JPH0456210B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The invention relates to a water heater heated by gas or oil, in particular operating on the once-through principle, in which a burner and combustion gases flow inside or outside. It has a heat exchanger and an oxygen sensor arranged downstream of the heat exchanger in the flow path of the combustion gases, the oxygen sensor being configured as an electrochemical solid-state measurement value detector. Both electrodes of this solid-state reading detector are exposed to the combustion gases, and the oxygen sensor is connected to a controller to maintain a constant combustion air ratio or to control the air ratio. of the type adapted to act on a control element.

BACKGROUND OF THE INVENTION An oxygen sensor for use in water heaters of the type mentioned above is known from DE 26 31 819 A1. Compared to potentiometric sensors, this known oxygen sensor has a high sensitivity even in the lean range of fuel-air mixtures in which the water heater is often operated, and the signal given by the oxygen sensor is also significant. It has the advantage that it is proportional to the oxygen content of the combustion gas over a range and is therefore easily evaluated for adjustment. Furthermore, both electrodes have a measuring gas reference, that is, they are exposed to the combustion gas, so that they can be easily integrated into the measuring device.
Of course, in this case, as λ decreases in the range λ<1, the sensor characteristic curve rises again, so that the sensor signal has the same magnitude for each of the two different λ values. Therefore, the sensor characteristic curve is secondary. Therefore, even though λ has already fallen below a value of 1 and the controller has to increase the amount of combustion air, the controller indicates a large sensor signal as a large λ to enrich the fuel-air mixture. try to become Therefore, due to the enrichment of the air-fuel mixture, the amount of combustion air is reduced even further until the controller finally stops supplying air altogether.

OBJECT OF THE INVENTION It is an object of the invention to ensure, by simple measures, that the controller does not enrich the fuel/air mixture unnecessarily strongly due to erroneous indications of sensor signals.

Means for Solving the Problem The measures taken to solve the aforementioned problem are such that when the sensor signal reaches a certain value, which is related to the λ value corresponding to the oxygen content of the air, the water heater so that the fuel supply to the burner can be interrupted,
The measured value detector also forms the actuating element of the safety circuit, and the measured value detector is configured as a dual sensor with a limiting current sensor and a λ sensor, the voltage of the λ sensor being λ = 1, the electrodes of each sensor are electrically connected to each other such that when raised to a high voltage, the sign of the final output signal of the measured value detector is reversed. .

Effects of the invention When the excess air ratio λ falls below the value 1, the sensor signal rises steeply to a value that cuts off the fuel supply;
This quickly guides the air ratio λ to a range that lies above the value λ=1, in which the sensor signal controls the air ratio in the correct sense. Additionally, the invention allows a water heater safety switch to be released if heat is required but no fuel supply occurs. Due to the good proportionality between the oxygen content and the sensor signal in the limiting current sensor (polarographic sensor), the cut-off point above the sensor in the sensor signal is well defined.

Furthermore, since the sensor is constructed as a dual sensor with a limiting current sensor and a lambda sensor, a unique sensor signal is obtained in reference to the measuring gas of both electrodes of the sensor. λ sensor is λ<
1, this λ sensor reverses the sign of the output signal of the limiting current sensor.

A dual sensor with a limiting current sensor and a λ sensor is disclosed in patent application no.
It is known from specification No. 2855012.

Example Next, embodiments of the present invention will be described with reference to the drawings.

The water heater shown in FIG. 1 has a gas burner 10, which is supplied with fuel via a conduit 12 and a continuously controlled solenoid valve 14.
A combustion tube 16 is arranged above the gas burner 10, and a heat exchanger 1 is disposed in the upper part of the combustion tube 16.
8 is installed. The heat exchanger 18 is constructed as a fin block penetrated by a corrugated pipe 20 which guides the water to be heated. This flexible pipe 20 is connected to a conduit 22,
The conduit 22 is guided by a plurality of turns surrounding the combustion tube 16 and opens into a hot water valve 24 from which heated water can be removed. A box-shaped waste gas collection hood 26 is placed above the heat exchanger 18.
A fan 28 is fixed to the upper end wall of the waste gas collection hood 26. This fan 28 has a central suction opening that coincides with the exhaust opening in the upper end wall of the collecting hood 26 and a tangential outlet connection 30 .
is attached to the device and communicates with the outside through the wall of the chamber.

This water heater is equipped with a continuously operating control device consisting of two independent control circuits 31 and 32. The controlled variable of this control circuit 31 is the discharge water temperature x ₁ which is detected by the temperature feeler 33 at the outlet and corrected by the electronic controller 34 to a predetermined target value W ₁ . In this case, the electronic controller 34 considers the discharged water flow rate detected by the speed measuring device 36 as the disturbance amount z ₁ . The control element of this control circuit 31 is a solenoid valve 14.
4, an electronic controller 34 can start and stop the water heater and throttle the output of the gas burner 10 to a value approximately 50% of the rated output of the gas burner 10.

The control variable x ₂ of the control circuit 32 is an excess air ratio λ, and combustion progresses according to the excess air ratio λ, and oxygen content in the combustion gas is one factor for the excess air ratio λ. It is. This excess air ratio λ is detected by the oxygen sensor 38 and sent to the electronic controller 40, which compares the adjustment amount x ₂ with a predetermined target value w ₂ . The control element of the control circuit 32 is a fan 28, and this fan 28 has a split-pole motor as its drive device, and the rotation speed of the split-pole motor can be adjusted steplessly by phase control. . The electronic controller 40 generates a control signal y ₂ from the control variable x ₂ and the setpoint value w ₂ , which control signal y ₂ correspondingly controls the components for the phase control.
According to the invention, the oxygen sensor 38 is an electrochemical solid-state measurement value detector, which is equipped with a special diffusion layer and a specific heater adjusted to approximately 600°C. . This sensor is shown in FIG. 4 and will be described in more detail later.

The two control circuits 31 and 32 described above operate independently of each other, so that the connection of the two control elements (magnetic valve 14 and fan 28) is omitted, but in addition the control device 42 (FIG. 2) A controller 42 is provided which temporarily disables the control circuit 32 for the air excess rate by a predetermined limit value when the required heat signal suddenly increases.
can be switched to full speed, thus avoiding starvation or overenrichment of the fuel/air mixture. However, air starvation may occur due to the unavoidable response delay of the control circuit 32 relative to the control circuit 31, which corresponds in time to the signal transit time through the water heater. The individual switching elements of control device 42 are integrated, for example, in electronic controller 34 and are connected to control circuit 32 via control lines 44 (FIG. 1). The two electronic controllers 34 and 40 and the control device 42 can also be combined into one component and housed in a common housing. Next, the mode of operation of the control device 42 will be described using the block circuit diagram shown in FIG.

The aforementioned control circuit 32 regulates the amount of combustion air in its front region via an electronic controller 40 and a fan 28 . At the intersection point at the gas burner 10, a gas flow is applied from above. The mixer burns in the combustion tube 16 and after the combustion period enters the collecting hood 26 where it is fed back via the oxygen sensor 38. The control device 42 detects a change in the control signal y ₁ of the electronic controller 34 and differentiates it with a differentiating element 42.1. If the variation of the control signal y ₁ , depending on magnitude and speed, exceeds a predetermined limit value, then the asymmetric on-off element 42.2 reacts;
The on-off element 42.2 controls the fan 28 via an element 42.3 having a slow falling characteristic.

In addition, the element 4 having this slowly falling characteristic
Instead of 2.3, a timing element may be installed in the control device, which controls the rotational speed-control signal y ₂ for continuing the signal transmission time in the combustion tube 16 to the on-off element 42. It is held at the value adjusted by .2 and then lowered so as to have an integral or slow decreasing characteristic. In both cases, the fan 28 is perfectly adjusted to the rotational speed, so that the electronic controller 40 always starts working from a thin gas range, yet ensures that no harmful components are formed in the waste gas. Become.

If both electrodes of the sensor have a measuring gas reference, i.e. are exposed to the combustion gas, a relatively simple construction and advantageous installation conditions of the electrochemical solid-state measurement value sensor are obtained. It will be done. However, in this case, as shown in FIG. 3, the sensor characteristic curve is no longer unambiguous. Initially, as λ becomes smaller, the sensor signal s decreases, and λ=
1 gives the value 0. However, as λ decreases further, the sensor signal s again rises sharply into a range lying above the minimum sensor signal s min, which corresponds to the minimum permissible value λ min. If such a limiting current sensor is involved in order to safely shut off the water heater in case of a decrease in the λ value, there is a logical case that the sensor and the electronic controller controlled by it respond incorrectly. is assumed. This case occurs when irregularities in the discharge of combustion gases or irregularities in the water heater in question cause the λ value of the fuel to drop rapidly, which means that the sensor does not detect any Either they don't respond, or they can't respond quickly enough. Accordingly, the sensor signal is λ
=1, in which the sensor signals an erroneously large λ value to the electronic controller. This causes the electronic controller to enrich the fuel/air mixture even more, which again causes the sensor signal to rise further and further restricts the combustion air supply even more significantly. Put it away.

In order to eliminate such incomplete combustion, a safety device must detect a predetermined upper limit value signal s of the measured value detector.
It was proposed to make it also responsive to max,
This upper limit value signal s max is selected so that the λ value does not drop significantly from 1 even in the above-mentioned special case. The upper limit value s max for this sensor signal can be associated with the oxygen content, which corresponds to the oxygen content of the air, for example. In this case, the sensor also signals a lack of fuel supply, which likewise makes it possible to switch off the safety switch of the water heater.

The ambiguity of the sensor signal of an electrochemical solid-state measuring value detector in which both electrodes have a measuring gas reference makes it possible to convert the detector into a dual-acting measuring sensor according to FIGS. 4 to 6. Can be removed by configuring. This sensor has two of the same type.
Two sensor elements 50 are provided, each of which has a ceramic plate 51 as a support base member through which oxygen ions pass. Two measuring electrodes 52 and 53 (FIG. 5) are crimped or vapor-deposited on one end face of the plate 51 on the measuring gas side. , contact side end 5
It has reached 6. These conductor tracks 54 and 55
may likewise be crimped or vapor-deposited. Measuring electrodes 52 and 53 are connected to the diffusion layer 5
8, coated with, for example, a spinel layer. Board 51
A heat conductor in the form of a metal thin plate serving as a specific heater 60 is fixed to the other end surface side of the plate 51 via an insulating layer, and the heat conductor is connected to the end 56 of the plate 51 on the contact side. Two conductor circuits 61 and 62 are provided. This heater is designed in such a way that it heats the end of the sensor element 50 on the measuring gas side to approximately 600°C.

The sensor element 50 is arranged in a housing 64, which has a threaded connection tube 65 for fixing on the measuring gas side in a wall hole of the exhaust gas collecting hood 26 (FIG. 1). ing. A plastic part 66 serves to hold the sensor element 50 in the casing 64, which plastic part 66 is injected into the casing 64 and is simultaneously injection molded around the contact-side end 56 of the sensor element 50. There is. A ceramic part 69 is fixed between the projection 68 in the casing 64 and the plastic part 66, which serves as a thermal protection for the plastic part 66. A flange of a protective peripheral wall 70 is tightened between the casing 64 and the threaded connection pipe portion 65.
0 surrounds the end of the sensor element on the measuring gas side at a distance and has a hole 71 at the bottom of the protective wall for passage of the combustion gas.

One of the two sensor elements 50 acts as a λ sensor and the other sensor element 50 is operated as a limit current sensor. A member for applying an external voltage to the electrode of the element operated as a limiting current sensor and a tap member for taking out the λ sensor voltage are provided in a connecting member (not shown), and the connecting member is connected to a contact point. side sensor element 50
can be mounted on the end 56 of. The λ sensor is used as a switch which, by means of a comparator, reverses the sign of the output signal of the limiting current sensor when a positive enriching voltage occurs.
This double-acting configuration of the measured value detector results in the sensor characteristic curve shown in FIG. 7, which tends to move further downwards as λ falls below the value 1. , and therefore it is unique.

[Brief explanation of the drawing]

The drawings show one embodiment of a water heater according to the present invention, in which FIG. 1 is a schematic diagram thereof, and FIG. 2 is a block circuit diagram of a control device for the water heater shown in FIG. Fig. 3 is a sensor characteristic curve diagram of the electrochemical solid-state measured value detector, Fig. 4 is a vertical cross-sectional view of the measured value detector with dual action, and Fig. 5 is the measured value detection shown in Fig. 4. 6 is a partial detail view of FIGS. 4 and 5, and FIG. 7 is a sensor characteristic curve of the measured value detector shown in FIGS. 4 and 5. It is a diagram. 10... Gas burner, 12... Conduit, 14...
Solenoid valve, 16... Combustion cylinder, 18... Heat exchanger, 2
0...Serial pipe, 22...Conduit, 24...Hot water valve, 2
6... Waste gas collection hood, 28... Fan, 30
...Blowout connection pipe section, 31, 32...Control circuit, 3
3...Temperature feeler, 34...Electronic controller, 36
... Speed measuring device, 38 ... Oxygen sensor, 40 ...
Electronic controller, 42... Control device, 44... Control line, 42.1... Differential element, 42.2... On/off element, 42.3... Element, 50... Sensor element, 51... Board, 52, 53...Measuring electrode, 5
4, 55...Conductor path, 56...End, 58...Diffusion layer, 60...Inherent heater, 61, 62...Conductor path, 64...Casing, 65...Screw connection pipe section, 66... ...Plastic member, 68...Protrusion,
69... Ceramic member, 70... Protective peripheral wall, 7
1...hole.

Claims (1)

[Claims] 1. A water heater heated by gas or oil, which includes a burner, a heat exchanger through which combustion gas flows inside or outside, and a heat exchanger in which the combustion gas flows. an oxygen sensor arranged downstream of the combustion chamber, the oxygen sensor being configured as an electrochemical solid-state measurement value detector, with both electrodes of the solid-state measurement value detector being connected to the combustion gas. and in which the oxygen sensor is adapted to act on a control element of a controller in order to maintain the combustion air excess rate constant or to control the air excess rate. , said measured value detector so that the fuel supply to the burner of the water heater can be interrupted when the sensor signal reaches a certain value, which is related to a λ value corresponding to the oxygen content of the air. 38 also forms the actuating element of the safety circuit, and furthermore the measured value detector 38 is constructed as a dual sensor having a limiting current sensor and a λ sensor, the voltage of the λ sensor being λ=1. The electrodes 52, 53 of each sensor are electrically connected to each other such that when raised to a high voltage below the sensor, the sign of the final output signal of the measured value detector 38 is reversed. A water heater featuring 2 The solid-state measurement value detector 38 is connected to the diffusion layer 58
and a specific heater 6 regulated to at least 550°C.
0. The water heater according to claim 1, comprising: 0.