Patent Abstract:
A material handling vehicle includes a cyclonic motor cooling system for a motor compartment that accommodates an ergonomically designed operator compartment. Together, the motor compartment and cyclonic motor cooling system include a generally cylindrical housing with a tangentially arranged cooling air injection port at a lower end and exhaust port at a radially and axially opposite end. An air blower directs cooling air into the compartment where a cyclonic cooling air flow and a vortex cooling flow is produced. The cyclonic air flow cools more effectively than conventional linear air flow while also reducing dust contamination and buildup of the motors in the motor compartment.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/356,652 filed on Jan. 21, 2009 now U.S. Pat. No. 8,136,618. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to material handling vehicles, interchangeably referred to herein as “lift trucks”, and more particularly, to a cyclonic motor cooling system for use in motor compartments of material handling vehicles. 
     Lift trucks are designed for use in various types of environments and applications. Lift trucks are configured to perform functions necessary in a given environment of use or application. Lift truck operator compartments are, in turn, designed to allow the operators to assume an operating position allowing them to perform the required material handling task. 
     To this end, some lift trucks operator compartments have been designed so that an operator has the option of operating the lift truck in either a standing or a seated position. Operator compartments for these types of lift trucks (e.g., a ‘sit/stand’ truck) have been modified to include, among other things, a foldable seat and an elevated footrest. Adding such a footrest, however, is difficult due to the design limitations of crowded operator compartments. One known modification for adding an elevated footrest to an operator compartment is to decrease the size of the adjacent motor compartment. This, however, comes at a cost, namely, reduced motor cooling capacity as explained below. 
     Standard motor compartments typically house two, and sometimes three, motors: one for propelling the forklift truck (i.e., a traction motor), one for steering (i.e., a steering motor) and one for driving a hydraulic pump to lift the fork carriage (i.e., a lift motor). These motors usually have an attached cooling fan that provides adequate cooling if housed in a standard motor compartment. When housed in a smaller motor compartment, however, the temperature therein rises at much faster rate and quickly overwhelms the capacity of the cooling fans to effectively cool the motors and other heat-generating components located therein. 
     To protect the motors from high temperatures, some lift trucks were outfitted with a thermal switch whereby the entire lift truck is shut down if the motor temperature is high. Other lift trucks are provided with advanced control schemes that reduce the speed and/or acceleration of overheated motors to cool them. However, both of these schemes require additional logic and circuitry and do not act to dissipate the heat once generated. 
     Most lift trucks are therefore provided with some sort of ventilated motor compartment. The most basic of which is a compartment with one or more openings therein to allow for the circulation of ambient air. If the motor compartment or openings are large enough, or if there is only a minimal amount of heat generated, the limited cooling capacity of such openings may suffice. However, forklifts are typically operated indoors at low speeds (and even standing still) and as a result, only minimal ventilation (and thus cooling) occurs. 
     Some lift trucks are provided with motor compartments having a forced-air cooling system. In such a system, hopefully cooler ambient air is directed through the motor compartment to remove an amount of heated air therefrom for conventional heat dissipation away from the compartment. In such a system, however, the forced cooling air has a generally linear air flow profile as it passes through the motor compartment. The linear flowing cooling air is impeded by the motors, reducing the amount of air flowing through the compartment and transferring heat from the motors therein. Utilizing a larger blower merely results in the greater introduction of dust and debris into the motor compartment which then accumulates on the motors and decreases the heat removal effectiveness of the forced cooling air. 
     To this end,  FIGS. 1 and 2  illustrate an operator compartment  10  for a material handling vehicle  12  having a forced air motor cooling system  40 . The operator compartment  10  is defined by an operator station  14  with an opening  16  for entering and exiting the compartment  10 . Operator controls includes a steering wheel  18  and a control handle  20 . The operator compartment  10  further includes a seat  24  adjacent to the control handle  20  and an elevated footrest  25  for use when the lift truck  12  is operated from a seated position. The seat  24  can be folded flat to provide additional space in the operator compartment  10  when the lift truck  12  is operated from a standing position. First and second deadman switches  21 ,  22  are provided in the floor  23  and footrest  25  of the operator compartment  10 . As is known, one of the deadman switches  21 ,  22  must be actuated in order to operate the vehicle  12 . 
     Adjacent to the operator compartment  10  are two motor compartments  26 ,  28 . The first motor compartment  26  has two electric motors therein—a larger traction motor  30  and a smaller steering motor  32 . The second motor compartment  28  houses the lift motor (not shown) and associated hydraulic circuit for lifting the fork carriage up and down and is not discussed in further detail herein. A more detailed discussion on the various components of a similar, side stance, lift truck can be found in U.S. Pat. No. 6,871,721 assigned to the present assignee, the contents of which are fully incorporated herein by reference. 
     The traction motor  30  is mounted to a gear box (not shown) and propels the truck  12  at a directed speed. The steering motor  32  controls the direction of travel of the lift truck  12 . Both motors  30 ,  32 , along with other electrical control components contained in the motor compartment  26  not shown, generate an appreciable amount of heat. 
     The motor compartment  26  is defined on the bottom by a lift truck chassis  34 , on the sides by walls  36 , and on to by a cover  38 . A number of openings, e.g. air intake port  42  and exhaust port  44 , are formed in the walls  36  of the motor compartment  26 . The air intake port  42  directs cooling air from a fan or blower  46  into the compartment  26 . The cooling air flows in a generally linear path, as shown by arrows  48 , through the motor compartment  26 , removes heat from the motors  30 ,  32  via convection, and is subsequently discharged through the exhaust port  44 . 
     While the conventional forced air system  40  is an improvement over the cooling provided by ambient air ventilation, the linear flow profile of the cooling air limits the cooling capacity especially in point-to-point applications such as in the motor compartment  26 . This is because the motors  30 ,  32 , being located directly in the path of the cooling air for the greatest heat transfer, act to impede the cooling air and shield the back surfaces of the motors  30 ,  32  from the cooling air. The linear flow profile also contributes to the accumulation of thermally insulating dust and debris on the motors  30 ,  32  further limiting the heat removing capacity of the forced air system  40 . A larger blower may help increase the air flow through the compartment  26 , but this results in increased manufacturing and operating costs of the lift truck  12 . Further, a larger blower would introduce even more dust and debris into the compartment  26  perhaps negating the effect of the larger blower. 
     Accordingly, a need exists for a motor cooling system that effectively and efficiently cools motors located in small enclosed spaces, such as found in a material handling vehicle with an ergonomically designed operator compartment. The present invention addresses these issues. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a method of operating a material handling vehicle having an operator compartment and a motor compartment with at least one heat generating component inside, the method comprising the steps of directing cooling air into through the motor compartment in a generally helical manner to create a cyclonic air flow, resulting in a vortex effect, to efficiently cool the heat generating components when the vehicle is enabled for operation. 
     This and other aspects of the present invention will be apparent from the following description. In the Detailed Description section, preferred embodiments of the invention will be described in reference to the accompanying drawing figures. These embodiments do not represent the full scope of the invention. Rather the invention may be employed in other embodiments. Reference should therefore be made to the Claims section for interpreting the breadth of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 , already described, is a perspective view of an operator compartment and motor compartment with a conventional motor cooling system for a material handling vehicle; 
         FIG. 2 , already described, is a cross sectional side view of the motor compartment of  FIG. 1  taken along line A-A showing a point-to-point forced air cooling system; 
         FIG. 3  is a perspective view of an operator compartment and motor compartment with a cyclonic motor cooling system for a material handling vehicle; 
         FIG. 4  is a cross sectional side view of the motor compartment of  FIG. 3  taken along line B-B illustrating a first embodiment of a cyclonic motor cooling system constructed in accordance with the present invention; 
         FIG. 5  is a cross sectional top view of the motor compartment of  FIG. 3  taken along line C-C; and 
         FIG. 6  is a cross sectional side view of the motor compartment of  FIG. 3  taken along line B-B illustrating a second embodiment of a cyclonic motor cooling system constructed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring generally to  FIGS. 3-5  a material handling vehicle  12  constructed in accordance with the present invention includes an operator compartment  10  and a motor compartment  126  provided with a cyclonic motor cooling system  140 . The motor compartment  126  is defined on the bottom by a lift truck chassis  134 , on the sides by a generally cylindrical wall  136 , and on the top by a cover  138 . An air injection port  142  coupled to a blower  146  is disposed low in the wall  136  of the motor compartment  126  and an exhaust port  144  is disposed high in the wall  136  and generally radially disposed from the injection port  142 . A generally annular enclosed space  152  of the motor compartment  126  is defined by an inner surface  145  of the cylindrical wall  136  and the outer surfaces of the motors  30 ,  32 . 
     The cyclonic motor cooling system  140  cools the motors  30 ,  32  more efficiently than the conventional forced air motor cooling system  40  by, among other things, providing a cyclonic, i.e., having a helical profile, cooling air flow within the air space  152  of the motor compartment  126 . Cooling air flowing in a helical path, indicated by arrows  148 , cools the motors  30 ,  32  more efficiently than the conventional cooling system  40  for a number of reasons. One such reason is that the increased cooling air velocity and motor surface contact provided by the helical profile allows for more convective cooling of the motors  30 ,  32 . A further reason is that the cyclonic cooling air flow, causes a vortex effect within the compartment  126 , and thus allows for convective cooling of motor surfaces shielded from linear cooling air flow. Still further, the increased velocity and centripetal forces of the cyclonic cooling air keep thermally insulating dust and debris away from the motors  30 ,  32 , thus maximizing the convective cooling effect of the cyclonic cooling air. 
     With reference to the common operation of both cyclonic motor cooling systems  140 ,  240  illustrated in  FIGS. 4 and 6 , respectively, the motor compartment  126  receives a stream of cooling air from the blower  146  substantially tangential with the cylindrical wall  136  via the air injection port  142 . The cooling air is redirected from a linear tangential flow, represented by an arrow  147 , into a laminar cyclonic flow (i.e., following the helical path  148 ) via, e.g., a scoop-shaped channel  154  and helical air aligners  158  ( FIG. 4 ) or a baffle cylinder  160  with vanes  162  ( FIG. 6 ). 
     The cyclonic cooling air travels upwardly through the annular space  152  following the generally helical-shaped path  148  around the motors  30 ,  32 . Because of the helical flow profile,  148 , the cyclonic cooling air has greater axial and circumferential contact with the motor surfaces, minimizing the motor surface areas shielded from the cooling air. The cyclonic cooling air causes a vortex effect within the compartment  152 , resulting in an additional, linear cooing air flow following a vertical path, represented by arrows  149 , about the central axis of the compartment  152 . The additional cooling air flow  149  created by the vortex effect transfers heat away from portions of the motors  30 ,  32  shielded from the cyclonic cooling air. Heated cooling air is discharged into the surrounding environment through the exhaust port  144 , having a similar scoop-shaped channel  156  formed in the wall  136 . 
     Dust and debris carried into the motor compartment  126  by the cooling air flow or already present in the compartment  126  is directed away from the motors  30 ,  32  by the centripetal force of the cyclonic cooling air and carried out of the exhaust port  144  due to the velocity of the cooling air. Thus, the insulating dust and debris does not accumulate on the motors  30 ,  32 , permitting still greater convective cooling of the motors  30 ,  32  by the cooling air, as well as improving motor cleanliness and bearing life. In applications where less cooling air is needed due to the increased cooling efficiency of the cyclonic motor cooling system  140 , a further benefit is that less dust and debris is introduced into the compartment  126  than with a similar-sized conventional cooling system  40 . 
     With specific reference to  FIGS. 3-5 , a first embodiment of the cyclonic motor cooling system  140  is shown. A number of helical air aligners  158 , or alternatively, a continuous helical baffle  158 , extend axially upwardly throughout the compartment  126 . The helical air aligners  158  extend radially inwardly from the inner surface  145  of the wall  136 , at an acute angle Θ, to form spiral cooling air channels  159  therebetween. The spiral channels  159  direct the cooling air vertically towards the exhaust port  144  and help maintain the helical flow path  148  of the cyclonic cooling air. 
     A variety of factors are taken into consideration in designing the appropriate air aligner  158 /cooling channel  159  arrangement to ensure that the cyclonic cooling system  140  has the capacity to adequately cool the motor compartment  126 . Environmental factors affecting the cooling capacity include the size of the motor compartment  126 , amount of heat generated by the motors  30 ,  32 , and the temperature of lift truck operating environment. Structural factors affecting the cooling capacity include the radial width of the air aligners  158 , the axial width of the channels  159  formed by the air aligners  158 , and the vertical distribution of the air aligners  158  between the air injection port  142  and the exhaust port  144 . 
     With specific reference to  FIG. 6  now, a second embodiment of the cyclonic motor cooling system  240  is shown. The cyclonic cooling system  240  includes an upwardly extending baffle cylinder  160  circumferentially disposed about the inner surface  145  of the motor compartment  126 . The baffle cylinder  160  receives the linearly or tangentially directed cooling air from the air injection port  144  and redirects the cooling air circumferentially. The cooling air is deflected axially upwardly as it travels circumferentially through the cylinder  160 . The cooling air is given a helical swirling motion as it flows past a number of inclined deflector vanes  162  arranged at the upper end of the baffle cylinder  160 . 
     Thus, the cyclonic motor cooling systems  140 ,  240  provide more effective heat removal from motor compartments  126 , reducing the need for larger blowers or other types of cooling system, e.g., liquid cooling, for smaller motor compartments  126 . Those of ordinary skill in the art will understand that the efficacy of the cooling air will depend on a variety of design factors, including, but not limited to the velocity of the cooling air, the shape and volume of the compartment  126 , the orientation and size of the injection and exhaust ports  142 ,  144 , and the like. 
     The two exemplary cyclonic cooling systems  140 ,  240  are illustrated as open loop systems wherein the cooling air is drawn in directly from the surrounding environment and discharged directly back to the surrounding environment. Alternatively, a closed loop system having a heat exchanger (not shown) coupled to the injection port  142  to supply cooled air thereto and to the exhaust port  144  to receive heated air therefrom may be utilized. 
     Temperature or current sensors may be utilized in connection with the motors  30 ,  32  to control the blower  146 , and thus the vortex-induced forced convection of the cooling air, as a function of motor temperature or current draw. For example, the blower  146  may be turned on only when the motor  30 ,  32  temperature is too high, or the current drawn correlates to a large amount of generated heat. Alternatively, a variable speed drive may be provided so as to minimize the total power required under light loads and to increase torque output under heavy loads by being able to momentarily run the motors  30 ,  32  harder without the risk of overheating. 
     Although the material handling vehicle  12  as shown by way of example is a standing or sitting, side stance operator configuration lift truck, it will be apparent to those of skill in the art that the present invention is not limited to vehicles of this type, and can also be provided in various other types of material handling and lift truck configurations. 
     While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that other changes and modifications can be made therein without departing from the scope of the invention as defined by the appended claims.

Technology Classification (CPC): 1