FIELD OF INVENTION

The present invention relates to a device for connecting and disconnecting a current supply to an electric circuit dependent on the ambient temperature.

STATE OF ART

In addition to a heating element, some type of regulation is required for heating electrically the seats of a vehicle, for exemple. This regulation is demanded from comfort as well as a safety point of view. Usually, ordinary electromechanic thermo switches are used for attaining this regulation. In that connection there is the disadvantage that such a thermo switch is arranged near the heating element in the seat, causing that it is perceptible through the covering. Another disadvantage is that the technical characteristics of the thermo switch do not give the desired effects in connection with disconnections too soon and the like. Besides, there is a technical problem with electromechanic thermo switches, namely the difficulty to make a thermo switch that is able to switch off currents of 10 A, for exemple. with a temperature difference which is small enough between the connections and disconnections, without increasing the cost too much. Often, to reduce the cost, a thermo switch is chosen with a difference between the connections and disconnections being as high as 10° C. resulting in a reduced comfort

From the Swedish patent application 9002285-6. a device for the regulation of a heating element for a seat in a car, for exemple. is known, which device includes a temperature sensing switch with a fixed breaking temperature in series with an electric conducting element, e.g. a transistor or a thermistor, in which device a thermal mass is arranged between the electric conducting element and the switch, the mass receiving losses of energy from the electric conducting element, transporting the heat to the switch which is arranged to disconnect the supply on attaining the breaking temperature.

It is difficult to modify this known device for different applications, and likewise, the device has the disadvantage that sparks can be established owing to the fact that

the thermal mass does not provide a protection against electric contact between the parts.

For the present, more sophisticated electronic solutions are used. too. but these are considered as too expensive.

SUMMERY OF THE INVENTION

The object of the invention is to provide a device for connecting and disconnecting a current supply to an electric circuit dependent on the ambient temperature, the device specially having the following advantages:

- it protects against sparking,

- it is easy to modify for different applications.

- it can have a small temperature difference between switching on - switching off

- it can be placed at a distance from the current supply as well as the circuit to be regulated,

- it detects the ambient temperature.

- it is less expensive than previous known devices.

The characteristics of the invention are evident from the following claims

DESCRIPTION OF THE DRAWINGS

Figure 1 indicates a principle outline of the device according to the invention Figure 2 indicates an embodiment of the invention

Figure 3a. b. indicates the course of the connections and disconnections as a function of time at two different ambient temperatures.

DESCRIPTION OF AN EMBODIMENT

A principal outline of the invention is indicated in the figure 1. in which 1 represents a current source delivering current to an electric circuit 2. Between the current source 1 and the electric circuit 2 a conducting element 4 is arranged in a housing 3. the conducting element 4 being connected to a temperature sensing switch 5 with a

certain breaking temperature T ₀ A heat conducting material 6 is enclosed in the housing

The device operates in the following way When the current supply 1 , with closed switch 5, conducts the current via the current conducting element 4, the current conducting element 4 is emitting heat to the temperature sensing switch 5. via the heat conducting mateπal 6, the switch disconnecting the current supply when the breaking temperature T ₀ is attained The ambient temperature, which is supposed to be below the breaking temperature, has an effect on the temperature of the material 6, and when the material 6, and the switch 5 have cooled down below the breaking temperature the switch 5 is closed and the process is repeated

The figure 2 indicates schematically a preferred embodiment of the invention A cable 8 from the current supply 1 (not shown) is connected directly to the cover 9 of the housing 3, for exemple by welding, preferably the housing being formed of electric conducting material The cover 9 is arranged tightly on the bottom part of the housing 11 by means of an electrical insulating seal 10 The current conducting element 4 is arranged maintaining contact with the inside of the cover 9 In the housing there is oil as the heat conducting material 6 The housing 3 is filled by oil UD to an appropriate level 12 For exemple the temperature sensing switch 5 could be a temperature dependent bimetal spring being mounted in contact with the bottom part 11 of the housing 3, by means of an electrical insulation 13 The contact connections 14 and 15 respectively, are arranged on the bimetal spring and on the inside of the bottom part of the housing 11 , respectively Outside the bottom part of the housing 11 , a cable 16 is connected to the electπc circuit 2 (not shown) directly from the bottom part of the housing 3, correspondingly

The material enclosed in the housing, oil for exemple, have the purpose to protect the contact connections 14 and 15 from sparking" with following migration etc The oil is chosen such that it has the appropπate thermal conductivity for the intended application The oil can be replaced by gas

Of course, the housing 3 can have any adequate design.

The heat conducting material 6 can be volume variable by means of external or internal devices, such as pumps, communicating vessels or by introducing another material in the container. The heat conducting material 6 can be made partly of a fluid, partly of another material, a volume varying material for exemple, as a gel with specific electrical or thermal characteristics. Also, the variation of the volume of the fluid can be done by introducing solid substances, hollow plastic balls, for exemple. These substances can have thermal characteristics for the accumulation of heat.

The variation of the relative volume of the fluid may take place by deformation of the surrounding housing.

The device according to the figure 2 indicates a condition where the temperature in the device is higher than the breaking temperature T ₀ , i.e. the temperature sensing switch 5 is open and no current passes from the battery 1 to the electric circuit 2. In the embodiment, the electric circuit 2 consists of a heating element for the heating of a seat in a vehicle. As a whole, the heating element should be surrounded by a fixed or variable thermal insulation.

According to the invention, for connecting and disconnecting the heating element of a seat, the device is located such that the heat of the body from the person sitting on the chair does not have an effect on the temperature of the device. We choose to connect the heating element at an ambient temperature below +18° C. The contacts 14, 15 are closed and current flows through the conducting element 4, the heat losses being emitted to the oil up to the breaking temperature T ₀ of the temperature switch, thereafter the current is disconnected. For example, according to the embodiment, T ₀ is selected to be 5° higher than the operation temperature.

When the element 4 does not heat the oil any more, the temperature adjacent to the oil, the temperature of the rest of the oil and the housing will lower the temperature at the contacts 14, 15 and a closure of the contacts is effected once again.The process

is repeated and the duration and the character of the process are determined of the following parameters:

- the volume of the heat conducting material (fluid/ oil),

- the thermal conductivity of the heat conducting material (fluid/oil),

- the breaking temperature of the temperature sensing switch,

- the effect of the temperature sensing switch,

- the location of the temperature sensing switch,

- the selected material etc.

Those and other parameters that can be actuated are important for the device and can be varied easily in the manufacturing process.

The figures 3a, b indicate the process for the regulation of the connection and disconnection of the current supply 1 to the heating element 2 according to the embodiment.

If, according to the figure 3a, the temperature in the car is -10° C when sitting down in the car, the heating element is arranged to be closed as long as the breaking temperature is attained, after which the current is disconnected, and the device is cooled and the heating element is connected once again, this time for a shorter period. Thereafter, the process is repeated at short intervals.

For exemple, if the temperature is +5°C the element will be connected for a corresponding shorter time, as indicated in the figure 3b.

This course gives a good regulation of the seat heater and is known to be implemented by means of electronic components. This implies high costs and the present invention relates to a device implementing this function in a less expensive way.

It is evident that the device can be used for other purposes than these indicated above. Selecting the material of the heating elements and the connecting temperatures, the device can be used as a thermostat of different heating/cooling devices or, generally, to connect and disconnect an electric circuit dependent on the temperature and on the time, i.e. as an electric timer. Also, the device can be connected to an altering current supply and the currrent conducting element can be an electrical/electronical element giving energy losses usable in a heating conducting material.

It is obvious that other types of thermo switches than bimetal switches can be used within the scope of the accompanying claims.