Valve actuators

Abstract

An actuator for operating a poppet valve (30) of an internal combustion engine. The actuator comprises a rotary portion (4) and a body portion (2), and the rotary portion defines a cam surface (50, 60). A cam follower (10) is engaged with the cam surface, and a linkage is coupled to the cam follower at one end and coupled to a valve stem (12) at its other end. The cam surface (50, 60) is shaped such that exertion of a closing force on the valve stem, by a piston of the engine following failure of the actuator for example, causes the cam follower (10) to exert a turning force on the rotary portion (4).

1 . An actuator for operating a valve, the actuator comprising:
 a rotary portion and a body portion, wherein the rotary portion is rotatable relative to the body portion about an axis of rotation by actuation of the actuator, and the rotary portion defines a cam surface;   a cam follower engaged with the cam surface as the cam surface rotates; and   a linkage which is coupled to the cam follower at one end and to be coupled to a valve stern at its other end,   wherein rotation of the rotary portion from a first rotational position to a second rotational position causes displacement of the cam follower, which in turn causes the other end of the linkage to move from a first position to a second position, and   wherein the cam surface is shaped such that exertion of a force on the other end of the linkage which urges the other end from its second position towards its first position causes the cam follower to exert a turning force on the rotary portion so as to rotate it towards its first rotational position.   
     
     
         2 . The actuator of  claim 1 , wherein the cam surface is shaped such that when the rotary portion is in its second rotational position, a reference line which lies in a plane perpendicular to the axis of rotation of the rotary portion and is normal to the cam surface at a point of contact by the cam follower is spaced from the axis of rotation of the rotary portion. 
     
     
         3 . The actuator of  claim 2 , wherein the cam surface is shaped such that when the rotary portion is in its second rotational position, or in a rotational position in a range from the second rotational position to an intermediate rotational position between the first and second rotational positions, the reference line is spaced from the axis of rotation of the rotary portion. 
     
     
         4 . The actuator of  claim 1 , wherein the first position corresponds to a valve closed position and the second position corresponds to a valve open position. 
     
     
         5 . The actuator of  claim 4 , wherein the second position corresponds to a valve fully open position. 
     
     
         6 . The actuator of  claim 1 , wherein the actuator is an electromagnetic actuator, the rotary portion comprises a rotor and the body portion comprises a stator. 
     
     
         7 . The actuator of  claim 1 , wherein the actuator is a hydraulic actuator. 
     
     
         8 . The actuator of  claim 1 , wherein the actuator is a pneumatic actuator. 
     
     
         9 . An internal combustion engine including at least one cylinder having at least one inlet or exhaust valve, a piston and the actuator of  claim 1 , wherein the at least one inlet or exhaust valve is operable independently of rotation of a crankshaft of the engine, and the other end of the actuator linkage is coupled to the at least one inlet or exhaust valve to enable the actuator to actuate the at least one inlet or exhaust valve. 
     
     
         10 . The engine of  claim 9 , wherein the engine is a diesel engine. 
     
     
         11 . The engine of  claim 9 , wherein the valve includes a valve stem which is arranged to reciprocate along a valve axis, the piston is arranged to reciprocate along a piston axis, and the valve axis is substantially parallel to the piston axis.