Variable force valve spring

Abstract

Devices and related methods are disclosed that generally involve variable force valve springs for controlling the motion of an engine valve. The force exerted by the valve spring can be adjusted by altering the pressure at which a fluid is supplied to a fluid chamber thereof, by altering the volume of the fluid chamber, and/or by changing the aggregate surface area over which fluid pressure is coupled to the engine valve. Associated fluid control systems are also disclosed herein, as are various methods for adjusting the force of a valve spring based on a variety of engine parameters, such as engine speed, engine load, and/or a combination thereof.

1 . An engine, comprising:
 a pneumatic valve spring coupled to an engine valve; and   a control module configured to adjust a spring force of the pneumatic valve spring based on at least one of engine speed and engine load.   
     
     
         2 . The engine of  claim 1 , wherein the control module is configured to increase the spring force when the engine speed exceeds a first speed threshold. 
     
     
         3 . The engine of  claim 1 , wherein the control module is configured to increase the spring force when the engine load exceeds a first load threshold. 
     
     
         4 . The engine of  claim 1 , wherein the control module is configured to decrease the spring force when the engine speed is below a first speed threshold. 
     
     
         5 . The engine of  claim 1 , wherein the control module is configured to decrease the spring force when the engine load is below a first load threshold. 
     
     
         6 . The engine of  claim 2 , wherein the first speed threshold is 3000 rpm. 
     
     
         7 . The engine of  claim 2 , wherein the first speed threshold is four times higher than an idle speed of the engine. 
     
     
         8 . The engine of  claim 3 , wherein the first load threshold is 50 percent of a maximum load of the engine. 
     
     
         9 . The engine of  claim 3 , wherein the first load threshold is three times higher than an idle load of the engine. 
     
     
         10 . A valve spring system, comprising:
 a vessel having a piston reciprocally disposed therein;   an engine valve coupled to the piston;   a first source of pressurized air having a first pressure;   a second source of pressurized air having a second pressure that is greater than the first pressure; and   a control valve configured to adjust a force exerted on the piston by controlling a first fluid communication between the vessel and the first source, and a second fluid communication between the vessel and the second source.   
     
     
         11 . The valve spring system of  claim 10 , wherein the engine valve is actuated by a lost motion system. 
     
     
         12 . The valve spring system of  claim 10 , wherein the engine valve is outwardly-opening. 
     
     
         13 . The valve spring system of  claim 10 , wherein the engine valve is a crossover valve in a split-cycle engine. 
     
     
         14 . The valve spring system of  claim 13 , wherein the second source is supplied from a crossover passage of the split-cycle engine. 
     
     
         15 . The valve spring system of  claim 13 , wherein a first force exerted on the engine valve by a crossover charge in the crossover passage and a second force exerted on the engine valve by the piston together exceed a combustion force exerted on the engine valve. 
     
     
         16 . The valve spring system of  claim 10 , wherein the first pressure is between about 1 bar and about 10 bar. 
     
     
         17 . The valve spring system of  claim 10 , wherein the second pressure is between about 20 bar and about 85 bar. 
     
     
         18 . The valve spring system of  claim 10 , further comprising a control module configured to actuate the control valve. 
     
     
         19 . An engine comprising the valve spring system of  claim 10 . 
     
     
         20 . A valve spring system, comprising:
 a cap defining a first bore therein;   a piston coupled to an engine valve, the piston being slidably disposed within the first bore such that the piston and the cap define a first fluid chamber;   an outer housing defining a second bore therein, the cap being slidably disposed within the second bore such that the cap and the outer housing define a second fluid chamber; and   a fluid port configured to selectively release pressurized fluid from the second fluid chamber, thereby allowing the cap to slide relative to the outer housing such that a volume of the first fluid chamber is increased.   
     
     
         21 . The valve spring system of  claim 20 , wherein the cap includes at least one aperture in fluid communication with the first fluid chamber. 
     
     
         22 . The valve spring system of  claim 21 , wherein the aperture remains in fluid communication with a pressurized fluid supply line throughout a full engine cycle. 
     
     
         23 . The valve spring system of  claim 21 , wherein fluid disposed in the first fluid chamber is forced out of the first fluid chamber through the aperture when the engine valve is open. 
     
     
         24 . The valve spring system of  claim 21 , wherein the first fluid chamber is filled with fluid through the aperture when the engine valve is closed. 
     
     
         25 . The valve spring system of  claim 20 , wherein the pressure in the first fluid chamber is substantially equal to the pressure in the second fluid chamber when the engine valve is closed for at least 100 degrees crank angle. 
     
     
         26 . A method of varying a spring force exerted on an engine valve by the valve spring system of  claim 20 , comprising:
 coupling the fluid port to a vent to release pressure from the second fluid chamber and increase the spring force exerted on the engine valve; and   coupling the fluid port to a pressurized fluid supply to increase pressure in the second fluid chamber and decrease the spring force exerted on the engine valve.   
     
     
         27 . The method of  claim 26 , wherein the spring force is increased when a load of the engine exceeds a first predetermined threshold and is decreased when the load of the engine is below a second predetermined threshold. 
     
     
         28 . The method of  claim 26 , wherein the spring force is increased when a speed of the engine exceeds a first predetermined threshold and is decreased when the speed of the engine is below a second predetermined threshold. 
     
     
         29 . A valve spring system, comprising:
 a first housing defining a first bore therein in which a first piston is reciprocally disposed, the first piston being coupled to a valve stem of an engine valve;   a second housing defining a second bore therein in which a second piston is reciprocally disposed, the second piston being coupled to an extension stem;   a third housing defining a hydraulic plenum, the hydraulic plenum being in fluid communication with a proximal end of the valve stem, a distal end of the extension stem, and a control valve;   wherein the plenum is in fluid communication with an accumulator when the control valve is opened such that the valve stem is movable independently from the extension stem; and   wherein the plenum is sealed when the control valve is closed such that movement of the valve stem requires movement of the extension stem.   
     
     
         30 . The valve spring system of  claim 29 , wherein the first housing, the second housing, and the third housing are formed integrally. 
     
     
         31 . The valve spring system of  claim 29 , wherein a first fluid chamber defined by the first housing and the first piston is supplied with pressurized fluid through a first aperture formed in the first housing and wherein a second fluid chamber defined by the second housing and the second piston is supplied with pressurized fluid through a second aperture formed in the second housing. 
     
     
         32 . The valve spring system of  claim 31 , wherein fluid disposed in the first fluid chamber is forced out of the first fluid chamber through the first aperture when the engine valve is open. 
     
     
         33 . The valve spring system of  claim 31 , wherein fluid disposed in the second fluid chamber is forced out of the second fluid chamber through the second aperture when the engine valve is open and the control valve is closed. 
     
     
         34 . A method of varying a spring force exerted on an engine valve by the valve spring system of  claim 29 , comprising:
 closing the control valve to increase the aggregate surface area over which fluid pressure is coupled to the engine valve and thereby increase the spring force; and   opening the control valve to decrease the aggregate surface area over which fluid pressure is coupled to the engine valve and thereby decrease the spring force.   
     
     
         35 . The method of  claim 34 , wherein the spring force is increased when a load of the engine exceeds a first predetermined threshold and is decreased when the load of the engine is below a second predetermined threshold. 
     
     
         36 . The method of  claim 34 , wherein the spring force is increased when a speed of the engine exceeds a first predetermined threshold and is decreased when the speed of the engine is below a second predetermined threshold. 
     
     
         37 . A method of actuating a valve of an engine, comprising:
 increasing a spring force of a valve spring associated with the valve based on an increase in an engine parameter; and   decreasing the spring force of the valve spring based on a decrease in the engine parameter.   
     
     
         38 . The method of  claim 37 , wherein the engine parameter is selected from the group consisting of engine speed, engine load, engine temperature, throttle position, and engine age. 
     
     
         39 . The method of  claim 38 , wherein the spring force is increased by increasing a pressure supplied to a fluid chamber of the valve spring. 
     
     
         40 . The method of  claim 38 , wherein the spring force is increased by decreasing a volume of a fluid chamber of the valve spring. 
     
     
         41 . The method of  claim 38 , wherein the spring force is increased by increasing an aggregate surface area over which fluid pressure is coupled to the engine valve.