Abstract:
A coffee-making apparatus for making normal coffee has a steam boiler ( 7 ) for generating steam for making cappuccino. The coffee-making apparatus has only one water reservoir ( 1 ) for making the coffee and for filling the steam boiler. The boiler has a venting valve ( 12 ) for automatically venting the boiler when the boiler is filled with cold water from the water reservoir. The influx of cold water into the boiler causes a sensor ( 12 ) to cool down, thereby opening a vent opening. With this apparatus it is possible to make coffee and steam for a second time, directly after making a cup of coffee and steam for the first time.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a coffee-making apparatus having a water reservoir, a filter device, means for heating and conveying water from the water reservoir to the filter device, and having a device for the generation of steam, comprising a steam reservoir, a water supply conduit between the water reservoir and the steam reservoir, for supplying cold water to the steam reservoir, a steam outlet conduit having a steam valve and means for heating the water in the steam reservoir. 
     Such a coffee-making apparatus is known from EP-A-0 797 945. In said coffee-making apparatus cold water from the water reservoir is heated in a flow heater, after which the hot water is optionally conveyed either to the filter device for brewing coffee or to the steam reservoir. In the steam reservoir steam and water are separated. The steam is fed to a steam nozzle via a pipe. The hot water flows into the bottom of the steam reservoir and then back to the flow heater, where it is heated further and is subsequently fed again to the steam reservoir. Owing to a number of restrictions and non-return valves a water circulation is obtained in order to make the water in the steam reservoir as hot as possible and build up pressure in the steam reservoir. The restrictions restrict the water flow to the flow heater in such a manner that after some time substantially all the water fed to the flow heater is discharged to the steam reservoir as steam. 
     In order to obtain a cup of cappucino it is required to have enough steam for making the milk frothy as soon as possible after the regular coffee has been made. In espresso machines this steam is available immediately. However, espresso machines are comparatively expensive coffee-making apparatuses. The apparatus described hereinbefore is an example of a coffee-making apparatus with which regular coffee can be made, which is subsequently turned into cappucino by means of frothed-up milk. The drawback of this known apparatus is that it takes some time before steam is available by means of which milk can be frothed up. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to make the steam for frothing up milk available as soon as possible after the coffee has been made. 
     To this end, the coffee-making apparatus in accordance with the invention is characterized in that the steam reservoir comprises a steam boiler having a heating element, and means have been provided for automatically venting the steam boiler when the water reservoir is filled with cold water. By means of a steam boiler having a heating element of its own steam can be generated far more rapidly than by means of the construction in accordance with EP-A-0 797 945. When the coffee-making apparatus is switched on the heating element for the boiler is also switched on. When a pot of coffee has been made the boiler is also ready for steaming. Owing to the venting facility of the boiler the boiler is automatically filled with water when the water reservoir is refilled with cold water. This means that immediately after one pot of coffee has been made another pot of coffee can be made by filling the water reservoir with cold water, upon which the boiler is vented automatically and is subsequently filled with water, as a result of which steam is available again immediately after coffee has been made. 
     A preferred embodiment is characterized in that the steam boiler has been provided with a temperature sensor and a venting valve which is responsive to the sensor, which sensor, on the one hand, is thermally coupled to the boiler and, on the other hand, is arranged in the proximity of a cold water supply duct of the boiler so as to make thermal contact with the cold water in the supply duct. When the heating element for the boiler is energized the housing parts of the boiler become hot. Since the sensor is in thermal contact with the housing of the boiler, the sensor responds thereto and the venting valve is closed. The temperature of the water in the boiler rises and at the boiling temperature the boiler is pressurized, as a result of which steam can be produced. By arranging the sensor close to or in a cold-water supply duct of the boiler the sensor will respond immediately to the influx of cold water, as a result of which the venting valve opens. Subsequently, the boiler is filled with water. After the influx of water into the boiler has ceased the temperature of the parts of the boiler rises again and, consequently, the temperature of the sensor also rises, as a result of which the venting valve is closed gain. 
     Preferably, the sensor is a memory-metal spring having an actuator, which spring is situated in the cold water supply duct of the boiler. A memory metal responds very rapidly to a temperature change, as a result of which in particular the venting valve opens rapidly, thereby enabling the boiler to be vented rapidly. However, it is obvious that other temperature sensors are also possible. 
     Further embodiments are defined in the Claims and in the following description with reference to the Figures. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will now be described in more detail with reference to an example shown in a drawing. In the drawing 
     FIG. 1 diagrammatically shows a coffee-making apparatus having a steam boiler, and 
     FIG. 2 is a detailed cross-sectional view of the steam boiler of FIG.  1 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The coffee-making apparatus, as shown diagrammatically in FIG. 1, comprises a water reservoir  1  which can be filled with cold water, a filter device  2 , a conduit  3  between the water reservoir and the filter device, a heating element  4  for heating the water in the conduit  3  and conveying it to the filter device, a receptacle or cup  5  for receiving coffee brew which flows out of the filter device. The conduit  3  includes a non-return valve  6 , which prevents the water from being forced back to the water reservoir  1  when it is heated, as a result of which the hot water can flow to the filter device  2  only. The present apparatus is a conventional coffee-making apparatus having a so-called thermally operating pump system. For making a cup of cappucino milk should made frothy by means of steam. For this purpose, the coffee-making apparatus has a steam boiler  7 , which is connected to the water reservoir  1  by means of a conduit  8 . The water in the water reservoir can flow to the boiler  7  under the influence of gravity. However, it is also possible to use a pump. The boiler has a separate heating element  9  for bringing the water in the boiler rapidly to the boiling temperature. The steam produced in the boiler can be blown into the milk via a steam outlet conduit  10  having a steam valve  11 , as a result of which the milk is frothed. The boiler has a venting valve  12  to allow the boiler to be filled with water. 
     The steam boiler  7  shown in FIG. 2 comprises a water drum  13  with a steam dome  14  situated above it. A fitting  15  arranged on top of the steam dome has a cold water supply duct  16  having its inlet connected to the conduit  8 , which connects to the water reservoir  1 . A vertical portion  17  of the supply duct opens into the water drum  13 . The heating element  9  lies around the water drum  13 . However, it is also possible to use other heating means. The steam outlet conduit  10  is connected to the steam dome  14 . An outlet opening  18  of the cold water supply duct  16  can be closed by means of a shut-off valve  19 . This shut-off valve is formed by a float  20  having a shut-off plate  21 . The float carries a central pin  22 , which projects into the vertical portion  17  of the supply duct. When the water level in the water drum  13  has dropped the float rests on ridges  24  in the water drum, while the pin  22  remains in the portion  17 . The pin  22  has recesses  23 , thus allowing water to flow into the water drum. In the upper part of the steam dome  14  the venting valve  12  is situated, which valve has a diaphragm  25  by means of which a vent opening  26  of the steam dome can be closed or left open. When the diaphragm does not close the vent opening this opening communicates with the atmosphere via a venting duct  27 . The steam boiler further has a temperature sensor  28 , which controls the opening and closure of the venting valve  12 . For this purpose the diaphragm  25  of the venting valve carries an actuator in the form of an actuating pin  29  and the temperature sensor  28  is formed by a memory-metal spring arranged around the actuating pin. The memory-metal spring  28  and the actuating pin  29  are arranged in the cold water supply duct  16 . The memory-metal spring  28  is enclosed between a wall  30  of the supply duct and a rim  31  of the actuating pin. The actuating pin and the spring leave the duct  16  open to such an extent that an adequate influx of water into the water drum  13  is guaranteed. An end portion  32  of the actuating pin  29 , which end portion faces the diaphragm  25 , extends through an opening  33  of the wall  30  of the supply duct beyond the fitting  15 . The opening  33  is covered with a diaphragm  34 , the end portion  32  of the actuating pin lying against the underside of the diaphragm  34 . The upper side of the diaphragm makes contact with a switch  35 , which controls the turn-on and turn-off of the heating element  9 . The boiler further has a second venting duct  36  having a vent opening  37 , which is opened or closed by the shut-off valve  19  simultaneously with the inlet opening  18  of the cold water supply duct. The cold water supply duct  16  further has a narrow passage  38 , which opens into the second venting duct  36  and is thus in open communication with the atmosphere. Viewed in the direction of flow of the water the narrow passage is disposed downstream of the temperature sensor  28 . 
     The coffee-making apparatus with the steam boiler operates as follows. The water reservoir  1  is filled with cold water. The water flows into the conduit  3  to the heating element  4  and the filter device  2  and into the conduit  8  to the steam boiler  7 . The water drum  13  is filled with water via the supply duct  16  in the fitting  15  of the boiler. The shut-off valve  19  is open. During filling air can escape via the second venting duct  36 . Air can also escape via the venting valve  12 . When the water reservoir is full the float  20  shuts off the outlet opening  18  of the supply duct and the influx of water into the boiler stops. This process occurs fairly rapidly after the water reservoir has been filled. Now, first of all, normal coffee is made in the well-known manner. Both the heating element  4  for making coffee and the heating element  9  of the boiler are energized. During the coffee-brewing process the boiler is also heated. When the coffee-brewing process is ready, the boiler is also ready for the generation of steam for making the milk frothy. As the boiler is heated all parts of the boiler, i.e. including the steam dome  14  and the fitting  15 , are heated through conduction of heat. The memory-metal spring  28  and actuating pin  29  become also warm. The memory-metal spring expands and urges the actuating pin  29  downward against the diaphragm  25  of the shut-off valve  12 . As a result of this, the diaphragm  25  closes the vent opening  26  and the boiler is fully closed. The temperature and the pressure in the boiler rise. As a result of this, the outlet opening  18  and the vent opening  37  are sealed effectively by the shut-off valve  19 . Sealing is more effective as the pressure rises. The temperature of the housing parts of the boiler also rises, as a result of which the force exerted on the diaphragm  25  by the memory-metal spring  28  via the actuating pin  29  also increases. Thus, the vent opening  26  is sealed even better. At this stage the pressure exerted on the diaphragm via the memory-metal spring should be higher than the steam pressure. When the water in the boiler begins to boil the generated steam can be blown into a cup of milk via a steam nozzle  39  in that the steam valve  11  is opened, as a result of which the milk becomes frothy. Temperature control means  40 ,  41  maintain the correct temperature of the boiler. If a following cup of coffee is not made immediately, the coffee-making apparatus may be turned off or is turned off automatically. The boiler cools down slowly, the steam condenses and, after a while, the pressure will again be equal to the atmospheric pressure. The float  20  is lowered onto the ridges  24 , as a result of which the boiler is filled automatically when the water reservoir is filled again. 
     However, if another pot of coffee is made immediately after a pot of coffee has been made and subsequently steam is used for making the milk frothy, the boiler is still under pressure, as a result of which the shut-off valve  19  remains closed. Filling the boiler with water would then be impossible. However, after the water reservoir has been filled with cold water the narrow passage  38  yet allows water to flow through the supply duct  16 . A small stream of water already suffices to cool down the memory-metal spring  28 , as a result of which the actuating pin  29  and, as a consequence, the diaphragm  25  are moved upward. The vent opening  26  is cleared and the steam can escape from the boiler through the vent opening  27 , as a result of which the boiler is depressurized. The shut-off valve  19  is lowered and opens the outlet opening  18  of the supply duct, as a result of which the boiler is again filled with water. Thus, this system enables another pot of coffee to be made and also to have steam available immediately after a pot of coffee has been made, use being made of steam for making milk frothy in order to prepare a cup of cappucino. 
     The heating element  9  of the boiler may remain energized during venting. The influx of cold water provides sufficient cooling of the sensor. If desired, the heating element  9  may be switched off as soon as venting takes place. For this purpose, the actuating pin  29  activates the switch  35  via the diaphragm  34 , as a result of which the heating element  9  of the boiler is switched off. 
     As long as the water reservoir  1  is not yet empty some water will flow through the narrow passage  38 . This occurs even when the boiler is filled with water and the shut-off valve  19  is closed. This water will automatically evaporate owing to the hot boiler and has no influence on the sensor. 
     The water that flows through the narrow passage  38  is collected in the venting duct  36 . This has the advantage that as soon as the boiler has been vented and the shut-off valve  19  opens this water flows into the water drum  13 . However, the water that flows through the passage  38  can also be collected in another manner, for example in a collecting tray. 
     The venting duct  27  can be connected to the steam outlet conduit  10  via a conduit  42 . However, the connection should then be made downstream of the steam valve  11 . The steam outlet conduit  10  further includes a safety valve upstream of the steam valve  11 . 
     For making regular coffee it is alternatively possible to include a motor-driven pump in the conduit  3  instead of a thermal pump system in order to feed the water to the filter device.