WO1996006306A1 - Vehicle heater with flame monitor - Google Patents

Abstract

The vehicle heater proposed has a combustion chamber (9) round the outside of which a heat-transfer fluid passes, and heat exchange takes place between the heat-transfer fluid and the gases heated by the flame (F) in the combustion chamber (9). The flame (F) is produced by a burner. The burner includes a nozzle (18), designed to produce a spray of fuel, and a combustion-air fan. In order to avoid dangerous concentrations of fuel building up in the combustion chamber after the heater is turned on, the heater turns itself off automatically if no flame (F) is detected in the combusiton chamber (9) after a defined length of time after switching on. To this end, a flame monitor designed as a flicker sensor is fitted on the rear side of the burner (12), i.e. on the side facing away from the combustion chamber (9). The flicker sensor is mounted in a housing (24), and light from the combustion chamber (9) reaches it through a window (22) in the floor (14) of the combustion chamber. A processing circuit eliminates the constant component of the flicker-sensor output signal. The alternating signal thus obtained can be reliably processed.

Description

 Vehicle heater with flame detector

The invention relates to a vehicle heating device, with a combustion chamber around which a heat transfer medium flows, on one side of a

Burner is closed, and a flame guard, which provides an output signal when it detects a flame in the combustion chamber.

Vehicle heaters of this type, often also referred to as "auxiliary heating" or the like, are used in cars and trucks, in mobile homes, caravan trailers, ships and messengers, buses, but also in construction machinery. The burner, which is fed in the usual way from a metering pump with fuel and from a combustion air blower with combustion air, is produced, for example, with the aid of a

Nozzle in the combustion chamber a flame. The area of the flame is surrounded by a hollow housing, through which a heat transfer medium, for example water, flows, the heat transfer medium absorbing heat energy.

If the vehicle heater is used in vehicles with an internal combustion engine, the heater is arranged in the area of the engine for various reasons. Basically, but especially when installing the heater in the engine compartment of a vehicle, certain safety requirements must be met to prevent damage

Exclude people and material.

A requirement resulting from safety considerations is that a flame must be generated in the combustion chamber within a certain time after the heater is switched on (which means the start of the fuel and combustion air supply). This period of time, which lasts several seconds, must not be exceeded because this means with a high probability that there is a fault, in particular fuel is being supplied to the combustion chamber, but either the ignition does not work or there is no ignitable fuel-air mixture. By limiting the "flameless" time in the burner chamber to one maximum permissible value, the possibility should be excluded that fuel can accumulate in the burner chamber, which could lead to an explosion.

So far, for the purpose of flame monitoring

Enclosed combustion chamber housing a photo cell, the light-sensitive surface facing the combustion chamber. In addition to the complex mounting of the sensor designed as a photocell in the area of the combustion chamber where the flame is formed, there are also certain risks in flame detection. If one evaluates the photocurrent of a photocell, for example a phototransistor, by comparing the photocurrent with a reference value, there is a risk that a flame will be displayed due to the temperature-dependent dark current, although there is no flame. If the photocell is still cold, it may be too late

Signaling the flame may be the result.

The invention has for its object to provide a vehicle heater of the type mentioned, in particular a vehicle heater with a burner designed as a nozzle atomizer, in which the

The presence of a flame in the combustion chamber can be determined with high reliability.

This object is achieved in a vehicle heater of the type mentioned in that the flame detector is designed as a flicker sensor.

While the previously common photocells, e.g. phototransistors, provide an output signal that depends on the incidence of light in a certain wavelength range (e.g. UV light), he speaks

Flicker sensor for rapid changes between light and dark. While the previously usual photocells were afflicted with the errors discussed above and were also fooled by glowing parts inside the combustion chamber, such sources of error are excluded when using a flicker sensor. By using a flicker sensor, the DC component of the output signal of a photocell, for example a phototransistor, can be filtered out because only the higher-frequency AC component of the signal is of interest. It has been found that a conventional vehicle heater has a photocell output

State changes with a frequency between approx. 40 and 2,000 Hz. This alternating component of the output signal of the flicker sensor can be rectified by suitable filtering and compared with a reference value (threshold value). In this way a reliable signal is obtained.

Flicker sensors have been known per se for a long time. They are used in burners for building heating. In heating systems of this type, there is considerable space available in the area of the burner for holding the flicker sensor. Because of the not inconsiderable space requirement, vehicle heaters of the type in question have previously been of the opinion that flicker sensors cannot be used due to structural difficulties.

There were a number of serious reasons for this prejudice, one of the reasons being the earlier exercise of placing the flame sensor (providing a DC signal) as close as possible to the area of the flame within the combustion chamber, i.e. as close as possible to the flame tube that is normally used. Due to the cramped spatial conditions, there was no possibility of installing a flicker sensor, which takes up even more space than the conventional flame sensor, at a suitable location.

The inventor has now found that the flicker sensor can also be arranged at a location that is comparatively far away from the flame, without the reliability of the signaling being impaired thereby. Accordingly, the invention proposes in a special development that the flicker sensor is arranged on the side of the burner facing away from the combustion chamber. In particular, the flicker sensor is attached to the burner, which is particularly advantageous when the burner as a one-piece component with one to which Combustion chamber forming housing attached combustion chamber base is formed so that the flicker sensor can be attached to the back of the combustion chamber facing away.

With this attachment of the flicker sensor, there is a relatively large one

Distance between the location of the flicker sensor and the flame; nevertheless, the flicker sensor delivers a reliable signal even if the light incident on the flicker sensor does not come directly from the flame, but is generated indirectly by reflections on parts inside the combustion chamber.

In certain types of vehicle heaters with a burner of the type explained in more detail above, in particular a nozzle atomizer burner, elements of the control are located on the rear of the combustion chamber floor. For this reason, this location is particularly suitable for receiving a flicker sensor, because the flicker sensor contains not only a photo cell, for example a photo transistor, but also an evaluation circuit. These circuit elements can then also be expediently arranged directly in the region of the phototransistor.

The light signal reaching the flicker sensor via a viewing window in the combustion chamber floor is evaluated by the evaluation circuit. In particular, the flicker sensor contains:

a photocell, which is fed by a regulated operating voltage,

a filter that filters the DC component out of the flicker signal supplied by the photocell,

a rectifier, and

a comparator that compares the output signal of the rectifier with a reference signal. Because the photocell, which is preferably a phototransistor, is supplied with a regulated operating voltage, the operating point can be automatically set with a suitable selection of the operating voltage such that the photocell always delivers the maximum output signal when a certain amount of light strikes it .

Eliminating the DC component eliminates false alarms (both incorrectly displaying a flame and not displaying an existing flame). The reference voltage supplied to the comparator is expediently fed to the comparator via a variable resistor, so that the optimum threshold value can be set.

Because an alternating signal with a frequency of approximately 40 to 2,000 Hz is supplied when the flame is present, the flicker sensor according to the invention delivers a corresponding signal immediately after the flame has arisen. If the flicker sensor itself is controlled, the same reaction takes place through the device control as with a flame that has not arisen in the combustion chamber. The flicker sensor therefore offers a high level of reliability.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawing. Show it:

1 is a schematic view of a vehicle heater with nozzle atomizer,

Fig. 2 is an enlarged detail view of part of the combustion chamber floor with a flicker sensor attached, and

Fig. 3 shows a flicker sensor circuit.

Most • parts of the vehicle heater shown schematically in FIG. 1 are known and are only explained here in broad outline.

A vehicle heater, generally designated 10, has an outer housing 2 and an inner housing 4, which is smaller in comparison thereto. Between the housings 2 and 4, an annular space 6 is formed, which is spiraled by a heat transfer medium through the guide surfaces indicated by dashed lines

(Water) is flowed through. In Fig. 1, the water entry and exit are designated WE and WA, respectively.

During the flow around the inner housing 4, the water is heated by the flame F.

The flame F is generated by a burner designed as a one-piece burner insert 12 with the aid of a flame tube 8. The flame tube ensures a deflection of the hot gases, so that they first in Fig. 1 from left to right inside the flame tube 8 and then in the opposite direction between the outside of the flame tube 8 and the opposite inner wall of the inner housing 4 to one here flow shown exhaust outlet.

The burner 12 is attached in Fig. 1 on the left side of the outer housing 2 and consists of a one-piece casting, in which here Fuel channels (not shown), air passages for combustion air (this comes from a blower (not shown here) from the left-hand side and passes through the burner 12 into the area of the flame tube).

Fuel reaches a nozzle 18 via a fuel feed line 20 and the fuel channels (not shown) in the burner insert 12 with the aid of a pump driven by an electric motor 16. The electric motor 16 also drives a combustion air blower (not shown), so that combustion air flows through in the direction of the arrow to the right Openings in the burner base 14 flow into the combustion chamber 9 in order to form a combustible fuel / air mixture together with the fuel ejected from the nozzle 18. When the burner is switched on, the mixture is ignited by an ignition device, not shown.

The operation of the burner, in particular the operation of the electric motor 16 and the operation of the fuel metering pump (not shown here) and further parts of the heater which are not of interest here are controlled by control electronics 26 which are located on the

Back of the combustion chamber bottom 14 is attached.

Also on the rear side of the combustion chamber base 14 facing away from the combustion chamber 9, a flicker sensor housing 24 is fastened, in which there is a flicker sensor, onto which a window 22 is located

Light falls which comes from the area of the combustion chamber 9, either directly from the flame F or from side walls of the combustion chamber parts in the form of reflected radiation.

FIG. 2 shows details of the in the flicker sensor housing 24 according to FIG.

1 housed flicker sensor. The flicker sensor housing 24 is firmly glued to the back of the combustion chamber base 14 shown on the left in FIG. 2 and contains an opening in a base region which is closed by a protective glass 32. The opening with the protective glass 32 sits on a window which penetrates the combustion chamber floor 14

22, and at the height of the window 22 is on a support 28 inside of the flicker sensor housing 24, the actual flicker sensor 30 is attached. Within the housing 24 or at other locations on the rear side of the combustion chamber base 14 there are circuit elements of an evaluation circuit belonging to the flicker sensor 30, which are roughly outlined in FIG. 3.

According to FIG. 3, the flicker sensor 30 consists of a photocell, here in the form of a phototransistor, which is fed by a circuit (not shown here) with a regulated voltage V _{f on the} collector side. The emiter is grounded.

The voltage V is essentially 2 volts, regardless of the ambient temperature, so that the photocell is always operated at an operating point which ensures maximum output level.

An alternating signal with a DC component is indicated on the collector of the photocell.

A filter 36 indicated by a capacitor eliminates the

DC component, so that a pure AC signal with a frequency of 40 to 2,000 Hz is obtained. This AC signal is rectified by a rectifier 38 and fed to a first input of a comparator 40. An adjustable reference voltage is fed to the other input of the comparator 40 from a reference voltage source V _ref via a variable resistor R _v .

If the output signal of the rectifier 38 exceeds the level of the reference signal present at the other input of the comparator 40, the output signal at the output A of the comparator 40 changes from a logic low to a logic high level. A clear display is thus obtained which signals the existence of a flame in the combustion chamber 9. Depending on the respective spatial conditions of the vehicle heater shown in FIG. 1, the flicker sensor 30, the window 22 in the combustion chamber floor and the flicker sensor housing 24 can be arranged such that the "optical axis" SL in FIG. 2 penetrates the interior of the flame tube 8. In this case, relatively high signal levels are obtained in the area of the photosensitive surface of the phototransistor. But even if such a favorable position of the flickering sensor 30 is not possible, i.e. the optical axis SL of the flickering sensor is not directed directly at the flame F in the flame tube 8, the flickering sensor still functions faultlessly because of the flame tube 8, the inner wall of the Sufficient light is reflected by the flame F in the inner housing 4 and other parts not specified here in the region of the combustion chamber 9 in order to generate corresponding output signals of the flicker sensor 30.

The mode of operation of the device described here is known per se, but should be briefly outlined for the sake of completeness:

When you turn on the vehicle heater 10, the fuel metering pump, not shown, is turned on, so that fuel on the

Fuel feed line 20 passes through the burner insert 12 to the nozzle 18 and is ejected there. The pump conveying the fuel to the nozzle 18 is driven by the electric motor 16, which also drives a combustion air blower, not shown here, so that combustion air corresponds to that to the left of the

Combustion chamber floor 14 arrows is blown through the combustion chamber floor into the area in front of the nozzle 18. The combustion air mixes with the fuel sprayed from the nozzle 18. An ignition device, not shown, for example a spark gap, ignites the fuel mixture, so that a flame F forms within the flame tube 8. The ignition device is switched off again after a certain time. The flicker sensor 30 in the flicker sensor housing 24 detects the existence of the flame F through the window 22 in the combustion chamber floor and delivers a corresponding signal at the output A of the one shown in FIG. 3

Evaluation circuit. This signal at output A is from the Control electronics 26 detected so that the operation of the vehicle heater continues.

When the vehicle heater is switched on, a counter is started in the control electronics 26, which counts up to a defined counter reading, this counter reading being a certain one

Corresponds to a time span of, for example, 15 seconds. Will that

Output signal from output A of the evaluation circuit of the

If the flickering sensor is not delivered to the control electronics 26 within this period, the control 26 automatically switches the burner off, that is to say in particular the supply of combustion air and

Fuel stopped so that it does not get into the bottom of the combustion chamber 9

Can accumulate fuel, which would result in an explosive mixture.

Claims

PATENT CLAIMS 1. Vehicle heater, with a heat carrier flowing around it Combustion chamber (9), which is closed on one side by a burner (12), and a flame monitor (30), which delivers an output signal when it detects a flame in the combustion chamber (9), characterized in that the flame monitor is used as a flicker sensor (30) is formed. 2. Vehicle heater according to claim 1, characterized in that the flicker sensor (30) facing away from the combustion chamber Side of the burner is arranged. 3. Vehicle heater according to claim 2, characterized in that the flicker sensor (30) on the burner (12) is attached. 4. Vehicle heater according to claim 2 or 3, characterized in that the burner as a one-piece component with a to which the combustion chamber (9) forming the housing (2,4) attached Combustion chamber base (14) is formed, on the back of which faces away from the combustion chamber (9) the flicker sensor (30) is attached. 5. flicker sensor according to claim 4, characterized in that in the combustion chamber bottom (14) a light window (22) is formed, on the back of which the flicker sensor (30) is held. 6. Vehicle heater according to one of claims 1 to 5, characterized in that the flicker sensor (30) contains: a photocell, which is fed by a regulated operating voltage V _t ); a filter (36) which filters out the direct current component from the flicker signal supplied by the photocell; a rectifier (38); and a comparator (40) which compares the output signal of the rectifier (38) with a reference signal. 7. A vehicle heater according to claim 7, characterized in that the operating voltage (V _t ) for the photo cell, in particular as a phototransistor, is set such that it delivers a maximum useful signal.