| 摘要 |
729,951. Emergency alarms. PERKINS, Ltd., F., and GIL, J. V. Nov. 10, 1953 [Dec. 4, 1952], No. 30807/52. Class 7(2). [Also in Groups XXVI and XXXVII] An alarm for an internalcombustion engine comprises a switch wherein one of the contacts is formed by a column of mercury disposed in a chamber connected with the engine induction manifold so that a fall in manifold pressure corresponding to a rise in engine speed above a predetermined value causes the column of mercury to close the switch and actuate the alarm. The switch comprises a metal body 1 having a sealed chamber 2 therein, formed by a recess closed by a cover 3 on which are mounted in air-tight manner, a connector 4 leading to the engine induction manifold and an adjustable rod contact 5, extending through a tubular insulator 6, and having a tapered end 12 projecting into the end of a tube 7 depending from the chamber 2 in a plugged bore 8, which is of larger diameter than the external diameter of the tube 7 and is vented to the atmosphere at 10. The tube 7 and the space 8 around it contain mercury such that, when the engine is at rest, the mercury is about ¥ in. from the top of the tube 7. When the engine is rtmning normally the depression in the chamber 2 due to the vacuum in the engine manifold causes the mercury to rise in the tube 7 but to be still clear of the contact 5. If the engine overspeeds, however, the mercury rises sufficiently to contact the rod 5 and close the switch to operate the alarm. In a modification a non-return ball valve is fitted in the connector 4 from the sealed chamber to the engine manifold to prevent mercury being drawn therein.
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