Solenoid valves are useful where fluid flow is repeatedly turned on and off. However, such valves have encountered several problems when used to handle large flows of pressurized fluid. When port size is increased to increase flow, the increased mass of the valve used to cover the port often consumes substantial energy to operate the solenoid armature since the mass increases proportionally to the square of the valve diameter. Furthermore, substantial hydraulic losses occur during opening and closing of the valve. Most of the hydraulic losses take place during the early stages of valve opening and the late stages of valve closing when the orifice area is small. An example of a valve system using solenoid valves for variable hydraulic control of the engine valve motion is defined in a co-pending application of the present inventor. Variable engine valve control can save energy by reducing the pumping losses in the engine. However, energy losses associated with an inefficient hydraulic control system can cancel out the benefits associated with reduced pumping.
Martin U.S. Pat. No. 3,368,789 discloses an electromagnetic valve with conical magnetic poles. However, the conical pole surface is formed on a disk carried by an armature in the shape of a frustum. A valve ring is also carried by the armature and rests against an annular valve seat in the valve body. This armature construction has substantial mass which would increase substantially as a function of the diameter of the armature. As a result, the armature has a high initial mass when made for a large valve orifice size.
Such a construction substantially restricts the practical size of the orifice which may be employed with the valve construction shown in the patent. In addition, hydraulic forces acting on the valve and the armature are not balanced. When the valve is closed, the armature is subject to axial fluid pressure force. Furthermore, a high spring force preload may be required to close the valve or to keep the valve closed. Higher spring forces require higher magnetic force to open the valve by displacing the armature. As a result, substantially more electrical energy is consumed, and the valve motion is relatively slow. As a result, the patented construction is subject to high hydraulic losses during opening and closing and less accurate control of the fluid flow than may be desired in particular applications such as engine valve operation.
Russian Patent No. 543,807 discloses a solenoid valve in which the armature includes a plurality of concentric sleeves. A valve stem is secured to the central sleeve and carries an enlarged head valve which closes against an annular valve seat. Like the construction of the valve in U.S. Pat. No. 3,368,789, increases in the size of the valve to correspond with enlargements of the outlet substantially increase the mass of material which must be moved to open and close the valve. Such mass reduces the reaction time of the valve and increases the energy required to move the valve. Moreover, the pressure of the fluid acts against the valve and further increases the energy required to open the valve, and slower reaction of the valve increases the hydraulic losses occurring during opening and closing of the valve. Furthermore, when the size of the valve outlet is small, a substantially longer stroke is required to avoid restriction of the flow of fluid through the valve outlet. Although the use of three concentric armature sleeves achieves a smaller air gap while permitting a long stroke of the stem, such a construction is substantially more expensive than conical pole solenoid armatures.
In both of the above-discussed prior art references, it may be appreciated that the magnetic field decays gradually once electrical power to the coil has been interrupted. The valve does not return to its seated position until the magnetic field force decays below the spring force to return the valve to its closed position. As a result, movement of the valve is initiated slowly as the spring force opposes the residual magnetic force. Moreover, when the valve is closed, the hydraulic pressure against the valve tends to keep it closed against the valve seat, and thus requires a higher magnetic force to move the valve from its closed position.