Variable force engine valve actuator

Abstract

An engine valve actuator is provided. The engine valve actuator includes a first piston and a second piston. The second piston is moveably received within the first piston. The engine valve further includes an actuator body that has a bore defining a first stop and a second stop. The first stop is configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel. The second stop is configured to engage the second piston to limit movement of the second piston at a second preselected distance. A valve element is operatively connected to the second piston to move in response to movement of the second piston.

What is claimed is:  
     
         1 . An engine valve actuator, comprising: 
 a first piston;    a second piston moveably received within the first piston;    an actuator body having a bore defining a first stop and a second stop, the first stop configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel, the second stop configured to engage the second piston to limit movement of the second piston at a second preselected distance; and    a valve element operatively connected to the second piston to move in response to movement of the second piston.    
     
     
         2 . The engine valve actuator of  claim 1 , wherein the first piston has a first contact surface area and the second piston has a second contact surface area that is smaller than the first contact surface area.  
     
     
         3 . The engine valve actuator of  claim 1 , wherein the actuator body defines a first chamber operatively associated with the first piston and a second chamber operatively associated with the second piston, each of the first and second chambers configured to receive a pressurized fluid.  
     
     
         4 . The engine valve actuator of  claim 1 , wherein the first piston includes an opening and the second piston is slidably disposed within the opening.  
     
     
         5 . The engine valve actuator of  claim 4 , wherein the second piston includes a shoulder configured to selectively engage the first piston adjacent the opening.  
     
     
         6 . The engine valve actuator of  claim 5 , wherein the actuator body defines a chamber configured to receive a pressurized fluid such that the pressurized fluid acts on the first piston and the second piston.  
     
     
         7 . The engine valve actuator of  claim 1 , wherein the first preselected distance is less than the second preselected distance.  
     
     
         8 . A method of actuating a valve, comprising: 
 providing a first piston having an opening;    disposing a second piston within the opening, the second piston operatively connected to a valve element;    providing an actuator body having a bore configured to receive the first and second pistons and defining a first stop and a second stop, the first stop configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel, the second stop configured to engage the second piston to limit movement of the second piston at a second preselected distance; and    directing a pressurized fluid against at least one of the first and second pistons to thereby move the valve element.    
     
     
         9 . The method of  claim 8 , wherein the first piston and second piston move together until the first piston engages the first stop.  
     
     
         10 . The method of  claim 8 , wherein the second piston moves independently of the first piston.  
     
     
         11 . An engine, comprising: 
 an engine block defining at least one chamber;    a cylinder head defining at least one passageway leading to the at least one chamber;    at least one valve actuator having a first piston;    a second piston slidably received within the first piston; and    an actuator body having a bore defining a first stop and a second stop, the first stop configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel, the second stop configured to engage the second piston to limit movement of the second piston at a second preselected distance; and    a valve element operatively connected to the second piston and disposed adjacent the at least one opening in the cylinder head, the valve element moveable between an open position and a closed position where the valve element blocks the opening in the cylinder head.    
     
     
         12 . The engine of  claim 11 , wherein the actuator body defines a chamber operatively associated with the first and second pistons and the engine further includes a source of pressurized fluid operable to supply a pressurized fluid to the chamber to move the first and second pistons together until the first piston engages the first stop.  
     
     
         13 . The engine of  claim 12 , further including a valve configured to control the rate of fluid flow into the chamber.  
     
     
         14 . The engine of  claim 11 , wherein the actuator body defines a first chamber operatively associated with the first piston and a second chamber operatively associated with the second piston and the engine further includes a source of pressurized fluid operable to selectively supply a pressurized fluid to at least one of the first and second chambers.  
     
     
         15 . The engine of  claim 14 , further including a first valve configured to control the rate of fluid flow from the source of pressurized fluid into the first chamber and a second valve configured to control the rate of fluid flow from the source of pressurized fluid into the second chamber.  
     
     
         16 . The engine of  claim 11 , further including a spring acting to bias the valve element into the closed position.  
     
     
         17 . The engine of  claim 11 , wherein the first piston has a first contact surface area and the second piston has a second contact surface area, the second contact surface area being less than the first surface area.  
     
     
         18 . The engine of  claim 11 , wherein the first piston includes an opening and the second piston is disposed within the opening, the second piston including a shoulder configured to engage the first piston adjacent the opening.  
     
     
         19 . The engine of  claim 11 , wherein the first preselected distance is less than the second preselected distance.  
     
     
         20 . The engine of  claim 11 , further including a cam shaft having a cam affixed thereto and a cam follower operatively engaged with the valve element to actuate the valve element as the cam shaft rotates.  
     
     
         21 . A method of actuating a valve, comprising: 
 providing a first piston having an opening;    disposing a second piston within the opening, the second piston operatively connected to a valve element;    directing pressurized fluid against the first piston to engage the first piston with the second piston and move the valve element a first preselected distance; and    directing pressurized fluid against the second piston to move the valve element a second preselected distance.