Hydraulic early engine exhaust valve opening system

A method for operating an early exhaust valve opening (EEVO) module of an engine, the method comprising:

• starting the engine;
• engaging, by the EEVO module, an injector rocker and an exhaust rocker so that rotation of the injector rocker caused by engagement of an injector cam of a camshaft of the engine causes the EEVO module to rotate the exhaust rocker to open an exhaust valve after a compression stroke of an engine piston in an engine cylinder;
• sensing an intake manifold pressure;
• continuing to engage the injector rocker and the exhaust rocker and rotate the exhaust rocker to open the exhaust valve in response to rotation of the injector rocker when the intake manifold pressure is less than a setpoint pressure;
• and
• disengaging the EEVO module from the injector rocker and the exhaust rocker so that rotation of the injector rocker does not cause the EEVO module to rotate the exhaust rocker when the intake manifold pressure is greater than the setpoint pressure.

An engine, comprising:

• an engine cylinder;
• an engine piston disposed within the engine cylinder;
• an exhaust valve for the engine cylinder biased toward an exhaust valve closed position;
• an exhaust rocker that is rotatable to move the exhaust valve from the exhaust valve closed position to an exhaust valve open position;
• a fuel injector;
• an injector rocker that is rotatable to cause the fuel injector to inject fuel into the engine cylinder;
• a camshaft having an exhaust cam engaging and rotating the exhaust rocker to move the exhaust valve to the exhaust valve open position as the camshaft rotates and an injector cam engaging and rotating the injector rocker to cause the fuel injector to inject fuel into the engine cylinder as the camshaft rotates;
• and
• an early exhaust valve opening (EEVO) module comprising:
• an EEVO housing mounted proximate the exhaust rocker and the injector rocker,
• a drive piston disposed within a drive piston bore of the EEVO housing, wherein the drive piston bore has a drive piston bore top wall and a drive piston bore bottom end, and the drive piston is biased toward the drive piston bore top wall,
• a driven piston disposed within a driven piston bore of the EEVO housing, wherein the driven piston bore has a driven piston bore top wall and a driven piston bore bottom end, and the driven piston is biased toward the driven piston bore top wall, and wherein an activation fluid passage intersects the drive piston bore and the driven piston bore proximate the drive piston bore top wall and the driven piston bore top wall, respectively, and a fluid supply passage places the activation fluid passage in fluid communication with a high pressure fluid source, and
• a low pressure timing valve disposed within a spill passage of the EEVO housing that intersects the drive piston bore at a position between the drive piston bore top wall and the drive piston bore bottom end and fluidly connecting the drive piston bore to a low pressure reservoir, wherein the low pressure timing valve has a timing valve release pressure,
• wherein the EEVO module is primed by providing pressurized fluid from the high pressure fluid source to increase an activation fluid passage pressure to an EEVO priming pressure that causes the drive piston to displace toward the drive piston bore bottom end and engage the injector rocker and open the spill passage to the drive piston bore, and causes the driven piston to displace toward the driven piston bore bottom end and engage the exhaust rocker, wherein the EEVO priming pressure is less than the timing valve release pressure,
• wherein, once the EEVO module is primed, displacement of the drive piston due to rotation of the injector rocker toward the drive piston bore top wall before the drive piston closes the spill passage increases the activation fluid passage pressure until the activation fluid passage pressure is at least equal to the timing valve release pressure and the low pressure timing valve opens to drain fluid from the drive piston bore to the low pressure reservoir, wherein the timing valve release pressure is less than an exhaust valve displacement pressure required for the driven piston to displace and cause the exhaust rocker to move the exhaust valve to the exhaust valve open position, and
• wherein, after the spill passage is closed by the drive piston, further displacement of the drive piston toward the drive piston bore top wall increases the activation fluid passage pressure until the activation fluid passage pressure is greater than the exhaust valve displacement pressure and the driven piston is displaced and rotates the exhaust rocker move the exhaust valve to the exhaust valve open position.