Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
1999-11-01
2001-08-07
Rivell, John (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
C251S129110, C251S129040, C251S065000
Reexamination Certificate
active
06269838
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to servovalves that are used to transfer quantities of fluid. The rotary servovalve and control system of the invention is particularly useful in situations requiring rapid response and precision control of fluid flow.
2. Description of the Prior Art
Many different mechanical and electrical servovalve systems have been employed for controlling fluid flow in industrial and manufacturing environments, as well as in other applications. Fluid servovalve control systems which require precise and highly responsive control are employed in a multitude of widely varying applications, including the control of robots, the operations of presses for manufacturing rubber and plastic parts, the control of tensioning devices in the paper industry, automotive vehicle and parts manufacturing, petroleum refining operations, and numerous other applications.
In many of the applications in which servo control valve systems are utilized, pressurized fluid is typically provided from a high pressure source and transmitted through a load from which the fluid is then exhausted to a low pressure reservoir. The load may, for example, take the form of a double-acting piston operating within a cylinder. The transfer of fluid from one side of the piston to the other within the cylinder causes the piston to move some mechanism to which it is connected.
Servovalves are widely utilized to control the flow of both pneumatic and hydraulic fluids. Conventional servovalves are often linear motion devices. That is, they typically consist of a spool element operated manually or electrically. Typically the spool element is shuttled back and forth within a chamber defined within a valve housing. By its movement the spool element covers and uncovers different fluid orifices or ports.
The function of a servovalve is to control the velocity and quantity of fluid flow and the direction of movement of a piston within a cylinder. Conventional servovalves typically contain a high torque motor connected to a flapper assembly. Such servovalve systems are expensive and require high manufacturing tolerances. They are also sensitive to contamination and clogging. Furthermore, they typically require continuous flow from a pump in order to operate.
Efforts have been made to develop rotary servovalves for use in servovalve systems. One such rotary servovalve is described in U.S. Pat. No. 4,794,845 which describes the application of a torque motor to a servovalve system. The torque motor controls flow by rotating a spool element within a complex sleeve assembly containing appropriate fluid passageways. In the event of a power failure a rather intricate arrangement of mechanical elements, including torque rods and springs, is required to center the servo valve in order to halt fluid flow. Also, when power is available, energy is required to center the valve for a zero command, no flow condition. This is necessary because torque motors are directional devices, but have no detent or zero position when power is removed. Consequently, the torque motor must always be energized or actuated throughout operation of a conventional rotary servovalve system.
U.S. Pat. No. 5,597,014 is directed to a high flow, direct drive rotary servovalve. This patent describes improvements in passageway designs, the function of which is to eliminate tangential Bernoulli reaction forces acting on the spool member. These forces tend to close the valve, thus requiring the torque motor to expend more energy in order to keep the valve open.
Prior rotary servovalve and control systems lack the requisite torque to be of commercial utility in many applications. This is because of the Bernoulli forces that are created with fluid flow and which tend to close the valve. Prior rotary servovalve and control systems provide elaborate means to combat the influence of these Bernoulli forces. For example, the rotary servovalve of U.S. Pat. No. 4,794,845 employs a very complex arrangement to overcome the Bernoulli forces.
SUMMARY OF THE INVENTION
The present invention is a rotary servovalve system that does not require a servomotor for actuation at all, but instead is able to utilize a rotary magnetic solenoid as the valve actuator. One type of suitable rotary solenoid actuator is a rotary magnetic solenoid having an armature that includes at least one permanent magnet and which is rotatable relative to a stator that is formed as an electromagnet. The stator is energizable by electrical current flow in alternative directions to alternatively and selectively create electromagnetic fields of opposite polarity from each other. Moreover, when the stator is deenergized, the permanent magnet or magnets of the armature return the armature to a neutral, null position from positions of rotation in opposite angular directions. The armature is coupled to carry a movable servovalve element in angular rotation therewith.
The rotary magnetic solenoid employed is a rotary bidirectional, high torque solenoid device. One line of suitable rotary magnetic solenoids for use according to the invention is manufactured by Lucas Control Systems Products located in Vandalia, Ohio and is sold as the Ultamag® series of rotary actuators. The armature of this type of rotary magnetic solenoid is centered through the use of permanent magnets and can be driven bidirectionally to either side of a zero or null position. This device is described in U.S. Pat. No. 5,337,030.
The armature of the rotary magnetic solenoid utilized in the invention rotates through arcs of twenty-two and one-half degrees to either side of the null position. The angular displacement from the null position and the direction of displacement therefrom is controlled by the amplitude and direction, respectively, of signals to the solenoid stator. When no driving signal to the stator is present, the force of the permanent magnet in the armature centers the armature relative to the stator at the zero or null position.
In a conventional rotary servovalve for the control of fluid flow, the fluid enters the valve housing at a single inlet port and exits the valve housing from a single outlet port. Flow through the valve is controlled by the position of the movable valve element which directs flow from the inlet port to alternative outlet ports. The flow to the outlet port of the valve housing is to a fluid reservoir, which is maintained at a reduced pressure from the pressure of the fluid source. Consequently, the pressure within the flow passage through the valve leading from the high pressure fluid source is greater than pressure within the fluid valve leading to the fluid reservoir. Since the fluid flow passageway within the valve which conducts fluid from the high pressure fluid source is typically located on the opposite side of the valve from the fluid passageway that conducts fluid to the fluid reservoir, there is an imbalance in internal pressure within the valve. The high pressure imbalance within the valve produces a load on the valve element that must be overcome in order to rotate the valve element. As the requirement for torque increases, so does the mass of the components of the driving motor or rotary solenoid.
In a preferred embodiment of the present invention the force imbalance within the valve is virtually eliminated. This is achieved by providing the valve housing with a pair of inlet ports and a pair of outlet ports. The inlet ports are located on diametrically opposite sides of the valve housing from each other. Similarly, the outlet ports are located on diametrically opposite sides of the valve housing from each other. By necessity, the valve ports in each pair must be longitudinally offset from each other so as not to interfere with the other ports in the valve. Corresponding pairs of fluid control ports are likewise provided in the valve housing. The fluid control ports within each pair are similarly diametrically opposed and longitudinally offset from each other in the valve housing.
The rotary element of the valve is likewise provided wi
Bobrow James Edwin
Woodworth Raymond Dexter
Rivell John
Thomas Charles H.
Woodworth Raymond Dexter
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