Patent Application
20180320914
None.
The present invention relates generally to the field of pneumatic control devices and systems, and more particularly to pneumatic thermostats used to vary a pressure or flow control signal in a pneumatic system based upon a sensed temperature.
Many systems are pneumatically controlled based on a gas (generally air) flow or pressure. Pneumatic control systems tend to be simple and robust, operating over a wide range of temperature and other environmental conditions, and have long working lives. Pneumatic control systems reduce the likelihood of fires, because air is non-flammable. Pneumatic control systems pose no danger of electric shock, present no possible failure mode due to electrical short circuiting, and are relatively unaffected by electro-static discharge. Pneumatic control systems are mechanical devices that may avoid the need for a power source (in short or long term), thereby reducing wiring requirements, and may be unaffected by electricity fluctuations or power outage. Pneumatic control systems are environmentally friendly, as leakages in the system do not negatively affect the outside environment or cause pollution.
The pneumatic control signal can be determined on any number of sensed input parameters, with a commonly sensed input being temperature, in which case the pneumatic control device is commonly called a pneumatic thermostat. Pneumatic thermostats convert a substantially constant pressure air supply into a pressurized air signal indicative of sensed ambient temperature. Pneumatic thermostats are used in many pneumatic systems, with a common use being to control variable air volume (VAV) units (such as disclosed in U.S. Pat. No. 4,957,238, incorporated by reference), ventilators, radiators, coil units, fans, dampers, valves and the like in heating, ventilation, air conditioning (HVAC) systems. Pneumatic thermostats are still reliable workhorses that control temperature in many older buildings across the country.
One example of a pneumatic thermostat is shown in U.S. Pat. Pub. No. 2011/0166712, incorporated by reference, which combines a valve unit (typically a diaphragm type valve), a “flapper” controlled nozzle, and a bimetallic strip. Supply air is passed through the valve unit, which controls the pressure at an outlet, after allowing a portion of the supply air to exit into the atmosphere through the flapper-controlled nozzle. The bimetallic strip is linked to the flapper, and the position of the flapper over the control nozzle (and hence the outlet pressure) moves responsive to changes in temperature witnessed by the bimetallic strip. While pneumatic thermostats such as described in U.S. Pat. Pub. No. 2011/0166712 provide certain advantages, they tend to have reduced accuracy particularly associated with the bimetallic strip.
Largely separate from the pneumatic thermostat industry, the field of piezo electrics is becoming more well-known. Piezo electrics are advantageous in that the power consumption is low. One of the rare instances in which piezo electrics are applied to a pneumatic thermostat is shown in U.S. Pat. No. 8,527,099, which teaches an embodiment using a piezo electric device as a prime mover controlled by a bimetallic strip based pneumatic thermostat.
The present invention is a low powered pneumatic control converter which produces a pneumatic control signal using as little power consumption as possible and in as small a package as possible. The pneumatic control converter is primarily envisioned to act as a pneumatic thermostat, in which accuracy (particularly at low temperature) is improved by using a temperature sensor which outputs an electronic value, and the pneumatic control converter changes that sensed electronic value into a pneumatic control. The pneumatic control converter utilizes a piezo electric rotary motor which powers a mechanical linkage to adjust the ball nozzle which controls the pneumatic control output pressure. The preferred mechanical linkage includes a rotary cam pushing a cam follower against a spring flexure, with an opposing arm of the spring flexure biasing the position of the ball nozzle.
While the above-identified drawing figures set forth a preferred embodiment, other embodiments of the present invention are also contemplated, some of which are noted in the discussion. In all cases, this disclosure presents the illustrated embodiments of the present invention by way of representation and not limitation. Numerous other minor modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.
A preferred embodiment of a low powered pneumatic control converter in accordance with the present invention is shown in
The pneumatic section is largely similar to prior pneumatic thermostat controllers, such as the two-pipe single set point pneumatic room thermostats available from KMC Controls of New Paris, Ind. under model numbers CTC-1621 and CTC-1622. On the back or bottom side, the pneumatic section includes a main or supply air port and a branch or output port. In the preferred embodiment, each of the supply air port and the branch port support 3/32 inch (2.5 mm) inner diameter tube fittings. In use, the supply air port is connected in fluid communication to the pneumatic power (pressurized air source) within the building, typically with a supply pressure in the 20-30 psig (138-207 kPa) range. A controlled device, typically a valve or damper actuator, is connected in fluid communication to the branch port.
The supply air port feeds to a supply pressure chamber with a valve disc, with main and exhaust valve seats on its upper surface. A restrictor is positioned between the supply pressure chamber and a signal chamber, with the signal chamber having a ball/signal nozzle which vents to ambient/atmosphere. The restrictor bleeds the air flow to the signal nozzle. The pressure then witnessed in the signal chamber depends upon the downward force applied to the ball in the signal nozzle. The signal chamber extends over the signal diaphragm, such that pressure in the signal chamber pushes downward on the signal diaphragm. A branch diaphragm extends over a branch chamber, with the signal diaphragm and the branch diaphragm both linked to the valve disc. If pressure on the signal diaphragm is greater than pressure on the branch diaphragm, the valve disc opens the main valve seat allowing more pressure to build in the branch chamber. If pressure on the signal diaphragm is less than pressure on the branch diaphragm, the exhaust valve seat opens allowing branch pressure to escape to ambient/atmosphere. In the preferred embodiment, there is also a pressure sensor port exposed on the front or top side of the pneumatic section. A pressure sensor (not shown) can then be connected in fluid communication to monitor the branch port pressure at the pressure sensor port.
Like prior art pneumatic thermostats, the branch port pressure is controlled over a range of about 3 to 13 psig. Like prior art pneumatic thermostats, the output capacity is about 200 scim (55 mL/s) and the consumption is about 20 scim (5.5 mL/s).
In the piezo electronic section of the pneumatic control converter, a piezo electronic rotary motor is provided and makes up the general footprint of the piezo electronic section. A preferred piezo electronic rotary motor includes a surface mounted stator on a piezo electronic printed circuit board and a rotor rotationally mounted immediately above the stator. In the preferred embodiment, the stator and rotor are each about 0.8 inches (20 mm) in diameter. Such piezo electronic rotary motors are available from PCBMotor ApS of Ballerup, Denmark.
A rotary cam, best shown in
The flexure linkage, shown individually in
The flexure linkage acts as a spring mechanism, translating the elevation of the cam follower into a downward force on the ball of the signal nozzle in the pneumatic section. To achieve the desired spring action, the flexure linkage is preferably formed of a shape retaining elastic spring material, which (unlike prior art bimetal strips) does not flex based upon temperature, but rather flexes to provide a spring force which is generally temperature insensitive and only based on the position of the rotary cam. In the preferred embodiment, the flexure linkage is stamped out of 0.005 inch (0.13 mm) thick ¾ hardness 301 stainless steel sheet material. The preferred flexure linkage has a W-shape, with the outer legs of the W-shape having mounting openings. The outer legs of the flexure linkage are about ⅛ inches (3 mm) wide and almost 1 inch (24 mm) long, providing a spring force which biases the cam follower downward but allows the cam follower to change its elevation by the amount of the entire change of elevation of the cam surface. The center leg of the W-shape is similarly about ⅛ inches (3 mm) wide and almost 1 inch (24 mm) long. When the cam follower moves upward due to rotation of the cam and rotor, the outer legs of the flexure linkage act as elastic beams which curve under bending stress, changing the angle of the bottom of the W-shape (near the cam follower) relative to the mounting angle of the flexure linkage. This changing of the angle of the bottom of the W-shape in turn causes the opposite end of the center leg to push downward, i.e., the more the cam follower raises the bottom of the W-shape, the harder the center leg pushes the ball of the signal nozzle downward.
The preferred cam has a lift within a range of 0.02 to 0.5 inches (0.5 to 13 mm), with the most preferred lift being about 0.075 inches (2 mm). The cam has a total throw during operation (from lowest to highest achievable branch pressure) which is less than 360°, and more preferably within the range of 180 to 360°, with the most preferred total throw being about 340°, such that positioning of the rotor across about a 340° rotational range changes the cam follower elevation by about 0.075 inches (2 mm). The preferred translation from rotational position to cam height is linear, i.e., each 1° of rotation of the rotor changes the elevation of the cam follower by an equal amount, but alternative embodiments permit a curvature to the cam surface so different circumferential positions have different sensitivities.
The preferred arrangement, with the motor, cam and flexure linkage as described, is believed to be more precise and consistent than the downward spring force provided by temperature induced flexing of the bimetal strip in prior art pneumatic thermostats. The precision and consistency is believed to exist across a wide range of temperatures, altitudes, humidities and mounting orientations, over years or decades of life. Using a stainless steel sheet material for the spring helps minimize any corrosion or change in spring force across the years of life of the pneumatic control converter. The cam and the flexure linkage are particularly inexpensive and relatively simple to manufacture.
In the electronics section of the pneumatic control converter, a driver board is mounted for supporting electronic components on a printed circuit board, such as the driver chips and other electronic components (not shown). For instance, the driver board may include the pressure sensor, if an electronic value of sensed pressure is desired. The driver board may also include a temperature sensor having an electronic output, as well as a microcontroller to convert the sensed electronic output of the temperature sensor into an electronic control signal for the piezo-electronic rotary motor. The driver board may also include communication electronics, permitting wired or wireless communication with the microcontroller. Such communication electronics may permit remote monitoring of temperature and branch pressure, automatic setpoint changes based on time-of-day schedule and night setback, and/or automatic calibration for setpoint offsets. Alternatively, the pressure sensor electronics, the temperature sensor electronics, the microcontroller chip/electronics and/or the communication electronics may be housed on a separate controller board (not shown). The preferred embodiment includes a power supply, which may be electronic components to smooth or control electric building power (such as either 120V AC or 24 V DC), but more preferably includes a battery (not shown) and electronic components to control/smooth the battery output.
The present invention is preferably housed in a package which is aesthetically pleasing for mounting in a building, similar to prior art pneumatic thermostats. For instance, the preferred embodiment fits within a cover (not shown) which has dimensions of about 5⅛ inches (130 mm)×3½ inches (89 mm)×1 7/16 inches (37 mm). The cover may include a door and a mounting arrangement for one or more batteries. The cover may also include a display, such as for displaying the sensed temperature or other information, as well as an input device such as for changing the setpoint temperature or throttling range. For optimum performance, the pneumatic control converter when used as a thermostat should be mounted on an interior wall and away from heat sources, sunlight, windows, air vents, and air circulation obstructions (e.g., curtains, furniture). Units may be mounted horizontally or vertically to either a 2″×4″ electrical box or a hollow wall.
The accuracy of the preferred pneumatic control converter is more than sufficient for pneumatic control, and is usually limited by the accuracy of the temperature sensor and its electronic output rather than the accuracy of either the piezo-electric motor or the cam and flexure linkage. For instance, a preferred embodiment has a setpoint temperature range of 55° F. to 85° F. in 1° F. increments. The preferred temperature sensor is connected with a 10 bit A/D register providing a resolution of about 0.16° F. The preferred embodiment has a sensitivity which is controllable over a range of 2-12 psi/° F., i.e., its most needed resolution/greatest number of steps is at 2 psi/° F. where each 0.16° F. temperature change results in 0.32 psi output pressure change. From minimum (1 psig) to maximum (20 psig) output pressure, the 0.32 psi/step resolution results in about 60 different steps from minimum to maximum output pressure. With 340° of possibly cam rotation provided in 60 steps, the highest needed resolution for each differently sensed temperature is 5°-6° of cam rotation. Due to the limits of the temperature sensor and sensitivity settings, no greater fidelity is required. However, it should be noted that the piezo electric motor and cam arrangement allows much greater fidelity and accuracy if needed for using the pneumatic control converter for other applications. High resolution piezo electric motors available from PCBMotor ApS with encoders have sensitivities from 200 to 800 lines per 360° revolution, and micropulsing can be used to increase the resolution to as small as 1/2,500,000 of a revolution.
In embodiments that include a pressure sensor, the difference between the setpoint temperature and the sensed temperature can be combined with the input throttling range to have the microcontroller compute what the output pressure should be. The pneumatic control converter then measures the output pressure electronically and compare this to the desired pressure. The position of the rotor and cam is then adjusted to cause the pneumatic valve to put out the desired pressure. Embodiments that include a pressure sensor are particularly beneficial if there is any wear or change in the performance of the ball in the signal nozzle over time or based on operating conditions (operating temperature, humidity, elevation, etc.).
An alternate arrangement might replace the cam with a lead screw and nut assembly. This would provide linear motion which could move the input of the flexure. A benefit of using a lead screw in place of the cam/cam follower is that the rotation of the cam is limited to a value less than 360°, whereas the lead screw can be rotationally advanced over a number of 360° turns, allowing even less precision of the piezo electric motor. Another alternate arrangement would use a compression spring, a tension spring or a leaf spring acting on the ball of the signal nozzle rather than the preferred flexure.
The preferred embodiment uses a piezo electric motor instead of a stepper motor to reduce power consumption. In the case of the thermostat application, the pneumatic control converter is a battery powered device, where low power consumption is a necessity. The main valve arrangement of the preferred embodiment is such that it can supply a continuous flow of air if the control device is consuming air even while the piezo electric motor is unpowered. The preferred embodiment is believed to provide a battery life, in most applications, of about 2 years or more.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
