Hydraulic systems in an engine valvetrain having lost motion and/or braking hydraulic circuits are provided with a conditioning circuit that may include a supplemental supply passage, which provides continuous and supplemental supply of hydraulic fluid from a supply source to the braking and lost motion circuits, as well as a venting of the circuits to ambient, such that the hydraulic fluid in these circuits is kept in a refreshed and conditioned state without air contamination. A vented three-way solenoid valve may be utilized. The supplemental supply passage may be provided at various locations in the valvetrain and in the engine head environment. The supplemental supply passage may include flow and pressure control devices to control the flow of the supplemental supply of hydraulic fluid.

Methods and systems are provided for providing secondary air to an exhaust system during catalyst warm-up. In one example, a method may include, during a cold start condition, operating an engine with a first number of cylinders unfired and a remaining number of cylinders fired during an engine cycle, opening an intake valve of an unfired cylinder of the first number of cylinders during an expansion stroke of the unfired cylinder, and opening an exhaust valve of the unfired cylinder during a compression stroke of the unfired cylinder. In this way, the unfired cylinders may provide the secondary air to the exhaust system during a stroke that increases mixing of the secondary air with burned exhaust gas from fired cylinders, thus increasing exotherm production in the exhaust system to increase a temperature of the catalyst.

Methods and systems are provided for providing secondary air to an exhaust system during catalyst warm-up. In one example, a method may include, during a cold start condition, operating an engine with a first number of cylinders unfired and a remaining number of cylinders fired during an engine cycle, opening an intake valve of an unfired cylinder of the first number of cylinders during an expansion stroke of the unfired cylinder, and opening an exhaust valve of the unfired cylinder during a compression stroke of the unfired cylinder. In this way, the unfired cylinders may provide the secondary air to the exhaust system during a stroke that increases mixing of the secondary air with burned exhaust gas from fired cylinders, thus increasing exotherm production in the exhaust system to increase a temperature of the catalyst.

A slide element for displacement of a cam segment in an axial direction along a camshaft may include a slide sleeve, which has a longitudinal toothing formed at least sectionally along an inner wall of the slide sleeve and has a latching section formed on the inner wall and serving for interaction with a latching means. The latching section comprises a latching means receiving part, which comprises at least two latching grooves formed adjacently in an axial direction and at least one latching elevation formed between the latching grooves of the latching means receiving part and directed inward. The latching elevation may be partially hardened exclusively in a latching means transfer region.

Methods and systems are provided for providing secondary air to an exhaust system during catalyst warm-up. In one example, a method may include, during a cold start condition, operating an engine with a first number of cylinders unfired and a remaining number of cylinders fired during an engine cycle, opening an intake valve of an unfired cylinder of the first number of cylinders during an expansion stroke of the unfired cylinder, and opening an exhaust valve of the unfired cylinder during a compression stroke of the unfired cylinder. In this way, the unfired cylinders may provide the secondary air to the exhaust system during a stroke that increases mixing of the secondary air with burned exhaust gas from fired cylinders, thus increasing exotherm production in the exhaust system to increase a temperature of the catalyst.

Methods and systems are provided for providing secondary air to an exhaust system during catalyst warm-up. In one example, a method may include, during a cold start condition, operating an engine with a first number of cylinders unfired and a remaining number of cylinders fired during an engine cycle, opening an intake valve of an unfired cylinder of the first number of cylinders during an expansion stroke of the unfired cylinder, and opening an exhaust valve of the unfired cylinder during a compression stroke of the unfired cylinder. In this way, the unfired cylinders may provide the secondary air to the exhaust system during a stroke that increases mixing of the secondary air with burned exhaust gas from fired cylinders, thus increasing exotherm production in the exhaust system to increase a temperature of the catalyst.

A valve actuation system for an internal combustion engine is disclosed. The engine has a first set of cylinders having a first set of exhaust valves and a second set of cylinders having a second set of exhaust valves. The valve actuation system for the exhaust valves includes one or more first cams having a compression-release lobe and a main exhaust lobe adapted to transfer valve actuation motion to the first set of exhaust valves, and one or more second cams having an early exhaust valve opening (EEVO) lobe and a main exhaust lobe adapted to transfer valve actuation motion to the second set of exhaust valves. The valve actuation system may provide any combination of (i) main exhaust valve actuation with or without compression release actuation with (ii) main exhaust valve actuation with or without EEVO for the two sets of cylinders.

A valve actuation system for an internal combustion engine is disclosed. The engine has a first set of cylinders having a first set of exhaust valves and a second set of cylinders having a second set of exhaust valves. The valve actuation system for the exhaust valves includes one or more first cams having a compression-release lobe and a main exhaust lobe adapted to transfer valve actuation motion to the first set of exhaust valves, and one or more second cams having an early exhaust valve opening (EEVO) lobe and a main exhaust lobe adapted to transfer valve actuation motion to the second set of exhaust valves. The valve actuation system may provide any combination of (i) main exhaust valve actuation with or without compression release actuation with (ii) main exhaust valve actuation with or without EEVO for the two sets of cylinders.

Methods and systems are described for an engine with a cam torque actuated variable cam timing phaser. Phaser positioning control is improved by reducing inaccuracies resulting from inadvertent spool valve and/or phaser movement when the spool valve is commanded between regions. In addition, improved spool valve mapping is used to render phaser commands more consistent and robust.

A valve gear includes a camshaft, a first cam and a second cam that drive an intake valve or an exhaust valve, and a synchronous cam that rotates in synchronism with the first and second cams. The valve gear includes a rocker shaft, a rocker arm, and a cam follower swingably supported by the rocker shaft and that comes into contact with the synchronous cam. The valve gear includes a thruster that converts the swinging motion of the cam follower into a thrust and moves the rocker arm to a first side or a second side in the axial direction. The valve gear makes the camshaft compact, and also increases the reliability of operation at high rotations and reduces an operation sound at low rotations.