Patent Application
20240337326
This application claims priority to European (EP) Patent Application No. 23166614.0, filed Apr. 4, 2023, and to German (DE) Patent Application No. 102024104558.2, filed Feb. 19, 2024. The entireties of European (EP) Patent Application No. 23166614.0 and German (DE) Patent Application No. 102024104558.2 are incorporated herein by reference.
The present disclosure relates to a valve actuator and a method of reducing current consumption of the same.
Fail safe systems are increasingly incorporated into products and systems. One example fail safe system is with valves in machinery. If a system experiences a problem and power is lost, the system needs to fail in a safe manner. With respect to valves, this means that any valves should automatically close off preventing the undesirable continued flow of fluids which may present a hazard in a shut off system.
In order to achieve this automatic valve actuators may be provided with a return means, that, in the absence of power or when in an off state, places the actuator in a deactivated state, that is one where the valve would be closed.
This means that for a valve to be open, the actuator must be in an actuated state. Following the above fail safe requirements, the system must be on and drawing power to maintain the actuator in the activated state, as to not do so would engage the fail safe with the return means returning the valve to the closed position by deactivating the actuator.
While providing the advantageous properties of a fail safe, the down side is the continuous power draw by the activator to maintain the valve in the open state, against the return means. This means the activator is inherently inefficient as it requires a current draw constantly when in the activated position.
Therefore, it is an object of the present disclosure to provide a valve actuator, and method of controlling a valve actuator, that minimises the current draw even when in the activated position.
According to a first aspect of the disclosure, there is a provided valve actuator comprising a motor configured to move the actuator to an activated position; a return means, the return means biasing the actuator to a default deactivated position; a controller in communication with the motor, the controller configured to receive instructions regarding the actuation state of the actuator and to operate the motor according to those instructions; wherein the controller is further configured to operate the motor using a pulse width modulated current to allow the motor to overcome the return means and thereby maintain the actuator in the actuated position. The use of pulse width modulation means that the motor is controlled using a pulsed current rather than a constant current flow. The off periods therefore provide efficiency savings in reducing the amount of current consumed, thereby prolonging, for example, battery life in electric vehicles. Ideally the amount of pulse width modulated current supplied is the minimum required in order to prevent the force applied by the return means from dominating the system, which would lead to deactivation of the actuator.
Advantageously, the pulse width modulation comprises on periods and off periods, wherein a duration of the off periods is determined based on a time required by the return means to overcome a static friction of the valve actuator. In this way the minimum pulse length required to supply sufficient current to the motor to maintain the activated position of the actuator may be determined.
Preferably, the duration of at least one of the off periods is less than about 1 ms. Although it will be apparent that other durations may be required depending on a given system. Where, for example, the return means is a spring, the time required for the spring to overcome static friction in the system of a valve actuator is typically more than 1 ms. Therefore, by ensuring the duration of the off periods is less than the time required for the spring to overcome static friction, less current is required. The static friction and any other inherent impeding force in the system may be used to increase the duration of the off periods as no additional power is required by the motor to maintain the position of the actuator. The actuator is momentarily held in its activated position by the static friction inherent in the system.
Suitably a valve may be provided with the above described valve actuator, such that the actuator may be integrally formed with the valve during manufacture or pre-attached to the valve post manufacture of the valve. Alternatively, the actuator may be supplied separately to the valve and designed to be retro-fitted to suitable valves.
According to a second aspect of the disclosure, there is provided method of reducing current consumption of a valve actuator, the valve actuator comprising a motor configured to move the actuator to an activated position; a return means, the return means biasing the actuator to a default deactivated position; a controller in communication with the motor, the controller configured to receive instructions regarding the actuation state of the actuator and to operate the motor according to those instructions; wherein the method comprises applying, via the controller, a current to the motor to cause the motor to move the actuator from a deactivated position to an activated position; once the actuator is in the actuated position, applying, via the controller, a pulsed current to allow the motor to overcome the return means and thereby maintain the actuator in the actuated position. In this way current consumption may be reduced as only the current required to maintain the actuator in an activated position is used. The method can take advantage of static friction inherent in the system to prolong the off periods, thereby making additional savings of current consumption.
Example embodiment(s) of the disclosure are now described, by way of example only, hereinafter with reference to the accompanying drawings, in which:
The described example embodiment relates to a valve actuator and a method of reducing current consumption of the same. However, the disclosure is not necessarily restricted to valve actuators but may also be used with any other system that would benefit from the method of reducing current consumption as disclosed herein.
Certain terminology is used in the following description for convenience only and is not limiting. The words ‘right’, ‘left’, ‘lower’, ‘upper’, ‘front’, ‘rear’, ‘upward’, ‘down’ and ‘downward’ designate directions in the drawings to which reference is made and are with respect to the described component when assembled and mounted. The words ‘inner’, ‘inwardly’ and ‘outer’, ‘outwardly’ refer to directions toward and away from, respectively, a designated centreline or a geometric centre of an element being described (e.g. central axis), the particular meaning being readily apparent from the context of the description.
Further, as used herein, the terms ‘connected’, ‘attached’, ‘coupled’, ‘mounted’ are intended to include direct connections between two members without any other members interposed therebetween, as well as, indirect connections between members in which one or more other members are interposed therebetween. The terminology includes the words specifically mentioned above, derivatives thereof, and words of similar import.
Further, unless otherwise specified, the use of ordinal adjectives, such as, ‘first’, ‘second’, ‘third’ etc. merely indicate that different instances of like objects are being referred to and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking or in any other manner. Like reference numerals are used to depict like features throughout.
Referring now to
The valve actuator may suitably be used to activate any valve where, for safety or other reasons, the valve is to be placed in a closed position by default, e.g. when the system comprising the valve is in an off state or an error state, the valve will automatically close. The present actuator and method may be used to minimise power consumption by the valve actuator in having to actively maintain the valve in an open position during operation of the system comprising the valve. Example systems include, by way of non-limiting example, process control valves, safety relief valves, ballast system valves, heating, ventilation, and air conditioning systems (HVAC systems), fire protection system valves, and automotive vehicles, particularly electric vehicles and cooling systems for vehicles (such as battery and other cooling systems for electric vehicles).
The motor is any suitable for moving the valve actuator 100 from a deactivated position to an activated position, such as but not limited to, a DC motor; servo motor; stepper motor; AC motor with variable frequency drives (VFDs); or a brushless DC electric motor (BLDC motor). It should be noted here that deactivated position means a position in which the valve actuator places a valve connected thereto into a closed position. Activated position means a position in which the valve actuator places a valve connected thereto into a non-closed position, such as fully open or an intermediate state between closed and open such that a fluid flow is permitted but restricted below the full flow capacity of the valve in the open state. The motor must also be suitable to be controlled by pulse width modulation of a current.
The return means 102 is any suitable for moving the valve actuator 100 from an activated position to a deactivated position. Preferably the return means 102 is passive and automatic. That is, no outside control or instruction is required in order for the return means to perform the function of placing the valve actuator into a deactivated position. The return means 102 may be overcome by the motor, when the motor places the valve actuator into the open position. When the motor is not acting on the system the return means returns the valve actuator to a deactivated position, thereby ensuring any connected valve is always placed in the closed position when not in use.
The controller 101 supplies current to the motor to move the valve actuator 100 to an activated position according to the needs of the system, such as, by way of non-limitative example, opening a valve to permit the flow of coolant in a battery cooling system for an electric vehicle. The controller may operate the motor such that the valve is fully open, or turn off the motor thereby allowing the return means to operate and close the valve. The controller may be able to finely control the motor thereby permitting control of the volume of fluid allowed to pass through the valve in a given time. The controller may achieve this using pulse width modulation of current to the motor.
With reference to
The duration of the off periods may be tailored, and preferably maximised, in order to reduce the amount of current consumed by the motor. Due to inertia in the system and the time required for the return means to be able to begin moving the actuator into the deactivated position, the motor does not need to be provided with a constant current. The actuator will momentarily remain static, and in the state into which it was placed by the motor, without a current being supplied to the motor to maintain that state. The present disclosure takes advantage of that delay by only supplying current to ensure the actuator is maintained in the required state and using the delay in the return mechanism acting to stop supplying current for that period.
The inertia in the system is predominantly due to static friction which naturally resists motion and helps hold the valve in place. Static friction makes it possible to temporarily rest the motor without compromising the valve's position. Static friction is important at the beginning of movement because it requires a certain amount of force to overcome the initial resistance of the components of the actuator, for example a stationary geartrain, if present. This initial resistance is caused by the interaction of, for example, gear teeth and their contact with each other. Once the actuator is set in motion, the friction decreases considerably, and the motor/return means can then provide less torque to maintain the speed of operation of the valve actuator. However, at the start, it is important to have sufficient torque to overcome the static friction.
The duration of the off periods for a given system may be determined as follows:
Where I is the moment of inertia, a is acceleration, and Cn are the torques present in the system. It will be apparent that the torques comprises various components, including but not limited to the torque of the return means (such as a spring), torque provided by the load, and torque provided by static friction. The moment of inertia (I) may be calculated using:
I=mr
2
Where m is mass and r is the distance from the center of the mass to the axis of rotation.
Angular acceleration (a) may then be derived by:
T=Ia
Where T is the torque. The time may then be calculated using:
θ=0.5at2
Where e is the angular displacement, a is the angular acceleration and t is time. In an example system, rotation of 0.5° by the return means, for example, is required to overcome the static friction. This equates to, using the above formulae, approximately 1 ms (where the required torque is, by way of example, 0.2 Nm. The torque required will be system dependent). As the required torque is used in the above equations the pulse width modulation can be varied to inject the minimum required current to provide the necessary torque to the motor periodically, the period matching, or being less than, the time required to overcome the static friction.
It will be appreciated by persons skilled in the art that the above embodiment(s) have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departing from the scope of the invention as defined by the appended claims. Various modifications to the detailed designs as described above are possible.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23166614.0 | Apr 2023 | EP | regional |
| 102024104558.2 | Feb 2024 | DE | national |
