[0001] The present invention relates to a boiler for heating water and outputting steam. Technical Background

[0002] Such a boiler is commonly known and typically used in various types of household appliances, including steam ironing devices, facial sauna devices, steam cleaning devices, coffee makers, steam ovens and breadmakers. The boiler is generally arranged within the housing of the household appliance, and receives water from a water supply such as a tank and heating the water, and then outputs steam via a hose to the household appliance for further use.

[0003] For this kind of boiler it is important to realize a consistent steam supply during operation. To this end, the risk that water in the boiler is boiled dry should be avoided. In addition, water newly supplied into the boiler during operation had better have a temperature close to that of water already presented in the boiler so as to minimize the temperature difference between the two portions of water, thereby ensuring a steady mix of water.

[0004] EP 0821096 discloses a boiler which has an inclined bottom onto which a heating plate is externally mounted. As a result of the inclined configuration of the bottom of the boiler, it is ensured that the boiler always contains a quantity of water, so that the steam production is not subject to interruptions, even if the water level falls below a predetermined minimum level.

[0005] Further, WO 2006/067722 discloses a boiler for heating water also, wherein the wall of the boiler housing, which is hot during operation of the boiler, is involved in the process of heating water entering the boiler space before this water l mixes with water which is already present in the boiler space. In this way, the steam production is not interrupted when this new supplied water mixes with the water which is already present in the boiler space. However, the boiler disclosed in WO 2006/067722 still has an inclined configuration of the bottom of the boiler.

[0006] Nowadays there is a trend to design the household appliance more and more compact so as to save space. However, the above mentioned inclined configuration of the bottom of the boiler causes the boiler occupying a relatively large space within the household appliance for which the boiler is intended to be used. This will force the household appliance to be made larger, or other necessary components such as the water tank inside the household appliance to be smaller. Therefore, there is a need in the industry to improve the inclined configuration of the bottom of the boiler, providing a boiler with horizontal bottom configuration but still with the function of avoiding water being boiled dry and minimizing the temperature difference between old water and new water.

Summary of the Invention

[0007] To solve the above mentioned problems, according to a first aspect of the present invention a boiler for heating water to generate steam and outputting steam is provided. The boiler comprises a boiler housing enclosing a boiler space, into which an inlet pipe extends through the wall of the boiler housing for feeding water therein from a water supply, and from which an outlet pipe extends through the wall of the boiler housing for outputting steam generated. The bottom wall of the boiler comprises at least two horizontal portions having different levels. A heating means is provided for each of the horizontal portions. The inlet pipe is positioned so that water from the inlet pipe firstly flows onto the horizontal portion with the highest level and finally flows to the horizontal portion with the lowest level. [0008] In the boiler according to the present invention, the bottom wall of the boiler is divided into at least two horizontal portions having different levels. Therefore, one or several steps will be defined by the horizontal portions. Therefore, when there is a need for new water after the startup phase during operation, water that is newly supplied to the boiler space will be firstly received on the horizontal portion with the highest level, where it is preliminarily heated by the heating means associated with the horizontal portion with highest level. Then, water flows through the horizontal portions with intermediate levels, if any, where it is further heated by the heating means associated with the horizontal portions with intermediate levels. When water that is newly supplied finally flows to the horizontal portion with lowest level, it has been already heated to a relatively high temperature. Therefore, this portion of new water with a relatively high temperature will mix up with water already contained within a recess defined by the horizontal portion with the lowest level, the step and the wall adjacent thereto. In this case, no interruption of steam generation will occur.

[0009] In a preferable embodiment, a sensor for detecting the temperature difference between the horizontal portion with the highest level and that with the lowest level. As a variant, the sensor can be used to detect the temperature variation on the top surface of the horizontal portion with the highest level. When the temperature difference or the temperature variation detected by the sensor exceeds a predetermined threshold value, the sensor triggers a signal demanding the water supply to resume the supply of water. In this way, the risk of water in the boiler is boiled dry is avoided. In an example, the sensor is a negative temperature coefficient (NTC) sensor. With this sensor, the time of reactivating the pump and the volume of water resupplied can be more precisely controlled in a way of real time. Therefore, the risk of interruption of steam generation is minimized and a steady generation of steam can be obtained. The sensor can be, for example, arranged in the area of the horizontal portion with highest level. [0010] In an advantageous embodiment, the bottom wall of the boiler comprises only two horizontal portions, i.e., a first horizontal portion with a relatively low level and a second horizontal portion with a relatively high level. The first horizontal portion occupies a relatively large area of the entire bottom wall. The heating means associated with the first horizontal portion is always under working state. Therefore, most part of the bottom wall is heated, and the inside of the boiler is kept under a certain pressure so that generation and output of steam are facilitated.

[0011] In an example, the heating means associated with the first horizontal portion has a substantial C shape whereas the heating means associated with the first horizontal portion has a substantial U shape, and the U-shaped heating means is contained with the area of C-shape heating means. By means of this, a compact structure with desirable heating efficiency is obtained. [0012] According to a second aspect of the present invention, a home appliance including the boiler as mentioned above is provided.

Brief description of the Drawings [0013] The present invention will now be explained in greater detail with reference'to the Figures, in which similar parts are indicated by the same reference signs, and in which:

[0014] Figure 1 diagrammatically shows a steam ironing device comprising a boiler according to an embodiment of the present invention;

[0015] Figure 2 diagrammatically shows the plan view of the boiler from bottom side; [0016] Figure 3 is the perspective view of the lower part of the boiler from top side;

[0017] Figure 4 is the perspective view of the lower part of the boiler from bottom side; and

Detailed description of the invention

[0018] Figure 1 diagrammatically shows a steam ironing device 100 comprising a boiler 20 according to an embodiment of the present invention. Although in the following text the boiler according to the present invention will be described in combination with the steam ironing device, one of ordinary skills in the art can realize the boiler according to the present invention can be used in any kind of home appliances, including but not limited to steam ironing devices, facial sauna devices, steam cleaning devices, coffee makers and toasters, or any other devices need steam. [0019] The boiler 20 comprises a boiler housing enclosing a boiler space 30 therein. The boiler housing, preferably made of stainless steel, is formed by two parts, i.e, an upper part 1 and a lower part 2 as shown. The two parts 1, 2 are connected to each other by means of a suitable connecting method, for example by means of welding. Of course, it is also conceivable to design the boiler housing as a unitary structure.

[0020] The boiler 20 further comprises an output pipe 11 for outputting the steam generated inside the boiler 20 to the steam iron 10 of the steam ironing device 100. The output pipe 11 is generally place at the upper part 1. In addition, a magnetic valve 12 is placed in the output pipe 11 for steam release.

[0021] In the upper left corner of Fig. 1 it shows a water supply unit, in which a water pipe 14 supplies water from a water tank 17 to the boiler space 30 via an inlet fitting 13. Pump 19 connects the water pipe 14 and an outlet line 18 of the water tank 17 so as to drive the flow of water. The water supply unit further includes a return valve 15 and a return line 16. This unit, together with the output pipe 11 and magnetic valve 12 as mentioned above, is already known in the art, and thus the detailed structure and function thereof are omitted here for the sake of conciseness.

[0022] During operation of the steam ironing device 100, water which is supplied to the boiler space 30 is converted to steam by means of heating, and the steam generated is supplied to the steam iron 20 via the output pipe 11. According to the present invention, the boiler 20 is oriented such that the bottom wall of the lower part 2 of the boiler housing is in the horizontal direction. In order to ensure a continuous steam production and avoid a situation of boiling dry, the bottom wall of the lower part 2 is divided, in this embodiment as shown in Fig. 1, into two horizontal portions, i.e., the first horizontal portion 24 and the second horizontal portion 26. The two horizontal portions are positioned in different levels. In the embodiment as shown in Fig. 1, the second horizontal portion 26 is higher than the first horizontal portion 24. Thus a step 22 is formed between the two horizontal portions. As such, a recess 35 is defined by the step 22 and the side wall of the lower part 2. In some advantageous examples, the level difference between the two portions or the height of the step 22 can be selected from a range of 0.2 to 30 mm. The step 22 is made as gradually inclined to ensure a smooth and quiet flow of water from the second horizontal portion 26 to the first horizontal portion 24. In addition, the position of the second horizontal portion 26 is such selected that water from the water fitting 13 will firstly flow onto the second horizontal portion 26, and then flow along the step 22 to the first horizontal portion 24.

[0023] Figs. 2 and 4 show the bottom surface of the bottom wall of the lower part 2 in a plan view and a perspective view respectively. A first heating plate 3 and a second heating plate 7, both of which can be made of aluminum for example, are respectively mounted on the bottom surface, for example by means of bolts, in the areas corresponding to the first horizontal portion 24 and the second horizontal portion 26. A groove 32 is formed between the two heating plates 3, 7 so as to isolate the possible heating conduction therebetween. On the first heating plate 3 a first heating means 4 and a first temperature controller 5 for controlling the heating energy provided by the first heating means 4 are positioned. In the example as shown, the first heating means 4 is a substantially C-shaped heating pipe arranged along the peripheral part of the bottom surface of the lower part 2 so as to provide an approximately even heating effect for the boiler.

[0024] Similarly, on the second heating plate 7 a second heating means 6 and a second temperature controller 8 for controlling the heating energy provided by the second heating means 6 are positioned. In the example as shown, the second heating means 6 is a substantially U-shaped heating pipe to provide an even heating effect. In particular, the U-shaped second heating means 6 is substantially contained within the C-shape first heating means 4. With this structure water can flow to the recess 35 from the second horizontal portion 26 more steadily and evenly. However, other shapes or structures of the first heating means are also conceivable. For example, the second horizontal portion 26 can be formed as an island entirely surrounded by the first horizontal portion 24. In this case, both of the first and second heating means 4, 6 can be formed as ring shape, with the second heating means 6 located within the first heating means 4.

[0025] At the startup phase of operation of the steam ironing device 100, the pump 19 pumps a suitable volume of water from the tank 17 to the boiler space 30 via the water pipe 14 and the inlet fitting 13. Due to the alignment of the inlet fitting 13 with the second horizontal portion 26, water will firstly flow onto the second horizontal portion 26 and then flow along the step 22 to the first horizontal portion 24. Water should be supplied so that it not only fills the recess 35 but also submerges the top surface of the second horizontal portion 26. The pump 19 is deactivated so that the supply of water is cut off after a certain time.

[0026] The first heating means 4 and the second heating means 6 are switched on immediately after the startup phase, and heat the water contained within the boiler space 30. The first heating means 4 continuously heat water in the recess 35, so that this volume of water is always under a state of being heated. Therefore, the inside of the boiler is kept under a certain pressure so that output of steam is facilitated. At the same time, water in the recess 35 is always heated, thus causing the steam can be generated steadily.

[0027] Once steam is generated and conveyed to the steam iron 10 via the output pipe 11, the volume of water inside the boiler space 30 will be decreased. Therefore, the pump 19 will be turned on again and the supply of water is resumed. Due to the alignment of the inlet fitting 13 with the second horizontal portion 26, water that is newly supplied will firstly flow onto the second horizontal portion 26, where it is preliminarily heated, and then flow along the step 22 into the recess 35 where it is mixed up with the heated water already present therein. As such, the mix-up of two volume of water will not cause the interruption of steam generation, thus facilitating a steady generation of steam.

[0028] According to the present invention, a sensor 9 is arranged on the second heating plate 7 for detecting the temperature difference between the first heating means 4 and the second heating means 6. In a preferred embodiment, the sensor 9 is a Negative Temperature Coefficient (NTC) sensor.

[0029] Since the second horizontal portion 26 is at a higher level than the first horizontal portion 24, it is always the water in the area of the second horizontal portion 26 will be dried out first. In this case, the temperature in the area of the second horizontal portion 26 will be higher than that in the area of the first horizontal portion 24. The temperature difference can be detected by the NTC sensor 9, and further sent to a controller (not shown). When the temperature difference is beyond a certain threshold value, say 25 degree C, the pump 19 is activated accordingly to supply additional water into the boiler space 30. Water will flow onto the second horizontal portion 26 directly due to the alignment of the inlet fitting 13 and the second horizontal portion 26, thus reducing the temperature on the second horizontal portion 26 and avoiding the risk of water dry-out. When sufficient volume of water is supplied, the temperature in the area of the second horizontal portion 26 will be reduced, therefore causing the temperature difference is below the threshold value. In this case,. the pump 19 is deactivated again.

[0030] With this sensor 9, the time of activating the pump 19 and the volume of water resupplied can be more precisely controlled in a way of real time. Therefore, the risk of interruption of steam generation is minimized and a steady generation of steam can be obtained.

[0031] Although in the foregoing the boiler according to the present invention includes two horizontal portions 24, 26, its variations including more than three horizontal portions are obvious to one of ordinary skills in the art. For example, in the example including three horizontal portions, water will flow onto the horizontal portion with the highest level, then to the horizontal portion with the intermediate level, and finally to the horizontal portion with the lowest level. In this case, water will be preliminarily heated twice before mixing up with water already present in the recess 35. As such, the temperature difference between the water newly supplied and the water already present is further reduced, thus decreasing the possibility of interruption of steam generation.

[0032] It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the present invention as defined in the attached claims. While the present invention has been illustrated and described in detail in the Figures and the description, such illustration and description are to be considered illustrative or exemplary only, and not restrictive. The present invention is not limited to the disclosed embodiments.

[0033] For example, the sensor 9 can be set to detect the temperature variation of the horizontal portion with the highest level, instead of the temperature difference between the horizontal portions with the highest level and that with the lowest level. In this case, as long as water on the top surface of the horizontal portion with the highest level is boiled dry and causes the temperature of the horizontal portion with the highest level higher than a predetermined value, the sensor triggers a signal demanding the water supply to resume the supply of water.

[0034] Variations to the disclosed embodiments can be understood and effected by a person skilled in the art in practicing the claimed invention, from a study of the Figures, the description and the attached claims. In the claims, the word "comprising" does not exclude other steps or elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the present invention.