GB2150821A - Screen washer - Google Patents

Abstract

An outlet jet assembly (10) incorporates an electrically powered heater (16, 31) which consists of a material having a positive temperature coefficient of electrical resistance (thermistor) so as to have a lower resistance at lower temperatures and vice versa. The heater can have a through passage therein constituting a liquid supply jet (fig. 2) or can be in close thermal contact with a body, e.g. a sphere (23), of thermally conductive material which itself has a flow passage (24) constituting a fluid supply jet as shown. <IMAGE>

Description

SPECIFICATION Screen washer This invention relates to a screen washer for a vehicle. The screen may be a front windscreen, a rear windscreen or a screen on a headlamp or other component of the vehicle which may be travelling on land, sea or air.

A screen washer operating on at least the windscreen of a road vehicle is now a legal requirement in the UK. In addition to a windscreen washer, several vehicles, notably the so called "hatch-back" style of vehicle, incorporate or can be fitted with a screen washer operative on the rear window. Additionally, more expensive cars are now being fitted with headlamp washing systems.

The inability of the screen washer to operate is not to be considered just inconvenient but also potentially dangerous.

In cold weather the jet(s) supplying washing fluid can become blocked due to freezing of tHe fluid.

Such freezing most often occurs at the extreme end of the jet which is exposed to atmosphere. This may occur when the vehicle is left standing overnight, particularly in freezing weather, or when the vehicle is travelling because the jet is exposed in the vehicle slipstream which has a cooling effect.

The bulk fluid container and supply lines are less likely to freeze since these are usually protected by the vehicle body and when travelling are warmed to some extent by the vehicle engine.

Other patented devices, known for example from UK Patents specifications Nos. 5559505, 1318498 and 2044601, have sought to heat the washing fluid, either in the storage tank or in the supply lines to the jets but it is the object of the present invention to provide a screen washer wherein the jet is heated at the outermost extremity where it is most required and which takes account of the fact that the colder the atmosphere the more energy will be required to defrost the jet or maintain it freeze-free.

Accordingly the invention provides a vehicle screen washer having an outlet jet assembly (10, 30) which incorporates an electrically powered heater to prevent or discourage freezing of washing liquid in cold weather characterised in that the heater is constituted by a material (16, 31) having a positive temperature coefficient of electrical resistance.

Such materials are sometimes called "thermistor" but other names are used and the washer of the present invention can utilize any such material in which the electrical resistance is reduced when its temperature is reduced and vice versa. Each jet may be constituted by a passage extending through the thermistor material or alternatively the fluid supply jet in a particular version of the invention may be sphere engaging in a part spherical socket in the body of thermistor material.

The thermistor material can be connected to the usual vehicle accumulator by means of a switch and/or thermostat wiring.

Alternatively the thermistor material may be chosen and shaped such that its resistance is high at relatively high temperatures when the current drain from the accumulator is negligible, enabling the device to be permanently connected to the accumulator. In this arrangement, as the temperature becomes lower the resistance becomes lower permitting more current flow and greater heating at the jet. The washer requires no additional switch either manually or by thermostat and the temperature of the jet is controlled automatically. In consequence the fluid at the jet is never permitted to freeze.

A screen washer of the invention may have a heated reservoir for the fluid and/or heated supply lines from the reservoir to the jet, but these are not essential.

The thermistor material may be moulded or fitted into a housing of insulating material, such as plastics, to minimise the heat conduction from the jet and/or to provide electrical insulation for the electrical lead(s) to the thermistor.

The housing for the thermistor material may be shaped so that it may easily be fitted to vehicle body as is known by those skilled in the manufacture of vehicles.

The electrical contact(s) to the thermistor material may be made to the vehicle body as is known by those skilled in the electrical wiring of motor vehicles.

The invention will be described further, by way of example, with reference to the accompanying drawings which illustrate preferred embodiments thereof, it being understood that the following description is illustrative and not limitative of the scope of the invention. In the drawings: Fig. 1 is a cross-sectional view through an outlet jet assembly of a first preferred embodiment of screen washer of the invention; Fig. 2 is a similar view of a second embodiment; Fig. 3 is a graph showing the variation of resistance with temperature of a particular preferred piece of thermistor material; and Fig. 4 is a graph showing the variation of power consumption with temperature of a particular preferred piece of thermistor material.

A first preferred embodiment of screen washer of the invention includes a reservoir (not shown) for washing fluid, fluid supply lines and a pump and associated controls. Such parts are conventional and are therefore not illustrated. The washer has, at its fluid supply end, one or more outlet jet assemblies 10 illustrated in Fig. 1.

The assembly 10 has an interior tubular body 11 whose illustrated lower end 1 lea can be connected to a fluid supply pipe. A metallic sleeve 12 surrounds the body 11 and is itself surrounded by a tubular casing 13 which has an external thread 14. An internally threaded annular cap 15 is engaged with the upper part of thread 14 and secures an annular heater 16 to the top of the body 11 and casing 13.

Casing 13 passes through an aperture in a vehicle body panel 17 and a nut 18 secures the assembly 10 thereto.

The heater 16 is constituted by a piece of material having a positive temperature coefficient of electrical resistance. Characteristics of a typical piece of material are shown in the graphs of Figs. 3 and 4. Heater 16 has an upper electrical contact surface 19 which is in electrical contact with cap 15 which is in turn electrically connected to panel 17. A lower electrical contact surface 20 is connected to sleeve 12 whose lower end carries a tag 21 for connection to an electrical supply cable.

The upper end of body 11 has an enlarged diameter portion 22 which accommodates the bulk of a metallic sphere 23 having a through passage 24 constituting a jet. An upper part of the sphere 23 engages a complementary part-spherical surface of the heater 16 to be in good thermal transfer contact therewith. A spring (not shown) can urge the sphere 23 into engagement with the heater 16. The provision of the sphere 23 enables the disposition of the passage 24, and thus the ultimate destination of the liquid jet, to be varied to suit the requirements of the user or different conditions.

Fig. 2 shows a simpler version of jet assembly 30.

This assembly 30 has many parts similar to those of the first embodiment and such parts have been allotted the same reference numeral as used in Fig.

1. However, the heater is constituted by a mass 31 of thermistor material having a throughpassage 32 constituting a jet. This eliminates the adjustability feature of the Fig. 1 assembly but gives more immediate contact between the liquid and the heater.

In each embodiment the supply of current to the heater can be via a switch and/or thermostat However, by careful choice of the characteristics of the heater material and its dimensions, it can be ensured that the resistance thereof is so great at normal ambient temperatures that current drain at such temperatures is low enough to enable the heater to be permanently connected to the vehicle electrical supply without having a deleterious effect thereon.

The invention can be applied to land, sea or air vehicles and can be used in relation to windscreens, rear view screen, headlamps, and any other screen which needs to be kept clean.

In each of the embodiments just described, the size and nature of the material of heater 16,31 is advantageously chosen to have a resistance of not more than 100 ohms at 0 C ambient temperature.

This has been found to give a reasonable rate of heat supply to the jet assembly when used in connection with a 12 volt power supply and for washer systems of the liquid flow capacity commonly encountered in road vehicle windscreen washers. Variations in this value can be made to deal with different situations and different installations.

The value of the positive temperature coefficient of electrical resistance should be sufficient to ensure that the resistance of the heater at 150C is at least three times the resistance at 0 C. Advantageously, however, and particularly for use in a system where the heater is permanently in electrical connection with the power supply without a switch and/or thermostat, the resistance at 1 50C should be ten or more times the resistance at 0 C. Although 0 C is used as the lower reference temperature, and is related specifically to the freezing point of pure water, a lower reference temperature can be used if the washing liquid has a freezing temperature lower than 0 C due to the addition of antifreeze or for other reasons.

Claims (13)

1. A vehicle screen washer having an outlet jet assembly (10,30) which incorporates an electrically powered heaterto prevent or discourage freezing of washing liquid in cold weather, characterised in the heater is constituted by a material (16,31) having a positive temperature coefficient of electrical resistance.

2. A washer as claimed in claim 1 characterised in thatthe material (16,31) is shaped to be complementary to a member (23) of thermally conductive material through which a flow passage (24) is formed to constitute a fluid supply jet, the fluid being heated by thermal conduction through said member (23).

3. Awasher as claimed in claim 2, characterised in that said member (23) is in the form of a sphere mounted to be limitedly movable in a socket of the assembly (10) to enable the direction of the jet to be varied.

4. A washer as claimed in claim 3, characterised in that said material is annular, having a central aperture which is shaped to be part-spherical to engage the sphere (23).

5. A washer as claimed in claim 1, wherein said material (31) has a through passage (32) constituting a fluid supply jet.

6. A washer as claimed in any preceding claim, characterised in that the heater is connected to an electrical power supply via a switch and/or thermostat.

7. A washer as claimed in any of claims 1 to 5, characterised in that the material is chosen to have dimensions and resistance characteristics such that its resistance is high at normal ambient temperatures and falls when ambient temperatures approach freezing point, thus enabling the heater to be permanently connected to the electrical power supply and to draw a minimal current therefrom at all reasonably high ambient temperatures.

8. A screen washer as claimed in any preceding claim, characterised in that the heater and/or the flow passage within the jet assembly (10) is or are thermally insulated to discourage outward flow of heat therefrom.

9. A screen washer as claimed in any preceding claim, characterised in that the assembly (10) includes two electrical contacts (19, 20) between metallic members (15, 12) and the material (16,31), one such contact (19) connecting with an electrically conducting path leading to structure (17) of a vehicle, and the other contact (20) connecting with a connector (21) for an electrical lead.

10. A screen washer as claimed in any preceding claim, characterised in that a liquid supply line and/ or a liquid reservoir of the washer is provided with additional means for preheating the liquid before it reaches the jet

11. A screen washer for a vehicle as claimed in any of claims 1 to 6 wherein said coefficient of the heater is such that resistance of the heater at 1 50C is at least three times its resistance at O"C.

12. A screen washer as claimed in claim 7 wherein said coefficient is such that the resistance of the heater at 15 C is at least ten times its resistance at O,C.

13. A screen washer for a vehicle substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.