DE10306634A1 - Low-volt pencil-type glow plug for an internal combustion engine's combustion chamber has a heat conductor linked to a defined operating voltage and fitted with an electrical resistor - Google Patents

Abstract

A pencil-type glow plug protects against destruction through surge voltage. An electrical resistor in a heat conductor is so designed that the heat conductor's resistor rises above the operating temperature so that increased operating voltage causing it is compensated.

Description

The invention relates to glow plugs, especially low-voltage glow plugs for arrangement in a combustion chamber of a fuel engine, wherein the glow plug a voltage source designed with a defined operating voltage Connectable electrical resistance heating conductor comprises and the heating conductor can be brought to a defined operating temperature is.

State of technology

Glow plugs as part of one Annealing device used among other things in cold starting and cold running of diesel engines. They serve to close the combustion chamber before the actual engine start heat and the running behavior of the diesel engine (noise, exhaust emissions) positive to influence.

To even during a voltage drop the electrical system, which is usually during the operation of the Tempering results in a short heating up time of the glow plug to ensure, these are often designed as low-voltage glow plugs. The Reduction of the vehicle electrical system voltage to the necessary operating voltage takes place by clocking the vehicle electrical system voltage with a defined clock ratio. On Operation with overvoltage can reach temperatures far above the maximum operating temperature the materials used of the glow plug and thus to destroy the glow plug to lead.

Task of invention

The object of the invention is to design the glow plugs known from the prior art in such a way that a quick warm-up time is guaranteed, and that at the same time low initial currents with an increased Protective function against Voltages can be realized.

Solution of task

The essence of the invention is a protective function, especially for Niedervoltglühstiftkerzen to accomplish. This is achieved by operating above the operating temperature the specific resistance of the heating conductor increases so much that the causing increased Operating voltage is almost compensated, and the implemented electrical Performance only marginal increases.

It is therefore proposed as a solution that that the specific electrical resistance of the heating conductor is such is designed to be above the operating temperature of the specific electrical resistance of the heating conductor increases so that the causing increased Operating voltage is compensated.

Advantages of invention

The main advantage of the invention consists of the material design of the glow plug or the pen opposite the flatter temperature-voltage characteristic in the prior art high operating temperatures is reached. This makes possible, selectively adjust the temperatures, but the destruction Operation with overvoltage to avoid.

It is therefore possible to have a heating rate the glow plug with a flat control characteristic at high operating temperatures to combine.

Another advantage is a steeper one Resistance-temperature characteristic curve, which allows the resistance measurement to more accurate temperature results leads.

Temperatures above the maximum Operating temperature of the materials used can be avoided in this way become.

Further advantageous configurations are shown in the diagrams below.

drawings

Show it

1 A schematic representation of the ratio of specific resistance to temperature;

2 A schematic representation of the ratio of temperature to operating voltage.

description

In the 1 and 2 on the one hand, the relationships between the specific resistance of the heating conductor and the temperature or temperature and operating voltage known from the prior art are shown, the relationships known from the prior art having been given the designation “standard design”.

The interpretations according to the invention have received the designation “idealized” or “real”. Material properties for the glow plug are set so that up to a limit temperature, for example in the 1 and 2 1,200 ° C, which roughly corresponds to the operating temperature, the temperature coefficient of resistivity is low. This brings a very high average power with low initial currents. However, the temperature coefficient is much higher at this limit temperature. This leads to a strong curtailment of the operating current and thus the destruction of the glow plug cores is avoided in a simple manner.

Alternatively, the specific resistance ratio to the temperature can also be achieved via a voltage-dependent resistor, which is designed such that the specific resistance of the Heating conductor increases significantly at high operating voltages.

example

The operating temperature is 1,200 ° C. In order to achieve that the temperature of the glow plug is only around 25 ° per volt increases (compared to the prior art) it is proposed according to the invention that the temperature coefficient of the material above the target operating temperature is about three times higher than below the operating temperature. With this estimate only the heat transfer for heat radiation considered, because it is proportional to the fourth power of temperature. Under consideration of heat conduction and convection is the control behavior with the same choice of material even stronger. To the same control behavior in the estimate just mentioned is obtained, there is thus a slight difference in the temperature coefficients necessary.

Claims (3)

Glow plug, in particular low-voltage glow plug to be arranged in the combustion chamber of a fuel engine, the glow plug comprising a heat conductor which can be connected to a defined operating voltage and has an electrical resistance, and the heat conductor can be brought to a defined operating temperature, characterized in that the glow plug has a protective function against destruction by overvoltage, in which the electrical resistance of the heating conductor is designed such that the resistance of the heating conductor rises above the operating temperature in such a way that the resulting increased operating voltage is compensated for. glow plugs according to claim 1, characterized in that up to a limit temperature the temperature coefficient of the special resistance of the heating conductor is low and from a defined limit that is above the Operating temperature is significantly increased. glow plugs according to claim 1, characterized in that the special resistance of the heating conductor depending on the voltage is designed, and from a defined limit that is above the Operating temperature is, increases sharply.