WO2000038488A1

WO2000038488A1 - Liquid cooled elevator machine drive

Info

Publication number: WO2000038488A1
Application number: PCT/US1999/018637
Authority: WO
Inventors: Randall S. Dube; Ronald R. Laliberte; David J. Lanesey; Andrew P. Weise; Christopher S. Czerwinski
Original assignee: Otis Elevator Company
Priority date: 1998-12-22
Filing date: 1999-08-16
Publication date: 2000-06-29

Abstract

A liquid cooled elevator machine drive employs a closed circuit coolant circulation system having a heat exchanger, reservoir, pump and piping or tubing (rigid or non-rigid) connected to one or more cold plates which are highly thermally conductive structures through which the coolant flows in the closed circuit. The one or more cold plate(s) are strategically placed with respect to the elevator machine and electronics thereof to maintain controlled temperature operation of the elevator machine drive resulting in enhanced reliability, more compact electronics packaging, reduced acoustic noise over forced convection air-cooled systems and higher performance.

Description

J

LIQUID COOLED ELEVATOR MACHINE DRIVE

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to the field of elevators. More particularly, the invention relates to a liquid cooling system for an elevator machine drive and or machine (hoisting).

Prior Art

Traditionally elevator machine drives have been air cooled by forced convection air cooling (FCAC). These systems employ fans, blowers, heat sinks, etc. as will be recognized by one of ordinary skill in the art. Design parameters for machine drive assemblies require spacing between power generating components that results in relatively large enclosures for the components enclosed. In relatively lower speed and/or lower capacity (lighter duty) elevators, the FCAC systems are economical and effective and machine drive cabinet dimensions are manageable. In higher load systems, however, the cabinets for machine drives can become unwieldy. Because of the relatively small size of the components in lower load applications the FCAC components are relatively quiet. Larger load designs, because of the larger FCAC components, can become unattractively loud.

As demand for higher load capacities in elevators, such as weight, speed, etc. continues to grow, so does the size and thermal output of the machine drives used. FCAC systems may of course be employed with these larger higher capacity machine drives as noted, however they must grow in size from conventional units in order to displace enough air and have enough spacing between components to obtain the desired effect which is to run at an efficient heat level and to conserve the service life of the drive. As components such as J fans, blowers, etc. grow in size, they also produce higher noise levels and require much more space than prior art models. Also as noted, the machine drive cabinet must also grow disproportionately to the size of its housed components. Space is always at a premium in any building and using significant amounts of it to mounting of cooling structures for necessary building machinery is highly undesirable. Moreover, regardless of the environment in which the elevator is placed, the generation of the significant noise of large machinery is not tolerated by consumers of the products. For both of these reasons, FCAC systems are disfavored for high-speed high capacity elevator systems. Thus, the art is in need of a cooling system that is compact and efficient to maintain proper operational parameters of the newer higher speed, high capacity machine drives for elevators and to allow more condensed component placement and packaging of the components to reduce machine drive cabinet size.

SUMMARY OF THE INVENTION

The above-identified drawbacks of the prior art are overcome or alleviated by the liquid cooled elevator machine drive of the invention.

The invention provides a liquid cooling system thermally coupled to the machine drive to maintain a plurality of components at temperatures calculated to enhance operation of the elevator system while prolonging the service life of the machine drive(s), thereof. The cooling system includes a heat exchanger fluid conveyingly connected to a reservoir, which is subsequently connected to a motorized pump. The fluid flowing out of the pump is channeled to one or more cold plates which are constructed of a highly thermoconductive material. The fluid flows through the one or more plates and is circulated back to the heat exchanger. The system is preferably a closed circuit. The one or more cold plates are placed in a thermally conductive condition with a machine drive for the elevator. Heat generated by the machine drive and particularly the insulated J gate bipolar transistor(s) contained therein is absorbed by the cold plates and dissipated through the heat exchanger.

Larger or higher capacity machine drives may be employed without the drawbacks of prior art FCAC systems by employing the invention. In addition, machines and machine drives designed into an elevator system may be made smaller when combined with the cooling system of the invention because efficiency of operation is not lost due to heat as is the case in the prior art.

BRIEF DESCRIPTION OF THE INVENTION Referring now to the drawings wherein like elements are numbered alike in the several FIGURES:

FIGURE 1 is a schematic drawing of the invention providing a preferred flow path for coolant; and

FIGURE 2 is a perspective broken away schematic view of a cold plate of the invention;

FIGURE 3 is a perspective view of a manifold of the invention;

FIGURE 4 is an alternate embodiment of the invention where two machine drives share a common heat exchanger;

FIGURE 5 is another alternate embodiment wherein the heat exchanger 12 is a liquid to liquid exchanger;

FIGURE 6 is schematic view comprising the view of Figure 1 but adding machine cooling in a preferred location in the cooling circuit; and

FIGURE 7 is a perspective view of a machine drive motor stator illustrating one embodiment of coolant channels therein.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1, the concept of the invention is illustrated where in the cold plate(s) 10 are provided in a coolant loop (preferably a closed loop) comprising a heat exchanger 12, reservoir 14, pump 16 having motor 18, inlet i manifold 20, cold plates 10 and outlet manifold 22. All of the foregoing components are connected via fluid conduit 24. The lengths of individual portions of the conduit are of course variable so that the individual components may be mounted in any location desired. It will be understood that one such desired configuration would be to remotely mount the heat exchanger to avoid heat in the machine room or even to use the heat at another location.

Acoustic noise in the system of the invention is significantly lower than a comparable output drive employing an FCAC system. More specifically, in one example the measured noise level in an FCAC system is at more than 10 dB A SPL (sound pressure level) higher than with the invention where other conditions are comparable. The noise reduction is due both to the noise of air moving over a tortuous path in the drive cabinet and the requirement for a high- pressure fan to keep that air moving. Since in the invention, air need only move through the heat exchanger, less noise is created and a lower pressure fan (or fans) may be employed.

Moreover, because of the higher heat capacity of the liquid cooling medium in the invention, lower absolute junction temperatures within the power electronics switching device such as an Insulated Gate Bipolar Transistor (IGBT) are attainable. Since junction temperature is directly related to service life of IGBTs, such a reduction in absolute junction temperature is highly beneficial and, at least for continuous duty applications, significant additional service life can be expected by employment of the invention.

Liquid cooling as prescribed in the invention also allows a cost saving for construction of machine drives and cooling units over FCAC systems. More specifically, a liquid cooling device of the invention is less costly to construct than a comparable capacity FCAC system.

There may be any number of cold plates 10 subject only to coolant flow characteristics and practicality. Figure 1 illustrates the system with one cold plate in solid line, and two in broken line to designate the optional nature _ϊ thereof. The cold plate itself is preferably constructed from a thermally conductive metal (such as 6061-T6 Aluminum alloy, copper, etc. for the shell and copper, aluminum, etc. for the fins) fluid impermeable shell and preferably a thermal conductivity enhancing structure such as a fin structure therewithin. Referring to Figure 2, a schematic perspective broken away representation of a cold plate 10 is provided. Shell 26 is provided around a plurality of fins 28 as described. One preferred fin arrangement employs about 27 fins per inch in density which fins are about .003 inch thick and about .324 inches tall and preferably comprise a turbulence creating configuration (e.g. lanced offset convoluted) to improve heat absorption from shell 26 into the cooling fluid traveling inside shell 26. Cold plate 10 further includes plenum 30 (shown in the figure on the inlet side another plenum similar thereto exists at the outlet side of cold plate 10) and an inlet 32 and outlet 34. Fins 28 preferably are secured to the shell 26 at top and bottom by a suitable and known procedures such as vacuum oven brazing, thermally conductive adhesive, etc. Other brazing methods are also effective but vacuum brazing is preferred due to reduced cleaning processes and better control. Shell 26 is preferably constructed of a material having a high thermal conductivity so that a heat source in thermal conductivity therewith (e.g. an IGBT) will be spread over the entire surface area thereof. The spread heat will be quickly absorbed by the coolant traveling within the shell and then dissipated by the heat exchanger 12. The heat exchanger itself is preferably a copper tubing-aluminum fin type and is complemented by one or more fans preferably moving about 550 CFM. It should be noted that the heat exchanger could be of other materials better suited to lower corrosion rates depending upon the fluid used (e.g. stainless steel tubing) or copper fins for higher heat transfer efficiency.

Each cold plate 10 preferably includes a quick disconnect NPT (National Pipe Thread) fluid inlet and outlet at opposite ends of the plate. The arrangement allows for very expeditious removal and replacement of cold plates J while minimizing cooling fluid loss. Indeed, due to the modularity, the entire system of the invention is extremely easy to assemble and disassemble. This is of great benefit to the art since it makes maintenance and repair of the system or the drive a more expeditious procedure. In the invention, cold plates 10 are preferably placed in close proximity to one or more IGBTs (one embodiment places the plate(s) between two adjacent IGBTs). IGBTs are known to generate significant heat, particularly larger ones. When in thermal contact with the cold plate however the heat is easily managed and the IGBT can be maintained at a highly efficient temperature. Since the temperature can be well managed by the invention, one of the benefits of the invention is realized. A second benefit is also concurrently realized in that since the heat can be controlled, smaller cabinets are useable. As is known, prior art drive cabinets are quite large due to the necessity of the air volume that must flow therethrough for effective cooling and the reduced heat transfer efficiency of such systems. In the present invention, components of the machine drive may be much more tightly packed within the machine drive cabinet, which may consequently be collapsed by 60% of its conventional size.

Effective cooling of cold plate(s) 10 requires a steady flow of cooling fluid through each of the plates 10. An equal distribution of the cooling fluid is provided by inlet manifold 20. Depending upon the number of cold plates (or machine(s)) used, different manifolds will be indicated with the overriding premise being roughly equal distribution of cooling fluid from a feed to the number of manifold openings that are present. Alternatively, the distribution may be intentionally unequal to balance the flow consistent with the heat load. Referring to Figure 3, a perspective view of one manifold (22 or 20) embodiment of the invention is illustrated. This embodiment includes inlet 40 to receive conduit 24, distribution bar 42 and five outlets 44. This embodiment will handle as many as five cold plates or machines or five of a combination i thereof. More or fewer outlets are possible, three being used in the Figure 1 embodiment and four being used in the Figure 6 embodiment. The manifolds, that is the inlet and outlet manifolds, are preferably identical and merely are used in reversed directions on the ends of the cooling apparatuses, i.e., the inlet 40 in Figure 3 will be employed as an outlet and the outlets 44 are employed a plurality of inlets for outlet manifold 22.

Referring to Figures 4 and 5, alternate embodiments of the invention are illustrated and will be understood by one of ordinary skill in the art. In Figure 4, the elevator machine drives are plumbed to share a common heat exchanger. The coolant may or may not be intermingled as desired and the exchanger must merely be sized to have a heat dissipation property sufficient to maintain the two drives. It should be understood that the shared heat exchanger concept is not limited to two drives. More drives could share a heat exchanger with the same caveat relating to size being applicable. In Figure 5, an alternate heat exchanger embodiment is illustrated which employs a liquid heat exchange process. This may be preferable where the heat exchanger is located in small quarters where insufficient air flow to cool the liquid is present. The liquid to liquid exchanger is connected to another system by conduits 32 or where convenient access to building systems utilizing circulating coolant can be advantageous.

The invention, cooling elevator system components with a liquid cooling system is further utilizable to reduce required machine size for particular applications. More specifically, the cooling fluid in this embodiment of the invention is routed through the machine to maintain the machine itself at a temperature where peak efficiency is maintained indefinitely. Thus, in this embodiment the machine does not need to be oversized to compensate for reduced machine efficiencies at higher operating temperatures. Referring to Figure 7, machine drive motor stator 50 is illustrated separately from other and common machine components to illustrate one embodiment of a cooling arrangement for the machine itself. A plurality of passages 52 through machine drive motor stator 50 thereof to allow through passage of coolant liquid. Certainly there are other patterns and means of providing circulating cooling fluid through the machine such as off axis passages, different shapes of passages, a helical passage, etc. which will be understood by one of ordinary skill in the art. Upon plumbing this machine in the coolant circuit of Figure 6, the machine is reliably temperature controlled. Manifold 30 in Figure 6 will be of the same type as manifold 22 in Figure 1 but will contain one additional outlet/inlet. Alternatively one of the outlet/inlets of manifold 22 could be used for machine 48 if one of the three illustrated cold plates is not used.

Another advantage of the invention is realized as a consequence of the condensed component placement occasioned by the cooling system of the invention. Because of the condensed placement, the electrical interconnects that electrically connect the various electronic components together are shorter and thus inherently exhibit lower inductance. This leads to higher performance of the circuit. Higher performances equate to smaller drive components needed and lower cost of manufacture as well as longer maintenance schedules. Additionally, the auxiliary components conventionally required to manage higher inductance circuit manifestations are avoided through employment of the cooling system of the invention due to reduction in length of connectors. The length reduction is a direct result of the condensed component placement of this invention.

In a particular example of the invention, useful to illustrate the particular effectiveness thereof, a liquid cooling unit in accordance with the invention has been constructed as set forth schematically in Figure 1 ; several cold plates were constructed as set forth hereinabove. Cold plates 10 were attached via the fluid inlet and outlets as stated above. A commercially available heat exchanger 12 having aluminum fins, silver brazed to copper tubing was obtained and connected to the system as set forth in Figure 1. Alternating current axial fans J operating on 115 volts at 50 to 60 Hz, said fans being of 10 inches in diameter and flowing 550 cubic feet per minute at .42 inches of water pressure was achieved at 60 Hz are in operable communication with the heat exchanger. Free air acoustic noise developed by the fans was tested at one meter therefrom at 60 Hz operation and measured 49.2 dBA, SPL (sound pressure level) a significant reduction over prior art similar capacity units. A one-half horse power alternating current motor rated at 120 volts, 50 to 60 Hz and 1725 rpm was connected conventionally to a positive displacement rotary vane type pump of brass construction with an internal rotor of stainless steel and graphite vanes. The pump's rating is approximately 4.4 gallons per minute at pressures up to 250 psi. The pump is rated for fluids up to 195EF and incorporates viton seals to accommodate these temperatures. An internal bypass feature was employed to avoid overpressurization damage of the pump. The reservoir is a three quart plastic flange-mounted container with sufficient volume to allow for fluid expansion in the system as well as filling thereof. In the test system volumetric flow meters were also provided but which, as will be understood by one of ordinary skill in the art, are not necessary for a commercial product. The volumetric flow meters are intended merely to monitor flow rates through the cold plates. The 30% inhibited propylene glycol and distilled water solution as employed are the cooling fluid. It will be understood that other fluids could also be used in the system such as water, ethylene glycol, etc. Considerations that affect the choice of fluid used are heat transfer capability of the fluid, corrosion inhibition, Freezing and boiling point variation, toxicity of the fluid, cost, etc. All components of the system were connected as is illustrated in Figure 1 by common tubing. The cold plates were then mounted within the electronics of the machine drive which include a number of IGBTs rated at 1000 amps, 1200 volts. The IGBTs are arranged in a bridge configuration. Cold plates were calculated to provide sufficient cooling for the drive. With the elevator weighted for a full load run, 74.6 decibels A-weighted sound pressure level acoustic noise was produced. This is significantly improved from the prior art where a like capacity system generated 83 decibels A-weighted sound pressure level under similar conditions. While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.

Claims

_»What is claimed is:

CLAIM 1. An elevator machine drive system comprising: a machine drive; a cold plate mounted in thermal conductivity with said machine drive; and a heat exchanger in fluid communication and fluid reciprocatingly attached to said cold plate.

CLAIM 2. An elevator machine drive as claimed in claim 1 wherein said machine drive includes a power electronic switching device, said device being in thermal conductivity with said cold plate.

CLAIM 3. An elevator machine drive as claimed in claim 1 wherein said cold plate and said heat exchanger are both mounted in a closed circuit coolant loop and wherein a pump circulates fluid through said loop to absorb thermal energy from said cooling plate and emit thermal energy from said heat exchanger.

CLAIM 4. An elevator machine drive as claimed in claim 3 wherein said loop further includes a reservoir, said reservoir being fluid conveyingly connected in said loop.

CLAIM 5. An elevator machine drive as claimed in claim 1 wherein said cold plate is constructed of a material having high thermal conductivity and includes an internal convoluted fin structure. J

CLAIM 6. A liquid cooled elevator machine comprising: a machine drive motor; having a plurality of through passages provided in said drive motor, said through passages being connectable to a liquid cooling system having a heat exchanger and a liquid conveyor.

CLAIM 7. A method for controlling temperature of a machine drive comprising: providing a cold plate having: a liquid impervious shell defining an inner chamber; an inlet to said chamber; an outlet from said chamber; placing said cold plate in thermal conductivity with a heat source in said machine drive; connecting said cold plate to a coolant circulatory system including a heat exchanger; and circulating coolant through said cold plate to absorb heat and through said heat exchanger to dissipate said heat.

CLAIM 8. A method as claimed in claim 7 wherein providing said cold plate further includes the feature of a thermal conductivity enhancing structure in said cold plate.

CLAIM 9. A method as claimed in claim 8 wherein said thermal conductivity enhancing structure is a finned structure. J

CLAIM 10. A method for reducing the size of a machine drive cabinet comprising: providing a cold plate having: a liquid impervious shell defining an inner chamber; an inlet to said chamber; an outlet from said chamber; arranging components of said machine drive in a condensed component placement around said cold plate.

CLAIM 11. A method as claimed in claim 10 wherein providing said cold plate further includes the feature of a thermal conductivity enhancing structure in said cold plate.

CLAIM 12. A method as claimed in claim 10 wherein said thermal conductivity enhancing structure is a finned structure.

CLAIM 13. A high performance elevator machine drive comprising: a frame; a plurality of electronic components in a condensed placement relative to each other and mounted on said frame; a cooling system including at least one cold plate, said cold plate mounted in thermal conductivity with at least one of said plurality of components; a plurality of cables interconnecting said plurality of components, said cables being of sufficiently short length to reduce inductance to a level promoting high performance. J

CLAIM 14. A cooling system for an elevator machine comprising: a heat exchanger; a closed circuit fluid conduit system connected to said heat exchange; a pump connected in line with said conduit system; and a coolant fluid contained within said fluid conduit system.