GB2115241A - Heated window assembly - Google Patents

Abstract

A heated window assembly e.g. for a motor vehicle, comprises an array of heating elements (2) through which electrical current may be passed from a source of electrical energy (5). The supply of electrical energy to the heating elements is periodically interrupted e.g. as a result of the application of signals from a square-wave generator circuit (8) to the base of a transistor switch (7) in series with the heating elements (2) so that the power consumption of the elements (2) is reduced. The operation is controlled by a timer (9) which allows full-power consumption for an initial period. <IMAGE>

Description

SPECIFICATION Heated window assembly This invention relates to heated window assemblies.

Heated window assemblies are frequently incorporated in motor vehicles and other installations where the window is susceptible to freezing or misting. Such assemblies comprise an array of heating elements extending across the window, for example in the form ofwires adhered to the window, or conductive strips deposited there. In order to remove mistorice from the window reasonably quickly, a relatively high amount of electrical energy is required. For example the heated window assembly of a typical passenger car consumes about 150 watts of electricity. If the assembly remains switched on regularly for pro- longed periods, it can have a significant effect on the overall fuel consumption ofthe car.

According to the present invention, there is provided a heated window assembly comprising an array of heating elements extending acrossthe window th rough which electrical current may be passed from a source of electrical energy, characterised by means for reducing the rate of consumption of electrical energy by the heating elements by periodically interrupting the supply of electrical energy thereto.

By providing means for periodically interupting the supplyof energytothe heating elements, the amount of energy consumed by the window assembly can be reduced. The reduction in energy consumption is preferably initiated by a timer which actsto reduce the rate of consumption of electrical energy for a predetermined period afterthe supply of electrical energytotheheating elements is started,this period being selected to allow initial deposits of ice and mist to be cleared.

The means for reducing the rate of consumption of electrical energy preferably comprises means for generating a cyclic electrical signal and means, such as a transistor switch, operable in response to the signal for interrupting the flow of electrical current through the heating elements. Other switching devices, such as an electromechanical relay may be used as an an alternative to the transistor switch.

A preferred embodiment of the invention will now be described with reference to the drawing which is a schematic diagram of a heated window assembly according to the invention.

In the drawing, a rearwindow pane 1 of a passenger car carries an array of heating elements 2 bonded thereto by a conventional process. The heating elements 2 are electrically connected tan inputlead 3 which is connected in turn, via a manual switch 4, to a source of electrical energy, such as a battery 5. The heating elements 2 are also electrically connected to an output lead 6 which is connected to earth via atransistor switch 7. The base of the transistor switch 7 is connected to the output of a square-wave generatorcircuit8 having an output frequency of 1 Hz. The operation of the square-wave generator circuit 8 is controlled by a timer 9 whicn receives powerfrom the input lead 3.

In operation, closure of the switch 4 places the heating elements 2 in electrical contact with the battery5and initiatesthetimer9.Sincethetransistor switch 7 is in a conducting state, current flows continuouslythrough the heating elements2which therefore commence operation at full power consumption e.g. at about 150 watts. After a time interval determined by the timer 9, e.g. 10 minutes, the square-wave generator circuit 8 is activated by the timer 9. The cyclic electrical signals generated by this circuit are applied to the base ofthe transistor switch 7, causing itto become non-conducting for part of each cycle. As a result the flow of current th rough the heating elements 2 will be periodically interrupted, thereby reducing the rate at which electrical energy is consumed by the heating elements 2.The amount by which the energy consumption is reduced will depend upon the duty cycle, or mark/space ratio of the signals generated by the square-wave generator circuit 8. For example with a mark/space ratio of 50% the energy consumption of the heating element will be reduced by 50%.

The period determined by the timer 9 will be selected so as to be sufficient to clear ice and mist from the window. During this periodthe power consumption of the heating elements will be high.

Thereafter the power consumption is decreased to a level sufficient merelyto maintain the window free from mist and ice thereby economising energy conumption.

The embodiment of the invention illustrated can of course be varied. For example in practice it may be necessary to use more than one transistor switch, connected in parallel in order to accomodate the current flow.

1. A heated window assembly comprising an array of heating elements extending across the window through which electrical current may be passed from a source of electrical energy, characterised by means for reducing the rate of consumption of electrical energy by the heating elements by periodically interrupting the supply of electrical energythereto.

2. A heated window assembly according to claim 1 wherein the means for reducing the rate of consumption of electrical energy comprises means for generating a cyclic electrical signal, and means operable in response to the signal for interrupting the currentflowthroughthe heating elements.

3. A heated window assembly according to claim 2 wherein the means operable in response to the cyclic electrical signal comprises a transistor switch.

4. A heated window assembly according to any oneofclaimsl to3furthercomprisingatimerfor initiating the operation of the means for reducing the rate of consumption of electrical energy a predeter mined period after the supply of electrical energy to the heating elements is stated.

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

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Heated window assembly This invention relates to heated window assemblies. Heated window assemblies are frequently incorporated in motor vehicles and other installations where the window is susceptible to freezing or misting. Such assemblies comprise an array of heating elements extending across the window, for example in the form ofwires adhered to the window, or conductive strips deposited there. In order to remove mistorice from the window reasonably quickly, a relatively high amount of electrical energy is required. For example the heated window assembly of a typical passenger car consumes about 150 watts of electricity. If the assembly remains switched on regularly for pro- longed periods, it can have a significant effect on the overall fuel consumption ofthe car. According to the present invention, there is provided a heated window assembly comprising an array of heating elements extending acrossthe window th rough which electrical current may be passed from a source of electrical energy, characterised by means for reducing the rate of consumption of electrical energy by the heating elements by periodically interrupting the supply of electrical energy thereto. By providing means for periodically interupting the supplyof energytothe heating elements, the amount of energy consumed by the window assembly can be reduced. The reduction in energy consumption is preferably initiated by a timer which actsto reduce the rate of consumption of electrical energy for a predetermined period afterthe supply of electrical energytotheheating elements is started,this period being selected to allow initial deposits of ice and mist to be cleared. The means for reducing the rate of consumption of electrical energy preferably comprises means for generating a cyclic electrical signal and means, such as a transistor switch, operable in response to the signal for interrupting the flow of electrical current through the heating elements. Other switching devices, such as an electromechanical relay may be used as an an alternative to the transistor switch. A preferred embodiment of the invention will now be described with reference to the drawing which is a schematic diagram of a heated window assembly according to the invention. In the drawing, a rearwindow pane 1 of a passenger car carries an array of heating elements 2 bonded thereto by a conventional process. The heating elements 2 are electrically connected tan inputlead 3 which is connected in turn, via a manual switch 4, to a source of electrical energy, such as a battery 5. The heating elements 2 are also electrically connected to an output lead 6 which is connected to earth via atransistor switch 7. The base of the transistor switch 7 is connected to the output of a square-wave generatorcircuit8 having an output frequency of 1 Hz. The operation of the square-wave generator circuit 8 is controlled by a timer 9 whicn receives powerfrom the input lead 3. In operation, closure of the switch 4 places the heating elements 2 in electrical contact with the battery5and initiatesthetimer9.Sincethetransistor switch 7 is in a conducting state, current flows continuouslythrough the heating elements2which therefore commence operation at full power consumption e.g. at about 150 watts. After a time interval determined by the timer 9, e.g. 10 minutes, the square-wave generator circuit 8 is activated by the timer 9. The cyclic electrical signals generated by this circuit are applied to the base ofthe transistor switch 7, causing itto become non-conducting for part of each cycle. As a result the flow of current th rough the heating elements 2 will be periodically interrupted, thereby reducing the rate at which electrical energy is consumed by the heating elements 2.The amount by which the energy consumption is reduced will depend upon the duty cycle, or mark/space ratio of the signals generated by the square-wave generator circuit 8. For example with a mark/space ratio of 50% the energy consumption of the heating element will be reduced by 50%. The period determined by the timer 9 will be selected so as to be sufficient to clear ice and mist from the window. During this periodthe power consumption of the heating elements will be high. Thereafter the power consumption is decreased to a level sufficient merelyto maintain the window free from mist and ice thereby economising energy conumption. The embodiment of the invention illustrated can of course be varied. For example in practice it may be necessary to use more than one transistor switch, connected in parallel in order to accomodate the current flow. CLAIMS

1. A heated window assembly comprising an array of heating elements extending across the window through which electrical current may be passed from a source of electrical energy, characterised by means for reducing the rate of consumption of electrical energy by the heating elements by periodically interrupting the supply of electrical energythereto.

2. A heated window assembly according to claim 1 wherein the means for reducing the rate of consumption of electrical energy comprises means for generating a cyclic electrical signal, and means operable in response to the signal for interrupting the currentflowthroughthe heating elements.

3. A heated window assembly according to claim 2 wherein the means operable in response to the cyclic electrical signal comprises a transistor switch.

4. A heated window assembly according to any oneofclaimsl to3furthercomprisingatimerfor initiating the operation of the means for reducing the rate of consumption of electrical energy a predeter mined period after the supply of electrical energy to the heating elements is stated.

5. A heated window assembly substantially as hereinbefore described with reference to the drawing.

6. A motor vehicle incorporating a heated window assembly according to any one of the preceding claims.