CN120167020A - System and method for valve lift event timing - Google Patents

Abstract

A method for timing a valve lift event includes actuating an exhaust rocker arm based on an exhaust lift curve and actuating an engine brake rocker arm based on an engine brake curve. Specifically, the exhaust lift curve and the engine brake lift curve have a first intersection point and a second intersection point. In addition, the exhaust lift curve is tangent to the engine brake lift curve at the first intersection point and the second intersection point.

Description

System and method for valve lift event timing

Cross Reference to Related Applications

The present disclosure is based on and claims the benefit of U.S. provisional patent application No. 63/383,892 entitled "System and method for valve lift event timing for Engine braking" (SYSTEMS AND Methods for Timing of VALVE LIFT EVENTS for Engine Brake), filed on 11/15 of 2022, which is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates generally to valve train systems, and more particularly to systems and methods for valve lift event timing.

Background

Internal combustion engines typically use a valve train system to actuate engine valves. For example, these systems may include a combination of cams, shafts, rocker arms, and various motion transfer mechanisms that may be rotationally driven by the crankshaft of the engine to selectively transfer actuation motion to the downstream valves.

Disclosure of Invention

In order to deliver different valve lift events (such as for the main exhaust or engine braking modes), the timing of valve actuation needs to be strategically controlled to achieve the desired function of the valve train system and ensure proper engine operation. Embodiments disclosed herein may provide a solution to the above-described problems by timing and aligning individual valve lift events with the start and end moments of exhaust valve events. Such timing and alignment designs may reduce the impact forces between the different active portions of the valve train system, prevent cylinder pressure from overloading the intake side portion, and allow for 1.5-stroke and 1-stroke engine braking modes.

In one embodiment, a method of timing a valve lift event by a rocker arm assembly of an internal combustion engine is provided. The rocker arm assembly includes an exhaust rocker arm and an engine brake rocker arm and is configured to selectively actuate either the first exhaust valve or the second exhaust valve. The method includes allowing actuation of the first exhaust valve and the second exhaust valve by an exhaust rocker arm, actuating the exhaust rocker arm based on an exhaust lift profile, allowing actuation of the second exhaust valve by an engine brake rocker arm independent of actuation of the first exhaust valve, and actuating the engine brake rocker arm based on the engine brake lift profile. Specifically, the exhaust lift curve and the engine braking lift curve have a first crossover point and a second crossover point. Further, the exhaust lift curve is tangential to the engine braking lift curve at a first crossover point and a second crossover point.

In particular embodiments, the engine brake lift curve includes a first engine brake lift sub-curve, a second engine brake lift sub-curve, a third engine brake lift sub-curve, and a fourth engine brake lift sub-curve. In particular embodiments, the exhaust lift curve follows the second engine brake lift sub-curve and overlaps the third engine brake lift sub-curve at a first intersection and overlaps the fourth engine brake lift sub-curve at a second intersection. In particular embodiments, the exhaust lift curve is tangent to the third engine braking lift sub-curve at a first intersection and tangent to the fourth engine braking lift sub-curve at a second intersection. In particular embodiments, when actuation of the first and second exhaust valves is allowed by the exhaust rocker arm and actuation of the second exhaust valve is allowed by the engine brake rocker arm, actuation of the first exhaust valve is based on the exhaust lift profile and actuation of the second exhaust valve is based on the first engine brake lift sub-profile, the second engine brake lift sub-profile, and the exhaust lift profile. In particular embodiments, a cylinder pressure spike is generated during a four-stroke cycle of an internal combustion engine when actuation of a first exhaust valve and a second exhaust valve is allowed through an exhaust rocker arm and actuation of the second exhaust valve is allowed through an engine brake rocker arm. In particular embodiments, the second engine brake lift sub-curve is configured to release cylinder pressure such that a cylinder pressure peak is generated during a compression stroke of a four-stroke cycle of the internal combustion engine.

In particular embodiments, at the first crossover point or the second crossover point, the engine braking lift profile is configured to transfer valve lift in the same direction as the exhaust lift profile. In particular embodiments, at the first crossover point or the second crossover point, the engine braking lift profile is configured to transfer valve lift at a similar rate as the exhaust lift profile.

In a specific embodiment, the method further includes disabling actuation of the first exhaust valve and the second exhaust valve by the exhaust rocker arm. In particular embodiments, when actuation of the first and second exhaust valves by the exhaust rocker arm is inhibited and actuation of the second exhaust valve by the engine brake rocker arm is allowed, the first exhaust valve is not actuated and actuation of the second exhaust valve is based on the engine brake lift profile. In particular embodiments, two cylinder pressure peaks are generated during a four-stroke cycle of an internal combustion engine when actuation of a first exhaust valve and a second exhaust valve by an exhaust rocker arm is inhibited and actuation of the second exhaust valve by an engine brake rocker arm is allowed. In a specific embodiment, the second engine brake lift sub-curve is configured to release the cylinder pressure such that a first cylinder pressure peak is generated during a compression stroke of a four-stroke cycle of the internal combustion engine, wherein the fourth engine brake lift sub-curve is configured to release the cylinder pressure such that a second cylinder pressure peak is generated prior to an intake stroke of the four-stroke cycle of the internal combustion engine.

In particular embodiments, the rocker arm assembly further includes an intake rocker arm configured to actuate at least two intake valves. In particular embodiments, the method further includes allowing actuation of at least two intake valves by the intake rocker arm based on an intake lift profile.

In one embodiment, a method of timing a valve lift event by a rocker arm assembly of an internal combustion engine is provided. The rocker arm assembly includes an exhaust rocker arm and an engine brake rocker arm and is configured to selectively actuate either the first exhaust valve or the second exhaust valve. The method includes allowing actuation of the first and second exhaust valves by the exhaust rocker arm, actuating the exhaust rocker arm based on an exhaust lift profile, allowing actuation of the second exhaust valve by the engine brake rocker arm independent of actuation of the first exhaust valve, actuating the engine brake rocker arm based on an engine brake lift profile, maintaining actuation of the exhaust rocker arm and the engine brake rocker arm for at least one engine cycle including an intake stroke, a compression stroke, an exhaust stroke, and an intake stroke, and disabling actuation of the first and second exhaust valves by the exhaust rocker arm. Specifically, the exhaust lift curve and the engine braking lift curve have a first crossover point and a second crossover point. Further, the exhaust lift curve is tangential to the engine braking lift curve at a first crossover point and a second crossover point.

In particular embodiments, the engine brake lift curve includes a first engine brake lift sub-curve, a second engine brake lift sub-curve, a third engine brake lift sub-curve, and a fourth engine brake lift sub-curve. In particular embodiments, the exhaust lift curve follows the second engine brake lift sub-curve and overlaps the third engine brake lift sub-curve at a first intersection and overlaps the fourth engine brake lift sub-curve at a second intersection. In particular embodiments, the exhaust lift curve is tangent to the third engine braking lift sub-curve at a first intersection and tangent to the fourth engine braking lift sub-curve at a second intersection. In particular embodiments, at the first crossover point or the second crossover point, the engine braking lift profile is configured to transfer valve lift in the same direction as the exhaust lift profile. In particular embodiments, at the first crossover point or the second crossover point, the engine braking lift profile is configured to transfer valve lift at a similar rate as the exhaust lift profile. In particular embodiments, two cylinder pressure peaks are generated during a four-stroke cycle of an internal combustion engine when actuation of a first exhaust valve and a second exhaust valve by an exhaust rocker arm is inhibited and actuation of the second exhaust valve by an engine brake rocker arm is allowed. In a specific embodiment, the second engine brake lift sub-curve is configured to release the cylinder pressure such that a first cylinder pressure peak is generated during a compression stroke of a four-stroke cycle of the internal combustion engine, wherein the fourth engine brake lift sub-curve is configured to release the cylinder pressure such that a second cylinder pressure peak is generated prior to an intake stroke of the four-stroke cycle of the internal combustion engine.

Drawings

Embodiments in accordance with the present disclosure will now be described with reference to the accompanying drawings, in which:

FIG. 1 illustrates an exemplary embodiment of a valve train assembly according to the present disclosure;

FIG. 2 illustrates an exemplary valve operation in a drive mode of an engine braking system;

FIG. 3 illustrates an exemplary valve operation in a 1-stroke engine braking mode of an engine braking system;

FIG. 4 illustrates an exemplary 1.5-stroke engine braking mode of an engine braking system according to an embodiment of the present disclosure;

FIG. 5 illustrates an exemplary operation of an engine braking system as it transitions from a drive mode to a 1.5 stroke engine braking mode according to one embodiment of the present disclosure;

FIG. 6 illustrates an exemplary operation of a normal 1.5 stroke engine braking mode of the engine braking system;

FIG. 7 illustrates an exemplary operation of an improved 1.5-stroke engine braking mode of an engine braking system according to one embodiment of the present disclosure;

FIG. 8 illustrates how a conventional engine braking system may fail due to overload;

FIG. 9 illustrates an exemplary operation of an engine braking system as it is operated from a drive mode to a safe transition mode and a 1.5 stroke engine braking mode according to one embodiment of the present disclosure;

FIG. 10 illustrates exemplary braking levels of an engine braking system according to a specific embodiment of the present disclosure;

FIG. 11 illustrates an exemplary scaling of brake levels of an engine brake system according to an embodiment of the present disclosure, and

FIG. 12 illustrates a flowchart of an exemplary method for timing valve lift events, according to an embodiment of the present disclosure.

Detailed Description

Reference will now be made in detail to examples shown in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Directional references such as "upward", "downward", "rightward" and "leftward" are for convenience with reference to the figures, and are not intended to limit the scope of the present disclosure.

Various valve system designs have been produced in the past for use in conjunction with internal combustion engines to control valve actuation, such as for a main exhaust event. Generally, in a typical valve train, a rocker arm system is coupled to a camshaft on one side and to a plurality of engine valves via a valve bridge on the other side to synchronously transfer actuation motion from the camshaft to the downstream valves. In some scenarios, it may be desirable to provide auxiliary functions, such as compression engine braking, in addition to the main lift event so that selected valves may be controlled individually. To enable engine braking operations and assist in decelerating the vehicle, the valve train assembly may be operated by releasing compression in the engine cylinders during its compression stroke, which may reduce the power of the engine and create a braking effect. In other words, this may result in the engine acting as a power consuming compressor, which may slow down the vehicle. To achieve such an objective, the valve train assembly may need to control the timing of valve lift events associated with the main exhaust event and the engine braking event so that they may occur in a desired sequence and timing to ensure proper engine operation.

In certain embodiments, a valve train system that enables an engine braking mode may be equipped with a primary exhaust rocker arm (which is capable of being deactivated) and a dedicated engine braking rocker arm (which may be activated, for example, by a cabin). When there is an overlap between the engine braking valve lift curve and the standard exhaust valve lift curve, and the two curves cross each other at a high relative lift rate, a disabling device (e.g., hydraulic or mechanical pod) in the valve train system may experience strong mechanical impact forces during the drive mode (ignition mode of the engine) and also during the transition between engine braking and drive modes. Further, the system may not be able to operate both the standard rocker arm and the engine brake rocker arm simultaneously to facilitate a downsizing from the 1.5-stroke engine brake mode to the 1-stroke engine brake mode. The overlap of engine braking lift and standard intake lift may also overload the intake valve during intake valve opening due to high cylinder pressure.

Embodiments disclosed herein propose a particular alignment or timing of engine braking valve lift events that may ensure low overlap with standard exhaust valve lift curves while transitioning smoothly between the curves (e.g., the relative crossover rate between the two curves is low). Thus, such valve (cam) lift profiles may reduce mechanical impact forces between movable portions in the valve train system, allowing a smooth transition between the drive mode and the engine braking mode and a narrowing from the 1.5-stroke engine braking mode to the 1-stroke engine braking mode, and avoiding intake side overload.

Fig. 1 illustrates an exemplary embodiment of a valve train assembly 100 according to the present disclosure. Referring initially to FIG. 1, a valve train assembly constructed in accordance with one example of the present disclosure is shown in part at 100 and generally identified. In particular embodiments, valve train assembly 100 may be configured with auxiliary functions (such as engine braking) and may be used with a three cylinder bank portion of a six cylinder engine. By way of example and not limitation, the valve train assembly 100 may be mechanically mounted to one cylinder head of a three cylinder bank. While described as such, it will be understood that the systems, methods, and procedures described in this disclosure are not limited to such applications. In this regard, the systems, methods, and processes described in this disclosure may be used with any valve train assembly associated with any suitable engine configuration equipped with any suitable number of cylinders.

In particular embodiments, the valve train assembly 100 may be supported by a valve train carrier, and each cylinder may include three rocker arm structures. Specifically, in particular embodiments, each cylinder may include an intake rocker arm 102, an exhaust rocker arm 104, and an engine brake rocker arm 106. By way of example and not limitation, as shown in FIG. 1, the exhaust rocker arm 104 and the engine brake rocker arm 106 may be separate bodies and may act independently of each other and cooperatively control the opening or closing of two exhaust valves (i.e., the exhaust standard valve 108 and the exhaust brake valve 110). In this case, two switchable systems (e.g., exhaust chamber 112 and engine brake chamber 114) may be employed to control exhaust and engine braking operations, respectively. For example, the switchable system may be selectively controlled by a configuration of deactivation and activation. The deactivated configuration may inhibit actuation of the associated valve by the corresponding rocker arm, and the activated configuration may allow actuation of the valve. As another example and not by way of limitation, although not shown, the exhaust rocker arm and the engine brake rocker arm may be combined into a single rocker arm body and controlled to permit or inhibit valve actuation motions exclusively through their respective switchable systems. In particular embodiments, the intake rocker arm 102 may be configured to control movement of at least two intake valves 116A, 116B. The exhaust rocker arm 104 may be configured to control exhaust valve movement of both exhaust valves 108, 110. The engine brake rocker arm 106 may be configured to act on one of the two exhaust valves (i.e., the exhaust brake valve 110) in an engine braking mode, such as 1.5-stroke engine braking, as will be described later. In particular embodiments, each of the intake rocker arm 102, the exhaust rocker arm 104, and the engine brake rocker arm 106 may be mechanical, electrical, hydro-mechanical, or other suitable valve actuation systems.

With continued reference to FIG. 1, in particular embodiments, the rocker arm shaft 118 may be received by a valve train carrier and support rotation of the intake rocker arm 102, the exhaust rocker arm 104, and the engine brake rocker arm 106. By way of example and not limitation, the rocker shaft 118 may communicate a control fluid (e.g., oil) to the rocker arms 104, 106 for controlling actuation of the exhaust chamber 112 and the engine brake chamber 114. In particular embodiments, a camshaft (not shown) may be provided that may include a plurality of lift curves or cam lobes configured to rotate the rocker arms 104 and 106 under a desired lift sequence in accordance with the present disclosure. By way of example and not limitation, the cam end of the exhaust rocker arm 104 may be configured to be engaged by the exhaust lift lobe of the camshaft, which may cause the exhaust rocker arm 104 to rotate according to an exhaust lift profile, thereby actuating both the exhaust standard valve 108 and the exhaust brake valve 110 as desired. Similarly, as another example and not by way of limitation, the cam end of the engine brake rocker arm 106 may be configured to be engaged by an engine brake lift lobe of a camshaft, which may cause the engine brake rocker arm 106 to rotate according to an engine brake lift profile, thereby actuating the exhaust brake valve 110 as desired. Alternatively, in other embodiments, the valve train assembly 100 may include other suitable motion-transmitting features, such as a pushrod operatively coupled between the rocker body and the camshaft for transmitting valve actuation motion.

In particular embodiments, the exhaust rocker arm 104 and the engine brake rocker arm 106 may house an exhaust compartment 112 and an engine brake compartment 114, respectively. For example, the exhaust chamber 112 and the engine brake chamber 114 may be coupled to or coupled to each of the exhaust rocker arm 104 and the engine brake rocker arm 106, and may be configured to transfer force or motion to the valve bridge 120. By way of example and not limitation, the exhaust compartment 112 and the engine brake compartment 114 may be switchable between activated and deactivated. For example, when activated, the pod may be rigid, allowing movement from the associated rocker arm to be transmitted down to the valve bridge 120. Conversely, when deactivated, the pod may be collapsible, such as by means of a lost motion mechanism internal to the pod, such that valve actuation motion is absorbed by the lost motion mechanism or by relative movement of the pod and rocker arm such that downstream valve bridge 120 is not actuated.

In particular embodiments, valve bridge 120 may be configured to span and be positioned on top of the two exhaust valves 108, 110 to transfer motion thereto. As shown, in particular embodiments, a top surface of the valve bridge 120 may be engaged with the exhaust rocker arm 104. For example, a lower end of the exhaust chamber 112 of the exhaust rocker arm 104 may abut the valve bridge 120. When activated, the exhaust chamber 112 may push the valve bridge 120 downward along its center to push the two exhaust valves 108, 110 downward with the same lift. As further shown, in particular embodiments, the valve bridge 120 may include a movable member 122 (such as a sliding pin) that may move relative to the valve bridge body and may be operably coupled between a lower end of the engine brake compartment 114 and the exhaust brake valve 110. When activated, the engine brake capsule 114 may be pressed onto the movable member 122 to individually actuate the exhaust brake valve 110 without affecting the exhaust standard valve 108.

It should be understood that the valve train system described herein is provided for illustrative purposes only and is not intended to limit the scope of the present disclosure. Although this disclosure describes a valve train system having a particular configuration in a particular manner, this disclosure contemplates any suitable valve train system having any suitable configuration in any suitable manner. For example, in certain embodiments, the valve train system may not include the components disclosed herein, include some or all of the components. For example, in certain embodiments, the valve train system may include additional components not described herein without departing from the scope of the present disclosure.

FIG. 2 illustrates an exemplary operation in a drive mode of an engine braking system that may utilize the valve train assembly 100 described in detail above or any other suitable valve train assembly. In particular embodiments, the valve lift sequence of an engine braking system may be described in connection with a four-stroke cycle of an engine, i.e., an intake stroke, a Compression (CMP) stroke, a power stroke, and an exhaust stroke. In particular embodiments, in a drive mode where positive engine power is required to drive the vehicle, for example, valve operation may begin first with an intake stroke (although not shown, a first intake stroke may occur prior to the compression stroke in the figures, which is the same as the intake stroke after the exhaust stroke as shown). During the intake stroke, the intake valve may be lifted upward by the intake rocker arm based on the intake lift profile 202, opening a flow passage with, for example, an intake manifold, to allow air and fuel to enter the associated cylinder. By way of example, and not limitation, the opening timing of the intake valve may be timed to coincide with the downward movement of the cylinder piston, creating a vacuum in the cylinder to draw in the air-fuel mixture. Once the intake stroke is complete, the intake valve may be closed. The cylinder is sealed and ready to enter a compression stroke in which the piston can move upward, compressing the air-fuel mixture inside the cylinder in preparation for ignition. In particular embodiments, peak cylinder pressure may occur after the compression stroke, as shown by the cylinder pressure curve. With the intake and exhaust valves closed, the compressed air-fuel mixture may be ignited during the power stroke, for example, by a spark plug. The resulting combustion may force the piston downward, producing mechanical energy to power the vehicle. Subsequently, an exhaust stroke may be performed wherein the two exhaust valves are opened after the exhaust rocker arms are activated and actuated based on the exhaust lift profile 204, allowing the piston to move upward again, for example, under a pressure differential between the exhaust port pressure and in-cylinder pressure of the engine, pushing combusted gases out of the cylinder and into the exhaust system of the engine (e.g., through the exhaust manifold) for gas evacuation and emission control. After the exhaust stroke, in particular embodiments, the system may then perform another intake stroke to achieve a multiple cycle valve lift sequence as described above to continue to power the vehicle as desired.

For compression engine braking, the timing of valve lift may be configured and operated differently than conventional drive mode operation so that the system may act as a power consuming compressor generating negative engine power. To achieve this, in particular embodiments, the intake valve may operate substantially similarly to in the drive mode. On the other hand, the exhaust valve (or exhaust brake valve of the two exhaust valves) may be involved in the engine braking process, the opening and closing of which is precisely controlled to deliver the desired braking power. By way of example and not limitation, the exhaust brake valve may be opened in advance during the compression and power strokes to release the compressed air in the cylinder. By releasing the compressed air, the pressure in the cylinder can be released or reduced, preventing the air spring (compressed air) from returning energy to the piston (by pushing back the piston). Thus, engine braking may convert some of the engine power into braking force, assist in controlling the speed of the vehicle and reduce wear on conventional service brakes. This is particularly useful for heavy vehicles (such as trucks, buses, etc.) when traveling down steep grades or when maintaining control under severe driving conditions.

Referring to FIG. 3, an exemplary operation of the engine braking system in a 1-stroke engine braking mode is depicted. In particular embodiments, the intake valve may operate substantially similar to that in the drive mode of FIG. 2, e.g., the intake valve may lift during an intake stroke based on the intake lift profile 302 and remain closed during subsequent compression, power, and exhaust strokes. In particular embodiments, the exhaust lift profile 304 acting on both exhaust valves through the exhaust rocker arm during the exhaust stroke may also be similar to the actuation pattern. In particular embodiments, two additional engine braking lifts may be applied, for example, in the compression and power strokes. By way of example and not limitation, based on an engine braking lift profile having a braking gas recirculation lift sub-profile 306 and a first compression release lift sub-profile 308, an engine braking rocker arm may be actuated to act on one of the exhaust valves (i.e., the exhaust braking valve), as will be described in detail below.

In particular embodiments, the brake gas recirculation lift sub-curve 306 may be utilized, which may be timed to follow the first intake lift curve 302 and slightly overlap. By way of example and not limitation, the brake gas recirculation lift sub-curve 306 may recirculate a portion of engine exhaust back into the cylinder to supplement the cylinder charge. It is further explained that high pressure pulses (e.g., air may be compressed to peak pressure and released through the exhaust system at sonic velocity) originating from other cylinders of a six-cylinder engine and traveling in the exhaust system, for example, may be advantageously redirected and introduced into a particular cylinder undergoing engine braking to boost the cylinder with additional air. In the illustrated diagram, in particular embodiments, the exhaust brake valve may be opened late in the intake stroke to early in the compression stroke to introduce exhaust pressure pulses into the cylinder beyond the primary intake event. By loading the cylinders with a recirculated exhaust gas pulse, the brake gas recirculation lift sub-curve 306 may help to increase the amount of air in the cylinders and achieve a higher peak cylinder pressure, thereby providing higher retarding or braking power in engine braking mode because more energy is expended for compression.

In a specific embodiment, after the brake gas is recirculated in the compression stroke, the piston may be moved upward, compressing the air in the cylinder. Before the piston reaches its highest position in the cylinder (e.g., crank angle of 0 degrees), pressure may be released from the cylinder through the first compression release lift sub-curve 308, opening the exhaust brake valve for compressed air to escape. Opening of the exhaust brake valve may allow the cylinder to release compressed air, thus reducing the cylinder pressure so that energy does not return to the piston. In other words, any air spring effect of the compressed air in the cylinder (which would otherwise later press the piston down again) can be effectively eliminated or at least reduced.

In particular embodiments, the engine braking system may then be operated in accordance with the exhaust lift profile 304, wherein the exhaust rocker arm pushes both the exhaust braking valve and the exhaust standard valve open during the exhaust stroke, and the intake lift profile 302 is repeated again for another intake stroke if additional engine braking cycles are required.

FIG. 4 illustrates an exemplary operation in a 1.5 stroke engine braking mode of an engine braking system according to one embodiment of the present disclosure that may deliver higher retarding power and enhance engine braking performance. This may be achieved by having an additional braking valve event per engine cycle compared to the 1-stroke engine braking of fig. 3. In particular embodiments, the intake valve may operate substantially similar to that in the drive mode of FIG. 2, e.g., the intake valve may lift during an intake stroke based on the intake lift profile 402 and remain closed during subsequent compression, power, and exhaust strokes. On the other hand, in particular embodiments, the exhaust lift profile may be removed or disabled, which would otherwise be enabled during the exhaust stroke. By way of example and not limitation, this may be accomplished by disabling the exhaust rocker arm or the exhaust chamber of the exhaust rocker arm, thereby disabling actuation of both the exhaust standard valve and the exhaust brake valve by the exhaust rocker arm. That is, during an engine cycle, the exhaust standard valve may remain stationary and the exhaust brake valve may receive zero lift from the exhaust rocker arm. In particular embodiments, additional engine braking lift may be applied, for example, during the compression stroke, the power stroke, and the exhaust stroke. By way of example and not limitation, according to an engine braking lift profile that is timed for a plurality of actuation events and includes a braking gas recirculation lift sub-profile 406, a first compression release lift sub-profile 408, a re-inhaler lift sub-profile 410, and a second compression release lift sub-profile 412, an engine braking rocker arm may be controlled to act on one of the exhaust valves (i.e., an exhaust braking valve), as will be described in detail below.

In particular embodiments, the brake gas recirculation lift sub-curve 406 may be utilized and may be timed to follow the first intake lift curve 402 without overlapping. By way of example and not limitation, the brake gas recirculation lift sub-curve 406 may recirculate a portion of engine exhaust back into the cylinder to supplement the cylinder charge. It is further explained that high pressure pulses (e.g., air may be compressed to peak pressure and released through the exhaust system at sonic velocity) originating from other cylinders of a six-cylinder engine and traveling in the exhaust system, for example, may be advantageously redirected and introduced into a particular cylinder undergoing engine braking to boost the particular cylinder with additional air. As shown, in particular embodiments, the exhaust brake valve may be opened after the intake stroke up to the mid-or late-compression stroke to introduce exhaust pressure pulses into the cylinder beyond the main intake event. By loading the cylinders with a recirculated exhaust gas pulse, the brake gas recirculation lift sub-curve 406 may help to increase the amount of air in the cylinders and achieve a higher peak cylinder pressure, thereby providing higher retarding or braking power in engine braking mode because more energy is expended for compression.

In a specific embodiment, after the brake gas is recirculated in the compression stroke, the piston may be moved upward, compressing the air in the cylinder. Before the piston reaches its highest position in the cylinder (e.g., crank angle of 0 degrees), pressure may be released from the cylinder through the first compression release lift sub-curve 408, opening the exhaust brake valve for compressed air to escape. By way of example and not limitation, the first compression release lift sub-curve 408 may open the exhaust brake valve an amount greater than the 1-stroke engine braking mode (e.g., the first compression release lift sub-curve 308 of fig. 3), although other suitable values are also contemplated by the present disclosure. Opening of the exhaust brake valve may allow the cylinder to release compressed air, thus reducing the cylinder pressure so that energy does not return to the piston. In other words, any air spring effect of the compressed air in the cylinder (which would otherwise later press the piston down again) can be effectively eliminated or at least reduced.

In particular embodiments, after the first compression-release event is completed, the exhaust brake valve may then be actuated to lift again. This is referred to as the re-inhaler lift sub-curve 410, where the exhaust brake valve opens to again draw exhaust gas from the exhaust system, re-inhaling air that has been expelled into the exhaust system back into the cylinder. By way of example and not limitation, rebreathing may be due to a pressure differential between a high exhaust gas pressure and a low in-cylinder pressure. As shown by the cylinder pressure curve in fig. 4, for example, during re-suction, the pressure inside the cylinder may be minimized, although other suitable values are also contemplated by the present disclosure. Charging the cylinders with exhaust gas after the first compression release may allow the system to reuse the exhaust gas by compressing the exhaust gas in the exhaust stroke after the power stroke. By way of example and not limitation, the volume of exhaust gas mass drawn into the cylinder is low because the valve opening amount is not as high as the main intake event through the intake valve based on the intake lift curve 402. Thus, the second peak pressure of the cylinder generated as the piston is raised in the exhaust stroke may be lower than the first peak pressure of the cylinder in the compression stroke. By way of example and not limitation, the second peak pressure may be approximately half of the first pressure peak, thus denominating a 1.5 stroke engine brake, although other suitable values are contemplated by the present disclosure.

In particular embodiments, after re-ingestion in the exhaust stroke, as the piston moves upward to compress the air recovered in the cylinder, a second compression release lift sub-curve 412 of the exhaust brake valve may be implemented that functions similarly to the first compression release lift sub-curve 408, i.e., releasing air out of the cylinder to eliminate or at least reduce the air spring effect due to compression so that energy does not return to the piston. The second compression release valve lift may be lower than the first compression release valve lift, given that there is relatively little amount of air being re-drawn into the cylinder, but sufficient to release compressed air out of the cylinder, effectively reducing cylinder pressure.

In particular embodiments, if additional engine braking cycles are required, the engine braking system may repeat the intake lift profile 402 again for another intake stroke.

Fig. 5 illustrates how the valve train system may operate to transition between a standard drive mode and an engine braking mode. For purposes of explanation only and not limitation, exemplary operations are described with reference to the valve train assembly 100 depicted in FIG. 1. It should be appreciated that embodiments according to the present disclosure may be implemented with other suitable valve train systems. In particular embodiments, the intake valves 116A, 116B may be actuated, for example, by actuating the intake rocker arm 102, such that a valve actuation motion may be transmitted from the intake cams to the intake valves 116A, 116B following the intake lift profile 502. Throughout engine operation, actuation of the intake rocker arm 14 may be maintained such that the intake valves 116A, 116B are lifted periodically during the intake stroke of each engine cycle. In particular embodiments, during the drive mode, the exhaust valves 108, 110 may be activated, for example, by activating the exhaust rocker arm 104. By way of example and not limitation, actuation of the exhaust rocker arm 104 may be accomplished by opening the exhaust chamber 112 to enable valve actuation motion to be transmitted from the exhaust cam to the exhaust valves 108, 110 via the valve bridge 120. On the other hand, in particular embodiments, during the drive mode, the engine brake rocker arm 106 may be deactivated, for example, by closing the engine brake chamber 114, such that any movement of the exhaust brake valve 110 that acts independently via the movable component 122 of the valve bridge 120 is lost, in which case the lift of the exhaust brake valve 110 does not follow the rotation of the engine brake rocker arm 106, but only follows the exhaust rocker arm 104. In other words, when in the actuated mode, the exhaust standard valve 108 and the exhaust brake valve 110 are synchronously actuated by the exhaust rocker arm 104 based on the exhaust lift profile 504.

In particular embodiments, a transition mode may be introduced in a subsequent engine cycle following the drive mode during which both the exhaust rocker arm 104 and the engine brake rocker arm 106 may be activated. In this way, during the exhaust stroke, the exhaust standard valve 108 and the exhaust brake valve 110 may be simultaneously opened to the same valve position upon actuation by the exhaust rocker arm 104 based on the exhaust lift profile 504. In addition to this main exhaust lift event, the exhaust brake valve 110 may also perform additional braking lift based on rotation of the engine brake rocker arm 106, i.e., a brake gas recirculation lift sub-curve 506 and a first compression release lift sub-curve 508, similar to those discussed in detail above. Specifically, by way of example and not limitation, the engine brake chamber 114 of the engine brake rocker arm 106 may be opened and configured to press down on the movable member 122 of the valve bridge 120 in response to an engine brake lift profile to actuate the exhaust brake valve 110 independently of the exhaust standard valve 108. Note that in the illustrated embodiment, while the engine brake rocker arm 106 may be actuated throughout the engine brake lift curve by a brake gas recirculation lift sub-curve 506, a first compression release lift sub-curve 508, a re-inhaler lift sub-curve 510, and a second compression release lift sub-curve 512, similar to those discussed in detail above, the exhaust brake valve 110 in the exhaust stroke only follows the exhaust lift curve 504 of the exhaust rocker arm 104. In particular embodiments, by enabling both the exhaust rocker arm 104 and the engine brake rocker arm 106, the engine brake system may experience a smooth transition, particularly when the exhaust brake valve 110 transitions from the first compression release lift sub-curve 508 through the engine brake rocker arm 18 to the exhaust lift curve 504 through the exhaust rocker arm 104. Furthermore, in particular embodiments, the engine braking system in transition mode functions substantially similar to 1-stroke engine braking, wherein air in the cylinder is compressed once by the piston stroke to generate a high braking force. In the illustrated embodiment, the transition mode may be implemented one cycle before the valve train assembly 100 enters the engine braking mode. Alternatively, in other embodiments, the transition mode may last for several cycles before switching to the engine braking mode.

In particular embodiments, after the transition mode, the exhaust rocker arm 104 may be deactivated, allowing the system to operate in full-stroke or 1.5-stroke engine braking mode. Specifically, in the 1.5-stroke engine braking mode, the exhaust lift profile 504 is removed from the cycle by closing the exhaust rocker arm 104 (e.g., directly or by disabling the exhaust chamber 112) such that the exhaust standard valve 108 receives zero lift during the entire course of 1.5-stroke engine braking. In particular embodiments, the exhaust brake valve 110 is in an actuated state and is responsive only to movement of the engine brake rocker arm 106. By way of example and not limitation, the exhaust brake valve 110 may be opened based on the brake gas recirculation lift sub-curve 506, the first compression release lift sub-curve 508, the re-inhaler lift sub-curve 510, and the second compression release lift sub-curve 512, allowing air in the cylinder to be compressed twice against upward movement of the piston, thereby providing higher retarding power to slow the vehicle.

Referring now to FIG. 6, in certain embodiments employing normal 1.5-stroke engine braking and with different timings of the valve lift events than the embodiment of FIG. 5, the valve train components may experience severe mechanical shock due to overlapping main exhaust and engine braking operations. For example, in the illustrated embodiment, the exhaust rocker arm 104 may rotate based on a main exhaust lift profile and the engine brake rocker arm 106 may rotate based on an engine brake lift profile. Thus, when a normal 1.5-stroke engine braking event is coincident with the main exhaust event, two intersections 602, 604 between the main and engine braking lift curves may be formed, resulting in a significant difference in lift rate, represented by the different slopes of the two lift curves. By way of example and not limitation, when the valve train assembly 100 is operated with the exhaust rocker arm 104 activated and the engine brake rocker arm 106 deactivated (e.g., in a drive mode), the engine brake capsule 114 may be in a lost motion state in which the engine brake capsule 114 (e.g., shown as a bolt 124 resting on a top surface of the engine brake rocker arm 106) and lost motion components thereof are movable relative to the engine brake rocker arm 106. The free movement between the engine brake pod 114 and the engine brake rocker arm 106 may be particularly sensitive to changes in lift rate, which may result in poor dynamic behavior that may damage the system.

In particular embodiments, at the first intersection 602, the engine brake rocker arm 106 may pivot downward following an engine brake lift curve toward its lowest position of re-inhaler lift, while the engine brake pod 114 may move upward relative to the engine brake rocker arm 106 due to the upward support of the movable member 122 of the valve bridge 120. When this occurs, a lost motion clearance may be formed between the bolt 124 of the engine brake pod 114 and the engine brake rocker arm 106 to absorb valve actuation motions through engine brake lift. On the other hand, actuation of the exhaust rocker arm 104 may lag actuation of the engine brake rocker arm 106 due to the offset between the engine brake lift profile and the main exhaust lift profile. For example, when the engine brake rocker arm 106 is about to reach its lowest re-inhaler lift position, the exhaust rocker arm 104 may initially lower the valve bridge 120 based on the main exhaust lift profile, thereby disengaging the movable member 122 from the engine brake compartment 114 in a downward direction. Without support by the movable member 122, the engine brake pod 114 may fall under gravity, rapidly closing the lost motion clearance until it strikes the engine brake rocker 106, resulting in operational noise, severe mechanical shock, and possible system failure. In addition, in embodiments where a lost motion spring is provided in the engine brake compartment 114, the spring force may also accelerate downward movement of the engine brake compartment 114, causing the engine brake compartment 114 to more forcefully impact the engine brake rocker arm 106.

In particular embodiments, at the second intersection 604, the engine brake rocker arm 106 may rotate downward, e.g., substantially to its lowest position based on a second compression release lift of the engine brake lift profile. In contrast, the exhaust rocker arm 104, and thus the valve bridge 120, may travel upward to return to the zero lift position on the main exhaust lift curve. When this occurs, the movable member 122 may impinge with a greater force in an upward direction on the engine brake compartment 114. Further, the significant momentum and kinetic energy of the movable component 122 generated by the rate difference between the engine braking lift curve and the main exhaust lift curve may cause the engine braking pod 114 to spring upward away from the engine braking rocker arm 106 until the engine braking pod 114 suddenly stops, for example, when the aerodynamic component impacts a mechanical stop inside the engine braking rocker arm 106. This can introduce severe mechanical shock to the air components, shortening the service life of the system, and causing severe engine failure, among other things. Thereafter, the engine brake pod 114 may fall back and strike the engine brake rocker arm 106 again due to gravity.

To minimize the severity of mechanical shock, in particular embodiments according to the present disclosure, the timing of the valve lift sequences may be carefully designed to improve tangency and ensure low overlap between exhaust lift and engine braking lift, thereby reducing possible mechanical shock in the valve train system.

FIG. 7 illustrates an improved engine braking operation according to one embodiment of the present disclosure. For purposes of explanation only and not limitation, exemplary operations are described with reference to the valve train assembly 100 depicted in FIG. 1. It should be appreciated that embodiments according to the present disclosure may be implemented with other suitable valve train systems. In the illustrated embodiment, the exhaust rocker arm 104 may rotate based on a main exhaust lift profile and the engine brake rocker arm 106 may rotate based on an engine brake lift profile. Thus, when the modified 1.5 stroke engine braking event coincides with the main exhaust event, two intersections 702, 704 between the main exhaust lift curve and the engine braking lift curve may be formed. The timing of the two intersections 702 and 704 between the main exhaust lift curve and the engine brake lift curve may be specifically designed. In particular embodiments, since the main exhaust lift curve and the engine braking lift curve are substantially tangential to each other at two intersection points 702 and 704, the difference in lift rates may be reduced, allowing for a smoother transition in engine operation. The two crossover points 702 and 704 may be located near the start and end points of the main exhaust lift curve. In this way, the impact forces between the different moving parts that will be in contact with each other can be reduced or eliminated. By way of example and not limitation, when the valve train assembly 100 is operated with the exhaust rocker arm 104 activated and the engine brake rocker arm 106 deactivated (e.g., in a drive mode), the engine brake capsule 114 may be in a lost motion state in which the engine brake capsule 114 and its lost motion components are movable relative to the engine brake rocker arm 106. Since the change in lift rate is kept low, its effect on free movement between the engine brake pod 114 and the engine brake rocker arm 106 can be minimized, ensuring that the valve train assembly 100 operates with optimal system kinematics.

In particular embodiments, at the first intersection 702, the engine brake rocker arm 106 may pivot downward according to an engine brake lift curve, while the exhaust rocker arm 104 may also move downward based on the main exhaust lift curve substantially simultaneously and at a similar rate as the engine brake rocker arm 106, which may be due to tangency at the first intersection 702. In this way, the lost motion lash created by the relative movement between the engine brake pod 114 and the engine brake rocker arm 106 may be much smaller. In this way, as the engine brake capsule 114 translates downward under gravity and closes the gap, it may gently fall back onto the engine brake rocker arm 106 with less potential energy (e.g., a slight impact force), thereby minimizing mechanical shock that would otherwise damage the system.

In particular embodiments, actuation of the engine brake rocker arm 106 and the exhaust rocker arm 104 may also occur substantially simultaneously at the second crossover point 704. By way of example and not limitation, due to tangency at the second intersection 704, both the engine brake rocker arm 106 and the exhaust rocker arm 104 may rotate in an upward direction toward their zero lift positions at a similar rate. Although in this scenario, the engine brake pod 114 may still be pushed upward away from the engine brake rocker arm 106 due to the valve lift differential, the rate of travel and impact force of the engine brake pod 114 is significantly reduced, minimizing mechanical shock in the system and optimizing operating dynamics as compared to the normal 1.5 stroke engine brake described with reference to fig. 6.

Referring now to fig. 8, in some embodiments without a transition from the drive mode to the engine braking mode, a serious system failure may occur. For example, in the illustrated embodiment, in the drive mode shown at the top of fig. 8, the exhaust rocker arm 104 may be activated and the engine brake rocker arm 106 may be deactivated, i.e., both the exhaust standard valve 108 and the exhaust brake valve 110 are lifted open according to the exhaust lift profile during the exhaust stroke. When the valve train system is opened, in an attempt to switch the engine to an engine braking mode (as shown at the bottom of fig. 8), the exhaust rocker arm 104 may suddenly deactivate, thereby removing the exhaust lift profile from the operating cycle. At this time, however, the engine brake rocker arm 106 may not have been activated, for example, due to a delay in the transmission of the control signal. That is, in this scenario, only the intake valves 116A, 116B may be opened, drawing a large amount of air into the cylinder. The piston may then be raised during a compression stroke, compressing the air to a high pressure. Without any compression released through the exhaust valves 108, 110 after the power stroke, the air may be trapped inside the cylinder, and then compressed again as the piston moves upward in the exhaust stroke, creating significant pressure in the cylinder. Such high cylinder pressures are detrimental to the intake valves 116A, 116B because they attempt to open late in the intake stroke, particularly when the intake side design of the rocker arm assembly is unable to withstand high pressures, resulting in valve damage and engine failure.

Fig. 9 illustrates an improved engine braking operation according to the present disclosure, wherein a transition mode is introduced between a drive mode and an engine braking mode. In a specific embodiment, the engine may first be operated in a drive mode shown at 910, wherein the exhaust rocker arm is activated and the engine brake rocker arm is deactivated. If engine braking is desired, engine braking lift may be initiated. That is, in the transitional mode shown at 920, both a 1.5-stroke engine braking lift profile and an exhaust lift profile may be performed. In this way, high compression pressures, which might otherwise damage the system, can be effectively avoided. Further, since the engine brake lift curve is timed to be tangential to the re-suction lift sub-curve 922 and the second compression release lift sub-curve 924 of the 1.5 stroke engine brake lift curve, a smooth transition between engine brake lift and exhaust lift acting on the exhaust brake valve may be ensured. Note that while the transition mode may produce some braking power, it is not suitable for full 1.5 stroke engine braking. By way of example and not limitation, the peak cylinder pressure in the illustrated embodiment may only reach relatively low levels, thereby limiting the amount of braking power generated. In particular embodiments, the transition mode may be implemented one cycle before the valve train assembly enters the engine braking mode. Alternatively, in other embodiments, the transition mode may last for several cycles before switching to the engine braking mode. In particular embodiments, to perform the engine braking mode, the exhaust lift may then be deactivated such that only the exhaust brake valve may remain actuated based on the 1.5-stroke engine braking lift profile while the exhaust standard valve is not operating. At this point, the engine may be operated entirely in the engine braking mode. By allowing smooth transfer between the drive mode and the engine braking mode, special timing of the valve lift sequences according to the present disclosure may optimize engine braking performance and protect the intake valve system from overload due to high cylinder pressures.

FIG. 10 illustrates engine braking power adjustment according to the present disclosure. In particular embodiments, in the transitional mode that has been discussed in detail above, the exhaust lift profile and the engine braking lift profile may be activated simultaneously, allowing compressed air in the compression stroke to be quickly released from the cylinder. Further explained, since during the exhaust stroke, the exhaust brake valve is lifted open by the exhaust rocker arm in response to the exhaust lift profile, rather than by the engine brake rocker arm performing a re-breathe event based on the engine brake lift profile, no exhaust gas is circulated back into the cylinder after the first compression release. Due to the lack of gas in the cylinder, the cylinder pressure is still low even though the piston is compressed during the exhaust stroke. By way of example and not limitation, as shown in the cylinder pressure map at the bottom of fig. 10, the pressure profile during the transition mode may contain only one peak pressure, thereby allowing the valve train system to function substantially similar to the 1-stroke engine brake as described with reference to fig. 3. This transitional mode may also be referred to as 1-stroke engine braking because it generates less braking force than a full 1.5-stroke engine braking. Furthermore, in particular embodiments, during engine braking modes where the exhaust lift is off and the engine braking lift is on, two cylinder pressure peaks may be induced, one large peak due to intake operation and the other small peak due to re-ingestion of the exhaust braking valve (refilling of exhaust gas in the cylinder). By way of example and not limitation, the small peak pressure may be about half the large peak pressure, thus yielding a 1.5 stroke engine brake. This engine braking mode may also be referred to as 1.5 stroke engine braking and generates the full amount of braking power available to the engine. By designing the sequence of valve lift events in this particular manner in accordance with the present disclosure, a single system may be employed to provide two levels of engine braking.

FIG. 11 illustrates two exemplary power levels of an engine braking system according to the present disclosure, namely 1-stroke engine braking and 1.5-stroke engine braking. In embodiments where the engine braking system according to the present disclosure is used in a six cylinder engine, all six cylinders may remain activated and the scaling of braking power may be adjusted by opening or closing the exhaust lift. By way of example and not limitation, if low braking force is desired, the engine braking system may be reduced to 1-stroke engine braking by activating both the exhaust lift and the engine braking lift. Alternatively, as another example and not by way of limitation, if a higher braking force is required, for example, when the vehicle is traveling down a steep grade and rapid deceleration is required, the engine braking system may be scaled up to 1.5-stroke engine braking by closing the exhaust lift while maintaining the engine braking lift on. In the illustrated embodiment, 1.5-stroke engine braking may provide 80% more braking power than 1-stroke engine braking, but other suitable values are also contemplated. In contrast, in other embodiments employing a general braking strategy without the ability to deliver different braking powers through a single engine braking system, scaling of braking power may be achieved by actuating only a select number of engine cylinders, e.g., by actuating three cylinders for low braking power or six cylinders for high braking power, which undesirably increases operating costs and increases system complexity. The system and method for timing of valve lift events according to the present disclosure advantageously allows for simultaneous operation of both the exhaust rocker arm and the engine brake rocker arm, which facilitates a curtailment from a 1.5-stroke engine braking mode to a 1-stroke engine braking mode.

FIG. 12 illustrates a flowchart of an exemplary method for timing valve lift events, according to an embodiment of the present disclosure. In particular embodiments, the method may be implemented by a rocker arm assembly of an internal combustion engine. By way of example and not limitation, the rocker arm assembly may be similar to the rocker arm assembly described with reference to fig. 1 in that the rocker arm assembly may include an exhaust rocker arm (e.g., exhaust rocker arm 104) and an engine brake rocker arm (e.g., engine brake rocker arm 106) and may be configured to selectively actuate a first exhaust valve (e.g., exhaust standard valve 108) or a second exhaust valve (e.g., exhaust brake valve 110). Although this disclosure describes a method of using a particular rocker arm assembly to timing valve lift events in a particular manner, this disclosure contemplates using any suitable rocker arm assembly to timing valve lift events in any suitable manner. At 1202, an exhaust rocker arm may be actuated to allow actuation of a first exhaust valve and a second exhaust valve by the exhaust rocker arm. By way of example and not limitation, this may be accomplished by actuating the exhaust chamber of the exhaust rocker arm such that, upon rotation of the exhaust rocker arm, the exhaust chamber extends to contact a valve bridge coupled to the first and second exhaust valves. At step 1204, an exhaust rocker arm may be actuated based on the exhaust lift profile. By way of example and not limitation, an exhaust lift curve may relate the degree of rotation of an exhaust rocker arm or valve lift movement to the crank angle of an internal combustion engine crankshaft. At step 1206, an engine brake pod of the engine brake rocker arm may be actuated. By way of example and not limitation, as the engine brake rocker arm rotates, the engine brake pod may extend to contact a movable member of a valve bridge coupled to the second exhaust valve. Specifically, the engine brake rocker arm may actuate the second exhaust valve independently of the first exhaust valve. At step 1208, an engine brake rocker arm may be actuated based on the engine brake lift profile. By way of example and not limitation, an engine brake lift curve may relate the degree of rotation of an engine brake rocker arm or valve lift movement to the crank angle of an internal combustion engine crankshaft. In particular embodiments, the timing of the exhaust lift curve and the engine brake lift curve may be specifically designed such that the exhaust lift curve and the engine brake lift curve have a first crossover point and a second crossover point. Further, the exhaust lift curve may be tangent to the engine braking lift curve at a first crossover point and a second crossover point. This may reduce the difference in lift rates of the rocker arm assembly and ensure low overlap between exhaust lift and engine braking lift, thereby reducing possible mechanical shock in the rocker arm assembly. In particular embodiments, both the exhaust rocker arm and the engine brake rocker arm remain actuated for one or more engine cycles. When this occurs, the engine is in a transitional mode as described in detail above. for example, the transition mode may provide 1-stroke engine braking, where only one peak cylinder pressure is generated. At step 1210, the exhaust rocker arm may be deactivated. This may be accomplished by directly deactivating the exhaust rocker arm such that it ceases to rotate or by deactivating the exhaust chamber to inhibit transmission of motion from the exhaust rocker arm to the valve bridge. Thus, the engine may enter a 1.5-stroke braking mode in which only the engine brake rocker arm is operated to actuate the engine brake valve based on the engine brake profile. By introducing a transition mode between the drive mode and the engine braking mode, smooth operation of the rocker arm assembly may be ensured, thereby optimizing engine braking performance, facilitating an increase or decrease in braking power, and preventing overload of the rocker arm assembly.

Herein, "or" is inclusive, and not exclusive, unless explicitly indicated otherwise or the context indicates otherwise. Thus, herein, "a or B" refers to "A, B or both" unless explicitly stated otherwise or the context indicates otherwise. Furthermore, "and" are both common and separate unless explicitly stated otherwise or the context indicates otherwise. Thus, herein, "a and B" means "a and B, collectively or individually," unless explicitly stated otherwise or the context indicates otherwise.

The scope of the present disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments described or illustrated herein that will be understood by those of ordinary skill in the art. The scope of the present disclosure is not limited to the exemplary embodiments described or illustrated herein. Furthermore, although the present disclosure describes and illustrates respective embodiments herein as including particular components, elements, features, functions, operations, or steps, any of these embodiments may include any combination or permutation of any of the components, elements, features, functions, operations, or steps described or illustrated anywhere herein as would be understood by one of ordinary skill in the art. Furthermore, in the appended claims, reference to a device or system or component of a device or system being adapted, arranged, capable, configured, enabled, operable, or operative to perform a particular function includes the device, system, component whether or not that particular function or function is activated, turned on, or unlocked, so long as the device, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Additionally, although the disclosure describes or illustrates embodiments as providing particular advantages, embodiments may not provide such advantages and may provide some or all of such advantages.

Claims (20)

1. A method for timing valve lift events of a rocker arm assembly of an internal combustion engine, the rocker arm assembly including an exhaust rocker arm and an engine brake rocker arm and configured to selectively actuate a first exhaust valve or a second exhaust valve, the method comprising:

allowing actuation of the first exhaust valve and the second exhaust valve by the exhaust rocker arm;

Actuating the exhaust rocker arm based on an exhaust lift profile;

allowing actuation of the second exhaust valve by the engine brake rocker arm independent of actuation of the first exhaust valve, and

The engine brake rocker arm is actuated based on an engine brake lift curve, wherein the exhaust lift curve and the engine brake lift curve have a first crossover point and a second crossover point, and wherein the exhaust lift curve is tangential to the engine brake lift curve at the first crossover point and the second crossover point.

2. The method of claim 1, wherein the engine brake lift profile comprises a first engine brake lift sub-profile, a second engine brake lift sub-profile, a third engine brake lift sub-profile, and a fourth engine brake lift sub-profile.

3. The method of claim 2, wherein the exhaust lift curve is subsequent to the second engine brake lift sub-curve and overlaps the third engine brake lift sub-curve at the first intersection and overlaps the fourth engine brake lift sub-curve at the second intersection, wherein the exhaust lift curve is tangent to the third engine brake lift sub-curve at the first intersection and tangent to the fourth engine brake lift sub-curve at the second intersection.

4. The method of claim 2, wherein when the first and second exhaust valves are allowed to be actuated by the exhaust rocker arm and the second exhaust valve is allowed to be actuated by the engine brake rocker arm, the actuation of the first exhaust valve is based on the exhaust lift curve and the actuation of the second exhaust valve is based on the first, second, and exhaust lift sub-curves.

5. The method of claim 2, wherein one cylinder pressure spike is generated in a four-stroke cycle of the internal combustion engine when actuation of the first and second exhaust valves is allowed by the exhaust rocker arm and actuation of the second exhaust valve is allowed by the engine brake rocker arm.

6. The method of claim 5, wherein the second engine braking lift sub-curve is configured to release cylinder pressure such that the cylinder pressure peak is generated in a compression stroke of the four-stroke cycle of the internal combustion engine.

7. The method of claim 1, wherein at the first crossover point or the second crossover point, the engine braking lift curve is configured to transfer valve lift in the same direction as the exhaust lift curve.

8. The method of claim 7, wherein at the first crossover point or the second crossover point, the engine braking lift curve is configured to transfer valve lift at a similar rate as the exhaust lift curve.

9. The method of claim 2, further comprising:

Actuation of the first exhaust valve and the second exhaust valve by the exhaust rocker arm is prohibited.

10. The method of claim 9, wherein the first exhaust valve is not actuated and actuation of the second exhaust valve is based on the engine braking lift profile when actuation of the first exhaust valve and the second exhaust valve by the exhaust rocker arm is inhibited and actuation of the second exhaust valve by the engine braking rocker arm is allowed.

11. The method of claim 9, wherein two cylinder pressure peaks are generated in a four-stroke cycle of the internal combustion engine when actuation of the first and second exhaust valves by the exhaust rocker arm is inhibited and actuation of the second exhaust valve by the engine brake rocker arm is allowed.

12. The method of claim 11, wherein the second engine brake lift sub-curve is configured to release cylinder pressure such that a first cylinder pressure spike is generated in a compression stroke of the four-stroke cycle of the internal combustion engine, wherein the fourth engine brake lift sub-curve is configured to release cylinder pressure such that a second cylinder pressure spike is generated prior to an intake stroke of the four-stroke cycle of the internal combustion engine.

13. The method of claim 1, wherein the rocker arm assembly further comprises an intake rocker arm configured to actuate at least two intake valves, the method further comprising:

the at least two intake valves are allowed to be actuated based on an intake lift profile by the intake rocker arm.

14. A method for timing valve lift events by a rocker arm assembly of an internal combustion engine, the rocker arm assembly including an exhaust rocker arm and an engine brake rocker arm and configured to selectively actuate a first exhaust valve or a second exhaust valve, the method comprising:

allowing actuation of the first exhaust valve and the second exhaust valve by the exhaust rocker arm;

Actuating the exhaust rocker arm based on an exhaust lift profile;

Allowing actuation of the second exhaust valve by the engine brake rocker arm independent of actuation of the first exhaust valve;

actuating the engine brake rocker arm based on an engine brake lift curve, wherein the exhaust lift curve and the engine brake lift curve have a first crossover point and a second crossover point, and wherein the exhaust lift curve is tangential to the engine brake lift curve at the first crossover point and the second crossover point;

maintaining actuation of the exhaust rocker arm and the engine brake rocker arm for at least one engine cycle including an intake stroke, a compression stroke, an exhaust stroke, and an intake stroke, and

Actuation of the first exhaust valve and the second exhaust valve by the exhaust rocker arm is prohibited.

15. The method of claim 14, wherein the engine brake lift profile comprises a first engine brake lift sub-profile, a second engine brake lift sub-profile, a third engine brake lift sub-profile, and a fourth engine brake lift sub-profile.

16. The method of claim 15, wherein the exhaust lift curve is subsequent to the second engine brake lift sub-curve and overlaps the third engine brake lift sub-curve at the first intersection and overlaps the fourth engine brake lift sub-curve at the second intersection, wherein the exhaust lift curve is tangent to the third engine brake lift sub-curve at the first intersection and tangent to the fourth engine brake lift sub-curve at the second intersection.

17. The method of claim 14, wherein at the first crossover point or the second crossover point, the engine braking lift curve is configured to transfer valve lift in the same direction as the exhaust lift curve.

18. The method of claim 17, wherein at the first crossover point or the second crossover point, the engine braking lift curve is configured to transfer valve lift at a similar rate as the exhaust lift curve.

19. The method of claim 15, wherein two cylinder pressure peaks are generated in a four-stroke cycle of the internal combustion engine when actuation of the first and second exhaust valves by the exhaust rocker arm is inhibited and actuation of the second exhaust valve by the engine brake rocker arm is allowed.

20. The method of claim 19, wherein the second engine brake lift sub-curve is configured to release cylinder pressure such that a first cylinder pressure spike is generated in a compression stroke of the four-stroke cycle of the internal combustion engine, wherein the fourth engine brake lift sub-curve is configured to release cylinder pressure such that a second cylinder pressure spike is generated prior to an intake stroke of the four-stroke cycle of the internal combustion engine.