Abstract:
An air blower unit operates with reduced noise while providing a stream of warmed air. The blower unit includes a housing with an inlet at a first end and an outlet at a second end. A support positions the housing above a support surface such that the inlet points toward the support surface, and the outlet does not point away from the support surface. A rotatable blower creates an airstream by flowing air into the housing through the inlet and out of the housing through the outlet. The outlet is coupled to a delivery conduit having an elbow that absorbs some noise from the blower, and reflects remaining noise downward. The delivery conduit may be connected to a convective thermal blanket, for example. A motor, mechanically linked to the blower, rotates the blower and resides in the housing upstream of the blower. A heater, interposed between the blower and the motor, heats the fluid stream as it passes the heater.

Description:
RELATED APPLICATION 
     This application is a continuation application of U.S. patent application Ser. No. 08/525,407, filed on Sept. 8, 1995, now U.S. Pat. No. 6,126,393. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a low-noise air blower unit that produces a stream of warmed air to inflate a thermal blanket. 
     2. Description of the Related Art 
     Augustine, et al. first described the use of temperature-controlled forced air to regulate  10  the body temperature of patients, especially during and after surgery. U.S. Pat. No. 4,572,188, for example, used convective warming to prevent or treat hypothermia. In the &#39;188 patent, temperature-controlled air is supplied by a blower unit that is connected to an airflow cover by a hose. In later-issued patents owned by the assignee of this application, the term “inflatable thermal blanket”, synonymous with “airflow cover”, is introduced. See, for example, U.S. Pat. No. 5,324,320, for “Thermal Blanket”. 
     Inflatable thermal blankets assume a variety of shapes and sizes for specialized use. and include various inflatable structures that wrap around or drape over a patient. See, for example, U.S. Pat. Nos. 5,300,102 and 5,336,250. The mechanism for delivering heated air to a patient has also been expanded, beyond inflatable blankets, to include self-supporting tubes and plenums. See, for example, U.S. Pat. Nos. 5,300,101 and 5,350,417. 
     For ease of description, the various mechanisms for delivering a flow of temperature-controlled air to bathe a patient are referred to herein as “thermal blankets.” Patient-warming systems that use thermal blankets such as these may be collectively referred to as “convective warming systems.” The basic convective warming system includes an air blower unit, a thermal blanket, and a flexible delivery hose connecting the two. These convective warming systems provide acknowledged clinical benefits. However, in certain situations, patients and medical personnel alike would benefit from having an air blower unit that operates as quietly as possible. Some patients, for example, may be sensitive to noise due to their particular medical conditions. Also, the operating room must be kept quiet to avoid distracting the operating team, and to aid the doctors and nurses in hearing vital sign monitors. Furthermore, quiet surroundings are desirable in post-operative recovery rooms, to help patients gently emerge from anesthesia-induced sleep. Moreover, a reduced-noise air blower unit provides a competitive advantage in selling and marketing such units, whether for use in operating rooms, intensive care units, or a patient&#39;s hospital room. 
     FIGS. 1 and 2 illustrate the components of a typical air blower unit  100  (also “blower unit”) in greater detail. The blower unit  100  includes a blower  102  powered by an electric motor  104 . In many cases, the blower  102  comprises a squirrel cage blower. This type of blower typically has a short cylinder with a plurality of fan blades that are positioned around the circumference of the cylinder and oriented longitudinally. The blower  102  withdraws ambient air into an inlet  106  and creates an airstream that continues through an outlet  108 . The outlet  108  is coupled to a tube  116  that connects to a thermal blanket  118  via a coupling ring  120 . Filter media  10  may be provided proximate the inlet  106  to cleanse the ambient air. The stream of air created by the blower  102  is heated by a heater  112 . which may comprise a resistive heating coil, receiving power from an electric power supply  114 . 
     In operation, the blower unit  100  rests on the supporting surface  122 , supported by feet or rollers  124 . In this position, the blower  102  revolves about an axis of rotation  126 . The blower  102  generates an airstream by drawing in air through the intake  106  in a direction  128  that is substantially parallel to the axis of rotation  126 . The airstream flows through the intake  106  and is redirected by the blower  102  in a direction  130  that is substantially perpendicular to the axis of rotation  126 . The airstream flows in the direction  130  out of the blower  102 , through the heater  112  and out of the outlet  108  into the tube  116 . In the prior art blower unit  100 . the heater  112  is downstream of the blower  102 . between the blower  102  and the outlet  108 . The motor  104  is entirely out of the airstream, being neither upstream nor downstream of the blower  102 . 
     Viewed differently, the vertical orientation of the axis of rotation  126  with respect to the air flow means that noise  132  will be emitted vertically upwardly, and noise  134  will be emitted parallel to the floor  122 . 
     As mentioned above, known blower units would further benefit their users by operating with reduced noise. As an example, a significant amount of noise occurs as the airstream created by the blower  102  exits the unit  100  through the outlet  108 . This airstream typically carries a measurable amount of noise generated by the motor  104  and the rotating blades of the blower  102 . Since the airstream flows in the direction  130 , so does the accompanying noise  132 . And, if the unit  100  rests upon the floor  122 , the noise  132  will be projected upward  130  in the direction  130 , toward the patient. Moreover, a significant portion of the noise  132  may be carried via the tube  116  directly into the blanket  118 , as shown by the noise  136 . 
     Another significant source of noise is found at the inlet  106  of the blower  102 . In particular, some noise from the blower  102  and motor  104  projects outward through the inlet  106 , opposite to the direction  128 . Depending upon the placement of the blower unit  100 . this noise  134  may be projected directly at medical staff and patient. 
     One approach to reducing the noise of a convective warming system is found in U.S. patent application Ser. No. 08/383.880, filed Feb. 6, 1995, for “A Source of Inflating Medium With Active Noise Cancellation for an Inflatable Thermal Core Apparatus”, which is assigned commonly with this application and incorporated herein by reference. Here noise reduction is achieved by positioning active cancellation elements in the blower hose. This approach, however. does not quiet the blower unit itself. 
     In view of these considerations, then, there is a manifest need for a blower unit that is compact and operates with reduced noise, while providing a regulated, thermally controlled airstream. 
     SUMMARY OF THE INVENTION 
     Broadly, the present invention concerns a low-noise air blower unit that produces a stream of warmed air for inflating a thermal blanket, while reducing noise caused by its own operation. The blower unit includes a housing with an inlet at a first end and an outlet at a second end. A support positions the housing above a support surface such that the inlet points toward the support surface, and the outlet does not point upward. The housing may be rested on a floor, for example, or hung above the floor, from a stand used to administer intravenous fluids. 
     A rotatable blower, such as a squirrel cage fan in the housing, creates an airstream by flowing ambient air into the housing through the inlet and out of the housing through the outlet. The outlet is coupled to a delivery conduit having an elbow that absorbs noise from the blower, and reflects other noise downward. The delivery conduit may be connected to a convective thermal blanket, for example. 
     The blower rotates under power supplied by a motor, mechanically linked to the blower. The motor, residing in the housing, is placed in the airstream upstream of the blower. A heater, interposed between the blower and the motor, heats the airstream as it passes the heater. 
     The present invention provides its users with a number of distinct advantages. For example, the motor&#39;s presence in the airstream helps warm the air, thereby reducing the heater&#39;s workload. Also, unlike prior arrangements, the heater heats the air prior to passing through the blower, thereby efficiently mixing the heated air and avoiding any “channeling.” 
     The invention provides another advantage by directing its outgoing airstream horizontally with respect to the support surface, rather than vertically, reducing noise sensed by those around the warming unit. This is possible since the blower is mounted on an axis of rotation that is substantially vertical with respect to the support surface. Along these lines, the outgoing airstream noise is further reduced by the delivery conduit&#39;s elbow, which absorbs some noise waves and reflects other noise waves downward. 
     Furthermore, the large filter media ensures reduction of a significant portion of blower noise that would otherwise pass through the inlet. Also, through the unit&#39;s positioning noise that passes through the filter media and the inlet is directed downward toward the support surface, away from people nearby the unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The nature, objects, and advantages of the invention will become more apparent to those skilled in the art after considering the following detailed description in connection with the accompanying drawings, in which like reference numerals designate like parts throughout, wherein: 
     FIG. 1 is a partially cut-away view at a first side of a known blower unit; 
     FIG. 2 is a partially cut-away view at a second side of the blower unit of FIG. 1; 
     FIG. 3 is a partially cut-away side cross-sectional view of a warming unit pursuant to the invention; 
     FIG. 4 is a is plan view of the warming unit of FIG. 3; 
     FIG. 5 is a top perspective view of a filter media of the invention; 
     FIG. 6 is a plan view of the filter media of the invention; 
     FIG. 7 is a bottom perspective view of the filter media of the invention: 
     FIG. 8 is am exploded cross-sectional side view of the filter media of the invention taken along the line  6 — 6 ; 
     FIG. 9 is a cross-sectional side view illustrating the filter media in relation to other components of the blower unit, illustrating the noise-reduction function of the filter media; 
     FIG. 10 is an assembly drawing showing a swivel collar in an elbow of the blower unit of the invention; 
     FIG. 11 is an exploded view of showing how the motor, heater, and blower of the invention are assembled; and 
     FIG. 12 is an illustration of how the blower unit may be mounted on an IV stand. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The inventor of the present application has observed that most of the sound generated by known blower units, such as the unit  100 , is found in the noise  132 . This noise  132  is primarily generated by the high-speed tips of the blower blades and turbulent airflow through the blower, ducting, and heater. As shown in FIG. 1, the noise  132  exits the blower unit  100  straight into the tube  116  and then straight through the tube  116  toward a patient or care giver. A secondary source of noise is the inlet  106 . With the squirrel-cage type blower, the inlet noise  134  projects perpendicularly from the plane of the blower wheel. 
     Having recognized the above-mentioned and other characteristics of known blower units, and after considering the desirable attributes for a new blower unit, the inventor has developed a low-noise air blower unit. FIGS. 3-4 illustrate the principal components of a blower unit  300  in accordance with the invention. The blower unit  300  includes a cabinet is  302  containing a blower  304  driven by an electric motor  306 . Preferably the cabinet  302  may assume different configurations, such as a compact, box-like shape. The blower  304  includes a plurality of fan blades, preferably arranged in a squirrel-cage configuration. The motor  306  preferably comprises an electric motor coupled to the blower  304  by a drive shaft  307 . The blower  304  creates a stream of air (“airstream”) by drawing ambient air through an inlet  308  and expelling the air through an outlet  310 . The direction of the airstream is therefore from the inlet  308  toward the outlet  310 . In the airstream, movement or location in the direction of the outlet  310  is therefore “downstream”, while movement or location toward the inlet  308  is “upstream”. 
     In the illustrated embodiment, the motor  306  is positioned upstream from the blower  304 . Placing the motor  306  in the airstream upstream of the heater  312  cools the motor  306  during operation, significantly extending its life span. Moreover, waste heat from the motor  306  is discharged into the airstream and out of the cabinet, helping to increase the temperature of the airstream. If the motor is not in the airstream, waste heat from the motor can accumulate in the cabinet, affecting any electronic components housed in the cabinet. Placing the motor  306  in the airstream also reduces the heater wattage necessary to produce a given airstream temperature. 
     Also positioned upstream from the blower  304  is a heater  312 . The heater  312  preferably comprises a resistive heating element, which may be provided with a selected level of current to adjustably dissipate heat into the airstream created by the blower  304 . Passing air through a b,eater within a conduit usually results in “channeling” and uneven heating of the air. In the present design, air is heated as it enters the blower  304  which thoroughly mixes the air, providing a uniform temperature as the airstream leaves the blower  304 . This occurs because the air is blown through the blower  304  after it is heated. 
     As recognized by the present inventor, much of the noise present at the inlet  308  emanates from the spinning blower  304 . Therefore, placement of components such as the heater  312  and the motor  306  between the inlet  308  and the blower  304  acts to reduce inlet noise by blocking noise that the blower  304  would otherwise direct out the inlet  308 . 
     FIG. 4 shows the low noise air blower unit of the invention coupled by air hose  322  to inflate a thermal blanket  330 . 
     Filter 
     An important noise-reducing feature of the warming unit  300  is the filter  314  constructed from sound-absorbent material. The filter  314  reflects and absorbs a significant portion of the downward-traveling noise produced by the blower  304 , thereby reducing the noise emanating from the inlet  308 . FIGS. 5-9 illustrate the construction and operation of the filter  314  in greater detail. The filter  314  includes a noise-absorbent, hollow shaft  500  defining an upper lip  502  that encloses a blower intake aperture  313 . Since the intake aperture  313  faces the inlet  308  of the housing  302 , the filter  314  forms a continuous sound absorbing conduit that encloses the airstream between the inlet  308  and blower  304 . The filter also includes a lower lip  700  (FIG.  7 ). The hollow shaft  500  preferably comprises a rigid or semi-rigid fibrous substance, or another sufficiently noise-absorbing material. High efficiency filters must have a large surface area or they will induce a very high resistance to airflow. Effective convective warming requires an airflow of at least 30 cubic feet per minute, for example. To accommodate this large airflow, the filter  314  preferably includes a plurality of pleats  315  to maximize the surface area of the filter material housed within the cabinet  302 . Further, to maximize the compact design, the motor and heater are placed within the tubular filter to use this otherwise wasted space. The filter  314  additionally includes a noise-absorbent convex base  800 . as clearly shown in FIG.  8 . The base  800  includes an outer edge  802  connected to the lower lip  700 . The base  800  preferably comprises a molded plastic cap, sealing the end of the hollow shaft  500 . The base  800  defines a convex shape, which may be embodied in a conical, convex, or another suitable shape. Preferably, the base  800  is slightly conical in shape and may be molded from or covered with a sound-absorbing material. Sound waves that pass the motor are either absorbed by the cap material or reflected laterally by the conical surface, to be absorbed by the pleats of the hollow shaft  500 . 
     More particularly, as shown in FIG. 9, the shape of the convex base  800  functions to receive sound waves from the blower  304  and reflect the sound waves outward to the noise-absorbent material of the hollow shaft  500 . In this respect, the material of the convex base  800  preferably comprises a material that is reflective to the frequency of noise generated by the blower  304 , which material may also be absorbent of the sound waves to a desired degree. Moreover, to further reduce noise in the cabinet  302 , sound mufflers or baffles may be placed inside the cabinet  302  within the filter  314 . 
     Positioning 
     Referring to FIGS. 3 and 4. another noise-reducing feature of the warming unit  300  is its positioning during use. Particularly, the warming unit  300  includes a support to position the unit , 00  during operation such that the inlet  308  is generally pointed toward the floor  316 . The support may comprise a floor support  320  such as feet, rollers, legs, or another device to support the unit  300  upon a horizontal support surface. Alternatively, the support may comprise a clamping support  348  to hang the unit  300  from a piece of equipment such as an IV drug stand. By supporting the warming unit  300  in this way, noise from the blower  304  that passes through the filter  314  and the inlet  308  is directed downward toward the floor  316 , away from the patient and others present in the room. 
     Side Projection 
     Referring to FIGS. 3 and 4, another noise-reducing feature of the warming unit  300  is the orientation of the outlet  310 . Unlike prior arrangements such as the blower unit  100 , the outlet  310  is provided on a side of the cabinet  302  rather than the top. Therefore, when the outlet  310  is coupled to air hose  322 , noise from the blower  304  that enters the conduit  322  travels outward (FIG. 3) rather than upward (FIG.  1 ). This placement of the outlet is possible because the blower  304  rotates upon a substantially vertical axis  328 . As a result, the plane of rotation of the blower  304  is horizontal, creating an airstream that flows laterally through the outlet  310 . 
     Sound and noise consist of pressure waves of different frequencies and amplitudes traveling through a medium, usually air. Like waves on a still pond, these waves are subject to destructive interference and cancellation. Sound waves, which follow substantially straight paths, wherein directed around a bend or along a serpentine path reflect off the walls of the pathway and lose energy. In the preferred embodiment, the hose  322  includes such a contour in the form of an elbow  324  that defines a rigid or semi-rigid bend in the hose  322  of between about 45 degrees and 90 degrees. The elbow  324  preferably comprises a soft, pliable rubber or plastic material that is sound-absorbing. So constructed, the elbow  324  absorbs a significant amount of noise outwardly projected by the blower  304 . The noise waves that are not absorbed by the elbow  324  are downwardly reflected by the elbow  324 , as shown by the arrows  326 . Therefore, these noise waves are directed toward the floor  316 , minimizing the impact of this noise upon the patient and others in the room. Preferably, the outlet  310  includes a swivel collar (shown in FIG. 10 in more detail) permitting the elbow  324  to rotate in respect to the outlet  310 . This reduces the stress on the hose  322  as it is stretched into different positions, yet allows the conduit  322  to hang neatly by the side of the warming unit  300  when not in use. 
     Swivel Collar 
     FIG. 10 shows, in more detail, an elbow  1024  which conforms to the description and function of the elbow  324 . In FIG. 10, the elbow  1024  is assembled from two opposing pieces  1010  and  1012  that, when assembled, form a flange that faces a corresponding flange  1014  on a blower/heater/motor unit  1015  constructed in accordance with the description of the blower unit shown in FIGS. 3 and 4. The elbow  1024  is swivelly coupled to the flange  1014  by a swivelling collar  1017  that is retained, on its inner annular surface  1018  in a collar race  1019  on the flange  1014 . The flange formed by the pieces  1010  and  1012  includes a race for engaging the outer annular surface  1019  of the swivelling collar  1017 . A portion of this race is indicated on the piece  1010  by reference numeral  1020 . 
     Blower/Heater/Motor Assembly 
     FIG. 11 shows, in an exploded view, how a blower, heater, and motor are assembled according to the best mode of the invention. In FIG. 11, a blower includes upper and lower enclosure pieces  1110  and  1112 , respectively. The pieces  1110  and  1112  are assembled to enclose a disc-shaped rotor  1114  having curved blades  1116 . The disc-shaped blower is substantially horizontally disposed in the preferred operating environment, as explained above in respect of FIGS. 3 and 4. Preferably the disc-shaped rotor  1114  is a molded plastic piece. An annular enclosure  118  is mounted on the underside of the lower enclosure piece  1112 . A heating coil  1120  is contained in the enclosure  1118  underneath (upstream of) the blower. The heating coil  1120  is conventionally mounted on a frame  1122  in the enclosure  1118  and is activated by conduction of electricity through a pair of wires  1124 . A motor  1126  is mounted to the enclosure  1118  beneath (upstream of) the heating coil  1120 . The motor  1126  includes a drive shaft  1128  that protrudes upwardly through a circular hole  1130  in the lower enclosure piece  1112 . The drive shaft  1128  receives and rotates the disc-shaped rotor  1114 . Air stream flow in the blower/heater/motor assembly of FIG. 11 is upward past the motor  1126  and heater coil  1120  through the circular hole  1130 , into the blower, where the rotor  1114  deflects the air stream sideways through the outlet in a flange formed by pieces  1132  and  1134 . 
     IV Pole Mounting 
     FIG. 12 shows a low noise air blower unit for inflating a thermal blanket in an embodiment adapted for mounting on an IV (intravenous) pole. Here, the blower unit  1210  is constructed according to the principles set forth in connection with FIGS. 3-11 for reduction of noise. The blower unit  1210  includes an elbow  1212  mounted to swivel on an enclosure  1214 . An air hose  1216  is mounted to the elbow  1212  for delivery of a warned air stream to an inflatable thermal blanket (not shown). The blower unit  1210  includes, mounted to a back surface  1218  of the enclosure  1214 , a C-shaped attachment clamp  1220  with a threaded clamping screw  1222  that engages the vertical pole  1224  of a conventional IV pole assembly  1226 . 
     OTHER EMBODIMENTS 
     While there have been shown what are presently considered to be preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims.