DE102020106645A1 - Pump unit for a cooking device, cooking device with such a pump unit and method for operating the pump unit of such a cooking device - Google Patents

Abstract

The invention relates to a pump unit for a cooking appliance, with a fluid container, a pump and a control unit, the fluid container having an inlet and an outlet, the pump being assigned to the outlet and having a pump wheel and a pump motor, the pump motor being an electronically commutated one Is an electric motor and wherein the control unit has an analysis module which is configured to analyze the back-induced voltage of a magnet rotor of the electric motor. The invention also relates to a cooking appliance with such a pump unit, as well as a method for determining various state parameters by analyzing the back-induced voltage of the magnet rotor.

Description

The invention relates to a pump unit for a cooking device, a cooking device with such a pump unit and a method for operating the pump unit of such a cooking device.

The cooking devices according to the invention are devices for professional use, for example, in restaurants, canteens and in large-scale catering. In the cooking space of the cooking devices, food can be cooked under the action of hot air, superheated steam and in a mixed atmosphere of hot air and superheated steam. Such cooking devices are also known under the name “combi steamer”. Microwave radiation can also be used to add energy to the food.

The pump unit can have various functions. One function is to take up the washing liquor when cleaning the cooking appliance, which is circulated by a pump.

One function is to take up fluid (either washing liquor or residues originating from the cooking chamber) and to pump this to a sewage pipe by means of the pump.

When operating conventional centrifugal pumps (e.g. synchronous or asynchronous pumps), such as those used in the pump units of cooking appliances, there is no feedback about the operating status of the pump or the conditions in the hydraulic system, e.g. whether the pump is really running, whether it is delivering, Whether the medium to be pumped is present, whether there are error states, and whether the pumping process has ended (fluid container empty).

If such feedback is desired or is even necessary for reliable operation, suitable sensors must be used in order to have information about state parameters of the cooking appliance and / or the pump unit available. On the basis of this information, the pump unit and the cooking appliance can then be controlled appropriately.

The object of the invention is to simplify the construction of the pump unit and the cooking appliance and to enable additional functionalities despite a less complex construction.

To achieve this object, a pump unit for a cooking appliance is provided according to the invention, with a fluid container, a pump and a control unit, the fluid container having an inlet and an outlet, the pump being assigned to the outlet and having a pump wheel and a pump motor, the The pump motor is an electronically commutated electric motor and wherein the control unit has an analysis module which is set up to analyze the back-induced voltage of a magnet rotor of the electric motor. To solve this problem, a cooking appliance with such a pump unit is also provided.

In general terms, according to the invention, by evaluating the back-induced voltage when the magnet rotor rotates by the excitation coils of the electronically commutated pump motor (EC motor), conclusions can be drawn about the speed of the rotor and the current consumption of the motor, so that feedback is generated without additional sensors the basis of which “intelligent” pump functions can be implemented. Furthermore, safety features can be implemented with which malfunctions in the cooking appliance can be prevented.

The analysis module makes it possible, without external sensors such as speed sensors, flow meters, fill level sensors, etc., to determine a large number of parameters that are relevant for the operation of the pump unit and the cooking appliance containing the pump unit.

• - Es kann aus der rückinduzierten Spannung erkannt werden, ob die Pumpe ein Fluid fördert oder ob sie leerläuft;
• - es kann aus der rückinduzierten Spannung der Verschmutzungsgrad des geförderten Fluids erkannt werden;
• - es kann aus der rückinduzierten Spannung der Anteil von Luft im geförderten Fluid erkannt werden;
• - es kann aus der rückinduzierten Spannung erkannt werden, ob die Pumpe blockiert ist;
• - es kann die Menge des sich im Fluidsystem befindenden Fluids ermittelt werden.

Examples of parameters that can be recorded by means of the analysis module in a method according to the invention are:

• - It can be recognized from the back-induced voltage whether the pump is delivering a fluid or whether it is idling;
• - The degree of contamination of the pumped fluid can be recognized from the back-induced voltage;
• the proportion of air in the conveyed fluid can be recognized from the back-induced voltage;
• - It can be recognized from the back-induced voltage whether the pump is blocked;
• - The amount of fluid in the fluid system can be determined.

Examples of new functionalities that can be implemented by analyzing the back-induced voltage are explained in detail below.

• „Hydraulisches System“: das vom Fluidbehälter, den Leitungen vom und zum Garraum und dem Garraum abgegrenzte Volumen zusammen mit der darin in einem betrachteten Betriebszustand enthaltenen Fluidmenge;
• „Fluid“: das in einem betrachteten Betriebszustand im hydraulischen System enthaltene Medium, das von der Pumpe gepumpt werden soll. Im Reinigungsmodus ist das Fluid die Waschflotte. Im Spülmodus ist das Fluid Wasser (zusammen mit ausgewaschenen Resten der Waschflotte). Das Fluid kann auch von den Nahrungsmitteln stammen, beispielsweise beim Garen ausgetretene Flüssigkeit, oder Kondenswasser.

The terms used in the following mean here:

• “Hydraulic system”: the volume delimited by the fluid container, the lines to and from the cooking chamber and the cooking chamber together with the amount of fluid contained therein in a considered operating state;
• "Fluid": the medium contained in the hydraulic system in a considered operating state that is to be pumped by the pump. In the cleaning mode, the fluid is the wash liquor. In rinsing mode, the fluid is water (together with washed-out residues of the washing liquor). The fluid can also come from the food, for example liquid that has leaked out during cooking, or condensation water.

1. 1. Pump out the fluid container until it is empty:
   • If the power consumption at constant speed (on average over a predefined time) is below a predefined value that is characteristic of the hydraulic system, it can be concluded that the hydraulic load is very low, i.e. there is little or no water in the fluid container ( Air-water mixture or just air).
   • If the speed is above a predefined value that is characteristic of the hydraulic system while the power consumption is kept constant, it can be concluded that the hydraulic load is very low, that is, there is little or no water in the fluid container (air-water mixture or only Air).
   • If the power consumption at constant speed (on average over a predefined time) falls from an initially high to a lower value below a predefined value that is characteristic of the hydraulic system, it can be concluded that the hydraulic load was initially high, i.e. the pump Has conveyed fluid, but then there is little or no fluid in the fluid container (eg air-water mixture or only air).
   • The opposite case is also conceivable: first low current => fluid container empty, then high current => fluid container full.

Speed profiles

The speed of the pump can be varied as required within certain limits. For example, a profile mode can be run: Change between high speed for a certain time (= pumping fluid) and low speed for a certain time (= pause time without pumping, so that the fluid can run back to the pump sump). To do this, the pump does not have to be switched on / off, which benefits its service life, as the very high starting currents when starting up are avoided.

Capacity detection / loss detection / adaptive profiles

• - Im Umwälzbetrieb wird ausgewertet, wie lange die Pumpe mit voller Förderleistung läuft (Stromauswertung), bevor der Volumenstrom abbricht, weil die Pumpe nicht mehr genug Fluid ansaugen kann und stattdessen ein Luft-Wasser-Gemisch ansaugt.
• - Diese „Vollförderzeit“ kann hinsichtlich ihrer Änderung im Verlauf der Umwälzphase überwacht werden. Eine Reduzierung dieser Zeit deutet auf Verlust der Waschflotte hin, z.B. durch Leckage, Schaumbildung, Benetzen von Oberflächen oder Verdampfung. Dementsprechend kann eine Fehlermeldung ausgegeben werden und/oder Waschflotte nachgefüllt werden.
• - Die Unterscheidung zwischen voller und geringer bzw. keiner Förderleistung geschieht über die Auswertung des Motorstroms, der wie oben im Beispiel 1 erfasst wird.

With a known hydraulic system, by recognizing when a fluid container is empty, conclusions can be drawn about the initial filling quantity via the delivery time. A loss of the pumped medium can be recognized on the basis of the initially recognized filling quantity:

• - In circulation mode, it is evaluated how long the pump runs at full delivery rate (current evaluation) before the volume flow breaks off because the pump can no longer suck in enough fluid and instead sucks in an air-water mixture.
• - This “full funding period” can be monitored with regard to its change in the course of the circulation phase. A reduction in this time indicates a loss of the wash liquor, for example through leakage, foam formation, wetting of surfaces or evaporation. Accordingly, an error message can be issued and / or washing liquor can be refilled.
• - The distinction between full and low or no delivery rate is made by evaluating the motor current, which is recorded as in example 1 above.

• - Nach Ablauf der „Vollförderzeit“ wird die Drehzahl reduziert, sodass die Waschflotte Zeit hat, zur Pumpe zurückzulaufen. Nach einer festgelegten Zeit wird die Drehzahl wieder erhöht, und es wird erneut so lange mit hoher Drehzahl gepumpt, bis ein Abbruch des vollen Volumenstroms detektiert wird. Dann wird die Drehzahl wieder reduziert usw.
• - Grundsätzlich ist es sinnvoll, eine Pumpe gar nicht erst so lange fördern zu lassen, bis sie Luft ansaugt, sondern kurz vorher schon die Pumpe zu stoppen oder die Drehzahl (und damit die Förderleistung) zu reduzieren.
• - Dies kann in Form eines Regelkreises geschehen. Beispiele sind die folgenden Szenarien:
  • • Pumpe läuft mit hoher Drehzahl so lange, bis sie Volumenstromabfall detektiert (t₁). t₁ wird etwas reduziert (z.B. von 6 s auf 5 s).
  • • Pumpe reduziert Drehzahl und läuft so für eine Zeit t₂.
  • • Pumpe erhöht Drehzahl wieder und läuft so für t₁ (neu).
  • • Falls in der Zeit t₁ kein Volumenstromabfall detektiert wird, bleibt t₁ unverändert.
  • • Pumpe reduziert Drehzahl und läuft so für eine Zeit t₂.
  • • Pumpe erhöht Drehzahl wieder und läuft so für t₁. t₁ wird reduziert oder beibehalten, wie oben beschrieben.
  • • usw.
  • • Um den Regelkreis robust zu gestalten, kann aus mehreren Zyklen (Drehzahl hoch/niedrig) ein Mittelwert für die „Vollförderzeit“ gebildet werden, der dann herangezogen wird. Auch sinnvolle Ober- und Untergrenzen sollten gewählt werden, damit t₁ nicht zu lang oder kurz wird.
  • • Damit t₁ nicht kürzer als nötig ist, d.h. die Pumpe eigentlich länger am Stück fördern könnte als sie es tut, kann auch in definierten Abständen t₁ wieder schrittweise erhöht werden, um sich von unten an die maximale „Vollförderzeit“ anzunähern.

The pump can react adaptively to fluctuations in the wash liquor volume or in the amount of wash liquor available in the suction area of the pump:

• - After the "full delivery time" has elapsed, the speed is reduced so that the wash liquor has time to return to the pump. After a specified time, the speed is increased again and the pump is again pumped at high speed until a break in the full volume flow is detected. Then the speed is reduced again, etc.
• - Basically, it makes sense not to let a pump run until it sucks in air, but to stop the pump shortly beforehand or to reduce the speed (and thus the delivery rate).
• - This can be done in the form of a control loop. Examples are the following scenarios:
  • • The pump runs at high speed until it detects a drop in volume flow (t ₁ ). t ₁ is reduced somewhat (e.g. from 6 s to 5 s).
  • • The pump reduces the speed and thus runs for a time t ₂ .
  • • Pump increases speed again and runs for t ₁ (new).
  • • If no drop in volume flow is detected in time t _{1 , t 1} remains unchanged.
  • • The pump reduces the speed and thus runs for a time t ₂ .
  • • Pump increases speed again and runs for t ₁ . t ₁ is reduced or maintained as described above.
  • • etc.
  • • In order to make the control loop robust, an average value for the “full delivery time” can be formed from several cycles (high / low speed), which is then used. Sensible upper and lower limits should also be chosen so that t ₁ does not become too long or too short.
  • • So that t _{1 is} not shorter than necessary, ie the pump could actually deliver longer at one time than it does, t ₁ can also be increased again gradually at defined intervals in order to approach the maximum “full delivery time” from below.

Vary volume flow

Setting a speed: With knowledge of the hydraulic system, conclusions can be drawn about the volume flow.

Setting the direction of rotation: If the pump has a preferred direction of rotation in which it has a higher delivery rate than the other (e.g. because the outlet connection is not arranged centrically, but tangentially to the impeller), the volume flow can be greatly changed. This can be used, for example, to generate different spray widths of the water jet in a fluid container to be cleaned (e.g. cooking space) in order to wet different surfaces to be cleaned in a targeted manner.

A constant volume flow can be set by regulating to a constant power consumption.

Pump as agitator / mixing accelerator

If the pump is operated at a very low speed, the delivery head is low. If it is below the height that is necessary to empty the connected fluid container, no volume is pumped out. However, the rotation of the impeller mixes the volume of the fluid container. The pump acts as an agitator.

If the pump has a preferred direction of rotation in which it has a higher flow rate than the other (e.g. in that the outlet connection is not arranged centrically, but tangentially to the impeller), it makes sense to use the direction of rotation for agitating operation Delivery rate is lower. A higher speed can then be used, which promotes turbulence without fluid being pumped out of the fluid container.

Another possibility to achieve a thorough mixing of a fluid container is as follows: The pump is operated for such a short time that the fluid column in the outlet hose is built up, but not so far that there is significant pumping. Then the pump is switched off again or the speed is reduced so far that the majority of the fluid column flows back into the fluid container. This swirls the contents of the fluid container. This can be done several times in a row.

As an alternative to switching the pump on and off, it can also be controlled one after the other at different speeds, each of which is so low that no fluid is conveyed away. Mixing can also be achieved in this way.

Determining the amount conveyed

By adding up the power consumption and / or the speed over time, conclusions can be drawn about the volume conveyed. In this way, for example, a desired amount can be pumped out of a fluid container or the pumped amount can be determined after a pumping process.

Control of volume flows

A column of fluid can be raised to different height levels by setting different speeds.

The power consumption shows whether there is a volume flow or whether the fluid column is merely raised without actually conveying.

• Eine Wassersäule wird nur bis zu der Höhe des tieferliegenden ersten Abgangs gehoben.
• Durch Beobachten der Stromaufnahme kann erkannt werden, ab wann in den Abgang gefördert wird (Strom nimmt zu).
• Eine Wassersäule wird so weit angehoben, dass auch der zweite, höher liegende Abgang mit Wasser versorgt wird.

This means that different paths in a hydraulic system can be supplied with the conveying medium, e.g. by placing two outlets of a vertical pipe at different heights:

• A column of water is only lifted to the level of the lower-lying first outlet.
• By observing the current consumption, it can be seen from when it is pumped into the outlet (current increases).
• One water column is raised so that the second, higher-lying outlet is also supplied with water.

Recognition of the operating status of the pump

Detection of particles / foreign bodies: Fluctuating current signal, e.g. occasional peaks. Their height, number and duration are an indicator of the amount and size of the particles.

Detection of the viscosity of the conveyed medium via the power consumption

Eliminate or prevent error conditions

Pump is blocked: No speed with very high power consumption.

Inlet to the pump and / or outlet from the pump blocked / narrowed: The power consumption is lower than would be expected at the measured speed at full volume flow. This scenario can be distinguished from pumping an air-water mixture on the basis of the different height of the current or through the reliable knowledge that the fluid container is full.

Impeller loose / damaged: Reduced power consumption

Pump not connected / electrically interrupted / has a short circuit: The resistance of the coils can be calculated. This can be used to infer error states.

“Deblocking”: When a blockage is detected, the pump tries to use a “shaking mode” to remove the blockage.

"Derating": If the pump is overloaded, e.g. because a high current consumption has been applied for a long time, the pump can continue to be operated with reduced operating parameters (speed, max. Current) instead of having to be stopped completely.

• • Die Zeit, die der Motor von der Steuerung zugestanden bekommt, um vom gesteuerten in den geregelten Betrieb (mit Auswertung der rückinduzierten Spannung wie bei EC-Motoren üblich) zu wechseln, wird verlängert.
• • Der maximale Strom, der in der Anlaufphase fließen darf, wird erhöht.

Increased start-up phase: If the pump control detects that it cannot reach the required speed in the required time, it can go through an intensified start-up phase:

• • The time the motor is allowed by the control to switch from open-loop to closed-loop operation (with evaluation of the back-induced voltage as is usual with EC motors) is extended.
• • The maximum current that can flow in the start-up phase is increased.

Prevent unsafe conditions in a cooking appliance

When the oven door is opened, the circulating pump that pumps the washing liquor into the oven stops. This can be done via software, but it is better to couple the door contact switch with the control of the pump so that opening the switch interrupts the control of the pump in terms of hardware, e.g. by interrupting the power supply of the power module of the pump control.

So that unintentional switching on of the circulation pump does not lead to fluid from the pump sump getting into the cooking chamber and thus potentially onto food, a logic is implemented on the pump control that only enables the circulation pump when the pump sump drain pump has been running shortly beforehand. Then you can be sure that the dirty water has been emptied from the pump sump and that switching on the circulation pump would not contaminate the food that has just been cooked. In the event that the cooking space needs to be cleaned, after the pump sump has been emptied, it is filled with fresh water via a solenoid valve. This can also be linked to the fact that the emptying pump of the pump sump has been running beforehand.

If there is no emptying pump for the pump sump, the release of the circulation pump can be linked to the activity of the fresh water filling valve. Then the circulation can only take place if the pump sump has previously been filled with fresh water, which displaces the dirty water.

The circulation pump is released decentrally on the pump control, not centrally via the main device control, which minimizes the risk of software errors because the logics are distributed over two assemblies.

• - Vermeiden unnötig langer Abpumpzeiten, Erkennen von Fehlern (falls Fluidbehälter nicht leer wird)
• - Verlängerung der Lebensdauer der Pumpen durch Vermeiden von Einschaltvorgängen und unnötig langer Laufzeit
• - Optimierte Benetzung/Spülung des Garraums, indem die Pumpe nur dann läuft, wenn sie ausreichend Wasser zum Fördern hat, und nicht bereits dann, wenn das Wasser noch dabei ist, zurückzufließen.
• - Leckageerkennung im Umwälzbetrieb, z.B. Undichtigkeiten an der Gerätetür, können erkannt werden
• -Gezieltes Benetzen von Flächen im Garraum durch Variieren des Volumenstroms bzw. der Austrittsgeschwindigkeit aus der Düse.
• - Abpumpen einer bestimmten Menge aus einem Fluidbehälter mit hoher Genauigkeit, indem die Pumpe mit geringer Drehzahl und/oder „falschherum“ läuft, sodass der Volumenstrom gering ist.
• - Rühren/Vermischen des Fluidbehälterinhalts z.B. zum beschleunigten Auflösen von Feststoffchemie oder zum Ausgleich von Temperatur- oder Konzentrationsunterschieden
• - Umlenken von Fluidsströmen durch verschiedene Pumphöhen statt mittels eines Schaltventils; hieraus resultiert eine Kosteneinsparung
• - Erkennen des Verkalkungsgrades des Dampfgenerators über die Anzahl oder Größe abgepumpter Kalkbrocken
• - Erkennen von Fehlerzuständen der Pumpen; hieraus resultieren detaillierte Fehlermeldungen, wodurch vermieden wird, dass unnötig Bauteile getauscht werden
• - Selbstheilung von Fehlerzuständen durch von der Pumpe selbst eingeleitete Gegenmaßnahmen (z.B. Rütteln beim Anlaufen)
• - Sicherheit gegen Softwarefehler (Freigabe der Umwälzpumpe)

Overall, the following advantages result according to the invention:

• - Avoid unnecessarily long pumping times, detection of errors (if the fluid container does not become empty)
• - Extension of the service life of the pumps by avoiding switch-on processes and unnecessarily long running times
• - Optimized wetting / rinsing of the cooking space, in that the pump only runs when it has enough water to pump and not when the water is still flowing back.
• - Leak detection in circulation mode, e.g. leaks on the appliance door, can be detected
• - Targeted wetting of surfaces in the cooking space by varying the volume flow or the exit speed from the nozzle.
• - Pumping a certain amount out of a fluid container with high accuracy, in that the pump runs at low speed and / or “the wrong way round” so that the volume flow is low.
• - Stirring / mixing the contents of the fluid container, for example to accelerate the dissolution of solid chemistry or to compensate for temperature or concentration differences
• - Diverting fluid flows through different pumping heights instead of by means of a switching valve; this results in a cost saving
• - Recognition of the degree of calcification of the steam generator via the number or size of the pumped out lime lumps
• - Recognition of error states of the pumps; this results in detailed error messages, which avoids unnecessary replacement of components
• - Self-healing of error states through countermeasures initiated by the pump itself (e.g. shaking when starting)
• - Security against software errors (release of the circulation pump)

Claims (9)

Pump unit for a cooking appliance, with a fluid container, a pump and a control unit, the fluid container having an inlet and an outlet, the pump being assigned to the outlet and having a pump wheel and a pump motor, the pump motor being an electronically commutated electric motor and wherein the control unit has an analysis module which is set up to analyze the back-induced voltage of a magnet rotor of the electric motor. Cooking appliance with a pump unit according to one of the preceding claims. Cooking appliance Claim 2 , characterized in that the inlet of the fluid container is connected to a cooking space of the cooking device. Cooking appliance Claim 3 , characterized in that the pump has an outlet which leads to the cooking chamber of the cooking appliance. Method for operating a pump unit of a cooking appliance according to one of the Claims 2 until 4th , characterized in that the analysis module detects from the back-induced voltage whether the pump is delivering a fluid or whether it is running empty. Procedure according to Claim 5 , characterized in that the analysis module detects the degree of contamination of the pumped fluid from the back-induced voltage. Procedure according to Claim 5 or Claim 6 , characterized in that the analysis module detects the proportion of air in the pumped fluid from the back-induced voltage. Method according to one of the Claims 5 until 7th , characterized in that the analysis module detects from the back-induced voltage whether the pump is blocked. Method according to one of the Claims 5 until 8th , characterized in that the analysis module determines the amount of fluid in the fluid system.