Abstract:
The invention relates to a heating device ( 9 ), for a mobile inhalation unit for the inhalation of active agents, comprising a heating wire ( 15 ), with two connector ends ( 23, 31 ) for the introduction of electrical energy and a thermal reservoir ( 13, 17 ) for heating air flowing along the thermal reservoir, whereby the thermal reservoir may be heated by means of the heating wire. The heating wire has a temperature coefficient of at least 0.001 K −1 . The invention further relates to an inhalation unit with such a heating device and a method for heating a thermal reservoir on such a heating device.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a mobile inhalation unit for the inhalation of active agents, comprising a heating device which has a thermal reservoir for the heating of air which flows along the thermal reservoir, with the thermal reservoir being able to be heated by means of a heating wire of the heating device. 
         [0002]    An inhalation unit of this type allows the inhalation of active agents, in particular of medical drugs and/or aromas. The user of such an inhalation unit sucks in air which first flows along the thermal reservoir and is hereby heated. Then the heated air flows along an active agent depot, with active agents located in the active agent depot being released by the heated air, being taken up by the heated air and finally being inhaled by the user. 
       BACKGROUND OF THE INVENTION 
       [0003]    A smoke-free cigarette is known from WO 2004/098324 A2. It has a replaceable piece (nicotine depot), a reusable piece with a sleeve and a heating device as well as a storage and charging station having an accumulator and a thermostat. The heating device of the reusable piece has a heating spiral and a heat-storing medium, with airflow passages being provided between the heat-storing medium and the sleeve. The reusable piece can be received in the storage and charging station for the purpose of heating, with the heating spiral of the reusable part been heated for so long until the thermostat ends the heating process. 
         [0004]    An ideal heat transfer to the thermal reservoir and a precise reaching of the desired temperature are not always ensured by ending the heating process on the basis of a corresponding signal of a thermostat. 
         [0005]    A mobile inhalation unit is known from EP-A-0 430 559 in which an active agent depot is maintained at a relatively constant operating temperature. 
         [0006]    U.S. Pat. No. 5,878,752 describes a mobile inhalation unit having a heating spiral which is used for cleaning purposes. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the invention to improve the heating of the thermal reservoir of a heating device in an inhalation unit of the explained type. 
         [0008]    This object is satisfied by an inhalation device having the features of claim  1 . 
         [0009]    The heating wire of the heating device has a high temperature coefficient. A simple and reliable determination of the instantaneous temperature of the thermal reservoir is thereby possible, as will be explained in the following, without additional temperature probes being required in the thermal reservoir. The heating wire itself rather serves as a temperature sensor (“thermal feedback”). 
         [0010]    The ratio of the relative change in the electrical resistance to the temperature change in accordance with the following formula is called the temperature coefficient (α): 
         [0000]    
       
         
           
             
               α 
               = 
               
                 
                   Δ 
                    
                   
                       
                   
                    
                   R 
                 
                 
                   
                     R 
                     · 
                     Δ 
                   
                    
                   
                       
                   
                    
                   T 
                 
               
             
             , 
           
         
       
     
         [0000]    where ΔR is the change in the resistance (or in the specific resistance), R is the resistance (or specific resistance) and ΔT is the change in temperature. The temperature coefficient therefore characterizes the dependence of the resistance R on the temperature T. 
         [0011]    In contrast, the heating wires in known heating devices have a comparatively low temperature coefficient to obtain a low dependence of the electrical resistance of the heating wire on the temperature and thus a substantially temperature-independent heating power. The alloy konstantan, for example, has a temperature coefficient of approx. 0.00004 K −1 . 
         [0012]    To heat the heating wire, electrical energy, that is an electrical current of a specific amount, is supplied to it. In order simultaneously to determine the instantaneous temperature of the thermal reservoir or of the heating wire, the instantaneous value of the electrical resistance of the heating wire is measured. The measured result can be used to control the further supply of the electrical energy on the basis of the resistance determined, that is, for example, to decrease or increase the current or to completely switch off the energy supply. Due to the high temperature coefficient of the heating wire (high gradient of the R/T curve), the instantaneous temperature of the heating wire can be determined with high accuracy from the measured resistance without additional temperature sensors being necessary. 
         [0013]    The precise observation of a predetermined temperature of the heating wire and thus of the thermal reservoir is particularly important in the inhalation of medical active agents so that the designated dosage is reliably reached, on the one hand, and is in turn not excessively exceeded, on the other hand. A precise temperature determination and a correspondingly precise control or feedback control of the heating power is also particularly important for mobile applications of the inhalation unit since the capacity of the electrical energy source used (accumulator) is limited and should always be utilized to an optimum. 
         [0014]    A particularly advantageous value of the temperature coefficient lies, for example, at 0.003 K −1 , with a better measuring resolution naturally being achieved, the higher the temperature coefficient is. 
         [0015]    The mobile inhalation can furthermore have an electrical energy source which can be connected to the heating wire and an evaluation and control circuit by which the electrical resistance of the heating wire can be determined and by which the electrical energy supplied to the heating wire can be set with reference to the resistance determined. 
         [0016]    Further embodiments of the invention are described in the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0017]    The invention will be described in the following only by way of example with reference to the drawings. 
           [0018]      FIG. 1  shows a perspective view of a heating device; 
           [0019]      FIG. 2  shows a perspective view of parts of the heating device; 
           [0020]      FIG. 3  shows a cut-away perspective view of the heating device; 
           [0021]      FIG. 4  is a detailed view of the region IV of  FIG. 3 ; 
           [0022]      FIG. 5  shows the heating device in a longitudinal section; 
           [0023]      FIG. 6  is a detailed view of the region VI of  FIG. 5 ; 
           [0024]      FIG. 7  shows a mobile inhalation unit with the heating device; 
           [0025]      FIG. 8  shows the dependence of the resistance of the heating spiral on the temperature; 
           [0026]      FIG. 9  shows a block diagram of the wiring of a heating wire and of an electrical energy source with an evaluation and control circuit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    The heating device  9  shown in  FIGS. 1 to 6  has an elongate shape with an almost rotationally symmetrical design. The heating device  9  has—radially from the inside to the outside—a center contact pin  11 , a ceramic inner tube  13 , a heating spiral  15  and a ceramic outer tube  17  (cf. in particular  FIGS. 3 and 5 ). The center contact pin  11 , the inner tube  13 , the heating spiral  15  and the outer tube  17  are arranged coaxially to one another. The center contact pin  11  has a high electrical conductivity and comprises, for example, copper-nickel or other metal alloys. 
         [0028]    The heating spiral  15 , in contrast, has a high electrical resistance. It serves for the heating of the inner tube  13  and of the outer tube  17  and has a high temperature coefficient, as will be explained in the following ( FIG. 8 ). The heating spiral  15  can, for example, comprise the nickel-iron alloy “Resistherm” (registered trademark) with the components aluminum (mass portion 0.6%), chromium (0.3%), iron (30%), manganese (0.5%) and nickel (rest), with a temperature coefficient of approx. 0.003 K−1. The inner tube  13  and the outer tube  17  together form a thermal reservoir for the heat output by the heating spiral and they comprise a ceramic material, for example titanate or steatite. 
         [0029]    A disk-shaped contact socket  21  is shaped at a front-side end of the center contact pin  11  (at the right in  FIG. 3 , at the top in  FIG. 5 ). The front side of the ceramic inner tube  13  contacts the rear side of this contact socket  21 . A front-side connector end  23  of the heating spiral  15  is bent over in U shape, with the U shape engaging around the front side of the ceramic outer tube  17  (cf.  FIGS. 2 and 3 ). A ring contact  25  of copper or of a metal alloy with a conductive covering is placed onto the front-side end of the outer tube  17  by press-fitting such that the front-side connector end  23  of the heating spiral  15  contacts the inner side of the ring contact  25  and thus an electrical connection is established between these two parts. 
         [0030]    An insulator sleeve  27  which electrically insulates the contact socket  21  and the ring contact  25  from one another is arranged between the front-side end of the center contact pin  11  with the contact socket  21  and the front-side end of the ceramic inner tube  13 , on the one hand, and the front-side end of the ceramic outer tube  17  with the ring contact  25  placed on, on the other hand. In the embodiment shown, the contact socket  21 , the insulator sleeve  27  and the ring contact  25  terminate flush with one another at the front side of the heating device  9  (cf.  FIGS. 3 and 5 ). The contact socket  21 , the insulator sleeve  27  and the ring contact  25  are arranged coaxially to one another 
         [0031]    A rear-side connector end  31  of the heating spiral  15  is electrically connected to a rear-side end  33  of the center contact pin  11 . This rear-side end  33  of the center contact pin  11  projects out of the ceramic inner tube  13  which is shorter than the center contact pin  11  and shorter than the ceramic outer tube  17 . The rear-side end  33  of the center contact pin  11  and the rear-side connector end  31  of the heating spiral  15  are fixed to the inner side of the ceramic outer tube  17  by means of a fastening mass  35 . The fastening mass  35  can, for example, be a cement which is cast into the inner space of the outer tube  17  from the rear side. The ceramic inner tube  13  is captured between the fastening mass  35 , on the one hand, and the contact socket  21  of the center contact pin  11 , on the other hand. 
         [0032]    The heating device  9  shown in  FIGS. 1 to 6  is provided for use in a mobile inhalation unit for the inhalation of active agents, with air flowing past the heating device  9  being heated and active agents which can then be inhaled being released from an active agent depot. 
         [0033]      FIG. 7  shows parts of such a mobile inhalation unit in a schematic cross-sectional view. This inhalation unit has a connection sleeve  41  which surrounds the heating device  9  peripherally and is connected at one end to an air-permeable active agent depot  43 . One or more flow passages  45  are formed between the connection sleeve  41  and the heating device  9 . The user of the inhalation unit fixes his mouth on the active agent depot  43  and sucks in air. The sucked in air flows through the flow passages  45  along the heating device  9  (cf. arrows in  FIG. 7 ). The air thus flows along the ceramic outer tube  17  ( FIGS. 1 ,  3 ,  5 ) which has previously been heated by means of the heating spiral  15 . The thus heated air then flows through the active agent depot  43 , heats it and thereby releases active agents stored in the active agent depot  43  which are taken up by the air and are taken along. The user therefore now inhales these active ingredients. 
         [0034]    It is important for many applications of such an inhalation unit that the active agents are released in a predetermined amount and/or as uniformly as possible during a predetermined period. It is in turn important for this purpose that the temperature of the heating spiral  15 , with which the thermal reservoir (inner tube  13  and outer tube  17 ) is heated, can be set as precisely as possible. It is therefore desirable for the actual instantaneous temperature of the heating spiral  15  to be able to be determined. 
         [0035]    Provision is made for this purpose for the heating spiral  15  to comprise a material which—as already mentioned—has a high temperature coefficient, i.e. the electrical resistance of the heating spiral  15  depends largely on its temperature.  FIG. 8  shows by way of example such a dependence of the resistance R of the heating spiral  15  on its temperature T. The high gradient of the graph shown in  FIG. 8  is characteristic for the material of the heating spiral  15  to be used. The corresponding temperature value can be determined with high accuracy from a determined resistance value on the basis of the high temperature dependence of the resistance. 
         [0036]      FIG. 9  shows further parts of the already described mobile inhalation device. It has an accumulator  51  or a battery as an electrical energy source as well as an evaluation and control circuit  53  which is connected to the two poles of the accumulator  51 . The evaluation and control circuit  53  has two connection contacts  55 ,  57  at the output side. The evaluation and control circuit  53  serves as a driver for the energy supply from the accumulator  51  to the heating spiral  15 . The heating device  9 , of which only the heating spiral  15  is shown in  FIG. 9 , is connected at times to the connection contacts  55 ,  57  by means of the contact socket  21  and the ring contact  25 , with an electrical current being led through the heating spiral  15  to heat it. 
         [0037]    The evaluation and control circuit  53  controls the current which is led through the heating spiral  15  in dependence on the temperature of the heating spiral  15 . For this purpose, the evaluation and control circuit  53  measures the electrical resistance R of the heating spiral  15 . Due to the high temperature dependence of the resistance R (cf.  FIG. 8 ), the temperature T results from it with high accuracy. 
         [0038]    In the following, advantages of the heating device in accordance with  FIGS. 1 to 6  and of the inhalation unit in accordance with  FIGS. 7 and 9  will be explained which can each be realized per se or in combination with one another: 
         [0000]    a) The thermal reservoir has both an outer part (outer tube  17 ) arranged outside the heating spiral  15  and an inner part (inner tube  13 ) arranged inside the heating spiral  15 . A uniform heat output over a long time period is hereby made possible by means of the heating spiral  15  after the heating of the thermal reservoir and the heat output proves to be less sensitive to different ambient temperatures of the thermal reservoir.
 
b) In accordance with a further development of the aforesaid embodiment, it is preferred for the heating spiral  15  to contact the outer side of the inner part of the thermal reservoir (inner tube  13 ) and for an air gap  61  to be provided at least along a longitudinal section of the heating device  9  between the heating spiral  15  and the inner side of the outer part of the thermal reservoir (outer tube  17 ) (cf.  FIG. 5 ). An air gap  61  of this type likewise contributes to the improvement of the uniformity of the heat output. The heat transfer from the heating spiral  15  to the outer tube  17  is namely worse than to the inner tube  13  due to the air gap  61 . After the interruption of the energy supply of the heating spiral  15 , this has the consequence that the heat output from the inner tube  13  to the outer tube  17  is delayed and the inner tube  13  acts as a thermal reservoir at a higher temperature level for the outer tube  17 . While the outer tube  17  outputs heat to the outside, the inner tube  13  can thus “reheat” the outer tube  17  longer.
 
c) Since the rear-side connector end  31  of the heating spiral  15 , the rear-side end  33  of the center contact pin  11  and thus also the rear-side end of the inner tube  13  are together fixed in position by means of the fastening mass  35 , the heating device  9 —in a substantially unchanged manufacturing process—can also be produced in an embodiment in which the contact socket  21  of the center contact pin  11  is offset with respect to the front side of the outer tube  17  and thus with respect to the ring contact  25 . In other words, alternatively to the embodiment shown in  FIGS. 3 and 5 , a pin engagement contact can be realized by which an electrical short-circuit at the energy source used can be avoided more reliably. A pin engagement contact of this type is not required or desired in all cases. A particular advantage of the explained aspect of the heating device  9 , however, consists of the fact that both variants (flush or offset contact socket  21 ) can be realized with substantially the same manufacturing process.
 
d) The contact socket  21  and the ring contact  25  have a rotationally symmetrical design (cf.  FIG. 1 ). A connection to the electrical energy source used is hereby possible in any desired angular position of the heating device  9 , which improves the operating comfort for the user.
 
e) The evaluation and control circuit  53  ( FIG. 9 ) can be configured for a feedback control of the energy supply to the heating spiral  15 , with the electrical energy supplied to the heating spiral  15  being set in accordance with a predetermined time development of the temperature T (or of the resistance R) of the heating spiral  15 . In other words, provision is not only made for the heating of the heating spiral  15  to be ended on the reaching of a predetermined temperature, but provision is also made for the heating process to follow a predetermined time development. The utilization of the capacity of the accumulator  51  can hereby be optimized.