DE112010004686T5 - Electrically heated by means of PTC heating element map-controlled thermostat device - Google Patents

Abstract

This invention relates to an electrically heated and map controlled thermostat that uses a PTC heating element placed in its piston to maintain a temperature of a coolant circulating inside a cooling system of an internal combustion engine in a defined range, with opening and closing movements a thermostatic valve. It has an assembly of a PTC heating element, which is placed inside an edge region of its piston (6) in order to use the heat it produces efficiently and to ensure rapid heat transfer to a wax mass (2).

Description

Technical area

The invention relates to an electrically heated, map-controlled thermostat, which uses a PTC heating element placed in its piston to maintain a temperature of a coolant circulating inside cooling systems of internal combustion engines in a defined range, wherein opening and closing movements of a thermostatic valve be accomplished.

State of the art

In liquid-cooled internal combustion engines, heating due to the combustion of fuel is passed through a coolant circulating through passages in the engine block and cylinder head. In this way, the engine can run in a suitable temperature range. Today, reducing the total emissions of harmful gases from internal combustion engines to the environment is one of the biggest development concerns due to regulations that reduce the allowable emission rate year by year. In the phases in which engines run at temperatures that differ from the designed temperature range, the engines emit harmful gases with high emission levels. To ensure engine running due to this cause in a suitable temperature range, stabilizing the coolant temperature and engine temperature helps to efficiently burn the fuel and reduce the release of noxious gas emissions. Therefore, stabilization of engine temperature is a major concern for design studies to reduce harmful emission rates.

Wax thermostats are the most common solution in today's engines to keep the engine in a suitable temperature range. Their mode of operation is based on an expandable by an increase in temperature wax mass. This expansion causes an opening of a valve for the cold coolant through a mechanism that varies according to the thermostat design.

The combustion in the engine causes overheating of the engine and consequently of the coolant on the thermostat. The mass of wax compressed inside a defined volume in the thermostat expands. The expansion of the wax creates a linear motion through a piston. The linear movement of the piston opens a valve which directs the flow of coolant toward a radiator to reduce the coolant temperature in the system for cooling the engine.

The heat transfer from the engine to the wax mass by the coolant and the expansion of the wax mass requires time called the thermostat response time. During this period, the engine temperature maintains its increasing trend because the thermostatic valve has not yet opened and the coolant does not flow to the radiator for cooling. During this response time period, engine temperature is higher than a suitable engine operating temperature, fuel combustion efficiency is lower, and the engine must run at much higher temperature conditions than it is designed for.

At the end of the response time, the thermostatic valve allows the coolant to flow to the radiator and thus the coolant causes a motor temperature drop to the designed design temperature range. When the coolant temperature drops below the design design temperature, due to shrinkage of the wax compound, the thermostat valve begins to move back to the closed position after a response time period. The thermostatic valve takes the closed position and stops the coolant circulation to the radiator and the coolant starts to warm up again. However, during this response period, the engine temperature is lower than the appropriate engine operating temperature, the fuel combustion efficiency is lower, and the engine must run at a lower than designed temperature.

Stabilization and maintenance of the coolant temperature in the designed range may not be possible due to the response time of the wax compound under some engine operating conditions. In these cases, the harmful emission rates increase due to insufficient fuel combustion.

Engine developers calculate these conditions. In order to eliminate response delays prior to engine overheat or coolant low temperature, the wax mass may be heated by forced convection under a coolant temperature independent control to determine the opening and closing movement of the thermostatic valve in accordance with the engine conditions calculated by the engine designers.

Therefore, electrical resistance wire heaters are used to heat the wax mass. When a voltage is applied to the electrical resistance wire, it heats up the wax mass by a forced confection, whereafter the wax mass expands. However, a continuous application of the voltage causes overheating (this can reach over 800 ° C) of the wax mass. Over time, the wax loses its physical properties and sealing components are damaged due to overheating. To avoid these errors, the electrical current is applied to the resistor with interruptions.

However, since the rate of heat transfer to the wax mass is less than heating of the electric resistance wire, it is not completely possible to prevent overheating on a contact surface between the wax mass and the electric resistance wire. On the other hand, in the case of insufficient heat transfer between the wax mass and the coolant environment, overheating of the entire wax mass and damage to the sealing components may be unavoidable.

Other risks of resistance wire heaters are: these are switched by a relay. In the case of a relay failure, the resistance heater performs a non-stop heating and caused due to overheating damage to the wax compound and the sealing components. In addition, their heating wire may break due to over-fatigue in the event of electrical overload. This failure causes a malfunction.

For electrically heated thermostats, use of a PTC (Positive Temperature Coefficient) heater is an option over the resistance wire. Until the present invention, an industry standard places a PTC heating element (in the form of a pill or disk) on the outside surface of a wax actuator. In this way, some of the heat generated by the PTC heater is lost to the engine coolant since it is in contact with the coolant.

In the present invention, a PTC heating element is placed in a flask which is completely covered with the wax mass in the thermostat. In this way, all of the heat dissipated by the PTC heating element is transferred directly to the wax mass with high efficiency. For optimum reliability, the PTC heater should be placed close to one end of the piston where it is constantly in contact with the wax mass during the thermostat piston and valve strokes (close-open).

The benefits of rearranging PTC heating elements in the interior of the piston are that the response time of the PTC heating element surrounded by the wax mass is reduced and energy losses caused by the sealing elements in the conventional PTC applications are reduced. Incidentally, an application inside the piston is easier than in the conventional PTC applications with sealing elements. This also has a cost advantage over conventional applications.

If an electronic engine control unit determines the start of the coolant flow to the radiator, this turns on the PTC heating elements and heats up the wax mass relatively faster than its conventional alternative arrangements to open the thermostatic valve and direct the flow of cooling liquid to the radiator. In this way, the coolant temperature is lowered.

Due to the self-limiting temperature characteristics of the PTC heating elements, these are even switched on continuously and never rise to a higher than their regulated reference temperature. This characteristic ensures the avoidance of damage to the wax mass and damage to the sealing elements. Above the reference temperature, the semiconductor and ferroelectric properties of the ceramic are used to produce several orders of magnitude increase in resistance, and thus its self-limiting properties. These self-limiting properties guarantee the operational safety of the device.

The temperature value at which the electrical resistance of the PTC heating element increases abruptly dramatically is referred to as switching temperature. The switching temperature can be structured during production. The switching temperature can be set between 50 ° C and 250 ° C during production. A PTC heating element whose switching temperature z. B. 250 ° C, its environment heats up as soon as it is turned on until reaching 250 ° C. When this temperature is reached, its electrical resistance increases dramatically and it loses its heating properties even when it is still on. When the ambient temperature drops below 250 ° C, it starts to heat up the environment again. This characteristic of the PTC heating element is called temperature self-regulation and the present invention employs this characteristic.

Overheating of the product never occurs due to this PTC characteristic, the physical properties of the wax compound and sealing elements are never damaged and ensure their long life unlike the resistance wire heaters whose wax mass and sealing elements show fatigue due to overheating. The response time is very short because the PTC heating element is surrounded by the wax mass.

Description of the figures:

The invention will be described in detail by the following figures. The figures are only examples.

It shows:

1 a cross-sectional view illustrating the structure and function of the invention;

2 a detailed view of a structure of PTC heating elements;

3 an application example of a thermostat with a PTC heating element.

LIST OF REFERENCE NUMBERS

1

wax container

2

wax material

3

Sealing element 1

4

Sealing element 2

5

cover

6

Piston with PTC heating element

7

Socket and power cable

8th

PTC heating element

9

Valve

Description of the invention

A wax container ( 1 ) is open at the top. A wax mass ( 2 ) is inside the wax container ( 1 ). For placing inside, the shape of the wax mass ( 2 ) the wax container ( 2 ). In this way, an expansion and a shrinkage of the wax mass ( 2 ) by a temperature change, a linear movement of a piston ( 6 ) axially to the wax container ( 1 ) up or down.

The piston ( 6 ) is inside a recess of the wax mass ( 2 ). The piston ( 6 ) converts the expansion and shrinkage of the wax mass ( 6 ) into a linear motion. This movement opens or closes a valve ( 9 ) to align the coolant flow.

A lid ( 5 ) closes and seals the open side of the wax container ( 1 ), also holds the piston ( 6 ) to ensure its axial linear movement sure. A sealing element 1 ( 3 ) is used for sealing from the external environment, a sealing element 2 ( 4 ) is used to make up the wax mass ( 2 ) inside the wax container ( 1 ) to keep.

A PTC heating element ( 8th ) is within a closed edge region of the piston ( 6 ) to effectively utilize the heat it produces and to rapidly transfer heat to the wax mass ( 2 ) to ensure. The PTC heating element ( 8th ) is energy via power cable ( 7 ), which are connected by a socket to the piston.

Claims (1)

For electrically heated map-controlled thermostats with PTC heating elements: mounting a PTC heating element ( 8th ), which within a closed edge region of a piston ( 6 ) to effectively utilize the heat it produces and to rapidly transfer heat to a wax mass ( 2 ) to ensure. The PTC heating element ( 8th ) is energy via power cable ( 7 ), which are connected by a socket to the piston.

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