System for measuring fluid levels in a vehicle transmission

Claim 3

The system of claim 1 wherein said circuit means comprises a source of alternating voltage and said impedance network comprises a bridge including one side and another side, said capacitance between said probe electrodes being located in one arm on said one side thereof, said detector means being connected to said bridge for detecting unbalance in said bridge due to changes in the level of said transmission fluid.

Claim 4

The system of claim 2 including first capacitance means in the span between said one side and said other side of said bridge, said detector means being connected across said first capacitance means, said temperature-sensitive impedance means being connected to said first capacitance means such that current flow in one direction through said first capacitance means resulting from a change in the level of said transmission level due to a change in temperature alone is substantially cancelled by current flow in an opposite direction through said first capacitance means due to said change in temperature.

Claim 5

The system of claim 1 wherein said circuit means and the capacitance between said probe electrodes form a first bridge network and a second bridge network, said first bridge network having one arm on one side thereof comprising the capacitance between said probe electrodes and said second bridge network having one arm on one side thereof comprising said temperature-sensitive impedance, said circuit means further comprising a source of alternating voltage coupled to said first bridge network and said second bridge network, said detector being coupled to said first bridge network and said second bridge network so as to measure the combined unbalance of said first bridge network and said second bridge network.

Claim 6

The system of claim 4 wherein said circuit means further comprises coupling circuitry connected to said source of alternating voltage, said coupling circuitry forming the other side of said first bridge network and the other side of said second bridge network.

Claim 7

The system of claim 5 wherein said circuit means further comprises a first capacitance means in the span from said one side to said other side of said first bridge network and a second capacitance means connecting said one side of said first bridge network to said one side of said second bridge network, current flow in one direction through said first capacitance means resulting from an increase in the level of transmission fluid due to an increase in temperature alone beinG substantially cancelled by current flow in the opposite direction from said second capacitance means.

Claim 8

The system of claim 6 wherein the change in capacitance of said one arm of said second bridge network for a given change in temperature is substantially greater than the change in capacitance between said probe electrodes due to said given change in temperature alone.

Claim 9

The system of claim 6 wherein said temperature-sensitive impedance comprises a negative temperature coefficient capacitor.

Claim 10

The system of claim 6 wherein said temperature-sensitive impedance comprises a resistor having a negative temperature coefficient, said one arm of said second bridge circuit comprising a series capacitance means in series with said resistor and a shunt capacitance means in parallel with the series combination of said resistor and said series capacitance.

Claim 11

The system of claim 6 wherein said temperature-sensitive impedance means of said circuit means further comprises third capacitance means in the span from said one side to said other side of said second bridge network, said system further comprises means for connecting said detector means across said third capacitance means so as to provide an output signal representing the temperature of said transmission fluid in said housing.

Claim 12

The system of claim 10 further comprising switch means for selectively connecting said detector means across said first capacitance means for measuring temperature compensated fluid levels or across said third capacitance means for measuring the temperature of said transmission fluid.

Claim 13

The system of claim 1 wherein said probe electrodes extend through the uppermost surface of said transmission fluid at an area substantially corresponding to the geometric center of said surface.

Claim 14

In a vehicle comprising a transmission including a transmission housing having transmission fluid therein, the improvement comprising a probe for measuring the level of transmission fluid in the transmission housing comprising: outer conductive electrode means extending above and below the uppermost surface of the transmission fluid; inner conductive electrode means extending above and below said surface of the transmission fluid, said inner conductive electrode means being located centrally with respect to said outer conductive electrode means; said inner and outer electrode means having a space therebetween along portions thereof for receiving said transmission fluid; solid insulation means separating said inner conductive electrode means and said outer conductive electrode means along other portions thereof; a conductive guard electrode interposed in all possible current leakage paths through said solid insulation means between said inner conductive electrode means and said outer conductive electrode means; temperature compensation impedance means in thermal communication with the transmission fluid in said housing; additional solid insulation means separating said temperature compensation impedance means and said inner conductive electrode means; and an additional guard electrode interposed in all possible current leakage paths through said additional solid insulation means between said temperature compensation impedance means and said inner conductive electrode means.

Claim 15

In a vehicle comprising a transmission including a transmission housing having transmission fluid therein, the improvement comprising a probe for measuring the level of transmission fluid in the transmission housing comprising: outer conductive electrode means extending above and below the uppermost surface of the transmission fluid; inner conductive electrode means extending above and below said surface of the transmission fluid, said inner conductive electrode means being located centrally with respect to said outer conductive electrode means; said inner and outer electrode means having a space therebetween along portions thereof for receiving said transmission fluid; solid insulation means separating said inner conductive electrode means and said outer conductive electrode means along other portions thereof; a conductive guard electrode interposed in all possible current leakage paths through said solid insulation means between said inner conductive electrode means and said outer conductive electrode means; temperature compensation impedance means in thermal communication with the transmission fluid in said housing; additional solid insulation means separating said temperature compensation impedance means and said inner conductive electrode means; and an additional guard electrode interposed in all possible current leakage paths through said additional solid insulation means between said temperature compensation impedance means and said inner conductive electrode means.

Claim 16

In a vehicle comprising a transmission including a transmission housing having transmission fluid therein, the improvement comprising a probe for measuring the level of transmission fluid in the transmission housing comprising: outer conductive electrode means extending above and below the uppermost surface of the transmission fluid; inner conductive electrode means extending above and below said surface of the transmission fluid, said inner conductive electrode means being located centrally with respect to said outer conductive electrode means; said inner and outer electrode means having a space therebetween along portions thereof for receiving said transmission liquId; solid insulation means separating said inner conductive electrode means and said outer conductive electrode means along other portions thereof; and a conductive guard electrode interposed in all possible current leakage paths through said solid insulation means between said inner conductive electrode means and said outer conductive electrode means; said outer conductive electrode means and said inner conductive electrode means of said probe apparatus being flared outwardly and inwardly respectively at the lower ends thereof.

Claim 17

In a vehicle comprising a transmission including a transmission housing having transmission fluid therein, the improvement comprising a probe for measuring the level of transmission fluid in the transmission housing comprising: outer conductive electrode means extending above and below the uppermost surface of the transmission fluid; inner conductive electrode means extending above and below said surface of the transmission fluid, said inner conductive electrode means being located centrally with respect to said outer conductive electrode means; said inner and outer electrode means having a space therebetween along portions thereof for receiving said transmission liquId; solid insulation means separating said inner conductive electrode means and said outer conductive electrode means along other portions thereof; and a conductive guard electrode interposed in all possible current leakage paths through said solid insulation means between said inner conductive electrode means and said outer conductive electrode means; said outer conductive electrode means and said inner conductive electrode means of said probe apparatus being flared outwardly and inwardly respectively at the lower ends thereof.

Claim 18

In a vehicle comprising a transmission including a transmission housing having transmission fluid therein, the improvement comprising a probe for measuring the level of transmission fluid in the transmission housing comprising: outer conductive electrode means extending above and below the uppermost surface of the transmission fluid; inner conductive electrode means extending above and below said surface of the transmission fluid, said inner conductive electrode means being located centrally with respect to said outer conductive electrode means; said inner and outer electrode means having a space therebetween along portions thereof for receiving said transmission liquid; solid insulation means separating said inner conductive electrode means and said outer conductive electrode means along other portions thereof; a conductive guard electrode interposed in all possible current leakage paths through said solid insulation means between said inner conductive electrode means and said outer conductive electrode means; and means for driving said guard electrode at substantially the same potential as said inner conductive electrode means.

Claim 19

In a vehicle comprising a transmission including a transmission housing having transmission fluid therein, the improvement comprising a probe for measuring the level of transmission fluid in the transmission housing comprising: outer conductive electrode means extending above and below the uppermost surface of the transmission fluid; inner conductive electrode means extending above and below said surface of the transmission fluid, said inner conductive electrode means being located centrally with respect to said outer conductive electrode means; said inner and outer electrode means having a space therebetween along portions thereof for receiving said transmission liquid; solid insulation means separating said inner conductive electrode means and said outer conductive electrode means along other portions thereof; a conductive guard electrode interposed in all possible current leakage paths through said solid insulation means between said inner conductive electrode means and said outer conductive electrode means; and means for driving said guard electrode at substantially the same potential as said inner conductive electrode means.