GB2108808A - Windscreen defroster - Google Patents

Abstract

A windscreen defroster has a transparent inner screen 13 spaced from a transparent windscreen 1. The inner screen is held in a frame 10, which defines an air space 14 between the two screens. A plurality of heating wire elements 17 are unevenly distributed over the air space, relatively densely in the lower part of the air space and relatively thinly in the upper part of the air space. <IMAGE>

Description

SPECIFICATION Windscreen defroster This invention relates to a defroster and more particularly to a heating apparatus for eliminating dew, frost, and ice on a windscreen or preventing their formation.

On most of modern motorcars is used the defroster which blows hot air along the windscreen. However, because of limited reach of air blow, this type of defroster can not serve a large-sized windscreen such as in a vessel. On the other hand, the windscreen made of sheet glass containing spaced electric heating wire elements is also known. In this type of screen, the heating elements are liable to break due to the difference in thermal expansion between the two substances. Also, the sheet glass is subjected to higher thermal stress by non-uniform heating.

Accordina to the invention there is provided a defroster for heating a windscreen, comprising a transparent inner screen spaced from windscreen, a frame holding said inner screen, said frame defining an air space between said windscreen and said inner screen, and a plurality of electric heating wire elements disposed in spaced relationship in said air space, said heating elements being distributed relatively densely in the lower part of said air space and relatively thinly in the upper part.

In this apparatus the windscreens and the heating elements are separated from each other, and therefore do not suffer from excessive thermal stress, thus providing higher dependability. Also, the uneven distribution of the heating elements over the air space provides uniform heating over the air space and hence windscreen; if the elements were evenly distributed, the upper part of the air space would overheat due to heat convection. Besides, the uneven distribution improves the view through the windscreen.

At least one end of each of the heating elements is preferably supported by a spring capable of absorbing the thermal expansion or contraction of the elements.

The heating elements are preferably provided a thermostat to maintain the air space at a constant temperature.

The invention will now be further described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a elevation of a defroster formed according to the invention; Fig. 2 is a cross-sectional view taken on the line 11-11 in Fig. 1, and Fig. 3 is a wiring diagram of the defroster shown in Figs. 1 and 2.

Referring now to the drawings, there is shown a defroster for a windscreen 1 installed on the wheelhouse front wall 2 of a vessel. The screen 1 is held in a frame 3 with a packing 4 between.

A plurality of studs 6 project from a plate 5, which is attached by means of screws 7 on each of the top and bottom of the frame 3. Knurled nuts 8 are screwed onto the studs 6 to hold an angle bar 9 which is fastened to a defroster frame 10 by means of bolts 11.

The frame 10 and a retainer 12 bolted thereto hold an inner screen 13 of transparent glass slightly smaller than the windscreen 1. The frame 10 defines air space 14 between the windscreen 1 and inner screen 13. The air space 14 is kept almost gastight both by a packing 1 5 placed between the frame 10 and inner screen 13 and by a packing 1 6 between the frame 10 and windscreen 1. To bring the packing 1 6 into close contact with the windscreen 1, it is desirable that the position of the angle bar 9 be adjustable relative to the defroster frame 1 0.

In the air space 14, a plurality of heating elements 17, which are actually made of a single Nichrome wire, are stretched in vertically spaced relationship between bow-like springs 1 8 attached to the sides of the frame 10 with insulators 1 9 between. The springs 1 8 will absorb expansion and contraction of the heating elements 17 due to changes in temperature, thus keeping the elements tight and preventing the element breakage.

As shown in Fig. 1 , the heating elements 1 7 are not evenly distributed over the air space 1 4, but densely in the lower part of the space 14 and thinly in the upper part. This element distribution will prevent overheating of the upper part of the air space 14 which might otherwise be caused by heat convection within the air space 14. Also, the uneven distribution of the heating elements provides an improved view through the windscreen 1 to a navigator.

At the top of the air space 14 is placed a thermostatic switch 20, which connects or disconnects the heating elements to a power line so that the air space temperature may be maintained at the presetting value such as at 500 C.

The defroster is provided with a controller 21 placed out of the frame 10. This controller consists of a step-down autotransformer 22 providing a plurality of secondary voltages, one of which is selected by a switch 23 and sent to the heating elements 1 7 through a line 24. If the heating elements 1 7 are in red-hot condition, they will disturb the view through the windscreen 1.

Therefore, it is desirable that the switch 23 should select relatively low voltage particularly at night.

For warm-up, however, higher voltage should be selected.

The windscreen heated by the defroster will melt frost and ice thereon or prevent their formation, thus keeping clear and providing satisfactory windscreen wiper operation.

1. A defroster for heating a windscreen, comprising a transparent inner screen spaced from the windscreen, a frame holding said inner screen, said frame defining an air space between said windscreen and said inner screen, and a plurality of electric heating wire elements disposed in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Windscreen defroster This invention relates to a defroster and more particularly to a heating apparatus for eliminating dew, frost, and ice on a windscreen or preventing their formation. On most of modern motorcars is used the defroster which blows hot air along the windscreen. However, because of limited reach of air blow, this type of defroster can not serve a large-sized windscreen such as in a vessel. On the other hand, the windscreen made of sheet glass containing spaced electric heating wire elements is also known. In this type of screen, the heating elements are liable to break due to the difference in thermal expansion between the two substances. Also, the sheet glass is subjected to higher thermal stress by non-uniform heating. Accordina to the invention there is provided a defroster for heating a windscreen, comprising a transparent inner screen spaced from windscreen, a frame holding said inner screen, said frame defining an air space between said windscreen and said inner screen, and a plurality of electric heating wire elements disposed in spaced relationship in said air space, said heating elements being distributed relatively densely in the lower part of said air space and relatively thinly in the upper part. In this apparatus the windscreens and the heating elements are separated from each other, and therefore do not suffer from excessive thermal stress, thus providing higher dependability. Also, the uneven distribution of the heating elements over the air space provides uniform heating over the air space and hence windscreen; if the elements were evenly distributed, the upper part of the air space would overheat due to heat convection. Besides, the uneven distribution improves the view through the windscreen. At least one end of each of the heating elements is preferably supported by a spring capable of absorbing the thermal expansion or contraction of the elements. The heating elements are preferably provided a thermostat to maintain the air space at a constant temperature. The invention will now be further described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a elevation of a defroster formed according to the invention; Fig. 2 is a cross-sectional view taken on the line 11-11 in Fig. 1, and Fig. 3 is a wiring diagram of the defroster shown in Figs. 1 and 2. Referring now to the drawings, there is shown a defroster for a windscreen 1 installed on the wheelhouse front wall 2 of a vessel. The screen 1 is held in a frame 3 with a packing 4 between. A plurality of studs 6 project from a plate 5, which is attached by means of screws 7 on each of the top and bottom of the frame 3. Knurled nuts 8 are screwed onto the studs 6 to hold an angle bar 9 which is fastened to a defroster frame 10 by means of bolts 11. The frame 10 and a retainer 12 bolted thereto hold an inner screen 13 of transparent glass slightly smaller than the windscreen 1. The frame 10 defines air space 14 between the windscreen 1 and inner screen 13. The air space 14 is kept almost gastight both by a packing 1 5 placed between the frame 10 and inner screen 13 and by a packing 1 6 between the frame 10 and windscreen 1. To bring the packing 1 6 into close contact with the windscreen 1, it is desirable that the position of the angle bar 9 be adjustable relative to the defroster frame 1 0. In the air space 14, a plurality of heating elements 17, which are actually made of a single Nichrome wire, are stretched in vertically spaced relationship between bow-like springs 1 8 attached to the sides of the frame 10 with insulators 1 9 between. The springs 1 8 will absorb expansion and contraction of the heating elements 17 due to changes in temperature, thus keeping the elements tight and preventing the element breakage. As shown in Fig. 1 , the heating elements 1 7 are not evenly distributed over the air space 1 4, but densely in the lower part of the space 14 and thinly in the upper part. This element distribution will prevent overheating of the upper part of the air space 14 which might otherwise be caused by heat convection within the air space 14. Also, the uneven distribution of the heating elements provides an improved view through the windscreen 1 to a navigator. At the top of the air space 14 is placed a thermostatic switch 20, which connects or disconnects the heating elements to a power line so that the air space temperature may be maintained at the presetting value such as at 500 C. The defroster is provided with a controller 21 placed out of the frame 10. This controller consists of a step-down autotransformer 22 providing a plurality of secondary voltages, one of which is selected by a switch 23 and sent to the heating elements 1 7 through a line 24. If the heating elements 1 7 are in red-hot condition, they will disturb the view through the windscreen 1. Therefore, it is desirable that the switch 23 should select relatively low voltage particularly at night. For warm-up, however, higher voltage should be selected. The windscreen heated by the defroster will melt frost and ice thereon or prevent their formation, thus keeping clear and providing satisfactory windscreen wiper operation. CLAIMS

1. A defroster for heating a windscreen, comprising a transparent inner screen spaced from the windscreen, a frame holding said inner screen, said frame defining an air space between said windscreen and said inner screen, and a plurality of electric heating wire elements disposed in spaced relationship in said air space, said heating elements being distributed relatively densely in the lower part of said air space and relatively thinly in the upper part.

2. A defroster as claimed in claim 1, further comprising a plurality of springs for supporting at least one end of each of said heating elements so as to absorb the expansion or contraction thereof.

3. A defroster as claimed in claim 1 or 2, further comprising a thermostatic switch for connecting or disconnecting said heating elements to a power source in response to the temperature in said air space.

4. A defroster as claimed in claim 1, 2 or 3, further comprising a voltage controller for regulating the output of said heating elements by transforming the voltage of the power supplied to said heating elements from said power source.

5. A defroster according to and preceding claim wherein the electric heating wire elements are disposed in vertically spaced relationship.

6. A defroster for heating a windscreen substantially as hereinbefore described with reference to and as shown in the accompanying drawings.