GB1046615A - Improvements in and relating to fluid pressure operated electric switches - Google Patents

Abstract

1,046,615. Fluid actuation of switches; thermal switches. AUTOMOTIVE PRODUCTS CO. Ltd. June 28, 1963 [June 28, 1962], No. 24907/62. Heading H2B. A combined fluid-pressure and thermal switch comprises contacts closed by increase in pressure in series with contacts closed by increase in temperature of the pressure fluid such that a signalling circuit is completed only upon coincident rises in pressure and temperature. The device is particularly applicable to signalling the condition of an oil filter, for example, of a road vehicle engine wherein a pressure difference across the filter when the oil is cold is not significant but the same pressure difference when the oil is hot is required to signal a warning that the filter is clogged. In a first embodiment (Fig. 2, not shown) the switch comprises two body parts 3 and 4 held together by screws (Fig. 1, not shown) clamping a diaphragm 6 therebetween. Screws 2 secure the switch to the cover of a filter such that passages 9 and 10 allow oil from opposite sides of the filter to pass respectively to opposite sides of diaphragm 6. A bell-shaped contact 12 is carried by diaphragm 6, while another 13 is insulatingly secured to the part 4 by a rivet 14. A terminal tag 18 is connected via rivet 14 and a spring 19 to contact 12. A circular bimetallic element 20 is clamped between contact 13 and insulating washer 16 and has tongues 21 which move into contact with the inner wall of part 4 when the oil is hot, but isolate contact 13 when the oil is cold. Thus when oil pressure lifts diaphragm 6 to close contacts 12 and 13 a signalling circuit between the casing and tag 18 is not completed unless the oil temperature is such as to cause the element 20 to connect contact 13 to the casing. In a second embodiment (Fig. 5, not shown), the switch is built into the filter cover itself. Oil inlet 28 communicates with an annular passage 30 and passages 29 from the other side of the filter connect with outlet 27. A ball 32 urged by spring 34 normally closes an opening between passages 30 and 27 but when lifted by oil pressure contacts the end of stud 35 which is mounted in insulation 36 and carries a bimetallic strip 38. When the oil is hot strip 38 engages contact 40 and a circuit between tag 45 and the casing can be completed by ball 32.