Abstract:
An exchangeable air-conditioning unit ( 1 ) is described for attachment to mobile equipment. The air-conditioning unit includes a compressor ( 5 ) operable to compress a refrigerant and a hydraulic motor ( 17 ) operable to drive the compressor. Hydraulic fittings ( 11 ) are provided in fluid communication with the hydraulic motor for transporting hydraulic fluid. The hydraulic fittings ( 11 ) are adapted to be releasably connected to a hydraulic system of the mobile equipment. Refrigerant fittings ( 7 ) are provided in fluid communication with the compressor for transporting refrigerant. The refrigerant fittings ( 7 ) are adapted to be releasably connected to a refrigeration circuit of the mobile equipment. An enclosure ( 3 ) houses the compressor and hydraulic motor and has at least one releasable connector ( 21 ) for releasably connecting the enclosure to the mobile equipment. The exchangeable unit may be pre-charged with gas in and stored in readiness for attachment to the mobile equipment.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to air-conditioning systems and, in particular, to air-conditioning systems for use in mobile plant. 
       BACKGROUND OF THE INVENTION 
       [0002]    Mobile plant such as haul trucks, loaders, dozers, shovels and draglines frequently operate in dirty or hazardous environments. Consequently, air-conditioning is generally required for the comfort and safety of personnel operating the mobile plant. The capital cost of the equipment may be large and there is a need to utilise the mobile plant productively, since the mobile plant may have a direct impact on the production capability of sites where the mobile plant is used. 
         [0003]    Experience at a site using a fleet of twelve large trucks has shown that one of the trucks was effectively out of use at any one time due to air-conditioning issues. Maintenance of air-conditioning systems may require input from skilled technicians, who may not be immediately available when the mobile plant is operated in remote locations. 
         [0004]    There is accordingly an on-going need to reduce the down-time of mobile plant due to maintenance issues. 
       SUMMARY OF THE INVENTION 
       [0005]    According to a first aspect of the invention there is provided an exchangeable air-conditioning unit for attachment to mobile equipment, the air-conditioning unit comprising: 
         [0006]    a compressor operable to compress a refrigerant; 
         [0007]    a hydraulic motor operable to drive said compressor; 
         [0008]    hydraulic fittings in fluid communication with said hydraulic motor for transporting hydraulic fluid, wherein said hydraulic fittings are adapted to be releasably connected to a hydraulic system of the mobile equipment; 
         [0009]    a first enclosure that houses said compressor and said hydraulic motor and has at least one releasable connector for releasably connecting the enclosure to the mobile equipment. 
         [0010]    Preferably the air-conditioning unit comprises at least one refrigerant fitting in fluid communication with said compressor for conveying refrigerant, wherein said refrigerant fittings are adapted to be releasably connected to a refrigeration circuit of the mobile equipment. 
         [0011]    In one arrangement, said air-conditioning unit further comprises a condenser arranged to receive compressed refrigerant from said compressor. 
         [0012]    The air-conditioning unit may comprise a second refrigerant fitting in fluid communication with said condenser for conveying refrigerant, wherein said second refrigerant fitting is adapted to be connected to the refrigeration circuit of the mobile equipment. 
         [0013]    The air-conditioning unit may further comprise an evaporator in fluid communication with said compressor and said condenser. 
         [0014]    In one arrangement the air-conditioning unit comprises a second enclosure that houses said condenser and said evaporator. 
         [0015]    The air-conditioning unit may comprise at least one quick-connect refrigerant fitting that, in use, provides fluid communication for refrigerant between the first housing and the second housing. 
         [0016]    The air-conditioning unit may comprise a centrifugal fan operable to blow air past said condenser. 
         [0017]    Preferably the at least one refrigerant fitting comprises:
       a valve assembly having a plurality of valves that, when closed, define a closed chamber within said valve assembly; and   a vacuum arrangement operable to remove refrigerant from the closed chamber.       
 
         [0020]    Preferably the valve assembly comprises a seal to limit the escape of refrigerant from the valve assembly. 
         [0021]    Also described herein is a refrigerant fitting for releasably connecting a first section of a refrigerant circuit to a second section of the refrigerant circuit, the refrigerant fitting comprising:
       a first valve having an open configuration in which a fluid passage is provided for refrigerant flows between the first section of the refrigerant circuit and the refrigerant fitting and a closed configuration in which the first valve prevents refrigerant flow between the first section of the refrigerant circuit and the fitting;   a second valve having an open configuration in which a fluid passage is provided for refrigerant flows between the second section of the refrigerant circuit and the refrigerant fitting and a closed configuration in which the second valve prevents refrigerant flow between the second section of the refrigerant circuit and the fitting;   a first part including said first valve;   a second part including said second valve; said first and second parts having an assembled configuration wherein a chamber is defined between said first valve and said second valve; and   a third valve formed between the chamber and a vacuum arrangement wherein, in use, said first and second valves are placed in the closed configuration and said third valve is opened to enable the vacuum arrangement to draw refrigerant from the chamber.       
 
         [0027]    Preferably the refrigerant fitting comprises a sealing arrangement to provide a seal between the chamber and the atmosphere if said first part and said second part are in the assembled configuration. 
         [0028]    Preferably said first part and said second part are shaped to provide mutually abutting surfaces if said first part and said second part are in the assembled configuration. 
         [0029]    Preferably, said sealing arrangement comprises at least one O-ring. 
         [0030]    Preferably, said refrigerant fitting comprises fastening means to hold said first part and said second parts in place in the assembled configuration. 
         [0031]    According to a further aspect of the invention there is provided a method of separating a first section of a refrigeration circuit and a second section of the refrigeration circuit using the refrigerant fitting described above, the method comprising
       closing said first valve and said second valve;   opening said third valve such that the vacuum arrangement draws refrigerant from the chamber;   closing said third valve; and   separating said first part and said second part to thereby separate the first and second sections of the refrigeration circuit.       
 
         [0036]    According to a further aspect of the invention there is provided a method of connecting a first section of a refrigeration circuit and a second section of the refrigeration circuit using the refrigerant fitting described above, the method comprising:
       placing said first part and said second part in the assembled configuration with said first, second and third valves in the closed configuration;   opening said third valve such that the vacuum arrangement draws air from the chamber;   closing said third valve; and   placing said first and second valves in the open configuration to provide a fluid passageway between the first and second sections of the refrigeration circuit.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]    Embodiments of the invention will now be described with reference to the drawings, in which: 
           [0042]      FIG. 1A  is a schematic diagram of a first embodiment of an exchangeable air-conditioning unit that includes a compressor and a hydraulic motor; 
           [0043]      FIG. 1B  is a schematic diagram showing an end view of the air-conditioning unit of  FIG. 1A ; 
           [0044]      FIG. 2A  is a schematic diagram of a second embodiment of the exchangeable air-conditioning unit that includes a condenser; 
           [0045]      FIG. 2B  is a cut-away end view of the air-conditioning unit of  FIG. 2A ; 
           [0046]      FIG. 3A  is a schematic diagram of a third embodiment of the exchangeable air-conditioning unit that includes an evaporator; 
           [0047]      FIG. 3B  is a cut-away end view of the air-conditioning unit of  FIG. 3A ; 
           [0048]      FIG. 4A  is a schematic diagram of a valve arrangement that may be used in the air-conditioning units of  FIGS. 1A to 3B ; 
           [0049]      FIG. 4B  is a schematic diagram of a male fitting for use in the valve assembly of  FIG. 4A ; 
           [0050]      FIG. 4C  is a schematic diagram of a female fitting that receives the male fitting of  FIG. 4B ; 
           [0051]      FIG. 5A  is a schematic diagram of a further embodiment of the exchangeable air-conditioning unit; and 
           [0052]      FIG. 5B  is a cut-away end view of the air-conditioning unit of  FIG. 5A . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0053]      FIG. 1A  shows an exchangeable air-conditioning unit  1  housed in an enclosure  3  that, in one arrangement, is made of stainless steel and is 60 cm in height and width and 20 cm deep. 
         [0054]    The air-conditioning unit  1  includes an air compressor  5  driven by a hydraulic motor  17 . An example of a suitable air compressor is the Unicla UP 200-4215™ and a suitable hydraulic motor is the Eaton 21301™ or the PLM Casappa 20-11.2 gear motor. The compressor  5  is connected to the motor  17  by a toothed rubber timing-belt  19 . Alternatively the compressor  5  may be driven via a direct drive from the motor  17 . Quick-connect refrigerant fittings  7  are provided on the enclosure  3 , and refrigerant lines  9  transport refrigerant between the quick-connect refrigerant fittings  7  and the compressor  5 . Examples of quick-connect refrigerant fittings that may be used are the Red Dot RD 2-0872-0P for the low-pressure side and the Red Dot RD-2-0871-0P on the high-pressure side. 
         [0055]    In use, the quick-connect refrigerant fittings  7  are connected to piping (not shown) that leads to the remaining components of a refrigeration circuit, including a condenser and an evaporator, mounted elsewhere on the mobile plant on which the air-conditioning unit  1  is used. Mobile plant on which the air-conditioning unit  1  may be used includes, but is not limited to, mobile mining or earthmoving equipment, locomotives, cranes, tractors and harvesters. 
         [0056]    The hydraulic motor  17  may be driven using the existing hydraulic system of the mobile plant. The enclosure  3  is provided with two quick-connect hydraulic fittings  11  and hydraulic lines  13  connect the hydraulic motor  17  to the hydraulic fittings  11 . The flow of fluid through the hydraulic lines  13  is controlled by a solenoid-operated directional control valve (DCV)  15 . The hydraulic circuit may include a flow control valve that is adjustable during commissioning to set the compressor speed. The hydraulic motor  17  may run at hydraulic pressures typically found in mobile plant, which are generally in the range of 2000-3000 psi. The air-conditioning unit may include a pressure relief valve to protect the hydraulic motor  17 . 
         [0057]    In use the hydraulic fittings  11  are connected to the hydraulic circuit of the mobile plant. In one arrangement Pirtek™ quick-connect hydraulic fittings are used. 
         [0058]      FIG. 1B  shows an end view of the enclosure  3 , the refrigerant quick-connect fittings  7  and the hydraulic quick-connect fittings  11 . The enclosure has quick-connect fasteners  21  that are used to attach the air-conditioning unit  1  to the mobile plant. The quick-connect fasteners  21  may be over-centre type clamps. The air-conditioning unit  1  may, for example, be attached to the outside of an operator&#39;s cabin in the mobile plant. The air-conditioning unit  1  may be disconnected and exchanged for a replacement unit in approximately 5 minutes without the need for specialised tools or the input of a specifically trained tradesperson. 
         [0059]    The air-conditioning unit  1  may be tested and pre-charged with gas according to predefined specifications. A supply of ready-to-use air-conditioning units may then be kept at an appropriate location. If an air-conditioning unit currently attached to the mobile plant no longer works adequately, the unit may be replaced with a ready-to-use unit from the supply. 
         [0060]    In operation, the compressor  5  may be driven by hydraulic pressure derived from the mobile plant&#39;s auxiliary hydraulic system. The hydraulic motor  17  runs continuously whilst a hydraulic pump (not shown) supplies hydraulic fluid via the hydraulic lines  13 . The hydraulic motor  17  may be turned off by activating the solenoid-operated control valve  15 . 
         [0061]      FIG. 1A  does not show the control wire connections to the DCV  15  and compressor  5 . The enclosure  3  is provided with fittings that enable the control wires to be quickly connected to the air-conditioning unit  1 . 
         [0062]    The refrigerant circuit may be protected by both high pressure (HP) and low pressure (LP) safety switches. These safety switches shut down the unit  1  should their respective setpoints be reached. Indicator lamps are provided in unit  1  for both switches. The LP lamp is an alarm indicating a loss of system pressure. The HP lamp is for indication only and shows when the unit  1  has cycled off due to high pressure. Whilst the HP switch does offer system control, the primary temperature control may be a thermostat located in the cab. This may control both the solenoid of DCV  15  and the condenser fan. 
         [0063]    The electrical box (not shown) located in the compressor housing  3  contains the necessary wiring and controls for the A/C system including circuit protection, relays and switches. A single 24v 30 amp supply from the main switch board of the mobile plant may enter the housing  3  and is distributed to the compressor  5 , and DCV  15 . In some arrangements the power is also supplied to a condenser and evaporator. Heavy duty Multipin IP64 rates plugs may be fitted to the compressor housing  3  to facilitate quick electrical connection and disconnection. 
         [0064]    The compressor  5  may have a clutch (not shown) that is controlled by a thermostat switch dependent on temperature in a designated location, typically the operator&#39;s cabin. When the temperature in the cabin rises above a set level, the thermostat switch triggers, sending a control signal to engage the compressor clutch. The refrigerant is then circulated through the refrigeration circuit in a fashion similar to a standard automotive air conditioning system. Alternatively, the compressor  5  may be controlled by the thermostat operating the solenoid DCV  15 . 
         [0065]    The refrigerant exits the compressor  5  as a superheated vapour. Elsewhere in the circuit, a condenser removes heat from the vapour and causes the vapour to condense into a liquid. The liquid refrigerant then passes through an expansion valve that causes flash evaporation of the refrigerant. After the expansion valve, the refrigerant passes through an evaporator. Warm air, for example from the operator&#39;s cabin, is cooled by being blown across the evaporator. From the evaporator the refrigerant is returned to the compressor  5 , completing the cycle. 
         [0066]      FIG. 2A  shows an exchangeable air-conditioning unit  100  that includes both a compressor and a condenser. 
         [0067]    The air-conditioning unit  1  includes compressor  5 , belt drive  19 , hydraulic motor  17  and solenoid-operated directional-control-valve  15  that operate substantially as described with reference to  FIG. 1A . In addition, the air-conditioning unit  100  includes a condenser  113  and a centrifugal fan  115  that blows air over the condenser  113  via ducting  117 . The centrifugal fan  115  may also be driven by the belt drive  19 . Alternatively, the fan  115  may be driven by a second hydraulic motor (not shown). 
         [0068]    The hydraulic lines  13  and quick-connect fittings  11  are arranged in substantially the same way as in the air-conditioning unit  1 . However, the refrigerant lines are arranged to accommodate the condenser  113 . The refrigerant quick-connect fitting  7   b  is connected to the compressor  5  by refrigerant line  9 . Refrigerant flows from the compressor  5  to the condenser  113  via refrigerant line  111 . From the condenser  113 , refrigerant line  109  leads to the refrigerant quick-connect fitting  7   a . External refrigerant lines (not shown) convey the refrigerant from fitting  7   a  to the expansion valve and the evaporator used to cool the air-conditioned space. 
         [0069]      FIG. 2B  shows a cut-away end view of the air-conditioning unit  100 , sectioned along line A-A, and showing the fan  115 , ducting  117  and condenser  113 . The air-conditioning unit  100  may be housed in two enclosures  103 ,  130  which are preferably made of stainless steel. The enclosures  103 ,  130  have quick-connect fasteners  21  to attach the air-conditioning unit  100  to the mobile plant. The overall volume of enclosures  103  and  130  is generally larger than enclosure  3  to accommodate the condenser  113 . In one configuration the enclosures measure 90×60×20 cm. 
         [0070]    The compressor  5 , hydraulic motor  17 , DCV  15  and fan  115  are positioned in housing  130 , and the condenser  113  is positioned in housing  103 . A quick-connect refrigerant fitting is placed in line  111 , enabling the housings  103 ,  130  to be separated. It is likely that the components in housing  130  will require maintenance more often than the condenser  103 . Accordingly, housing  130  is likely to be detached and replaced more often than housing  103 . 
         [0071]    Alternatively, a single housing may be used instead of the two housings  103 ,  130 . 
         [0072]      FIG. 3A  shows an air-conditioning unit  200  that includes a compressor, a condenser and an evaporator. The air-conditioning unit  200  has an enclosure  203  that contains compressor  5 , drive belt  19 , hydraulic motor  17 , DCV  15 , centrifugal fan  115  and condenser  113  configured substantially as described in the arrangement of  FIG. 2A . In use, refrigerant flows from the compressor  5  to the condenser  113  through refrigerant line  211 . From the condenser  113  the refrigerant flows to the evaporator  202  via refrigerant line  213 . From the evaporator  202  there is a further refrigerant line (not shown) that returns the refrigerant to the compressor, completing the cycle. Thus, the entire refrigeration circuit is included in the air-conditioning unit  200  and there is no need for refrigerant quick-connect fittings  7 . 
         [0073]    Alternatively, the air-conditioning unit  200  may be housed in two separate modules. A module  230  contains the compressor  5  and hydraulic motor  17 , and a second module includes the condenser  113  and evaporator  202 . In this case quick-connect refrigerant fittings are used to connect refrigerant lines in the module  230  and the second module. Such an arrangement is illustrated in  FIGS. 5A and 5B . A motivation for using the two modules is that the items in the module  230  (e.g. fan  115 , compressor  5  and motor  17 ) are more likely to require servicing or replacement than the condenser and evaporator. 
         [0074]      FIG. 3B  shows a cut-away view of the enclosure  203  sectioned along line A-A. Evaporator  202  is mounted to an external surface of the enclosure  203 . The quick-connect fasteners  21  are provided on the same external surface. When the air-conditioning unit  200  is attached to the mobile plant using fasteners  21 , the evaporator  202  is positioned in a corresponding cavity in the mobile plant in or adjacent to the operator&#39;s cabin. Air may be cooled by being blown across the evaporator  202 . The expansion valve is located adjacent to the inlet of evaporator  202 . 
         [0075]    One disadvantage of the exchangeable air-conditioning units shown in  FIGS. 1A to 2B  is that a small amount of refrigerant may escape while a unit is being connected or disconnected.  FIGS. 4A to 4C  show a valve assembly that may be used to limit the escape of refrigerant. The valve assembly  300  may optionally be used as the refrigerant quick-connect fitting  7 . 
         [0076]    The valve assembly  300  includes a female fitting  304 , valves  314  and  318  and vacuum canister  320 , which are all mounted on or within the enclosure 3,103,203 of the air-conditioning unit. A male fitting  302  connects to the external refrigerant lines and, during assembly, is fitted into the female fitting  304  of the valve assembly  300 . 
         [0077]    As most clearly seen in  FIG. 4C , the female fitting  304  has a generally cylindrical shape, at one end of which the internal valve  310  is positioned. The end of the female fitting  304  opposite internal valve  310  is open to the atmosphere if male fitting  302  is not inserted. Captive nut  306  is provided at the open end of female fitting  304  and is arranged to receive a complementary threaded fitting  330  of the male fitting  302 . 
         [0078]    Two annular grooves are defined on an internal surface of the female fitting  304 . An O-ring  308  is positioned in each of the grooves. When the male fitting  302  is inserted into the female fitting  304 , a surface  332  of the male fitting  302  presses against the O-rings  308  to form a seal that prevents refrigerant from escaping between the male and female fittings. 
         [0079]    From the internal valve  310  a refrigerant line  312  leads to the valve  314  that, in turn, connects to one of the refrigerant lines  9 ,  109  internal to the air-conditioning unit. The refrigerant line  312  has a side branch  316  that leads to valve  318  and vacuum canister  320 . When the valve assembly is assembled, the lines  312  and  316  define a chamber within valve assembly  300  that may be isolated from the first (internal) and second (external) sections of the refrigeration circuit. 
         [0080]    At one end of the male fitting  302  there is hole  336  that is sealed by the spring-operated non-return valve  334 . The valve  334  includes a ball that is pressed against the housing of the male fitting  302  to seal the hole  336 . When the male fitting  302  is positioned in the female fitting  304 , a protruding portion of the internal valve  310  passes through the hole  336  and displaces the ball of valve  334  to create a passageway for the refrigerant to flow between the male fitting  302  and the female fitting  304 . 
         [0081]    The following procedure may be followed when a user disconnects the air-conditioning unit. 
         [0000]    a) The user closes valve  314  to seal refrigerant within the air-conditioning unit.
 
b) The user undoes nut  306  and partially retracts the male fitting  302 . The spring-operated valve  334  then closes hole  336 , sealing the refrigerant present in the external portion of the refrigeration circuit. In this step the male fitting  302  remains within the female fitting  304  and the O-rings  308  still provide a seal between the surface  332  and the female-fitting  304 . At this stage a small volume of refrigerant is trapped in the refrigerant lines  312  and  316 , which define a closed chamber.
 
c) The user opens valve  318  and the trapped refrigerant in refrigerant line  312  is drawn into vacuum canister  320 .
 
d) Next, the user closes valve  318  and withdraws the male fitting  302  from the female fitting  304 , completing the disconnection of the valve assembly  300 .
 
         [0082]    To connect a new air-conditioning unit using the valve assembly  300 , a user follows the following procedure. 
         [0000]    i) The user inserts the male fitting  302  into the female fitting  304  until a shoulder of threaded portion  330  contacts the captive nut  306 . In this configuration the O-rings  308  provide a seal between the female fitting  304  and the surface  332 . The hole  336  is still sealed by the spring-operated valve  334  and thus refrigerant is still sealed in the external portion of the refrigerant circuit.
 
ii) The user opens and then closes valve  318 , removing air from the refrigerant line  312 .
 
iii) The user tightens captive nut  306 . This has the effect of fixing the male fitting  302  in place within the female fitting  304  and also urges the male fitting against the internal valve  310 . The internal valve  310  protrudes though hole  336 , displacing the ball of valve  334  and creating a passage for refrigerant to flow into refrigerant line  312 .
 
iv) The user opens valve  314 , permitting refrigerant to flow between refrigerant line  312  and refrigerant lines internal to the air-conditioning unit.
 
         [0083]    The vacuum canister may be evacuated via the quick-connect fittings, i.e. through the female fitting  304  with valve  318  open and valve  314  closed. 
         [0084]      FIGS. 5A and 5B  show a further embodiment  400  of the exchangeable air-conditioning unit. The unit  400  has a first housing  433  that contains the compressor and motor, and a second housing  435  that contains the condenser  113  and evaporator  202 . It is likely that the contents of housing  433  will require replacement more frequently than the contents of housing  435 . 
         [0085]    The depicted air-conditioning unit  400  uses a combined hydraulic motor and compressor unit  405 . Suitable direct-drive units are available from Red Dot Corporation. In operation, hydraulic fluid is pumped into housing  433  via quick-connect hydraulic fitting  11   a  and hydraulic line  13 . DCV  15  and flow control valve  407  are positioned in hydraulic line  13  to set the flow of hydraulic fluid. In use, a thermostat in the cabin of the mobile plant switches the hydraulic motor in unit  405  on and off by sending a signal to the solenoid-operated DCV  15 . 
         [0086]    From the combined motor/compressor  405 , the hydraulic fluid flows via line  409  to hydraulic motor  415 , which drives the centrifugal fan  115 . From the motor  415 , the hydraulic fluid flows out of the housing  433  via line  413  and quick-connect fitting  11   b.    
         [0087]    The fan  115  draws air through air-intake duct  419  and blows the air through air-supply duct  427  into housing  435 , where the blown air cools the condenser  113 . An air-intake screen  417  may be placed in front of air-intake duct  419  to filter particles from the air. Fan  115  may supply air to both the condenser  113  and the evaporator  202 . The fan  115  may be a twin-scroll type fan with independent air-flow to each coil. As an alternative, two independently-driven fans may be used. 
         [0088]    The compressor in unit  405  compresses refrigerant, which flows via line  423  to quick-connect fitting  421  arranged between the housing  433  and  435  and enabling refrigerant to flow to condenser  113 . From the condenser, line  429  transports the refrigerant to the evaporator  202 . Air passing over the evaporator  202  may be used to cool air in the required portions of the mobile plant. From the evaporator  202 , the refrigerant flows via a quick-connect fitting into refrigerant line  425  in housing  433  and is returned to the motor/compressor unit  405 , completing the refrigeration cycle. 
         [0089]    Air passing over the condenser  113  leaves the housing  435  via the condenser outflow screen  431 . 
         [0090]    The physical shape of housing  435  matches the configuration of the mobile plant such that the evaporator  202  is positioned to cool the required space within the mobile plant. The housing  435  and housing  433  have abutting surfaces accommodating the quick connect bulkhead fittings  421  that enable refrigerant to flow between the housings  433 ,  435 . The abutting surfaces also accommodate airflow from the fan  115  through duct  427  into housing  435 . One of the housings may have a rectangular hole that receives a complementary duct flange formed in the other housing. 
         [0091]    In the drawings, like numerals are used to refer to similar features. 
         [0092]    It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention. 
         [0093]    It will also be understood that the term “comprises” (or its grammatical variants) as used in this specification is equivalent to the term “includes” and should not be taken as excluding the presence of other elements or features.