Temperature compensating vehicle window heating system

• US 3,902,040 A
• Filed: 01/30/1974
• Issued: 08/26/1975
• Est. Priority Date: 02/07/1973
• Status: Expired due to Term

• Current Assignee: Kazuyoshi Tokuda, Masamitsu Nakano, Tsutomu Ikeda
• Original Assignee: Kazuyoshi Tokuda, Masamitsu Nakano, Tsutomu Ikeda
• Inventors: Ikeda, Tsutomu, Nakano, Masamitsu, Tokuda, Kazuyoshi
• Primary Examiner(s): Bartis, A.
• Application Number:
  US05/437,979
• Time in Patent Office: 573 Days
• Field of Search: 219/202,203,219,522,547,509,501 52/171 340/234,235 73/336.5 338/35 200/61.05
• US Class Current: 219/203
• CPC Class Codes: G01N 27/048 for determining moisture content of the material
• CPC Class Codes: G05D 22/02 characterised by the use of electric means
• CPC Class Codes: H05B 1/0236 for vehicles
• CPC Class Codes: H05B 2203/035 Electrical circuits used in resistive heating apparatus
• CPC Class Codes: H05B 3/84 Heating arrangements specially adapted for transparent or reflecting areas, e.g. for demisting or de-icing windows, mirrors or vehicle windshields
• CPC Class Codes: Y02B 30/00 Energy efficient heating, ventilation or air conditioning [HVAC]

Abstract

A vehicle window heating system for eliminating moisture deposited on the surface of a vehicle window is provided with a moisture detecting circuit having a temperature sensitive element adapted to compensate for temperature-dependent variation in impedance between a pair of dew-drop detecting electrodes. The deposit of dew drops between the aforesaid electrodes lowers impedance therebetween, whereupon moisture eliminating heating means operates due to such lowered impedance. A decrease in ambient temperature increases impedance, and the aforesaid moisture eliminating heating means will not operate unless a more pronounced dew depositing condition results. This device, however, compensates for such a temperature-dependent variation in impedance and thus may operate substantially in a temperature independent dew-depositing condition.

Claims

1. A moisture preventive device for a window glass of an automobile, which device has a pair of dew drop detecting electrodes mounted on the surface of glass, a circuit for detecting the variation in impedance between said electrodes and a moisture preventive means operating by means of the output from said detecting circuit, wherein the improvement comprises:

said dew drop detecting electrodes including a pair of electrodes extending in parallel with each other and mounted in a position on the window glass of an automobile which will not hinder the field of view of a driver;

said detecting circuit being provided with a resistor bridge circuit which incorporates said detecting electrodes therein, and a differential amplifying circuit, one of whose input terminals is directly connected to one of the detecting terminals of said bridge circuit and the other of which input terminals is connected to the other of said detecting terminals by way of a temperature sensitive semiconductor diode exposed to the same ambient temperature as are the detecting electrodes such that the variation in resistance of said diode cancels out the variation in resistance between the detecting electrodes caused by ambient temperature variation;

means for impressing A.C. voltage on said bridge circuit; and

said moisture preventive means being provided with heating means for heating said window glass, switch means for connecting an electric power source or said heating means and operating circuit means for closing or opening said switch means by the output from a differential amplifier.

2. A moisture preventive device for glass, as set forth in claim 1, wherein said voltage impressing means is an oscillator and said detecting circuit is connected to said oscillator by way of a capacitor.

3. A moisture preventive device for glass, as set forth in claim 2, wherein said oscillator oscillates A.C. voltage of a frequency of 100 to 1,000 Hertz.