Abstract One or more liquid level sensors in the form of positive temperature coefficient (PTC) of resistivity elements suspended in probes are mounted in a fluid reservoir. The elements, electrically connected in a circuit, are either in a low or high resistance mode. When the elements are in a low resistance mode sufficient current passes through respective heaters to cause respective heat responsive, normally closed, switches connected to a liquid level indicator, to open. Initially upon energization of the system, the PTC elements are in the low resistance mode and the indicator is actuated until the switches receive sufficient heat to cause them to open. The PTC elements remain in the low resistance mode as long as the liquid level remains above the elements permitting heat generated in the elements to be dissipated; however, if the liquid level recedes sufficiently to expose the elements their temperature will rise until an anomaly point is reached beyond which resistance rapidly increases shutting off current to the heaters, permitting reclosing of the switches and reactuation of the indicator. The invention is particularly suited for use with a master cylinder of a vehicle as an indicator of an insufficient quantity of brake fluid in the braking system.
Switch means comprising an electrically insulative base; stationary contact means mounted on the base; a generally Wshaped movable contact assembly including a center leg of thermostatic material cantilever mounted on the base and having a free end spaced from the base, a supporting bar extending transversely in opposite directions from the free end and substantially longer than the width of the center leg, a first and second outer leg of thermostatic material cantilever mounted on respective ends of the support bar, each being adapted to move into and out of engagement with the stationary contact means, and a heater assembly cantilever mounted on each outer leg; and terminal means in the base for providing electrical connection to the heaters, stationary contact means and movable contact assembly.
Claim 2
Dependent Claim
126 words
Switch means comprising an electrically insulative base; stationary contact means mounted on the base; a generally Wshaped movable contact assembly including a center leg of thermostatic material cantilever mounted on the base and having a free end spaced from the base, a supporting bar extending transversely in opposite directions from the free end and substantially longer than the width of the center leg, a first and second outer leg of thermostatic material cantilever mounted on respective ends of the support bar, each being adapted to move into and out of engagement with the stationary contact means, and a heater assembly cantilever mounted on each outer leg; and terminal means in the base for providing electrical connection to the heaters, stationary contact means and movable contact assembly.
Claim 3
Dependent Claim
89 words
Switch means according to claim 1 in which each heater assembly compriseS a substrate having two ends and composed of electrically insulative material, an electrical resistance wire wrapped about the substrate between its two ends, two separate electrical leads and a clamp located at each end, each clamp biasing a respective lead into electrical contact with a portion of the electrical resistance wire, one of the clamps having two arms extending therefrom in clamping engagement with an outer leg of the movable contact assembly near the free end thereof.