridge pin (<NUM>), the lever configured to engage the first engine valve; and
an engine brake capsule (<NUM>) fixed to a cylinder head and operably associated with the valve bridge assembly, the engine brake capsule 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 capsulle engages the valve bridge assembly so as to partially open the first engine valve to perform the bleeder brake operation, 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 (<NUM>) so as to prevent a pump-up of the HLA lifter thereof.