Lost motion variable valve actuation system and method

Abstract

A compact, modular lost motion variable valve actuation assembly includes a dry start hydraulic circuit to enable rapid activation of a lost motion master-slave circuit from a dry start reservoir to a master piston chamber during engine starting. Movement of the master piston during engine starting can draw fluid from the dry start hydraulic circuit. The dry start assembly can be integrated into a compact modular rocker shaft base package suitable for retrofitting existing engine cylinder head assemblies. The master piston can include a push tube interface including a deep push tube cavity and lubrication capability in the master piston, the push tube interface providing improved wear resistance, stability, assembly and ease of alignment. The slave piston can be provided with a valve stop to reduce valve closing speed during cycles involving lost motion.

Description

[0001] This application is a divisional application of the invention patent application with application number: 201980059033.4 and invention name: "Lost Motion Variable Valve Actuation System and Method" filed on September 10, 2019.

[0002] Related applications and priority claims

[0003] This application claims priority to U.S. Provisional Patent Application Serial No. 62 / 729,214, filed on September 10, 2018, entitled “LOST MOTION HYDRAULIC VARIABLE VALVE ACTUATION SYSTEM AND METHOD,” the subject matter of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present disclosure generally relates to systems and methods for actuating one or more engine valves in an internal combustion engine. Specifically, embodiments of the present disclosure relate to systems for achieving reliable and fully operational variable valve actuation (VVA) assemblies immediately after a dry start of an engine. Embodiments of the present disclosure also relate to systems having modular and compact packaging for additional VVA assemblies. Embodiments of the present disclosure further relate to systems for docking valvetrain components (such as push tubes) with master pistons and other components in a master-slave VVA assembly. Embodiments of the present disclosure also relate to systems for controlling the speed of valvetrain components in a lost motion system (such as self-adjusting valve stops in a master / slave piston assembly used in a lost motion VVA device). Background Art

[0005] Internal combustion engines are commonly used in many applications and industries, including transportation and handling. These engines utilize engine valve actuation systems that primarily facilitate a positive power operating mode, in which the engine cylinders generate power from the combustion process. The intake and exhaust valve actuation motions associated with a standard combustion cycle are often referred to as "main event" motions. Known engine valve actuation systems can provide improved main event valve motions, such as early or late intake valve closing. In addition to main event motions, known engine valve actuation systems can also facilitate auxiliary valve actuation motions or events that allow the internal combustion engine to operate in other modes or variations of positive power generating modes (e.g., exhaust gas recirculation (EGR), early exhaust valve opening (EEVO), etc.) or in engine braking, in which the internal combustion engine essentially operates as an air compressor in a defueled state to generate retarding power to assist in decelerating the vehicle. Furthermore, variations of valve actuation motions for providing engine braking are known (e.g., brake gas recirculation (BGR), bleeder braking, etc.).

[0006] For both main-event and auxiliary-event valve operation, the engine cylinder intake and exhaust valves can be opened by respective fixed-profile cams having fixed lobes that interact with the respective valve trains. However, the use of fixed-profile cams may have limitations. For example, the use of fixed-profile cams may restrict valve motion or preclude adjustments to valve motion, such as valve timing and lift, which are necessary for optimal main-event and auxiliary valve operation under different engine operating modes, speeds, and conditions.

[0007] VVA systems have been developed in the prior art to overcome the limitations associated with fixed-cam valve actuation systems. VVA systems may include lost motion components to facilitate operation of internal combustion engines in positive power and engine braking modes. Lost motion is a term applied to a class of technical solutions in which the valve motion controlled by a cam profile can be modified with variable-length mechanical, hydraulic, or other linkages in the valve train. Lost motion components are well known in the art. These devices typically include an element that can collapse or change its length or engage / disengage adjacent components within the valve train in a controlled manner to alter the valve motion. Lost motion devices can facilitate certain valve actuation motions during the engine cycle that are different from the motion determined by a fixed-profile valve actuation motion source, such as a rotating cam. The lost motion device can selectively "lose" this motion, i.e., not transmit it to one or more engine valves via the valve train, in order to achieve an event that is a supplement to or a variation of the main event valve motion. In a VVA lost motion system, the cam lobe angle can dictate the "maximum" (longest dwell and maximum lift) motion required for the entire range of engine operating modes and conditions. A variable length system may be incorporated into the valvetrain, intermediate the valve to be opened and the cam, to reduce or "lose" a portion of the motion that would otherwise be imparted to the valve by the cam.

[0008] Unfortunately, despite the advantages that known VVA lost motion systems may offer, their implementation may face numerous challenges in the art in certain aspects. For example, during a dry or cold start of an engine, the working hydraulic components of known VVA lost motion systems may be depleted of hydraulic fluid (oil), which may drain from the components after engine operation ceases. This loss of hydraulic fluid may require several engine cycles and / or engine warm-up upon engine restart before full functionality of the VVA lost motion system is achieved.

[0009] Other needs in the art relate to a desired VVA lost motion assembly that can be easily assembled and / or assembled as an add-on component into an existing engine configuration to provide the benefits of a compact and modular configuration of a VVA lost motion system. Modularity can provide the benefits of ease of handling, shipping, and assembly. Relatedly, there is a need for a compact, modular package for a VVA lost motion assembly that can be easily integrated with an existing engine structure and provide for retention of the components of the assembly prior to assembly.

[0010] Overhead valve engine configurations can utilize push tubes or push rods in the engine's valvetrain. These components interface with the master piston on a master / slave VVA lost motion assembly. During assembly, existing VVA lost motion assemblies can require significant labor to align the push tube with the corresponding kinematic interface on the master piston or other components in the VVA lost motion assembly. Furthermore, in addition to misalignment, existing push tube interface configurations are prone to excessive friction and wear, poor lubrication, and less than optimal stability during operation.

[0011] Known lost motion VVA systems also face further challenges in controlling the valve closing motion (i.e., valve closing speed). Because lost motion components in the valve train may cause the engine valve motion to differ from the motion dictated by the associated cam surfaces, such as in delayed intake valve closing, the valve may have excessive closing speed, which, without appropriate control devices, may cause the valve to "bang" into its valve seat. Valve stops, such as that disclosed in U.S. Patent No. 6,474,277, the subject matter of which is incorporated herein by reference in its entirety, have been developed in the prior art to address the problem of excessive valve closing speed in lost motion systems. However, such systems may not provide optimal control in some VVA environments. For example, such systems may require components to be manufactured with very low tolerances, which can be expensive. In addition, when utilized in a master / slave piston assembly, such systems may exhibit high hydraulic resistance between the master piston and the slave piston.

[0012] It would therefore be advantageous to provide systems and methods that address the above-referenced and other shortcomings in the prior art. Summary of the Invention

[0013] In response to the aforementioned challenges, the present disclosure provides various embodiments of VVA assemblies and other components having improved features and advantages.

[0014] According to one aspect of the present disclosure, an engine valve actuation assembly is provided that provides rapid filling of a lost motion VVA assembly after a dry start of an engine. A system for providing variable valve actuation in an engine valve train may include: a housing; a master piston bore defined in the housing; a master piston cooperating with the master piston bore to define a master piston chamber; the master piston having a motion receiving interface for receiving motion from a motion source in the valve train; a slave piston bore defined in the housing; a slave piston cooperating with the slave piston bore to define a slave piston chamber; the slave piston having a motion transfer interface for transferring motion to a motion receiving assembly in the valve train; and a dry start hydraulic circuit cooperating with the master piston chamber for supplying working fluid to the master piston chamber during an engine start cycle.

[0015] The dry start hydraulic circuit facilitates rapid delivery of hydraulic fluid to the master-slave circuit in the lost motion VVA assembly. During the initial dry start cycle of the engine and VVA assembly, the master piston is used to generate a lower pressure in the initially empty VVA system hydraulic circuit, thereby drawing oil from the dry start reservoir into the master-slave circuit through the high-pressure check valve. The configuration of the dry start reservoir, along with the low-pressure and high-pressure check valves in the dry start hydraulic circuit, ensures that the dry start reservoir maintains a supply of hydraulic fluid that does not leak downward (deplete) when the engine is not operating. Additionally, the accumulator in the dry start hydraulic circuit is configured with a drain orifice that is blocked when the accumulator piston bottoms out in the bore, which occurs during the initial engine dry start. This further ensures that the dry start hydraulic circuit maintains sufficient hydraulic fluid in the dry start reservoir to quickly achieve full functionality of the lost motion master-slave circuit when the engine is restarted.

[0016] According to one aspect of the present disclosure, a master piston of a VVA assembly can be provided with advantageous features to ensure operational stability and durability of a motion receiving interface, such as a master piston / push tube interface for the VVA assembly. An engine valve actuation assembly for providing variable valve actuation in an engine valve train can include: a housing; a master piston bore defined in the housing; a master piston cooperating with the master piston bore to define a master piston chamber; the master piston having a motion receiving interface for receiving motion from a motion source in the valve train; a slave piston bore defined in the housing; a slave piston cooperating with the slave piston bore to define a slave piston chamber; the slave piston having a motion transfer interface for transferring motion to a motion receiving component in the valve train; wherein the master piston motion receiving interface includes a push tube receiving socket in the master piston for receiving an end of a push tube, the push tube receiving socket extending within the master piston to a sufficient depth such that the push tube end remains positioned in the master piston bore throughout operation. The push tube can be provided with a push tube cap that is slightly rounded on its end wall. The push tube can extend into the depth of the push tube receiving socket formed on the main piston by the end of the push tube (or push tube cap) being very close to the high-pressure surface of the main piston. In this way, the force applied by the push tube end is very close to the force applied to the high-pressure surface of the main piston, thereby reducing the possibility of generating torque and the resulting lateral load on the main piston and / or the push tube and end cap. This reduces the lateral force on the push tube and the main piston, provides more stable operation and reduces friction losses and wear.

[0017] According to another aspect, the motion receiving interface on the VVA assembly is provided with features for enhancing lubrication and reducing contact stress. Features are provided for collecting high-pressure hydraulic fluid at the push tube / master piston interface. This fluid may flow due to leakage from the master piston. An annular groove and one or more radially extending ports formed in the push tube cap can collect oil during operation and transfer the oil to the internal master piston push tube socket, thereby lubricating the inside of the master piston and the push tube and / or end cap. Contact stress can be reduced by an axisymmetric concave surface formed in the end wall of the master piston push tube socket and an axisymmetric convex surface with a smaller radius formed on the end of the push tube cap. This configuration provides a centering force relative to the master piston socket on the push tube during operation, and further ensures correct alignment and minimum side load of the push tube end cap and the master piston.

[0018] According to one aspect, the VVA system can be provided as a modular, integrated package that includes components of a dry starting hydraulic circuit and a primary piston push tube interface located in a compact manner in a VVA housing, which can be in the form of a rocker arm base and can be fitted or modified to the engine as an integral assembly using minimal fasteners and assembly resources.

[0019] According to one aspect, a VVA system can be provided with a self-adjusting valve catch (SAVC) to control the closing speed of the slave piston, and thereby the closing speed of one or more engine valves. The valve catch seat can be secured within a complementary-shaped valve catch seat recess formed within the housing between the slave piston bore and the master piston bore. The valve catch seat can include a central channel surrounded by an annular seating surface. The slave piston can include an internal cavity for receiving a control pin, which is provided with a control pin collar. The control pin collar allows guided movement of the control pin within the cavity, thereby maintaining the control pin in the center. The control pin collar includes an upper spring guide that cooperates with a control pin spring and a lower spring guide that cooperates with a check disc spring. The control pin spring provides a downward (seating) bias on the control pin relative to the slave piston. The check disc spring provides a downward (seating) bias on the check disc relative to the position of the control pin collar. During the valve catch operating mode, the port in the control pin can be gradually blocked by the check disc. When the engine valve approaches the engine valve seat, particularly when flow through a high-speed solenoid valve decouples the cam, the check disc can seat, causing oil from the slave piston's pressurization chamber to flow through multiple holes in the control pin, which are blocked by the metering edge of the check disc. As the control pin descends, the control pin holes gradually become blocked, causing slave piston pressure to increase, which slows the engine valve and associated valvetrain components. The slave piston can be provided with an automatic lash chamber between the top of the slave piston hole and the control pin collar. The automatic lash chamber can be filled by oil leakage through the slave piston control collar. When the engine valve seats on the valve seat, the leak-filled automatic lash ensures that the control pin seats on the valve detent. The SAVC ensures that as the control pin approaches the seating surface, the closing speed of the control pin, and therefore the closing speed of the slave piston and the engine valve, does not exceed acceptable levels. According to another aspect of the present disclosure, the guide features of the check disc spring and the control pin ensure that the control pin port is not contacted by the spring, thereby preventing wear on the port edge by the spring.

[0020] Other aspects and advantages of the present disclosure will be apparent to those skilled in the art from the detailed description below, and the above aspects should not be considered exhaustive or limiting. The foregoing general description and the following detailed description are intended to provide examples of the inventive aspects of the present disclosure and should in no way be interpreted as limiting or defining the scope defined in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other attendant advantages and features of the present invention will become apparent from the following detailed description and accompanying drawings, in which like reference numerals represent like elements throughout. It will be understood that the description and examples are intended as illustrative examples according to aspects of the present disclosure and are not intended to limit the scope of the invention, which is set forth in the appended claims. In the following description of the drawings, unless otherwise indicated, all illustrations relate to features of examples consistent with various aspects of the present disclosure.

[0022] Figure 1 is an illustration of an example modular lost motion VVA (LMVVA) assembly and an example engine valvetrain environment.

[0023] Figure 2 yes Figure 1 Illustration of an example modular LMVVA assembly shown in .

[0024] Figure 3 yes Figure 2 Detailed illustration of components of an example LMVVA assembly shown in .

[0025] Figure 4 yes Figure 2 Illustration of additional components and lower mounting surface of the example LMVVA assembly shown in .

[0026] Figure 5 is an exploded view of an exemplary LMVVA assembly and its components.

[0027] Figure 6 yes Figure 5 Another exploded perspective view of the LMVVA assembly and its components.

[0028] Figure 7 is a schematic diagram of an exemplary hydraulic dry starting circuit that may be used in applications such as Figures 1 to 6 is implemented in the LMVVA assembly shown.

[0029] Figure 8 yes Figures 1 to 6 A cross-sectional view of the LMVVA assembly is shown.

[0030] Figure 9 yes Figures 1 to 6 Another cross-sectional view of the LMVVA assembly is shown.

[0031] Figure 10 yes Figures 1 to 6 A third cross-sectional view of the LMVVA assembly is shown.

[0032] Figure 11 yes Figures 1 to 6Detailed cross-sectional view of an example LMVVA assembly from the piston and valve assembly.

[0033] Figure 12 It is applicable to Figures 1 to 6 Cross-sectional view of an exemplary piston / push tube interface assembly used in an LMVVA assembly.

[0034] Figure 13 yes Figure 12 Detailed cross-section of the main piston / push tube interface assembly. DETAILED DESCRIPTION

[0035] As used herein, the term "fluid communication" is intended to refer to a relationship between two or more elements or components through which a fluid may flow continuously, intermittently or selectively, and is not necessarily limited to direct, constant flow between such elements or components, but may involve the flow of fluid through an intermediate component, such as through a check valve, which may be disposed intermediate between the two or more components described as being "in fluid communication."

[0036] Figure 1 An example modular lost motion VVA assembly 100 is shown in the context of an engine valvetrain. A motion source, shown in the form of a lost motion VVA cam 10, can impart motion to one or more motion-receiving components, which in this example may be a cam follower 12, journaled in a cam follower arm 14, which may be pivotally mounted to allow the cam follower 12 to follow the working surface or profile of the cam 10. The cam follower 12 cooperates with a pushrod 20, which extends upward and can interact with a master piston assembly 200 on the VVA assembly 100. The pushrod 20 can extend into a pushrod cap 22, which in turn can extend into a master piston 210 of the master piston assembly 200. The master piston 210 can interact with a slave piston 310 of a slave piston assembly 300 to provide lost motion, as will be further described. The slave piston 310 can impart motion to a rocker arm 30 via a rotating foot or "e-foot" 32 extending therefrom. The rocker arm 30 may impart motion to one or more engine valves 50 , 52 via a valve bridge 40 .

[0037] As will be appreciated from this disclosure, the VVA assembly 100 may be secured to an engine cylinder head assembly (for clarity, see FIG. Figure 1 The VVA assembly 100 may include an integrated structure for supporting a rocker shaft 35 that supports the rocker arm 30 for pivotal movement, as will be further described.

[0038] Additional references Figures 2 to 4According to various aspects of the present disclosure, the VVA assembly 100 can have a compact, modular construction. This construction allows multiple components to be integrated into the VVA housing 110 in a manner that allows the VVA assembly to be installed as an add-on component without interfering with other components that may be nearby in the engine cylinder head environment. The housing 110 can be configured for attachment to an existing base or post extending from the engine cylinder head. The components integrated into the VVA assembly can include a rocker shaft support 112, a master piston assembly 200, a slave piston assembly 300, and a dry starting subsystem 400. As will be further described, the dry starting subsystem 400 can include a dry starting hydraulic circuit that provides fluid communication between a dry starting reservoir 410, a high-speed solenoid valve (HSSV) 420, an accumulator 430, a high-pressure check valve 450, a low-pressure check valve 460, and a hydraulic fluid path connecting them and extending within the housing 110. As will be described, these and other components are advantageously positioned and integrated into the VVA assembly housing 110 to provide a modular and compact VVA package that can be conveniently shipped and assembled as a modular unit.This VVA package configuration achieves the advantages described herein and other advantages.

[0039] Figure 5 and 6 According to various aspects of the present disclosure Figures 1 to 4 Exploded view of an exemplary VVA assembly 100. The housing 110 may include a rocker shaft support hole 114 disposed on a rocker shaft support 112. Mounting holes 116 may extend through the housing 110 and receive fasteners (i.e., bolts) for securing the housing 110 to a mounting surface within an engine cylinder head assembly (not shown). A pair of alignment pins 111 may be disposed in corresponding alignment pin holes 113 in a mounting surface 115 on the underside of the housing 110 to facilitate stable, aligned installation and assembly. The housing 110 may include an HSSV hole 120 for receiving a valve head 426 of the HSSV 420. A mounting bracket 422 and bracket fasteners 424 may secure the HSSV 420 to the housing 110. As will be appreciated, the HSSV bore 120 can include one or more fluid passages 122 in communication with the bore for transferring hydraulic fluid to / from the bore 120 and, in the valve's open state, through or past the valve head 426 of the HSSV 420. According to aspects of the present disclosure, a dry starting reservoir 410 can be defined within the housing 110 and sealed (i.e., via a threaded connection or a press-fit seal) with a reservoir cap 412. The reservoir cap 412 can have a reservoir drain orifice 414 therein for allowing hydraulic fluid to drain from the reservoir to the surrounding environment. This configuration offers manufacturing advantages, particularly for large, single cylinder heads.

[0040] The master piston 210 may include an annular collar or shoulder 212 extending about a lower portion thereof and a master piston socket 217 ( Figure 6 ). The annular shoulder 212 can define a spring seat for the primary piston spring 250. Another spring seat surface 123 can be defined on the housing 110 around the primary piston bore 120 for engaging the opposite end of the spring 250. The primary piston 210 can include an outer groove 213, which has a plurality of radially extending ports 215 defined therein, for communicating oil from the exterior of the primary piston 210 to the internal socket 217 for enhancing lubrication of the push tube / primary piston interface using primary piston leakage, as will be further described herein. The primary piston retainer 260 can include a threaded fastener that can be secured to the housing 110 so that the bolt head 262 can engage and retain the annular shoulder 212 of the primary piston 210, thereby securing the primary piston 210 and spring 250 in an assembled position on the housing 110. As will be appreciated from this disclosure, this configuration allows the master piston 210 and spring 250 to be secured to the housing 110 during assembly, wherein the master piston 210 is maintained in a fully inserted position relative to the master piston bore 120, for example, and the spring 250 is compressed. As will be appreciated from this disclosure, once the VVA assembly is assembled, the master piston spring 250 is advantageously secured to the housing 110. Figure 1 ) and provides cam following of the master piston, push tube 20, and cam follower regardless of the operation of the master-slave lost motion assembly of the VVA assembly. Specifically, the master piston 210 will follow the cam closing profile during dry starting, so that the master piston will act as a pump to draw oil from the dry starting reservoir into the high pressure circuit.

[0041] Still refer to the attached Figure 5 and 6 , the slave piston assembly 300 can be assembled in the slave piston bore 130, which allows the slave piston assembly 300 to interact with the master piston 210 and transmit motion to the motion receiving component (ie, Figure 1 The slave piston assembly 300 may include a self-adjusting valve control (SAVC) system to control the engine valve closing speed. The following will explain the details of the master / slave piston interaction and SAVC according to various aspects of the present disclosure.

[0042] The accumulator assembly 430 can be assembled in the accumulator bore 140 provided in the housing. The accumulator assembly can include an accumulator piston 432 having a sealing surface 433 on its end wall and a central relief orifice 435 centered within the sealing surface 433. An accumulator spring 434 can be housed within the interior of the accumulator piston 432 and engage the piston end wall. The accumulator assembly 430 can be retained in the accumulator bore 140 of the housing 110 by a C-clip retainer 438, which also retains a spring seat / washer 436, which engages the end of the accumulator spring 434 opposite the piston end wall. The accumulator assembly 430 is used to accumulate a pressurized supply of hydraulic fluid during normal (steady-state) engine operation, wherein the piston moves against the biasing force of the spring 434 until equilibrium is reached and a quantity of oil is accumulated in the chamber defined by the piston 432 and the bore 140. According to one aspect of the present disclosure, the bleed orifice 435 provides hydraulic fluid flow through the accumulator piston 432 for removing heat generated primarily in the valve train and HSSV. Although the dry start reservoir bleed orifice can provide some bleed cooling, the reservoir bleed cooling orifice 435 can be more effective because the hot oil from the high pressure circuit flows primarily to the reservoir. However, according to another aspect of the present disclosure, and as described below with reference to Figure 7 Explained in more detail, when engine operation is stopped, and during a dry start (restart) cycle, the biasing force of spring 434 will move piston 432 into engagement with the end wall of bore 140 , thereby preventing any flow through bleed cooling orifice 435 .

[0043] Two check valves associated with the dry starting hydraulic system may be mounted in housing 110. A low-pressure check valve (LPCV) 440 may be disposed in low-pressure check valve bore 170, having ports therein for allowing fluid communication between the LPCV and other system components. A high-pressure check valve (HPCV) 450 may be disposed in high-pressure check valve bore 150, also having ports therein for allowing fluid communication between the HPCV 450 and other system components.

[0044] Figure 7 is a schematic diagram of an exemplary dry starting hydraulic circuit 700 that may be implemented as a dry starting subsystem 400 ( Figures 2 to 4) to achieve the advantages described herein. The hydraulic circuit can be implemented in part as a series of conduits or channels disposed in the housing and providing fluid communication between the components depicted in the schematic diagram (i.e., accumulator, check valve, HSSV). According to one aspect, all of the components and conduits or channels can be integrated into the housing to provide a modular assembly that can be retrofitted to an existing engine, for example, as a replacement or supplement to a rocker arm base. The master piston chamber 214 can be defined by a master piston 210, which is disposed in a master piston bore 120 defined in the housing 110. The high pressure hydraulic sub-circuit 710 can include a first fluid passage from the master piston chamber 214 to the HSSV 420, which can be a normally open solenoid valve that closes when energized, and a second fluid passage 714 from the master piston chamber 214 to the high pressure check valve 450. The low-pressure hydraulic sub-circuit 720 may include a low-pressure check valve 440 disposed in a fluid passage 722 that provides engine oil to the VVA assembly HSSV 420, a dry starting reservoir 410 having a cap 412 and an orifice 414, and a reservoir 430 having a reservoir piston 432, a sealing surface 433, and a bleed cooling orifice 435. The dry starting reservoir is preferably located near the HPCV in the hydraulic circuit. As will be appreciated, the low-pressure hydraulic sub-circuit 720 is selectively isolated from the high-pressure hydraulic sub-circuit 710 by the check valve 450 and the HSSV 420.

[0045] During normal engine operation, the high speed solenoid valve 420 can be energized and therefore closed before the cam lift begins. In this configuration, the main piston 210 and the push tube 20 ( Figure 1 ) can almost follow the profile of the cam 10. Due to the hydraulic compliance in the master-slave piston assembly, the slave piston 310 and therefore the valve bridge 40 and the intake valves 50, 52 ( Figure 1) can have a lower opening lift. During normal operation, the high-speed solenoid valve 420 can be intermittently de-energized and therefore open to achieve the desired intake valve closing timing. As the slave piston closes, fluid flows from the slave piston chamber to the master piston chamber 214 and through the high-speed solenoid valve 420 to the accumulator 430. The accumulator 430 and the reservoir 410 are each provided with a discharge flow through the accumulator discharge orifice 412 and the accumulator discharge cooling orifice 435, which is discharged to the ambient environment. Below a threshold intake valve lift, for example, 3.0 mm, a self-adjusting valve control (SAVC) in the slave piston assembly 300 (the details of which will be explained) can provide a reduced valve seating velocity by gradually throttling the flow out of the slave piston pressurization chamber. The SAVC can cause the slave piston pressure to rise, thereby providing a force acting through the valve rocker arm to slow the intake valve to an acceptable seating velocity. The high pressure circuit 710 is refilled on the closing portion of the cam, and oil flows from the accumulator to the master piston through the HSSV and HPCV. When the accumulator pressure drops below the VVA supply pressure, the refilled oil can flow from the VVA supply to the accumulator 430 and the reservoir 410.

[0046] During engine shutdown, HSSV 420 opens, the valve spring closes the engine valve, and as oil flows out of the high-pressure circuit through HSSV 420, the slave piston retracts to the top of the slave piston bore. As oil flows out of the low-pressure circuit through accumulator drain cooling orifice 435, accumulator spring 434 retracts accumulator piston 432. The amount of oil in the high-pressure circuit during engine shutdown varies depending on the position of the master piston, with the minimum amount depending on cam peak lift. If the engine is shut down for an extended period, additional oil may leak from the hydraulic circuit. Because the LPCV, HPCV, and accumulator drain cooling orifice 435 are closed, oil remains in the dry start reservoir.

[0047] During a dry start, the initial condition will typically be with the intake valves closed and the cams may be at any lift, and the hydraulic circuit may have little or no oil other than the dry start reservoir 410. This is because a VVA system drain may occur after engine shutdown. Therefore, the worst case scenario for VVA refill occurs when the cams are at peak dwell, with no hydraulic fluid in the master-slave circuit. When the VVA supply oil pressure in passage 722 is lower than the pressure required to actuate the piston of the accumulator 430, the accumulator drain cooling orifice 435 is blocked by the accumulator piston and therefore oil cannot be drained from the accumulator. As will be appreciated from this disclosure, the accumulator spring 434 may be fitted with a preload to ensure that the accumulator piston 432 remains bottomed in the accumulator bore 149 when the oil pressure is at a level sufficient to refill the high pressure circuit. The accumulator spring preload is set to hold the accumulator piston on top of the bore only during dry starting when the oil supply pressure is between ambient pressure and a level significantly lower than the minimum oil supply pressure at low idle and insufficient to refill the high pressure circuit. In other words, the accumulator piston refill pressure will typically be set to a pressure higher than that required to refill the high pressure circuit.

[0048] HSSV 420 remains in the closed position during a dry start to retain oil in the high-pressure circuit 710. As the engine cranks during starting, the master piston reciprocates within the master piston chamber, generating a pressure in the master piston boost chamber sufficiently below ambient pressure to overcome the HPCV's rupture pressure, typically 0.3 bar. This allows the master piston to draw oil from the dry start reservoir 410 through HPCV 450. The dry start reservoir is located near the HPCV to avoid overcoming the LPCV's rupture pressure, which could draw air into the system. The accumulator piston rests on the top of the bore, thereby blocking the bleed cooling orifice 435. During the cam's open profile, the master piston check valve closes, and any oil in the master piston is pumped to the slave piston. When the slave piston is fully filled, the engine valve is actuated. During subsequent cycles, more oil is drawn from the reservoir through the master piston on the cam's closed profile. Therefore, as more oil is drawn into the master piston chamber, the intake valve lift will be full cam lift, with progressively less clearance (increasing lift) in each cycle. In this way, the lost motion system can quickly reach a state after engine start in which the master-slave piston assembly receives sufficient hydraulic fluid to provide full VVA cam lift, rather than operating for an extended period in a dry start (i.e., insufficient hydraulic fluid in the master-slave piston assembly to allow full operation).

[0049] In a preferred embodiment, the dry start reservoir will be located at a higher elevation than the main piston port. However, because the system can overcome small head pressure differences between the reservoir and the main piston port, other relative heights of the dry start reservoir can be implemented within the VVA housing 110. As will be appreciated from this disclosure, the HPCV provides an advantage in the dry start hydraulic circuit, namely, the presence of the HPCV allows the HSSV to be closed during a dry start, and the HPCV can be used to fill and retain oil in the high-pressure circuit. In other words, without the HPCV, it would be necessary to control the HSSV during a dry start, opening during cam closing to allow oil to be drawn from the dry start reservoir into the high-pressure circuit, and closing during cam opening and during any peak dwell to retain oil in the high-pressure circuit.

[0050] Figures 8 to 10 is through Figures 1 to 7 FIG. 1 is a cross-section of an example VVA assembly taken at different planes and further illustrating details of an example master piston assembly 200 and a slave piston assembly 300 . Figure 8 4 is a view from the side of the housing 110 with the accumulator 430 integrated therein. This view also shows further details of the master piston assembly 200, including the master piston 210, the master piston chamber 120, the push tube receiving socket 217, the tapered annular alignment surface 222 on the inlet of the push tube receiving socket 217, one of the master piston ports 215, and the piston retainer 262. The HSSV 420 and the slave piston assembly 300 are also shown in the assembled position in the housing 110. Figure 9 is a cross-sectional view in the plane of the high pressure hydraulic passage 712 between the primary piston chamber 120 and the HSSV 420. In this view, the end of the accumulator 430 is visible. Figure 10 is another cross-sectional view illustrating the high pressure hydraulic passage 714 between the HPCV 450 and the piston chamber 120 .

[0051] Figure 11is a cross-sectional view of an exemplary slave piston and SAVC according to aspects of the present disclosure. The slave piston 310 can be disposed in the slave piston bore 130 in the VVA housing 110, thereby defining an expandable slave piston chamber 314 in fluid communication with the master piston chamber 214 using the slave piston bore. A valve detent seat 318 is secured within a valve detent seat recess 132 of complementary shape formed within the housing between the slave piston bore 130 and the master piston bore 120. The valve detent seat 318 includes a central passage 319 surrounded by an annular seating surface 321. The slave piston 310 can include an inner cavity 330 for receiving a control pin 340, the control pin being provided with a control pin collar 342 which can be press-fitted thereon or secured with a retaining pin (not shown). The control pin collar 342 can function as a control piston and allow guided movement of the control pin 340 within the slave piston bore or cavity 330, thereby maintaining the control pin 340 centered within the slave piston cavity 330. The control pin 340 includes a check disc stop 345 that limits downward movement of the check disc 350 relative to the control pin 340. The control pin 340 can include a shoulder 349 to provide secure positioning and assembly of the control pin collar 342. The control pin collar 342 includes an upper spring guide 344 that cooperates with a control pin spring 354 and a lower spring guide 346 that cooperates with a check disc spring 356. The control pin spring 354 provides a downward (seating) biasing force on the control pin 340 relative to the slave piston 310. The spring 356 provides a downward (seating) biasing force relative to the position of the control pin collar 342 against the annular seating surface 321 on the check disc 350. The check disk 350 can be slidably disposed on the control pin 340. According to one aspect of the present disclosure, the control pin / collar assembly defines an automatic lash chamber 355 at the top of the inner cavity 330 of the slave piston 310. In response to the relative pressures between the chambers defined by each end of the control pin collar 342, oil can flow (leak) between the slave piston 310 and the automatic lash chamber 355 through the gap between the control pin collar 342 and the slave piston 310.

[0052] The control pin 340 includes an annular control pin seating surface 341 that engages the valve detent seat annular seating surface 321. Thus, the valve detent seat annular seating surface 321 provides a positive stop for the control pin. As the automatic lash chamber 355 can be filled with hydraulic fluid, the positive stop of the seating surface 321 operates to limit the automatic lash movement of the control pin 340. Similarly, the check disk 350 includes an annular check disk seating surface 351 that engages the valve detent seat annular surface 321. The control pin 340 includes a plurality of control pin ports 343, which can be radiused, grooved, or otherwise shaped, that allow flow through the control pin 340. The check disk 350 operates to direct flow through the control pin ports 343 and includes a metering edge 357 that operates to gradually block the control pin ports 343 as the control pin 340 moves (downward) relative to the check disk 350. Check disk 350 includes an outer skirt 353 that maintains a precise relationship between metering edge 357 and control pin port 343 because both check disk 350 and control pin 343 utilize a common seating surface 321. This configuration eliminates any tolerance stack-up issues that would otherwise affect the precision between metering edge 357 and control pin port 343.

[0053] According to one aspect of the present disclosure, the self-adjusting valve stop prevents the closing speed of the piston from Figure 11 The valve check disc and the control pin share a common seating surface. This common seating structure reduces the tolerance stack-up of the cooperating parts, making the valve lift seating profile and seating speed control less sensitive to dimensional variations (i.e., manufacturing tolerances) of the control pin and the check disc.

[0054] The control pin port 343 can be gradually blocked by the check disk 350 during the valve detent operating mode, as described below. During normal valve lift operation of the master-slave hydraulic circuit (i.e., as determined by the profile of cam 10), the increase in hydraulic pressure in the master piston chamber 214 caused by the upward movement of the master piston causes the slave piston and the control pin to move upward together and the engine valve to open. Due to the low leakage flow between the slave piston and the automatic clearance chamber, the slave piston and the control pin move essentially together. The check disk can initially move upward relative to the control pin to allow flow into the slave piston chamber. As the slave piston lift increases, the check disk moves downward relative to the control pin and contacts the control pin stop 345. The engine valve can be closed due to the opening of the cam profile or HSSV. As the engine valve initially closes, the slave piston and the control pin move together and the check disk remains in contact with the control pin check disk stop 345. At an engine valve lift of typically 3 mm, the check disc seating surface 351 contacts the valve detent annular seating surface 321, directing flow out of the piston chamber through the control pin radial orifice 343. Initially, when the check disc contacts the control pin check disc stop 345, the orifice's flow area does not significantly restrict flow. As the engine valve approaches zero lift, the check disc moves relative to the control pin, and the check disc metering edge 357 gradually obstructs the radial orifice. At an engine valve lift of typically 0.3 mm to 0.5 mm, the radial orifice is completely obstructed, directing flow out of the piston through the radial gap between the check disc 350 and the control pin 340. The relationship between the obstructed orifice area and lift profile is analogous to the acceleration portion of a cam profile's closing characteristic, while the check disc-control pin diameter clearance flow area is analogous to the constant velocity ramp of a cam profile.

[0055] During valve lift and valve seating, the automatic lash chamber pressure is lower than the slave piston pressure due to spring force and piston diameter. This causes oil to leak from the slave piston into the automatic lash chamber via the diametrical clearance between the control piston bore and the collar. At engine valve lift, typically less than 0.1 mm, the control pin seating surface contacts the valve detent annular seating surface. This causes the slave piston chamber pressure to drop to near ambient pressure, while the automatic lash chamber pressure increases due to engine valve spring load. Oil leaks from the automatic lash chamber into the slave piston chamber until the engine valve seats and unloads the valve spring. This provides additional deceleration of the engine valve and the automatic lash function, allowing the control pin to contact the valve detent seat approximately when the engine valve contacts the engine valve seat. According to further aspects of the present disclosure, the guide features of the check disc spring 356 and the control pin ensure that the control pin port is not contacted by the spring 356, thereby preventing wear on the port edge by the spring 356. The control pin check disc diametrical clearance is large enough to prevent the check disc control pin from locking due to friction and provides acceptable sensitivity to oil viscosity.

[0056] Figure 12 and13 is a cross-sectional view showing details of an exemplary push tube / master piston interface. According to aspects of the present disclosure, the master piston of the VVA assembly can be provided with advantageous features to ensure operational stability and durability of the motion receiving interface for the VVA assembly. The push tube 20 can cooperate with a push tube cap 22 that engages the end of the push tube 20 and extends into the master piston push tube socket 217 to a considerable depth such that the end 24 of the push tube cap 22 is very close to the outer surface 221 of the master piston end wall 219. Preferably, the depth should be sufficient to position the interface between the push tube end 24 and the master piston end wall 219 within the master piston bore 120 of the housing 110. The socket depth can be such that the interface between the push tube and the master piston (i.e., the thickness of the master piston end wall) is preferably less than the diameter of the piston. If any, this configuration provides minimal side loads on the push tube cap. That is, the combination of the forces exerted by push tube 20 and push tube cap 22 and the high pressure applied to outer surface 221 will not produce any significant side loads on push tube cap 22, particularly near end wall 219. This reduces lateral forces on the push tube, cap, and main piston, providing more stable operation and reducing frictional losses and wear.

[0057] In order to further enhance the alignment of the push tube cap 22 within the primary piston push tube socket 217, the push tube cap 22 can be provided with a slight radius on the end 24 to accommodate very slight angular variations in alignment and maintain low contact stresses. As a further measure, the primary piston end wall 219 can be provided with a flat or slightly concave surface, preferably with a radius greater than the radius provided on the push tube cap end 24, to further reduce contact stresses and ensure alignment of the push tube cap 24 within the primary piston push tube socket 217. In order to further enhance alignment, the push tube cap 22 can be provided with a radially extending annular protrusion or ridge 29, which provides axial alignment of the push tube cap within the primary piston socket. This configuration provides a centering force on the end of the push tube cap 22 opposite the end wall 24. The push tube end / push tube cap end can define an annular shape together with the push tube receiving socket of the primary piston.

[0058] According to aspects of the present disclosure, an exemplary VVA assembly can provide enhanced lubrication capabilities at the master piston / push tube interface. Figure 13 And refer to it again Figure 5 、 6and 8 to 10, the annular groove 213 and radially extending port 215 on the master piston can supply engine oil to the master piston push tube socket 217 and therefore to the push tube / master piston interface. According to one aspect of the present disclosure, the respective sizes of the master piston and the master piston bore are configured to provide an annular gap which, under high pressure in the master piston chamber, allows oil to vent or leak into the annular space where it is collected by the master piston annular groove and directed into the master piston push tube receiving socket. The oil can originate from the master piston chamber and can leak between the lateral outer surface of the master piston 210 and the master piston chamber 120. Thus, the groove 213 can be used to collect or "clean" oil that leaks from the master piston cavity into this space and deliver it to the push tube / master piston interface. The above-mentioned radial centering feature can keep the push tube convex piston face centered inside the master piston and also maintain a periphery containing a hydraulic fluid film to prevent leakage out of the high pressure circuit.

[0059] Although the embodiments of the present invention have been described with reference to specific exemplary embodiments, it will be apparent that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the invention as set forth in the claims. Accordingly, the specification and drawings are to be regarded as illustrative rather than restrictive.

Claims

1. An engine valve actuation assembly for controlling movement of at least one engine valve in an engine, comprising: source of motion; an engine valve train for transmitting motion from the motion source to the at least one engine valve, the engine valve train comprising a housing; a primary piston bore defined in the housing; a primary piston cooperating with the primary piston bore to define a primary piston chamber; The main piston has a motion receiving interface for receiving motion from the motion source; a slave piston bore defined in the housing; a slave piston cooperating with the slave piston bore to define a slave piston chamber; The slave piston has a motion transfer interface for transferring motion to a motion receiving assembly in the engine valve train and the at least one engine valve, the slave piston chamber being in hydraulic communication with the master piston chamber; a control piston bore defined in the slave piston; a control piston cooperating with the control piston bore to define an automatic lash chamber; a control pin operatively connected to the control piston, the control pin having a plurality of control pin ports arranged to allow flow from the slave piston chamber to the master piston chamber; a check disk cooperating with the control pin such that the check disk progressively blocks flow through at least one of the plurality of ports in response to movement of the slave piston during engine valve closing; as well as a valve detent seat having a common seating surface for the control pin and the check disk, wherein the common seating surface facilitates precise positioning of the check disk relative to the control pin, Wherein, when the at least one engine valve is in the seated position, at least one of the plurality of control pin ports in the control pin is not blocked by the check disk.

2. The engine valve actuation assembly according to claim 1, wherein: The check disc is adapted to contact a valve seat when the lift of the engine valve decreases below a threshold value.

3. The engine valve actuation assembly according to claim 2, wherein: The control pin is adapted to contact the valve seat before the engine valve is seated.

4. The engine valve actuation assembly according to claim 1, wherein: At least one of the plurality of control pin ports is a circular hole.

5. The engine valve actuation assembly according to claim 1, wherein: A check disc stop on the control pin brakes the check disc.

6. The engine valve actuation assembly according to claim 1, wherein: A non-return disk spring is disposed between the control piston and the non-return disk.

7. The engine valve actuation assembly according to claim 1, wherein: A control pin spring is provided between the slave piston and the control pin.

8. The engine valve actuation assembly of claim 1 further comprising a hydraulic passage between the master piston and the slave piston.

9. The engine valve actuation assembly according to claim 8, wherein: The hydraulic passage includes an opening at a top portion of the primary piston bore, the opening gradually becoming larger toward the primary piston bore.

10. The engine valve actuation assembly of claim 1, wherein: The control piston and the control pin are operatively connected by a press fit.

11. The engine valve actuation assembly of claim 1 further comprising a hydraulic control circuit in hydraulic communication with the master piston chamber.

12. The engine valve actuation assembly according to claim 11, wherein: The hydraulic control circuit includes an accumulator.

13. The engine valve actuation assembly of claim 11, wherein: The hydraulic control circuit includes a dry starting reservoir.

14. The engine valve actuation assembly of claim 11, wherein: The hydraulic control circuit includes a solenoid valve for controlling the flow of hydraulic fluid to and from the primary piston chamber.

15. The engine valve actuation assembly of claim 11, wherein: The hydraulic control circuit is integrated into the housing.

16. The engine valve actuation assembly of claim 1, wherein: The housing is a rocker shaft base suitable for mounting on an engine overhead assembly.

17. The engine valve actuation assembly of claim 1, wherein: The housing is a rocker arm base, and wherein the hydraulic circuit is integrated into the rocker arm base to provide a modular add-on assembly suitable for connection to an engine cylinder head.

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