Device for electrically monitoring oil level, particularly in automobile internal combustion engines

• US 4,845,469 A
• Filed: 06/05/1986
• Issued: 07/04/1989
• Est. Priority Date: 06/05/1985
• Status: Expired due to Fees

• Current Assignee: VDO Adolf Schindling AG (Vodafone Group PLC)
• Original Assignee: VDO Adolf Schindling AG (Vodafone Group PLC)
• Inventors: Benda, Franz
• Primary Examiner(s): Orsino, Joseph A.
• Assistant Examiner(s): Hofsass, Jeffery A.
• Application Number:
  US06/871,030
• Time in Patent Office: 1,125 Days
• Field of Search: 340/59, 340/618, 340/620, 340/622, 73/304 R, 73/290 R, 73/295
• US Class Current: 340/450.3
• CPC Class Codes: G01F 23/04 by dip members, e.g. dip-sticks
• CPC Class Codes: G01F 23/246 thermal devices

Abstract

In a device for electrically monitoring oil level, particularly in automobile internal combustion engines, a first temperature-dependent resistance element (1) is housed within a hollow space in an oil measurement rod and positioned at the height of a filling level. The device signals a dropping of the oil level below the filling level. A first resistance element is connected to an evaluation circuit having a source of current (17-23, 26, 27). A second temperature-dependent resistance element (16) is located in the oil measurement rod at a lower point than the first temperature-dependent resistance element (1). In order to be able to monitor the oil level over a large temperature range, the second temperature-dependent resistance element (16) can be switched to the evaluation circuit (emitter resistor 19) for correction of a switching threshold of the evaluation circuit as a function of temperature.

Claims

1. A device for electrically monitoring oil level, particularly in automobile internal combustion engines, comprising:

an oil measurement rod having a hollow space;

a display of oil temperature;

a first temperature-dependent resistance element housed in said hollow space;

an elevation circuit including an oil-level indicator and first switching means for activating said indicator, said first switching means having an oil-level sensitive switching thresholds; and

a second temperature-dependent resistance element housed in said measurement rod at a lower place than a location of said first resistance element; and

wherein

said first resistance element is positioned in said oil measurement rod at the height of a filling level, a dropping of the level of oil below the filling level activating said evaluation circuit to energize said indicator, said evaluation circuit being connected to said first resistance element and being responsive to current of a source of current applying current to said first resistance element, said evalution circuit switching at at least one switching threshold to energize said indicator; and

wherein

said evaluation circuit further comprises second switching means coupled to said second resistance element for switching said second resistance element to the evaluation circuit for adjusting the switching threshold as a function of the temperature, said first switching means being operative to direct current from said current source serially through said indicator and said second resistance element concurrently with a connection of said second resistance element to said evaluation circuit by said second switching means, said second switching means being operative to direct current from said current source serially through said display and said second resistance element upon a disconnection of said second resistance element from said evaluation circuit.

2. The device according to claim 1, wherein said evaluation circuit further comprises

a bridge circuit having a neutral branch, said first switching means including a transistor having a control terminal within said neutral branch, said transistor emitting a signal which signals that the filling level has dropped;

and wherein

said bridge further comprises a first arm and a second arm, said first bridge arm including said first resistance element, said second resistance element being switchable by said second switching means to said second bridge arm.

3. The device according to claim 1, wherein

said first resistance element is a PTC-resistor, and said second resistance element is an NTC-resistor;

said evaluation circuit further comprising;

a bridge circuit having a neutral branch; and

wherein

said first switching means includes an npn-transistor with a base-emitter path located in said neutral branch of the bridge circuit, the bridge circuit further comprising an emitter resistor coupled to the emitter of said transistor; and

wherein said second resistance element is switched by said second switching means to be in parallel to the emitter resistor.

4. A device for electrically monitoring oil level, particularly in automobile internal combustion engines, comprising:

an oil measurement rod having a hollow space;

a first temperature-dependent resistance element housed in said hollow space;

an evaluation circuit including an oil-level indicator and first switching means for activating said indicator, said first switching means having an oil-level sensitive switching threshold; and

a second temperature-dependent resistance element housed in said measurement rod at a lower place than a location of said first resistance element; and

wherein

said first resistance element is positioned in said oil measurement rod at the height of a filling level, a dropping of the level of oil below the filling level being signaled by said evaluation circuit, said evaluation circuit being connected to said first resistance element and having a source of current, said evaluation circuit switching at at least one switching threshold; and

wherein said evaluation circuit further comprises second switching means coupled to said second resistance element for switching said second resistance element to the evaluation circuit and adjusting the switching threshold as a function of the temperature;

the evaluation circuit further comprising

a bridge circuit having a neutral branch, said first switching means including a transistor having a control terminal within said neutral branch, said transistor emitting a signal which signals that the filling level has dropped; and

wherein

said bridge further comprises a first arm and a second arm, said first bridge arm including said first resistance element, said second resistance element being switchable by said second switching means to said second bridge arm;

the device further comprising

means coupled to said second resistance element and to said second switching means for displaying temperature; and

wherein

said second switching means is a push-button switch by which said second resistance element is switched, alternatively, for connection and disconnection to the second arm of said bridge for indicating the oil level and for displaying temperature.

5. A device for electrically monitoring oil level, particularly in automobile internal combustion engines, comprising:

an oil measurement rod having a hollow space;

a first temperature-dependent resistance element housed in said hollow space;

an evaluation circuit including an oil-level indicator and first switching means for activating said indicator, said first switching means having an oil-level sensitive switching threshold; and

a second temperature-dependent resistance element housed in said measurement rod at a lower place than a location of said first resistance element; and

wherein

said first resistance element is positioned in said oil measurement rod at the height of a filling level, a dropping of the level of oil below the filling level being signaled by said evaluation circuit, said evaluation circuit being connected to said first resistance element and having a source of current, said evaluation circuit switching at at least one switching threshold; and

wherein said evaluation circuit further comprises second switching means coupled to said second resistance element for switching said second resistance element to the evaluation circuit and adjusting the switching threshold as a function of the temperature; and

wherein

said first resistance element is a PTC-resistor, and said second resistance element is an NTC-resistor;

said evaluation circuit further comprising;

a bridge circuit having a neutral branch;

said first switching means includes an npn-transistor with a base-emitter path located in said neutral branch of the bridge circuit, the bridge circuit further comprising an emitter resistor coupled to the emitter of said transistor; and

wherein said second resistance element is switched by said second switching means to be in parallel to the emitter resistor;

the device further comprising

means coupled to said second resistance element and to said second switching means for displaying temperature; and

wherein

said second switching means is a push-button switch by which said second resistance element is switched, alternatively, to connect and disconnect the second resistance element from the emitter resistor for indicating the oil level and for displaying temperature.

6. A device for electrically monitoring oil level, particularly in automobile internal combustion engines, comprising:

an oil measurement rod having a hollow space;

a first temperature-dependent resistance element housed in said hollow space;

an evaluation circuit including an oil-level indicator and first switching means for activating said indicator, said first switching means having an oil-level sensitive switching threshold;

a second temperature-dependent resistance element housed in said measurement rod at a lower place than a location of said first resistance element;

said evaluation circuit further comprising a bridge circuit having a neutral branch, said first switching means including a transistor having a control terminal within said neutral branch, a first arm and a second arm connected by said transistor, said transistor emitting a signal which signals that the filling level has dropped, said first and said second arms including respectively said first and said second resistance elements; and

wherein

said evaluation circuit further comprises second switching means coupled to said second resistance element for switching said second resistance element to the evaluation circuit for adjusting the switching threshold as a function of the temperature of the oil;

said first resistance element is a PTC-resistor, and said second resistance element is an NTC-resistor; and

said first resistance element is positioned in said oil measurement rod at the height of a filling level, a dropping of the level of oil below the filling level being signaled by said evaluation circuit, said evaluation circuit being responsive to a source of current applying current through said first and said second resistance elements, said evaluation circuit switching at at least one switching threshold.