DIRECT CURRENT AIR CURTAIN

Abstract

Direct current air curtains are provided, which may be used to help reduce or prevent the exchange of heat between different areas. The direct current air curtain may be used in a variety of applications, including trailers, rail cars, vehicles and containers.

Description

This application claims the benefit of U.S. Provisional Application No. 61/252,925, filed Oct. 19, 2009.

FIELD

The present embodiments relate to direct current air curtains for use in transportation devices, including trailers, rail cars and containers.

BACKGROUND

In many commercial applications, it is desirable to maintain multiple areas at different temperatures. Maintaining this difference in temperature between two areas is complicated when it is necessary to move items between the areas. This is particularly true with the transportation of refrigerated or frozen goods.

Various methods and devices have been developed to address this challenge. In some cases, strips of plastic sheeting may be hung in an opening dividing two areas of various temperatures to reduce differential air flow between the areas while still permitting the movement of goods. While these strips help reduce heat exchange, they interfere with easy movement between the areas. Other designs involve two sets of doors between the colder and warmer areas, the doors being offset from one another and designed so that only one set of doors may be open at any given time. These offset doors require an intermediate space between the doors, and thus may not be suitable when space is limited.

Another method of limiting the exchange of heat between areas has been to employ air curtains. Some exemplary air curtains include those described in U.S. Pat. Nos. 6,112,546 and 6,874,331, which are incorporated herein by reference. Typically, air curtains slow the exchange of heat by using fans to blow air across an opening between two areas. The air flow is directed more or less parallel to a plane defined by the opening thereby creating a vertical wall of fast moving air that separates the two different temperature areas. The air curtain prevents or reduces the flow of air between the two areas. Most air curtains are designed for fixed applications (such as walk-in coolers) and they are designed to run on alternating current power sources. In addition, the size of the air curtain and the noise generated by the motor are less important in fixed applications than in mobile applications (such as a refrigerated trailer).

In the fields of transportation of refrigerated and frozen goods, efforts to prevent heat exchange at openings and doors have typically been limited by restrictions on the space available. For instance, some vehicles have employed the plastic strips described above; however, double doors are generally not practical. Also, because vehicles are not connected to a power grid, alternating current power sources are generally not available and the relatively low voltage direct current generated by a tractor trailer presents unique design challenges.

BRIEF SUMMARY

Direct current powered air curtains suitable for use in trailers, and other vehicles or containers, are presented. The direct current air curtains may include any of the following aspects in various combinations and may also include any other aspect described below in the written description or shown in the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a perspective view of an embodiment of a direct current air curtain;

FIG. 2 depicts a bottom view of an embodiment of the direct current air curtain;

FIG. 3 depicts a cross-sectional view of an embodiment of the direct current air curtain along line A-A as indicated in FIG. 2;

FIG. 4 depicts an exploded view of an embodiment of the direct current air curtain showing a direct current motor, a connection and a tangential fan;

FIG. 5 depicts an exemplary refrigerated trailer having one embodiment of the direct current air curtain placed above a side door to the trailer;

FIG. 6 depicts a closer view of an embodiment of the direct current air curtain and trailer door of FIG. 5; and

FIG. 7 depicts a side view of an embodiment of the direct current air curtain within a trailer.

DETAILED DESCRIPTION OF THE DRAWINGS

A direct current air curtain (“DC air curtain”) will be described with reference to FIGS. 1-7. While the DC air curtain is generally depicted and described in association with a trailer, it is contemplated that the DC air curtain may have other applications, including, but not limited to, walk-in coolers, rail cars, vehicles and portable containers.

FIG. 1 shows a perspective view of a DC air curtain 10. As will be explained in association with the figures, the DC air curtain 10 pulls air into the housing 16 through air intakes 14 (e.g., air inlets 14) and then expels the air through the air outlet 12 to generate a wall of air.

FIGS. 2-4 present various views of the DC air curtain 10 and its internal parts. These figures are discussed together in explaining the operation of an embodiment of the DC air curtain 10. The DC air curtain 10 is driven by a DC motor 18, which is shown in FIG. 4. The DC motor 18 connects to one or more tangential fans 20, so that when in operation, the fans 20 may generate the air flow required of the air curtain 10. The DC motor 18 may be a brushless DC motor, or any other type of DC motor known to persons of ordinary skill. In some embodiments, the DC motor may also be a moisture tight motor. Further, it should be understood that the DC motor 18 may have a drive shaft 22 that emerges on one end of the motor 18 or both ends of the motor 18, as shown in FIG. 4.

The tangential fan 20 may connect to the drive shaft in any of a number of different ways. As illustrated, the tangential fan 20 connects with the DC motor 18 using a connecting plate 24 with a collar that fits over a first end of the drive shaft 22. The connecting plate 24 may attach to the tangential fan 20 and the drive shaft 22 in any known method, including mechanical fasteners, adhesives, and threaded connections. While not shown in FIG. 4, it is contemplated that a second tangential fan 20 may attach to a second end of the drive shaft 22. That is, a single DC motor 18 may be used to drive two tangential fans 20 simultaneously through the use of a drive shaft 22 that extends from each end of the motor 18.

The DC motor 18 and tangential fans 20 of FIG. 4 are contained within the housing 16 shown in FIGS. 1-3. When multiple tangential fans 20 are used, one on each end of the DC motor 18, it may be desirable for the fans 20 to be equally sized such that the DC motor 18 is disposed in the center of the housing 16. Although not illustrated, it should be understood that the ends of the tangential fans 20, away from the motor, may be supported within the housing 16 on rotatable bearings.

As illustrated by the arrows in FIG. 3, when the DC motor 18 is activated, the tangential fan 20 rotates, and the blades 24 of the tangential fan 20 pull air through the air intakes 14 into the housing 16. As the tangential fans 20 continue rotating, the blades 24 drive the air through the tangential fan 20 to the inside of the housing 16 and out the air outlet 12 as shown by the arrows in FIG. 3. Some of the air intakes 14 may be rotationally positioned 90 degrees from the air outlets, as shown in FIG. 1. Therefore, some air is generally pulled into the housing 16, rotated roughly 270 degrees, and then expelled through the air outlet 12.

Some embodiments of the DC air curtain 10 may include a baffle 26 to help to divide the air intakes 14 from the air outlet 12 and thereby improve air flow within the housing 16. Further, an internal wall 30 may be included within the housing 16 to help direct the flow of air around the tangential fan 20 and towards the air outlet 12. Some embodiments of the DC air curtain 10 may include a fin 28 within the air outlet 12 to help direct the air flow that generates the wall of air. Alternatively, some embodiments of the DC air curtain 10 may include a nozzle that defines the air outlet 12. This nozzle may be reoriented (e.g., positionable) to direct the air flow.

In operation, the DC motor 18 may use an electronic controller 32. The electronic controller 32 regulates the rotational speed of the motor 18, which in turn regulates the rotation of the tangential fan 20 and the flow rate of air being emitted from the DC air curtain 10. As explained herein, the electronic controller 32 may be in communication with a switch or sensor to determine when the DC motor 18 should be activated and also how fast the motor should operate.

FIG. 5 illustrates an embodiment of a DC air curtain 10 mounted within a refrigerated trailer 34. In this figure, the DC air curtain 10 is positioned above a side door 36 of the refrigerated trailer 34. The DC air curtain 10 may be mounted to the refrigerated trailer 34 using a mounting plate 38 on the housing 16 (shown in FIG. 3), which is in turn mounted to the wall 40 of the trailer 34 using devices well known in the art, including mechanical fasteners such as nuts and bolts. In FIG. 5, the DC air curtain 10 is mounted adjacent to (e.g., above) the side door 36 in order to create a wall of air that flows from top to bottom. Alternatively, the DC air curtain 10 may be located on a side of the door 36 in order to create a wall of air that flows from left to right or right to left.

The refrigerated trailer 34 includes a refrigeration unit 42, which cools and circulates air within the trailer 34, thereby preserving and allowing shipment of goods that require refrigeration and/or freezing. Refrigeration units, such as the one shown in FIG. 5, may include alternators and batteries for producing and storing electricity. The power generated by the alternator and stored by the batteries may power not only the refrigeration unit itself, but also other trailer systems, such as lighting within the trailer. The alternator produces, and the batteries store, direct current electrical power. The alternator may produce roughly 65-120 Amps of current at around 11-13 volts potential. In other embodiments, the alternator and batteries may produce roughly 23-25 volts potential. In some embodiments, the electrical power used to power the trailer lighting system may also be used to power the DC air curtain 10.

FIG. 6 shows a close-up view of an embodiment of the air curtain 10 within a refrigerated trailer 34. As shown, the DC air curtain 10 is positioned on the wall 40 of the trailer 34 above an opening 44 for the side door 36. Trailers may range in height from about 95 to 110 inches (2.4 m to 2.8 m). The side doors in such trailers may be around 84 inches (2.1 m) tall. Therefore, the housing 16 of the DC air curtain 10 may be sized to fit within a space ranging from around 11 to 26 inches (28 to 66 cm) in height. However, other door sizes may be used, and the housing 16 may be sized accordingly. In one embodiment, the housing 16 is 10 inches in height. Furthermore, because the trailer 34 is generally filled with goods, it is desirable that the housing 16 maintain a low profile. Therefore, the housing 16 may be designed to have a depth of 7-12 inches (17.8 to 30.5 cm). The width of the DC air curtain 10 may be sized in accordance with the width of the side door 36. In some embodiments, it may be desirable for the DC air curtain 10 to be slightly wider than the door to create a sufficiently large wall of air to prevent heat exchange. In other embodiments, the width of the DC air curtain 10 may be less than the door width because the wall of air will tend to spread as the air travels away from the DC air curtain 10. Alternatively, the DC air curtain 10 and door 36 may have similar widths.

In practice, and as noted previously, it is desirable for the DC air curtain to run when the door 36 is open. Therefore, a sensor 46 may be included. The sensor 46 may be of any type known to those of skill in the art, including, but not limited to, a pressure sensor, light sensor, or electromagnetic sensor. Alternatively, a switch may be placed in the trailer or truck cab so that the operator may manually turn the DC air curtain 10 on and off. As shown in FIG. 6, the sensor 46 is a pressure sensor. When the door 36 is closed, a portion of the door 36 or a flange attached to the door 36 contacts the sensor 46, causing the sensor 46 to signal the DC air curtain 10 to turn off. In contrast, when the door 36 is ajar, the sensor 46 will signal the DC air curtain 10 to turn on, thereby preventing or slowing the exchange of heat with the outside environment. The sensor 46 may be located on a side of, above, or below the door 36.

As shown in FIG. 6, when the DC air curtain 10 is in operation, ambient air 48 from within the trailer is pulled into the housing 16 through the air intakes 14. As explained above, the air 48 is then expelled from the housing 16 through the air outlet 12 in a direction 50 that is generally towards the floor of the trailer. FIG. 7 depicts a side view of the air curtain 10 and the door 36. As illustrated, the air 48 is pulled through the air curtain 10 and then expelled through the air outlet 12 (visible in FIG. 2). The air 48 may be expelled from the air outlets 12 at a variety of angles relative to the plane of the door opening 44 (visible in FIG. 6), although the air 48 is still generally directed towards the floor of the trailer. In practice, the wall of air generated by the DC air curtain 10 may be directed roughly parallel to the plane of the door opening or at an angle 52 of as much as around 20 degrees to the plane of the door opening. In one embodiment, the angle 52 is oriented so that the direction 50 of air flow is towards the center of the trailer. Other orientations may also be used.

The wall of air generated by the DC air curtain 10 inhibits the flow of air between the spaces on either side of the air curtain. While this helps retain the desired temperature within the refrigerated trailer, it is important that the air curtain not generate so much noise as to make communications difficult or create an occupational hazard. Some embodiments of the DC air curtain generate around 85 decibels or less noise. Other embodiments produce around 80 decibels or less noise.

To generate the air wall described above, some embodiments of the DC air curtain 10 generate air flow of roughly between 1000 and 1500 cubic feet per minute (28.3 to 42.5 cubic meters per minute). Other embodiments generate air flow rates of roughly 1100 to 1300 cubic feet per minute (31.1 to 36.8 cubic meters per minute). However, other flow rates may be generated. Further, the required flow rate will depend upon a number of factors, which may include the size of the opening adjacent the air curtain and the angle of air flow.

Refrigeration units, such as the ones described above and shown in FIG. 5, are commercially available from a variety of manufacturers including the SPECTRUM and SB series of products from THERMO KING of Minneapolis, Minn., and the X2 series from CARRIER TRANSICOLD of Farmington, Conn. Those skilled in the art understand that refrigeration units produced by other manufacturers may also be used. Further, a variety of batteries and power packs may be used in conjunction with the refrigeration units. For example, batteries and power packs are commercially available from THERMO KING under the trade name EON and EON POWER PACK.

In some embodiments, the DC motor 18 for the DC air curtain 10 may draw between 15 and 40 amps current. In other embodiments, the DC motor 18 may draw between 22-35 amps. In still other embodiments, the DC motor 18 may be rated at 25 amps. In some embodiments, the DC motor 18 may generally require between 200 and 350 watts power. In other embodiments, the DC motor 18 may require roughly 250-300 watts power. The DC motor 18 should generate sufficient torque to rotate the tangential fan sufficiently fast to generate the required air flow. In some embodiments, the DC motor 18 may generate between approximately 1.5 and 2 N·m torque, and in other embodiments, the DC motor 18 may generate between 1.6 and 1.7 N·m torque. In some embodiments, the DC motor 18 may have rotational speeds of between 1300 and 1700 RPM, and in yet other embodiments, the DC motor 18 may rotate between 1400 and 1650 RPM. In another embodiment, the DC motor may rotate at 1400 RPM. The DC motor 18 may have class F insulation; however, as understood in the art, other classes of insulation may also be used. In some embodiments, the DC motor 18 has eight poles, three phases, and four windings per phase. However, those skilled in the art understand that these values may be varied. Additionally, some embodiments of the DC motor 18 may use Hall effect sensors to communicate rotor position with the electronic controller 32.

The electronic controller 32 may use any control method known to those of skill in the art, including open loop speed control. The electronic controller 32 may receive feedback from the DC motor 18 in any known method. In one embodiment, the electronic controller 32 receives motor feedback through three Hall sensors at 120 electrical degree spacing. The electronic controller 32 may be rated for a continuous current of 25 amps with a peak current of 40 amps. However, controllers rated for other current values may also be used, depending on the current draw of the associated DC motor 18. Additionally, the electronic controller 32 may include any of the transistor types known to those skilled in the art. In one embodiment, six metal-oxide-semiconductor field-effect transistors (MOSFET) are used that have a switching frequency of 33 kHz. The electronic controller 32 may be a digital signal controller. Digital signal controllers are commercially available, including from MICROCHIP TECHNOLOGY INC. of Chandler, Ariz. (e.g., P/N dsPIC33FJ12MC202-I/SO)

To prevent the electronic controller 32 from short circuiting and to prevent the windings of the DC motor 18 from overheating and burning when an obstruction prevents the tangential fan 20 from rotating (e.g., the tangential fan 20 is frozen), the electronic controller 32 may include a programmable current sense high side switch. The current sense high side switch senses current and temperature in the windings of the DC motor 18. Alternatively, a current sense switch senses current and temperature within the electronic controller 32. When the current sense high side switch detects a current or a temperature higher than a predetermined level, the switch shuts off the DC air curtain 10; when the obstruction is removed, and the current or the temperature falls below the predetermined level, the switch turns the DC air curtain 10 back on. Programmable current sense high side switches are commercially available, including from INTERNATIONAL RECTIFIER of El Segundo, Calif. (e.g., P/N IR3313PbF).

In one embodiment, the electronic controller 32 is electrically connected to a fast acting circuit breaker to further protect the DC motor 18 and the controller 32 from overload. In one embodiment, the circuit breaker is a 30 Amp circuit breaker. The circuit breaker may also provide reverse battery protection, such that the circuit breaker may be triggered when the batteries are installed backwards (e.g., with reversed polarity). Fast acting circuit breakers are commercially available, including from CARLING TECHNOLOGIES, INC. of Plainville, Conn. (e.g., P/N AC1-B0-32-630-1G1-C).

The electronic controller 32 may also be programmed for a motor soft start, such that the current through the DC motor 18 is temporarily reduced at start-up. The current is ramped-up slowly to prevent in-rush current and temporary overloads.

As noted above, the DC air curtain 10 may include a tangential fan. Tangential fans are also commercially available, including from EUCANIA INTERNATIONAL INC. of Dorval, Canada. In one embodiment, the DC air curtain 10 uses two 5.5 inch diameter (14 cm) and 17.5 inches long (44.5 cm) tangential fans that each have 36 blades. However, the size of the fan and the number of blades is dictated by several factors including the size of the housing, the volume of air required for a given door, and whether the DC motor 18 has fans on one or both ends. Therefore, other fans may also be used.

While the description generally discuses DC air curtains in conjunction with refrigerated trailers, it is contemplated that the DC air curtains disclosed herein may be used with other vehicles and containers, including heated vehicles.

It is intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of the invention.

Claims

1. A system comprising:

a refrigerated trailer comprising: a door, the door having open and closed positions; and a refrigeration unit attached to the refrigerated trailer, the refrigeration unit comprising a power source; and

an air curtain comprising: a housing comprising an air inlet and an air outlet, the housing being sized to fit within the trailer adjacent to the door, the air inlet being offset from the air outlet; a direct current motor attached to the housing; an electronic controller electrically coupled to the direct current motor and the power source of the refrigeration unit; a fan operatively coupled to the direct current motor; and a sensor positioned in the door and in communication with the electronic controller,

wherein the sensor signals the electronic controller when the door is in the open position, the electronic controller activating the direct current motor to rotate the fan after receiving the sensor signal,

wherein the fan pulls air from within the trailer into the housing unit through the air inlet and redirects the air so that the air is expelled through the air outlet.

2. The system of claim 1, wherein the air curtain requires around 12 volts electric potential and between 20 and 40 amps current.

3. The system of claim 1, wherein the direct current motor is a brushless direct current motor.

4. The system of claim 1, wherein the air curtain is operable to generate an air flow of between 1000 and 1500 cubic feet per minute.

5. The system of claim 1, wherein the air curtain is operable within an environment having a temperature of between −29 degrees C. and 43 degrees C.

6. The system of claim 1, wherein the air curtain generates an air flow that is oriented within 0 to 20 degrees of a plane of a door opening.

7. The system of claim 1, wherein the air curtain generates around 85 decibels or less noise when activated.

8. The system of claim 7, wherein the air curtain generates approximately 80 decibels or less of noise when activated.

9. The system of claim 4, wherein the air curtain generates an air flow of between 1100 and 1300 cubic feet per minute.

10. The system of claim 1, wherein the power source of the refrigeration unit comprises an alternator and a battery, and

wherein the direct current motor and the electronic controller are powered by an electrical output of the alternator, the battery, or the alternator and the battery of the refrigeration unit.

11. The system of claim 1, wherein the air inlet is offset from the air outlet by roughly 90 degrees.

12. The system of claim 1, wherein the fan is a tangential fan.

13. An air curtain comprising:

a housing comprising an air inlet and an air outlet;

a direct current motor attached to the housing, the direct current motor comprising an output shaft;

an electronic controller electrically coupled to the direct current motor;

a sensor in communication with the electronic controller and configured to signal the electronic controller to activate and deactivate the direct current motor; and

a fan positioned within the housing and mechanically coupled to the output shaft of the direct current motor,

wherein the air curtain generates air flow between 1000 and 1500 cubic feet per minute when in operation.

14. The air curtain of claim 13, wherein the air curtain generates less than 85 decibels of noise

15. The air curtain of claim 14, wherein the air curtain generates less than 80 decibels of noise when in operation.

16. The air curtain of claim 13, wherein the air curtain generates air flow between 1100 and 1300 cubic feet per minute when in operation.

17. The air curtain of claim 13, wherein the air curtain uses approximately 12 volts of electric potential and between 20 and 40 amps current.

18. The air curtain of claim 13, wherein the direct current motor is moisture tight.

19. The air curtain of claim 13, wherein the housing has outside dimensions of approximately 1 m in length, 25 cm in height and 22 cm or less in depth.

20. The air curtain of claim 13, wherein the air outlet further comprises a positionable nozzle.

21. The air curtain of claim 13, further comprising another fan,

wherein the output shaft of the direct current motor extends away from the direct current motor on each end of the motor, and

wherein one of the fan and the other fan is mechanically coupled to the output shaft adjacent to each end of the direct current motor.

22. The air curtain of claim 13, wherein the air curtain is operable within an environment having a temperature range of −29 degrees C. to 43 degrees C.

23. The air curtain of claim 13, wherein the fan is a tangential fan.