Electro hydraulic actuator with spring energized accumulators

An electro hydraulic actuator with built-in fail safes is provided. Multiple accumulators are integrated into the actuator to improve reliability and redundancy. One or more accumulators can fail and the remaining accumulators provide sufficient energy to move the actuator to its fail-safe condition.

FIELD OF THE INVENTION

This invention generally relates to electro-hydraulic actuators, and more particularly, to electro-hydraulic actuators having accumulators.

BACKGROUND OF THE INVENTION

Accumulators are devices that store energy in the form of fluid under pressure. Accumulators are useful tools in developing efficient hydraulic systems due to their ability to store excess energy and release it when needed. The accumulators can be used to provide various functions in hydraulic systems. These functions include leakage compensation, pulsation and shock absorption, noise elimination, and load counter-balance.

Traditional accumulators for electro-hydraulic actuators are the nitrogen gas loaded type. These accumulators are generally thought to consist of an elastic membrane charged with nitrogen to provide the potential energy to the hydraulic fluid to operate the actuators. The elastic membranes deteriorate over time, resulting in the nitrogen leaking into the hydraulic fluid. Typically, the nitrogen escapes slowly as the membrane deteriorates over time with no way of detecting the leak. The unknown failure of the accumulator can lead to unreliable operation of the hydraulic system.

Additionally, the accumulators are often added as an afterthought in hydraulic system designs and are haphazardly mounted around the hydraulic system wherever there is room with varying degrees of success.

The invention provides a failsafe electro-hydraulic actuator that overcomes the above-mentioned problems. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the invention provides an actuator system having multiple accumulators built into the actuator to provide fail-safe functionality. The integration of the accumulators results in a fully tested and validated, redundant fail-safe actuator.

In another aspect, the invention replaces the membrane and nitrogen charged base accumulator with a spring-loaded piston accumulator. With the use of multiple accumulators built into the actuator, any accumulator can cease to function properly when required and the other accumulators will fully stroke the actuator/valve to its fail-safe condition.

DETAILED DESCRIPTION OF THE INVENTION

The invention overcomes many problems of traditional accumulators by providing a failsafe electro-hydraulic actuator having multiple accumulators integrated into the actuator to provide fail-safe functionality. The integration of the accumulators results in a fully tested and validated, redundant fail-safe actuator. The membrane and nitrogen charged of the typical accumulator is replaced with a spring-loaded piston accumulator. With the use of multiple accumulators built into the actuator, any accumulator can cease to function properly and the other accumulators will fully stroke the actuator/valve to its fail-safe condition.

Turning now to the drawings wherein like reference numerals refer to like elements, the invention is illustrated as being implemented in a suitable operating environment. Although not required, the invention will be described in the general context of an electro-hydraulic actuator. Those skilled in the art will appreciate that the invention may be practiced with other configurations where accumulators are used.

Turning now to the figures, a hydraulic actuator100is illustrated. The actuator100is a double acting actuator. Those skilled in the art will appreciate that the invention may be implemented on other types of actuators, including, for example, single acting actuators. The hydraulic actuator100is only one example of a suitable operating environment and is not intended to suggest any limitation as to the scope of use or functionality of the invention. Neither should the actuator100be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary actuator100.

The hydraulic manifold102provides control fluid to the hydraulic piston104and to accumulators106. The piston104is connected to output rod108and may be used to control valves (not shown) by connecting the output shaft clevis110to the valve stem of the valve. The LVDTs (linear-voltage differential transformer [also known as linear variable differential transformer])112provide position information of the piston to the electrical junction box1114. While a single LVDT may be used, multiple LVDTs are used for redundancy and increased reliability of the system. Operation of the actuator is well known and need not be discussed in detail herein. For purposes of clarity, not all connections or piping is shown in the figures.

Each accumulator106is connected to actuator100via modular structures116,118. Modular structure116connects an accumulator106to the manifold102via a collection block120. Modular structure118connects the bottoms of the accumulators to the actuator100and support shafts122. The modular structures116,118have interlocking flanges124,126with bolt holes for attaching the structures to other structures. The collection block120has passageways128to connect fluid in the manifold102to the accumulators106. The support shafts122provide stiffness to the actuator100. Alternatively, the modular structures116and118along with collection block120may be replaced with hydraulic tubing that directly connects the accumulators106to the hydraulic manifold102.

The accumulators106replace the nitrogen of typical accumulators with coil springs140. The coil springs140are nested within the cylindrical housing142and are seated upon spring seat144and the spring bottom plate146. The spring bottom plate146forms the bottom of the accumulator106. The nested coil springs140and spring seat144are held within cylindrical housing142via a spring top plate148that is attached to the cylindrical housing142. The accumulators106replace the bladder of typical accumulators with piston150. The piston150does not deteriorate over time.

The piston150is located in a sleeve152that, in combination with the piston150, forms a storage cavity130for hydraulic fluid as will be discussed herein. The piston150has a base154that is attached to side wall156. The side wall156is also connected to spring seat144. Seals158prevent fluid from leaking into the area of the accumulator106where the springs140are located. During operation, the actuator hydraulic manifold102stores energy in the accumulator by allowing hydraulic supply pressure to push the piston150, thereby compressing the fluid (and the coil springs140from their default state). A check valve (not shown) prevents supply pressure from bleeding back into the supply system. During normal operation, the compressed fluid remains in the accumulators106. When the valve100is required to move to its fail-safe condition (i.e., piston104is in its open or closed condition), the manifold releases the stored energy from the accumulators106. The compressed springs140return to their default state, thereby releasing and pushing the compressed fluid (i.e., the stored energy) from the accumulators106to move the actuator to its safe condition.

The use of multiple accumulators106provides fault tolerance (i.e., redundancy). If an accumulator fails (e.g., a spring failure, a bound piston, etc.), the remaining accumulators provide sufficient energy to move the actuator to its safe condition. The charge stored in the accumulators in one embodiment are sized such that the remaining accumulators have sufficient stored energy to move the actuator to its fail-safe condition if an accumulator fails. In another embodiment, the accumulators are sized to move the actuator to its fail-safe condition if multiple accumulators fail.

It is possible that a spring140may fail. In one embodiment, visual indicators are provided on the cylindrical housing142that allow inspection of the springs140as well as confirmation of the charge status of the accumulator (i.e., position of spring seat144). The visual indicators also provide the ability to determine if the piston150is bound or otherwise stuck in the accumulator106.

As previously indicated, the accumulators106move the actuator to its fail-safe condition. The fail-safe condition may be either the open position (i.e., Fail Open) or the closed position (i.e., Fail Closed). In one embodiment, the actuator is easily modified in the field for either Fail Open or Fail Closed by setting the location of plugs160-166located in the manifold106. Plugs160,162are installed to put the actuator100in a Fail Closed mode. Plugs164,166are installed to put the actuator100in a Fail Open mode. The use of plugs provides the capability of using the same manifold in both Fail Open and Fail Closed modes of operation.

From the foregoing, it can be seen that a high loading actuator with built-in fail safes has been described. The invention can be used in many situations. For example, it can be used as a steam valve for a steam turbine. Multiple accumulators are integrated into the actuator to provide additional reliability. One or more accumulators can fail and the remaining accumulators provide sufficient energy to move the actuator to its fail-safe condition.