US3760352A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Liquid level indicating system
Assignee: Texas Instruments Inc
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Filing: 1971-07-06
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Granted: 1973-09-18
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Expires: 1991-07-06
Abstract
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.
Inventors
- 👤 L Marcoux
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 22:38
CPC Classifications
G; G01; G01F; G01F23/00; G01F23/22; G01F23/24; G01F23/246; G01F23/247; B; B60; B60T; B60T17/00; B60T17/18; B60T17/22; B60T17/225; Y; Y10; Y10T; Y10T137/00; Y10T137/7287; Y10T137/7306
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
249 words
A vehicle having braking means including a master cylinder, means defining two reservoirs in the cylinder, a probe extending into each reservoir, a thermistor having a positive temperature coefficient with a low resistance mode at temperatures below an anomaly temperature and a high resistance mode at temperatures above the anomaly temperature mounted in each probe, switching means and indicating means mounted in the vehicle, the switching means switchable from one condition to another in response to a change in resistance of the thermistor from one resistance mode to the other resistance mode, the indicating means being actuated by the switch in one of its two conditions, the switching means comprises an electrically insulative base; stationary contact means mounted on the base; a generally W-shaped 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; terminal means in the base for providing electrical connection to the heaters, stationary contact means and movable contact assembly, the heaters electrically coupled to respective thermistors and electrical power supply means for the thermistor and switch.
Claim 2
Dependent Claim
249 words
A vehicle having braking means including a master cylinder, means defining two reservoirs in the cylinder, a probe extending into each reservoir, a thermistor having a positive temperature coefficient with a low resistance mode at temperatures below an anomaly temperature and a high resistance mode at temperatures above the anomaly temperature mounted in each probe, switching means and indicating means mounted in the vehicle, the switching means switchable from one condition to another in response to a change in resistance of the thermistor from one resistance mode to the other resistance mode, the indicating means being actuated by the switch in one of its two conditions, the switching means comprises an electrically insulative base; stationary contact means mounted on the base; a generally W-shaped 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; terminal means in the base for providing electrical connection to the heaters, stationary contact means and movable contact assembly, the heaters electrically coupled to respective thermistors and electrical power supply means for the thermistor and switch.
Claim 3
Dependent Claim
68 words
A vehicle according to claim 1 in which each thermistor has two leads attached to spaced portions of the thermistor and extending in generally opposite directions, the probes supporting the respective thermistors only by the thermistor leads thereby permitting brake fluid in the cylinder, when there is sufficient quantity in the cylinder, to inundate the respective thermistors to obtain optimum heat transfer between the thermistor and the fluid.
Claim 4
Dependent Claim
195 words
Fluid level indicating apparatus comprising: means defining a reservoir, a probe mounted to extend into the reservoir, a thermistor having a positive temperature coefficient of resistivity with a low resistance mode at temperatures below an anomaly temperature and a high resistance mode at temperatures above the anomaly temperature, the thermistor mounted in the probe and adapted to be inundated by fluid when a sufficient quantity is contained in the reservoir, switching means interconnnected with the thermistor, the switching means comprises a thermostatic element movable to and from first and second positions responsive to respective high and low resistance modes of the thermistor, heating means in heat transfer relation with the thermostatic element and electrically interconnected with the thermistor, the heating means generating sufficient heat to cause the thermostatic element to move from said one position to said second position when the thermistor is in the low resistance mode, the heating means generating insufficient heat to cause the thermostatic element to move from said one position to said second position when the thermistor is in the high resistance mode and indicating means energizable when the switching means is in one of the first and second conditions.
Claim 5
Dependent Claim
195 words
Fluid level indicating apparatus comprising: means defining a reservoir, a probe mounted to extend into the reservoir, a thermistor having a positive temperature coefficient of resistivity with a low resistance mode at temperatures below an anomaly temperature and a high resistance mode at temperatures above the anomaly temperature, the thermistor mounted in the probe and adapted to be inundated by fluid when a sufficient quantity is contained in the reservoir, switching means interconnnected with the thermistor, the switching means comprises a thermostatic element movable to and from first and second positions responsive to respective high and low resistance modes of the thermistor, heating means in heat transfer relation with the thermostatic element and electrically interconnected with the thermistor, the heating means generating sufficient heat to cause the thermostatic element to move from said one position to said second position when the thermistor is in the low resistance mode, the heating means generating insufficient heat to cause the thermostatic element to move from said one position to said second position when the thermistor is in the high resistance mode and indicating means energizable when the switching means is in one of the first and second conditions.
Claim 6
Dependent Claim
124 words
Apparatus according to claim 3 further including power supply means adapted to provide power to the apparatus and in which said first position is a closed circuit position and the said second position is an open circuit position, the indicating means including an electrical lamp energized when the thermostatic element is in the first closed circuit position whereby upon initial energization of the apparatus the lamp is energized giving positive indication that the apparatus is operative and upon continued energization heat from the heating means causes the thermostatic element to move to the second open circuit position deenergizing the lamp and maintaining it deenergized as long as the level of fluid in the reservoir indundates the thermistor keeping it in the low resistance mode.
Claim 7
Dependent Claim
103 words
Apparatus according to claim 3 in which the probe comprises a generally elongated body having an open mounting end and a closed end, means on the open mounting end for fixedly mounting the probe in a probe receiving aperture, a terminal pin and electrically insulative header means closing the open end of the body with the terminal pin electrically isolated from the body, axially extending apertures formed in the body to permit fluid to flow freely therethrough, two electrical leads of fine wire attached to spaced portions of the thermistor and respectively to the terminal pin and the closed end of the body.
Claim 8
Dependent Claim
39 words
Apparatus according to claim 5 in which the portion of the probe extending from the mounting means to the closed end, the electrical leads and the thermistor are all coated with a thin layer of corrosion resistant polymeric material.
Claim 9
Dependent Claim
30 words
Apparatus according to claim 5 in which the axial slots extend from the mounting portion of the body along the major portion of the body length toward the closed end.
Claim 10
Dependent Claim
22 words
Apparatus according to claim 3 further including brake fluid contained in the reservoir, the thermistor having an anomaly Temperature of approximately 180*C.
Claim 11
Dependent Claim
87 words
Apparatus 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, an electrical lead 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.
Claim 12
Dependent Claim
23 words
Apparatus according to claim 9 including a layer of electrical insulating material interposed between each outer leg and the respective heater assembly. electrical
Claim 13
Dependent Claim
125 words
Apparatus according to claim 3 in which the switching means includes a base of electrically insulative material, a stationary contact mounted on the base, a movable contact assembly comprising an ambient compensating thermostatic element cantilever mounted on the base with the free end spaced from the base, a supporting bar having a distal end extending transversely from the free end of the ambient compensating element, a thermostatic leg cantilever mounted on the distal end of the supporting bar and adapted to move into and out of engagement with the stationary contact, a heater assembly cantilever mounted on the thermostatic leg near its free end, and terminal means mounted in the base to provide electricl connection for the stationary contact, movable contact assembly and heater assembly.
Claim 14
Dependent Claim
97 words
Vehicular brake fluid level indicating apparatus comprising: a vehicle; a master cylinder mounted in the vehicle, the cylinder defining a fluid reservoir; a probe mounted in the cylinder and extending into the reservoir, the probe mounting a positive temperature coefficient (PTC) element; switching means mounted in the vehicle, the switching means including a thermal element, a heater mounted in heat exchange relation to the thermal element and serially connected to the PTC element; and an electrical circuit including indicating means, the thermal element adapted to energize and deenergize the circuit upon sufficient deflection of the thermal element.
Claim 15
Dependent Claim
97 words
Vehicular brake fluid level indicating apparatus comprising: a vehicle; a master cylinder mounted in the vehicle, the cylinder defining a fluid reservoir; a probe mounted in the cylinder and extending into the reservoir, the probe mounting a positive temperature coefficient (PTC) element; switching means mounted in the vehicle, the switching means including a thermal element, a heater mounted in heat exchange relation to the thermal element and serially connected to the PTC element; and an electrical circuit including indicating means, the thermal element adapted to energize and deenergize the circuit upon sufficient deflection of the thermal element.
Claim 16
Dependent Claim
230 words
A vehicle having braking means including a master cylinder, a probe extending into the cylinder, a temperature sensitive thermistor having a first resistance mode at temperatures below an anomaly temperature and a second resistance mode at temperatures above the anomaly temperature mounted in the probe, switching means and indicating means mounted in the vehicle, the switching means switchable from one condition to another in response to a change in resistance of the thermistor from one resistance mode to the other resistance mode, the indicating means being actuated by the switch in one of its two conditions, the switching means includes a base of electrically insulative material, a stationary contact mounted on the base, a movable contact assembly comprising an ambient compensating thermostatic element cantilever mounted on the base with the free end spaced from the base, a supporting bar having a distal end extending transversely from the free end of the ambient compensating element, a thermostatic leg cantilever mounted on the distal end of the supporting bar and adapted to move into and out of engagement with the stationary contact, a heater assembly cantilever mounted on the thermostatic leg near its free end and electrically coupled to the thermistor, terminal means mounted in the base to provide electrical connection for the stationary contact, movable contact assembly and and heater assembly and electrical power supply means for the thermistor and switch.
Claim 17
Dependent Claim
230 words
A vehicle having braking means including a master cylinder, a probe extending into the cylinder, a temperature sensitive thermistor having a first resistance mode at temperatures below an anomaly temperature and a second resistance mode at temperatures above the anomaly temperature mounted in the probe, switching means and indicating means mounted in the vehicle, the switching means switchable from one condition to another in response to a change in resistance of the thermistor from one resistance mode to the other resistance mode, the indicating means being actuated by the switch in one of its two conditions, the switching means includes a base of electrically insulative material, a stationary contact mounted on the base, a movable contact assembly comprising an ambient compensating thermostatic element cantilever mounted on the base with the free end spaced from the base, a supporting bar having a distal end extending transversely from the free end of the ambient compensating element, a thermostatic leg cantilever mounted on the distal end of the supporting bar and adapted to move into and out of engagement with the stationary contact, a heater assembly cantilever mounted on the thermostatic leg near its free end and electrically coupled to the thermistor, terminal means mounted in the base to provide electrical connection for the stationary contact, movable contact assembly and and heater assembly and electrical power supply means for the thermistor and switch.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-09-17 | 1977-03-19 | 1977-09-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-09-17 | 1981-03-19 | 1981-09-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-09-17 | 1985-03-19 | 1985-09-18 | $7700.00 | Window Closed / Lapsed |