Electromechanical thermostatic mixing valve

Automatic temperature and humidity regulation – Mixing fluid of dissimilar temperature – Mixing valve with temperature motive means

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Details

236 122, 236101D, G05D 2313

Patent

active

054009618

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a thermostatic mixing valve for use with sinks, wash basins, bathtubs, showers and like facilities for mixing hot and cold water to deliver a mixture of a controlled temperature. More particularly, this invention is concerned with an electromechanical thermostatic mixing valve wherein transient fluctuation in the temperature is primarily compensated for by a mechanical feedback control performed by a thermostatic control element and persistent offset of the temperature is primarily compensated for by an electrical feedback control carried out by an electrical control circuit.


BACKGROUND ART

As is well-known, the conventional thermostatic mixing valves typically include a thermostatic control element of the so-called "wax" type wherein thermally expansive paraffin wax composition is charged. The control element is adapted to feedback control the position of a mixing valve member in response to the temperature of a mixture of hot and cold water in such a manner that a mixture having a desired temperature is provided. When fluctuation occurs in the supply line pressures, supply temperatures or flow rates, causing a change in the mixture temperature, the heat sensitive wax composition expands or contracts in response to such temperature change to automatically displace the valve member. After repeating a number of cycles of overshooting and undershooting, the valve member will finally be adjusted to a new position wherein the actual mixture temperature is brought close to the desired temperature.
Generally, the paraffin wax composition used in the thermostatic control elements is adapted to exhibit a volumetric change due to phase transformation between the solid and liquid phases. Because such change in phase necessarily involves absorption and evolution of the latent heat, in addition to transfer of the sensible heat, the heat capacity thereof is considerably large. Moreover, the paraffin composition has a poor thermal conductivity. Accordingly, the disadvantage of the wax type thermostatic element is that the responsiveness thereof is limited. It has often been observed that, once transitional change has occurred in water temperature for any reasons, several seconds of overshooting and undershooting of temperature of an intolerable magnitude unavoidably last in the conventional mixing valves before the delivery of water having the desired temperature is resumed.
In order to improve the responsiveness, use of a thermostatic control element made of a shape memory alloy such as an alloy formed of nickel and titanium has been proposed in the prior art (see, e.g., Japanese Utility Model Kokai Publication No. 58-11177; Japanese Patent Kokai Publication No. 58-24669; Japanese Utility Model Kokai Publication No. 58-187666; Japanese Utility Model Kokoku Publication No. 61-44062; Japanese Utility Model Kokoku Publication No. 61-23987; Japanese Utility Model Kokai Publication No. 61-150585). These references generally refer to the shape memory alloy (SMA) as being a metal having a shape memory effect wherein the shape of an article deformed below the martensitic transition temperature of the SMA tends to spring back to the initial shape imparted in the austenitic mother phase when heated above the transition temperature. It is believed, however, that the property of the SMA that the modulus of elasticity thereof varies with temperature is more important in its application to the thermostatic control elements.
The prior art cited above discloses a thermostatic mixing valve having a coiled spring made of the SMA. Throughout various references, a valve member controlling the flow of hot and cold water is supported between the coiled spring made of the SMA and another coiled bias spring made of the conventional spring steel. The valve member is held in such a position that the spring force of the SMA spring and that of the bias spring are balanced. During transitional condition wherein the mixture temperature is altered, the spring force of the SMA spring varies in resp

REFERENCES:
patent: 4029256 (1977-06-01), Dauga
patent: 4349149 (1982-09-01), Humpert
patent: 4640457 (1987-02-01), MacDonald
patent: 5025983 (1991-06-01), Akita
patent: 5261597 (1993-11-01), Perlman
Patent Abstracts of Japan, vol. 12, No. 160, M-697, abstract of JP, A, 62-278389, Dec. 3, 1987.

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