Lost motion variable valve actuation system for engine braking and early exhaust opening

A method and system for actuating an internal combustion engine exhaust valve to provide compression release actuation during an engine braking mode of engine operation and early exhaust valve opening actuation during a positive power mode of engine operation is disclosed. The system may include a first cam having a compression release lobe and an early exhaust valve opening lobe connected to a hydraulic lost motion system including a first rocker arm. A hydraulically actuated piston may be selectively extended from the hydraulic lost motion system to provide the exhaust valve with compression release actuation or early exhaust valve opening actuation. The hydraulically actuated piston may be provided as a slave piston in a master-slave piston circuit in a fixed housing, or alternatively, as a hydraulic piston slidably disposed in a rocker arm. The method and system may further provide exhaust gas recirculation and/or brake gas recirculation in combination with compression release actuation and early exhaust valve opening actuation.

FIELD OF THE INVENTION

The present invention relates generally to a system for actuating one or more engine valves in an internal combustion engine. In particular, the present invention relates to a lost motion system for providing variable valve actuation (VVA) for engine braking and early exhaust opening (EEO).

BACKGROUND OF THE INVENTION

Internal combustion engines typically use either a mechanical, electrical or hydro-mechanical valve actuation system to actuate the engine valves. These systems may include a combination of camshafts, rocker arms and push rods that are driven by the engine's crankshaft rotation. When a camshaft is used to actuate the engine valves, the timing of the valve actuation may be fixed by the size and location of the lobes on the camshaft.

For each 360 degree rotation of the camshaft, the engine completes a full cycle made up of four strokes, i.e., expansion, exhaust, intake, and compression. Both the intake and exhaust valves may be closed, and remain closed, during most of the expansion stroke, when the piston is traveling away from the cylinder head and the volume between the cylinder head and the piston head is increasing. During positive power operation, fuel is burned during the expansion stroke and positive power is delivered by the engine. The expansion stroke ends at the bottom dead center (BDC) point, at which time the piston reverses direction. The exhaust valve may be opened for a main exhaust event prior to BDC. A lobe on the camshaft may be synchronized to open the exhaust valve for the main exhaust event as the piston travels upward and forces combustion gases out of the cylinder. Near the end of the exhaust stroke, another lobe on the camshaft may open the intake valve for the main intake event at which time the piston travels away from the cylinder head. The intake valve closes and the intake stroke ends when the piston is near bottom dead center. Both the intake and exhaust valves are closed as the piston again travels upward for the compression stroke.

The main intake and main exhaust valve events are required for positive power operation of an internal combustion engine. Additional auxiliary valve events, while not required, may be desirable. For example, it may be desirable to actuate the intake and/or exhaust valves during positive power or other engine operation modes for compression-release engine braking, bleeder engine braking, exhaust gas recirculation (EGR), brake gas recirculation (BGR), or other auxiliary intake and/or exhaust valve events.

With respect to auxiliary valve events, flow control of exhaust gas through an internal combustion engine has been used in order to provide vehicle engine braking. One or more exhaust valves may also be selectively opened to convert, at least temporarily, the engine into an air compressor for engine braking operation. This air compressor effect may be accomplished by either opening one or more exhaust valves near piston top dead center position for compression-release type braking, or by maintaining one or more exhaust valves in a relatively constant cracked open position during much or all of the piston motion, for bleeder type braking. In both types of braking, the engine may develop a retarding force that may be used to help slow a vehicle down. This braking force may provide the operator with increased control over the vehicle, and may also substantially reduce the wear on the service brakes. Compression-release type engine braking has been long known and is disclosed in Cummins, U.S. Pat. No. 3,220,392 (November 1965), which is hereby incorporated by reference.

Generally, engine braking systems may control the flow of exhaust gas to incorporate the principles of compression-release braking, bleeder braking, exhaust gas recirculation, and/or brake gas recirculation. During compression-release engine braking, the exhaust valves may be selectively opened to convert, at least temporarily, a power producing internal combustion engine into a power absorbing air compressor. As a piston travels upward during its compression stroke, the gases that are trapped in the cylinder may be compressed. The compressed gases may oppose the upward motion of the piston. As the piston approaches the top dead center position, at least one exhaust valve may be opened to release the compressed gases in the cylinder to the exhaust manifold, preventing the energy stored in the compressed gases from being returned to the engine on the subsequent expansion down-stroke. In doing so, the engine may develop retarding power to help slow the vehicle down.

During bleeder engine braking, in addition to, and/or in place of, the main exhaust valve event, which occurs during the exhaust stroke of the piston, the exhaust valve(s) may be held slightly open during the remaining three engine cycles (full-cycle bleeder brake) or during a portion of the remaining three engine cycles (partial-cycle bleeder brake). The bleeding of cylinder gases in and out of the cylinder may act to retard the engine. Usually, the initial opening of the braking valve(s) in a bleeder braking operation is in advance of the compression top dead center, i.e., early valve actuation, and then lift is held constant for a period of time. As such, a bleeder type engine brake may require lower force to actuate the valve(s) due to early valve actuation, and generate less noise due to continuous bleeding instead of the rapid blow-down of a compression-release type brake.

Exhaust gas recirculation (EGR) systems may allow a portion of the exhaust gases to flow back into the engine cylinder during positive power operation. EGR may be used to reduce the amount of NO created by the engine during positive power operations. An EGR system can also be used to control the pressure and temperature in the exhaust manifold and engine cylinder during engine braking cycles. Generally, there are two types of EGR systems, internal and external. External EGR systems recirculate exhaust gases back into the engine cylinder through an intake valve(s). Internal EGR systems recirculate exhaust gases back into the engine cylinder through an exhaust valve(s) and/or an intake valve(s).

Brake gas recirculation (BGR) systems may allow a portion of the exhaust gases to flow back into the engine cylinder during engine braking operation. Recirculation of exhaust gases back into the engine cylinder during the intake stroke, for example, may increase the mass of gases in the cylinder that are available for compression-release braking. As a result, BGR may increase the braking effect realized from the braking event.

Many different actuation systems may be used to selectively actuate engine valves to produce brake gas recirculation and compression-release events. One known type of actuation system is a lost motion system, described in the above-referenced Cummins patent. Another example of a lost motion system for variable valve actuation is disclosed in Vanderpoel, et al., U.S. Pat. No. 7,152,576 (Dec. 26, 2006), which is hereby incorporated by reference. An example of a system with primary and offset actuator rocker arms for engine valve actuation is disclosed in Janak, et al., U.S. Pub. No. 2006/0005796 (Jan. 12, 2006), which is hereby incorporated by reference.

In many internal combustion engines, the intake and exhaust valves may be actuated by fixed profile cams, and more specifically, by one or more fixed lobes or bumps that are an integral part of each cam. The cams may include a lobe for each valve event that the cam is responsible for providing. The size and shape of the lobes on the cam may dictate the valve lift and duration which result from the lobe. For example, an exhaust cam profile for a system may include a lobe for a brake gas recirculation event, a lobe for a compression-release event, and a lobe for a main exhaust event.

It may also be desirable to increase the exhaust back pressure in the exhaust manifold during engine braking. Higher exhaust back pressure may increase gas mass and pressure in the engine cylinder available for engine braking, and thereby increase braking power. Increased exhaust back pressure, however, may undesirably increase the force required to open the exhaust valve for a compression-release event because the opening force applied to the exhaust valve must exceed the increased pressure in the engine cylinder resulting from the increased exhaust back pressure. To some extent the increased exhaust back pressure may also increase the pressure applied to the back of the exhaust valve, which may counter-balance the increased pressure in the cylinder and thus reduce the loading on the exhaust valve opening mechanism used for the compression-release event.

Increasing the pressure of gases in the exhaust manifold may be accomplished by restricting the flow of gases through the exhaust manifold. Exhaust manifold restriction may be accomplished through the use of any structure that may, upon actuation, restrict all or partially all of the flow of exhaust gases through the exhaust manifold. The exhaust restrictor may be in the form of an exhaust engine brake, a turbocharger, a variable geometry turbocharger, a variable geometry turbocharger with a variable nozzle turbine, and/or any other device which may limit the flow of exhaust gases.

Exhaust brakes generally provide restriction by closing off all or part of the exhaust manifold or pipe, thereby preventing the exhaust gases from escaping. This restriction of the exhaust gases may provide a braking effect on the engine by providing a back pressure when each cylinder is on the exhaust stroke. For example, Meneely, U.S. Pat. No. 4,848,289 (Jul. 18, 1989); Schaefer, U.S. Pat. No. 6,109,027 (Aug. 29, 2000); Israel, U.S. Pat. No. 6,170,474 (Jan. 9, 2001); Kinerson et al., U.S. Pat. No. 6,179,096 (Jan. 30, 2001); and Anderson et al., U.S. Pat. Appl. Pub. No. US 2003/0019470 (Jan. 30, 2003) disclose exhaust brakes for use in retarding engines.

Turbochargers may similarly restrict exhaust gas flow from the exhaust manifold. Turbochargers often use the flow of high pressure exhaust gases from the exhaust manifold to power a turbine. A variable geometry turbocharger (VGT) may alter the amount of the high pressure exhaust gases that it captures in order to drive a turbine. For example, Arnold et al., U.S. Pat. No. 6,269,642 (Aug. 7, 2001) discloses a variable geometry turbocharger where the amount of exhaust gas restricted is varied by modifying the angle and the length of the vanes in a turbine. An example of the use of a variable geometry turbocharger in connection with engine braking is disclosed in Faletti et al., U.S. Pat. No. 5,813,231 (Sep. 29, 1998), Faletti et al., U.S. Pat. No. 6,148,793 (Nov. 21, 2000), and Ruggiero et al., U.S. Pat. No. 6,866,017 (Mar. 15, 2005), which are hereby incorporated by reference.

Over the years there have been improvements to lost motion systems for engine braking and there continues to be a need for improvements as technology evolves and new problems are discovered. Improvements are needed for many reasons, including providing a mechanically-driven exhaust main event for cold start and failsafe modes, meeting loading limits, (e.g., cam Hertz stress), avoiding separation and impact loading between cams and rollers, avoiding bridge tilt, meeting exhaust valve seating velocity limits, and protecting against valve-piston contact. There is a risk of valve-piston contact in many electronically-controlled variable valve actuation (VVA) systems. For example, lost motion VVA systems that provide early valve opening and spill oil near peak lifts have an increased risk of valve piston contact if the spill does not function, which may occur, for example, due to a clogged spill port or a broken valve spring. The valve/cam lift ratio of a rocker-actuated VVA system is more limited by the valve-train layout than that of a master-slave system, where the valve/cam lift ratio is governed by hydraulic piston diameters.

SUMMARY OF THE INVENTION

Responsive to the foregoing challenges, Applicant has developed an innovative system for actuating an internal combustion engine exhaust valve to provide compression release actuation during an engine braking mode of engine operation and early exhaust valve opening actuation during a positive power mode of engine operation, said system comprising: a first cam having a compression release lobe, an early exhaust valve opening lobe, and optionally a BGR lobe; a hydraulic lost motion system operatively contacting said first cam, said hydraulic lost motion system including a first rocker arm; a hydraulically actuated piston extending from said hydraulic lost motion system, said hydraulically actuated piston adapted to provide said exhaust valve with compression release actuation during an engine braking mode of engine operation and early exhaust valve opening actuation during a positive power mode of operation; a second cam having a main exhaust lobe; and a main exhaust rocker arm operatively contacting said second cam and adapted to provide a main exhaust actuation to said exhaust valve.

Applicant has further developed an innovative system for actuating an internal combustion engine exhaust valve comprising: a first means for imparting motion for a compression release engine braking actuation optionally including BGR actuation, and an early exhaust valve opening actuation; a hydraulic lost motion system operatively contacting said first means for imparting motion, said hydraulic lost motion system including a first rocker arm; a hydraulically actuated piston extending from said hydraulic lost motion system, said hydraulically actuated piston adapted to selectively provide said exhaust valve with compression release engine braking actuation and early exhaust valve opening actuation; a second means for imparting motion for a main exhaust actuation; a main exhaust rocker arm operatively contacting said second means for imparting motion; and means for controlling said hydraulic lost motion system to selectively provide the compression release engine braking actuation and the early exhaust valve opening actuation.

Applicant has further developed an innovative method of actuating an internal combustion engine exhaust valve to selectively provide compression release engine braking actuation and early exhaust valve opening actuation using a cam with a compression release engine braking lobe and a early exhaust valve opening lobe, and with optional BGR actuation, said method comprising: imparting compression release engine braking actuation motion and early exhaust valve opening actuation motion from said cam to a hydraulic lost motion system including a first rocker arm; determining whether the internal combustion engine is in an engine braking mode of operation; selectively hydraulically locking and unlocking a hydraulically actuated piston in said hydraulic lost motion system to provide said exhaust valve with compression release engine braking actuation when the internal combustion engine is in the engine braking mode of operation; determining whether the internal combustion engine is in a positive power mode of operation and early exhaust valve opening is desired; and selectively hydraulically locking and unlocking the hydraulically actuated piston in said hydraulic lost motion system to provide said exhaust valve with early exhaust valve opening actuation when the internal combustion engine is in the positive power mode of operation and early exhaust valve opening is desired.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated herein by reference, and which constitute a part of this specification, illustrate certain embodiments of the invention and, together with the detailed description, serve to explain the principles of the present invention.

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Embodiments of the present invention may be used to provide variable valve actuation for compression-release engine braking and brake gas recirculation during an engine braking mode of engine operation, as well as early exhaust valve opening during a positive power mode of engine operation.

FIG. 1is a block diagram that illustrates a valve actuation system100in accordance with a first embodiment of the present invention. The valve actuation system100may include a first motion imparting means102, such as a cam with one or more lobes or bumps, operatively contacting a lost motion system104, which in turn may be operatively connected to one or more engine valves106. The valve actuation system may further include a second motion imparting means103operatively connected to the one or more engine valves106. It is appreciated that any number of valve train elements, such as push tubes, rocker arms, and or valve bridges may be provided between or as part of the first and second motion imparting means102and103, the lost motion system104, and the engine valves106, without departing from the intended scope of the present invention. The first motion imparting means102may preferably include both a early exhaust valve opening lobe or bump, a compression release lobe or bump, and optionally a BGR lobe or bump, which may provide input motion to the lost motion system104. The motion selectively transferred to the engine valves106by the lost motion system104may be used to produce various valve actuation events, such as, but not limited to, a compression release braking event, a bleeder braking event, an exhaust gas recirculation event, a brake gas recirculation event, an early exhaust valve opening event, an early intake valve closing event, and/or a centered lift valve event. Preferably, the lost motion system104may be switched on or off to selectively transfer either no motion, compression release motion or early exhaust valve opening motion to the engine valves106by a controller108. The second motion imparting means103may also provide valve actuation events, such as a main exhaust event. The engine valves106may be exhaust valves, intake valves, or auxiliary valves. The first motion imparting means102and the second motion imparting means103may actuate the engine valves106independently of each other.

The first motion imparting means102may comprise any combination of cams, push tubes, and/or rocker arms or their equivalents. The lost motion system104may comprise any structure that connects the motion imparting means102to the engine valves106and selectively transfers motion from the motion imparting means102to the engine valves106. In one sense, the lost motion system104may be any structure capable of selectively attaining more than one fixed length. For example, the lost motion system104may comprise a mechanical linkage, a hydraulic circuit, a hydro-mechanical linkage, an electromechanical linkage and/or any other linkage adapted to connect to the motion imparting means102to the engine valves106and attain more than one operative length. When the lost motion system104incorporates a hydraulic circuit, the lost motion system104may include pressure-adjusting means to adjust the pressure or amount of fluid in a circuit, such as, for example, trigger valves, check valves, accumulator, and/or other devices for releasing hydraulic fluid from or adding hydraulic fluid to the circuit. The lost motion system104may be located at any point in the valve train connecting the motion imparting means102with the engine valves106.

The controller108may comprise any electronic, mechanical, or hydraulic device for communicating with and controlling the lost motion system104. The controller108may include a microprocessor, which is linked to other engine components, to determine and select the appropriate instantaneous length of the lost motion system104. Valve actuation may be optimized at a plurality of engine speeds and conditions by controlling the instantaneous length of the lost motion system104based upon information collected by the microprocessor from engine components. Preferably, the controller108may be adapted to operate the lost motion system104at high speed (i.e., one or more times per engine cycle) using a high speed hydraulic trigger valve.

FIG. 2is a schematic diagram of a cam200which may serve as all or part of the motion imparting means102. The motion imparting means102ofFIG. 1may comprise the cam200, a rocker arm, and/or a push tube. The cam200may include one or more lobes corresponding to various valve actuation events, such as a compression release lobe202, an early exhaust valve opening lobe204, and a brake gas recirculation lobe208. The depictions (e.g., number, size, shape, location) of the lobes on the cam200are intended to be illustrative only and not limiting. Several embodiments of the invention contemplate using separate cams for the main valve opening event (i.e., main exhaust or main intake) and the auxiliary valve opening events such as compression release, early valve opening, and/or brake gas recirculation.

FIG. 3is a schematic top view in partial cross section of variable valve actuation system700in accordance with a second embodiment of the present invention. The variable valve actuation system700may include first and second valve train assemblies extending between the first and second motion imparting means,102and103, respectively, and the exhaust valves716. The first valve train assembly may include a first half (or main exhaust) rocker arm701pivotally mounted on a rocker shaft718, and a second half rocker arm702pivotally mounted on the rocker shaft directly behind the first half rocker arm which together comprise an articulated rocker arm. The first half rocker arm701may include an elephant foot or other valve bridge contacting portion712adapted to apply a valve actuation motion to the engine valves, preferably exhaust valves,716through a valve bridge714.

The second half rocker arm702may include a valve end portion703adapted to apply a pivoting motion to the first half rocker arm701so as to actuate the exhaust valves716. The second half rocker arm702may be biased towards the second motion imparting means103by a spring705, which may create such bias force by pushing against a flange or contact surface760provided on the second half rocker arm from a fixed stop or flange762provided on a fixed engine part so that a cam roller708provided with the second half rocker arm remains in relatively constant contact with the second motion imparting means103.

The second valve train assembly of the variable valve actuation system700may further include a third half rocker arm704pivotally mounted on the rocker shaft718adjacent to the first and second half rocker arms701and702. The third half rocker arm704may be biased by a second spring707through a master piston730and a rod711that acts on a contact surface713provided on the third half rocker arm so that a second cam roller710provided with the third half rocker arm remains in relatively constant contact with the first motion imparting means102. The rod711may include a contact surface to act on a master piston730which is slidably disposed in a master piston bore732provided in a lost motion system housing706. Hydraulic fluid may be provided to the master piston bore732. The lost motion system housing706may be fixed by bolts or other connection means to the internal combustion engine that includes the exhaust valves716. The master piston bore732may be connected to a high-speed trigger valve736and optionally to an accumulator722, and a slave piston720by a hydraulic fluid circuit or passages734.

The interaction of the third half rocker arm704and the lost motion system706are illustrated inFIG. 4. As shown inFIG. 4, a control valve or high-speed trigger valve736may be provided in the hydraulic circuit734such that it may control the supply of hydraulic fluid to and from the hydraulic circuit. Further, the accumulator722may include an accumulator piston724that biases an accumulator piston726into an accumulator bore. Similarly, a slave piston spring802may bias the slave piston720upward into the slave piston bore728towards an adjustable lash screw804. With continued reference toFIGS. 3 and 4, when the trigger valve736is maintained closed, hydraulic fluid may be trapped in the hydraulic circuit734and prevented from flowing into or out of the accumulator722, and conversely, when the trigger valve is maintained open, hydraulic fluid may flow freely out of the hydraulic circuit and into and out of the accumulator722. When the first motion imparting means102(shown inFIG. 3) causes the third half rocker arm704to pivot about the rocker shaft718, the contact surface on the third half rocker arm may push the master piston730into the master piston bore, which in turn may force the slave piston720downward and into contact with the first half rocker arm701. In turn the half rocker arm701may act through the valve bridge714to actuate or open the exhaust valves716. Use of a first motion imparting means102, such as a cam with a compression release engine braking lobe, a early exhaust valve opening lobe, and/or a brake gas recirculation lobe, coupled with selective operation of the trigger valve736may enable selective provision of compression release engine braking and brake gas recirculation during an engine braking mode of engine operation and variable degrees of early exhaust valve opening during a positive power mode of engine operation.

The interaction of the first and second half rocker arms701and702with each other and the lost motion system706is illustrated inFIG. 5. As shown inFIG. 5, the spring705may bias the second half rocker arm702away from the first half rocker arm701and into contact with the second motion imparting means103(shown inFIG. 3) by acting on flange760. Variations in the angle in which the spring705meets the flange760are contemplated to be within the scope of the present invention. For example, in some embodiments, the spring705may act almost directly downward on the second half rocker arm702over the cam roller708to save space by reducing the height of the spring-flange arrangement. When the second motion imparting means103provides a valve actuation motion, such as a main exhaust event actuation, to the second half rocker arm702, the second half rocker arm may, in turn, act on the first half rocker arm701to actuate the exhaust valves716for a main exhaust event. Because the first half rocker arm701is free to pivot away from the second half rocker arm702, the lost motion system706may also act on the first half rocker arm701to provide valve actuation events such as compression release engine braking, brake gas recirculation, and/or early exhaust valve opening independent of the pivoting of the second half rocker arm702.

FIG. 6is a schematic top view of a variable valve actuation system700in accordance with a third embodiment of the present invention, in which like reference characters refer to like elements. The first valve train assembly of the variable valve actuation system700may include a first (or main exhaust) rocker arm1002pivotally mounted on a rocker shaft718. The first rocker arm1002may include a cam roller708biased by a spring705which acts by pushing from a fixed stop762against a contact surface760provided on the first rocker arm so that the cam roller is maintained in relatively constant contact with a second motion imparting means103, such as a cam provided on a camshaft. The first rocker arm1002may include a valve actuation end1004adapted to contact and act on a valve bridge714which in turn may actuate engine valves such as exhaust valves716.

The second valve train assembly of the variable valve actuation system700shown inFIG. 6may further include a third half rocker arm704pivotally mounted on the rocker shaft718adjacent to the first rocker arm1002. The third half rocker arm704and the lost motion system706may include the same elements as the variable valve actuation system described in connection withFIGS. 3-5above, save for the design of the slave piston720.

The slave piston720shown inFIG. 6may be designed as illustrated inFIG. 7, for example. With reference toFIG. 7, the slave piston720may include two forks721which may extend downward from the slave piston on either side of the valve end1004of the first rocker arm1002and into contact with the valve bridge714. The forked slave piston720may apply valve actuation motions for compression release engine braking, early exhaust valve opening, and/or brake gas recirculation, for example, without interfering with and independent of the operation of the first rocker arm1002.

Further variable valve actuation system embodiments of the present invention are illustrated byFIGS. 8-12. With reference toFIGS. 8 and 10, in a fourth embodiment of the present invention, the first valve train assembly of the variable valve actuation system700may include a first half rocker arm701pivotally disposed on a rocker shaft718, similar to that described in connection withFIG. 3. The first half rocker arm701may be acted upon by a second half rocker arm (702inFIG. 8) to provide a main exhaust valve event in the same manner as the system described in connection withFIG. 3. The first half rocker arm701may include a valve-side end with an elephant foot or other contact surface712adapted to provide exhaust valve actuation motion for exhaust valves716through a valve bridge714. The first half rocker arm701may further include a side flange709which is adapted to receive exhaust valve actuation motion from a lost motion rocker arm.

With continued reference toFIG. 8and in connection with the fourth embodiment of the present invention, the second valve train assembly of the variable valve actuation system700may include a lost motion rocker arm900pivotally mounted on the rocker shaft718adjacent to the first half rocker arm701. The lost motion rocker arm900may include a cam roller910adapted to receive exhaust valve actuation motions from a first motion imparting means102which may provide valve actuation motions such as those required for a compression release engine braking event, an early exhaust valve opening event, and a brake gas recirculation event. The lost motion rocker arm900may be biased toward the first motion imparting means102by a spring972(shown inFIG. 11) which may create such bias force by pushing against a flange or contact surface970provided on the lost motion rocker arm from a fixed stop or flange974provided on a fixed engine part so that cam roller910may remain in relatively constant contact with the first motion imparting means102. A hydraulic actuator piston960may be provided in one end of the lost motion rocker arm900. The hydraulic actuator piston960may be selectively extended to engage a side flange709provided on the first half rocker arm701. A hydraulic circuit may be provided in the lost motion rocker arm900so that hydraulic fluid may be selectively supplied to and drained from the hydraulic actuator piston960. The hydraulic circuit may include a first hydraulic passage770connecting the hydraulic actuator piston960with the high-speed trigger valve736located in the adjacent rocker shaft pedestal719via hydraulic passages772and774provided in the rocker shaft718and rocker shaft pedestal, respectively. In turn, the trigger valve736may be connected to the accumulator722via a hydraulic passage776.

The hydraulic actuator piston960may be slidably disposed within a bore in the lost motion rocker arm900. The hydraulic actuator piston960may be sized to slide within its bore926while maintaining a relatively secure hydraulic seal with the wall of its bore. A vertically adjustable lash member or screw962(seeFIG. 10) may be slidably received within the actuator piston960. The stroke of the hydraulic actuator piston960may be limited by contact with a stop964on lash member962to provide travel slightly greater than the maximum valve lift due to the first motion imparting means102.

With reference toFIGS. 10 and 11, in a fifth embodiment of the present invention, the lost motion rocker arm900may include a central opening920for receipt of the rocker shaft, a first bore922for receipt of an accumulator722, a second bore924for receipt of a control valve950, and a third bore926for receipt of a hydraulic actuator piston960with a stop964to limit the maximum stroke of the hydraulic actuator piston. A hydraulic circuit may be provided in the full rocker arm900. The hydraulic circuit may include a first passage930connecting the central opening920with the second bore924, a second passage932connecting the central opening920with the first bore922, a third passage934connecting the first bore922with the second bore924, and a fourth passage936connecting the second bore924with the third bore926. As a result of the hydraulic circuit, hydraulic fluid that may be provided to the central opening from one or more hydraulic fluid passages (not shown) in the rocker shaft718may be provided to the accumulator722, the control valve950and the hydraulic actuator piston960.

The hydraulic actuator piston960may be slidably disposed within the third bore926. The hydraulic actuator piston960may be sized to slide within the third bore926while maintaining a relatively secure hydraulic seal with the wall of the third bore. A vertically adjustable lash member or screw962may be slidably received within the actuator piston960with a stop964to limit the maximum stroke of the hydraulic actuator piston.

The lost motion rocker arms900shown in bothFIGS. 8 and 11may act on the flange709shown inFIG. 10to transfer valve actuation motion through the first half rocker arm701to one or more engine valves716.

An example of the control valve described above in connection withFIG. 11is illustrated inFIG. 12. With reference toFIG. 12, the control valve950may include a control valve piston952and a control valve spring954which biases the control valve piston into the second bore924. The second bore924in which the control valve piston is disposed may be connected with the first, third and fourth passages930,934and936, respectively. The selective supply of hydraulic fluid to the first passage930may cause the control valve piston952to shuttle back towards the spring954so that an annular recess956in the control valve piston places the third passage934in hydraulic communication with the fourth passage936. Thus, selective supply of hydraulic fluid by a high-speed trigger valve to the first passage930can be used to selectively provide hydraulic fluid from the accumulator722to the actuator piston960and/or to selectively drain hydraulic fluid from the actuator piston960to the accumulator722. When hydraulic fluid pressure is decreased in the first passage930, the control valve piston952may be forced towards the first passage by the spring954so that the hydraulic fluid communication between the third and fourth passages934and936is cut off and the actuator piston960is hydraulically locked into a fixed position.

The interaction of the second half rocker arm702and the first half rocker arm701is illustrated by reference toFIGS. 8,10and11. A spring may bias the second half rocker arm702away from the first half rocker arm701and into contact with the second motion imparting means103. When the second motion imparting means103provides a valve actuation motion, such as a main exhaust event actuation, to the second half rocker arm702, the second half rocker arm may, in turn, act on the first half rocker arm701to actuate the exhaust valves716for a main exhaust event. Because the first half rocker arm701is free to pivot away from the second half rocker arm, the full rocker arm900may also act on the first half rocker arm701through the flange709to provide valve actuation events such as compression release engine braking, brake gas recirculation, and/or early exhaust valve opening independent of the pivoting of the second half rocker arm.

The interaction of the full rocker arm900, the hydraulic actuator piston960and the first half rocker arm701is illustrated by reference toFIGS. 8,10-12. A spring972may bias the full rocker arm900into contact with the first motion imparting means102. As shown inFIGS. 11 and 12, a control valve950, which may operate under the control of a high-speed solenoid trigger valve (not shown) may be provided in the hydraulic circuit including passages930,932,934and936such that the control valve may control the supply of hydraulic fluid to and from the actuator piston960. Further, the accumulator722may include an accumulator piston spring724(FIG. 4) that biases an accumulator piston726(FIG. 4) into an accumulator bore. When the control valve950is maintained closed, hydraulic fluid may be trapped in the third bore926so that the actuator piston960is prevented from being pushed into the third bore. Conversely, when the control valve950is maintained open, hydraulic fluid may flow freely out of the third bore926and into and out of the accumulator722. When the control valve950is maintained open and the first motion imparting means102(FIG. 8) causes the full rocker arm900to pivot about the rocker shaft718, the actuator piston960is forced against the flange709. Because the control valve950is open, however, the actuator piston960is forced into the third bore926and the hydraulic fluid in the third bore is pushed back in the hydraulic circuit and absorbed by the accumulator722. When the control valve950is closed, however, and the first motion imparting means102(FIG. 3) causes the full rocker arm900to pivot about the rocker shaft718, the actuator piston960is hydraulically locked into position and the motion from the motion imparting means is transferred through the actuator piston to the flange709and from the flange to the first half rocker arm701. In turn the half rocker arm701may act through the valve bridge714to actuate or open the exhaust valves716. Use of the first motion imparting means102, such as a cam with a compression release engine braking lobe, an early exhaust valve opening lobe, and/or a brake gas recirculation lobe, coupled with selective operation of the control valve950may enable selective provision of compression release engine braking and brake gas recirculation during an engine braking mode of engine operation and variable degrees of early exhaust valve opening during a positive power mode of engine operation.

The sixth embodiment of the present invention consists of a variation of the second embodiment wherein the fixed housing lost motion system706described in connection withFIGS. 3-5is substituted for the lost motion rocker arm900described above. The sixth embodiment is illustrated inFIG. 9, in which like reference characters correspond to like elements described in connection with the foregoing embodiments. In the sixth embodiment of the present invention, the slave piston720may selectively provide exhaust valve actuation motions, such as those for a compression release engine braking event, an early exhaust valve opening event, and/or a brake gas recirculation event to a side flange709extending from the side of the first half rocker arm701, as shown inFIG. 9.

FIG. 13illustrates a first cam profile302,304,306and308corresponding to the lobes on the cam200, and a second cam profile300with a main exhaust lobe. The first cam profile may be used to provide the first motion imparting means with one or more auxiliary exhaust valve actuation motions and the second cam profile may be used to provide the second motion imparting means with a main exhaust valve actuation motion. In a preferred embodiment, the cam200may include a compression release lobe302, an early exhaust valve opening lobe304with a closing ramp306, and a brake gas recirculation lobe308. The first cam profile inFIG. 3may include, starting from the left, the compression release lobe302leading into the early exhaust valve opening lobe304, followed by a flat cam segment and a closing ramp306which meets the cam base circle307before the end of the main exhaust cam lobe300. The first cam profile may further include a brake gas recirculation (BGR) or exhaust gas recirculation (EGR) lobe308.

FIGS. 14-16illustrate the exhaust valve lifts that may be provided using the first and second cam profiles illustrated inFIG. 13in combination with the variable valve actuation systems described in connection with FIGS.1and3-12which may selectively transfer motion from the cam200to the exhaust valve(s). The trigger valve or control valve operation to provide three different sets of exhaust valve actuations are also illustrated inFIGS. 14-16. InFIGS. 14-16, a state of “0” indicates that the trigger or control valve is closed and the lost motion master-slave system (FIGS. 3-7and9) or the lost motion rocker arm system (FIGS.8and10-12) is in a state in which valve actuation motion is transferred to the exhaust valves from the first motion imparting means. A state of “1” indicates that the trigger or control valve is open and the lost motion master-slave system or the lost motion rocker arm system is in a state in which the valve actuation motion applied by the first motion imparting means is absorbed.

With reference toFIG. 14, during an engine braking mode of engine operation and when the trigger or control valve is initially in state “0”, or closed, the lost motion master-slave or rocker arm system may transfer motion from the compression release cam lobe302(FIG. 13) to produce a compression release valve event302′. When the compression release valve event is completed, at about (0) crank angle degrees (i.e., top dead center compression) the trigger or control valve may be opened to release hydraulic pressure in the master-slave circuit or actuator piston and close the exhaust valves. Thereafter the exhaust valves may be opened for the main exhaust event300′ by the second motion imparting means. At about (450) crank angle degrees (i.e., after the end of cam segment306) the trigger or control valve may be closed again so that the lost motion master-slave or rocker arm system may transfer motion from the brake gas recirculation lobe308(FIG. 13) to produce a brake gas recirculation valve event308′. Refill of the lost motion hydraulic circuit may occur between about (130) and (450) crank angle degrees, depending on whether a master-slave system or a rocker arm system is being used.

With reference toFIG. 15, during a first positive power mode of engine operation and when the trigger or control valve is initially in state “1”, or open, the lost motion master-slave or rocker arm system may absorb the motion received from the compression release cam lobe302(FIG. 13) of the first motion imparting means so that the exhaust valves remain initially closed. After the compression release cam lobe is passed, at about (0) crank angle degrees the trigger or control valve may be closed so that the lost motion master-slave or rocker arm system may transfer motion from the early exhaust valve opening lobe304(FIG. 13) to produce an early exhaust valve opening event304′. Thereafter, the main exhaust valve motion from the second motion imparting means may take over to provide the remainder of the actuation required for the main exhaust valve event300′. After about (130) or about (270) crank angle degrees, depending on whether a master-slave or rocker arm system is used, the trigger or control valve may be opened again for hydraulic circuit refill so that the lost motion master-slave or rocker arm system may absorb the motion from the brake gas recirculation lobe308(FIG. 13) of the first motion imparting means.

With reference toFIG. 16, during a second positive power mode of engine operation and when the trigger or control valve is initially in state “1”, or open, the lost motion master-slave or rocker arm system may absorb the motion received from the compression release cam lobe302(FIG. 13) of the first motion imparting means so that the exhaust valves remain initially closed. After the compression release cam lobe is passed, at about (45) crank angle degrees the trigger or control valve may be closed so that the lost motion master-slave or rocker arm system may transfer motion from the early exhaust valve opening lobe304(FIG. 13) to produce an abbreviated early exhaust valve opening event304″. Thereafter, the main exhaust valve motion from the second motion imparting means may take over to provide the remainder of the actuation required for the main exhaust valve event300″. After about (130) or about (270) crank angle degrees, depending on whether a master-slave or rocker arm system is used, the trigger or control valve may be opened again for hydraulic circuit refill and so that the lost motion master-slave or rocker arm system may absorb the motion from the brake gas recirculation lobe308(FIG. 13) of the first motion imparting means.

Embodiments of the present invention may have many advantages, including providing variable engine braking, brake gas recirculation, and variable early exhaust valve opening for exhaust gas temperature control for emissions after-treatment and/or turbo stimulation for improved transient torque. Additional advantages may include a mechanically-driven exhaust main event for cold start and failsafe, meeting loading limits, especially cam Hertz stress, avoiding separation and impact loading between cams and rollers, avoiding valve bridge tilt, meeting exhaust valve seating velocity limits, and protecting against valve-piston contact.

It will be apparent to those skilled in the art that variations and modifications of the present invention can be made without departing from the scope or spirit of the invention. For example, it is appreciated that selective control of the trigger valve or control valve operation may produce engine valve actuations with timing other than those illustrated inFIGS. 14-16. Further, it is appreciated that the variable valve actuation systems described in connection withFIGS. 1-12may be used to actuate not only exhaust valves, but also intake and/or auxiliary engine valves. Thus, it is intended that the present invention cover all such modifications and variations of the invention, provided they come within the scope of the appended claims and their equivalents.