Abstract:
A variable air circulation system for the cab enclosure of an off-highway vehicle is disclosed and described. The system provides for adjustment of the ratio between fresh air circulation and recirculation of cab air. Fresh air is introduced into the cab through a fresh air inlet having a fresh air filter therein. The air inlet leads to a circulation conduit. When a cab door is opened, a valve to the conduit is opened. When the door is closed, the air pulse created in the cab is effective, through the valve, to dislodge dust and dirt from the filter.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is related to co-pending U.S. patent application Ser. No. 11/456,938 entitled “Filter Purge Control For HVAC Fixed Air Circulation System, filed simultaneously herewith on Jul. 12, 2006. 
   BACKGROUND OF THE INVENTION 
   This invention relates in general to off-highway vehicles. It relates particularly to the heating, ventilating and air conditioning (HVAC) system in an off-highway vehicle and, more particularly, to a purge control for the fresh air filter in the HVAC system for an off-highway vehicle. 
   Off-highway vehicles are often operated in extremely dusty environments. As a result, the HVAC systems for off-highway vehicle cabs must employ highly effective fresh air filters to remove dust and other particulate matter before it enters the cab. They frequently use what is known as fresh air filter purging to dislodge dust and other accumulated debris from the fresh air filter medium. Purging the filter causes dirt to be released from the inlet face of the filter medium, thus prolonging the filter service life. 
   Typically, an off-highway vehicle cab is equipped with one of two types of interior air recirculation systems. One is known as a fixed system and the other as a variable system. 
   In a variable system, the relative amounts of fresh air taken in and recirculated air can be varied, i.e., the ratio between fresh air circulation and recirculation of cab air can be adjusted. A variable recirculation system, in a minimum recirculation/maximum fresh air setting, provides the highest cab pressurization and the best dehumidification. When at the maximum recirculation/minimum fresh air setting, filter life is generally extended and the system provides the greatest potential heating and cooling. Modern cab heating and air conditioning systems equipped with Automatic Temperature Control (ATC) are capable of taking advantage of these characteristics and can automatically optimize the ratio of fresh air to recirculated air within the cab, depending on system settings made by the operator, cab temperature at the time and the ambient conditions encountered. 
   In a fixed system, no adjustment of the recirculation opening takes place. One type of fixed system is equipped with at least two blowers, one or more blowers dedicated to pressurizing the cab with outside air and one or more for recirculating air within the cab. A second type of fixed system utilizes one or more blowers, with each blower(s) both pressurizing the cab and recirculating the air within the cab. 
   In any of these systems, fresh air is introduced into the cab through a fresh air filter. In an effort to extend filter life, it is conventional to reverse the air flow direction through the fresh air filter to dislodge the accumulated dust and debris from the filter medium. One method of filter purging takes advantage of the air pressure pulse created inside the cab when the cab door is closed. The pressure pulse momentarily reverses the air flow through the filter, causing dust and dirt to be released from the filter. 
   With existing methods, the effectiveness of the purge is often less than ideal. Furthermore, the operator can experience some undesirable effects. The cabin pressure pulsation associated with the purge can be substantial and may cause operator discomfort. The same pulse also makes closing the cab door more difficult. 
   It would be a distinct advantage to provide a variable air circulation system that overcomes the above-noted shortcomings of the prior art. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide improved fresh air filter purging for the cab HVAC system in off-highway vehicles. 
   It is another object to provide a cab HVAC system for off-highway road vehicles that assures improved cab pressurization and a cleaner cab interior environment. 
   It is still another object to provide increased fresh air filter service life and reduced filter maintenance in the HVAC system for off-highway vehicle cabs. 
   It is yet another object to provide an off-highway vehicle HVAC system for an off-highway vehicle cab wherein cab pressure pulses are optimized, resulting in a more comfortable operator environment. 
   It is a further object to provide an off-highway vehicle HVAC system that reduces cab door closing effort while maintaining an effective filter purge. 
   The foregoing and other objects are realized in either variable or fixed cab air recirculation systems for off-highway vehicles. According to the invention, whether with a variable or fixed system, the fresh air filter is more effectively purged outwardly of the cab each time the cab door is closed. 
   It has been found that filter purging is most effective when air flow restriction between the interior of the cab and the fresh air filter is minimized. Minimum restriction is achieved only when all possible air flow paths from the cab interior to the fresh air filter are optimized. According to the invention, a new path containing a bypass valve, and possibly a bypass duct, is created in the case where a dedicated pressurizer exists. Depending upon the type of cab air system, the invention would automatically have one of the following devices adjusted whenever the cab door is open: the variable recirculation device (in the case of a system without a dedicated pressurizer) or the bypass valve (in the case of a system with a dedicated pressurizer). According to the invention, one or more of these devices is adjusted automatically to its “full open” position whenever the cab door is opened, and remains open until after the cab door is closed. After door closure, the bypass valve closes fully and the recirculation device (in the case of no dedicated pressurizer) resumes the appropriate fresh air/recirculated air setting for the current conditions. 
   Also according to the invention, a signal is sent to the variable recirculation device/bypass valve, with or without the intervention of an ATC system. The signal, which occurs whenever the cab door is open, temporarily sets the variable recirculation vents/bypass valve to the “full-open” position. This ensures maximum purge effect when the cab door is subsequently closed. The best source of this signal is a cab door-activated switch, such as a dome light switch. The recirculation vent/bypass valve could also be temporarily forced to “full-open” by a signal from other sources. These could include (but are not limited to) engine oil pressure, alternator voltage, hydraulic system pressure or engine speed. This temporary opening of the recirculation vent(s)/bypass valve for purging could also be accomplished by means entirely independent of the electrical system. These could include (but are not limited to) a mechanical linkage from the vent(s) directly to the cab door, seat suspension, park brake, or transmission control. 
   For additional purging benefit, according to the invention, the signal to open the variable recirculation device could also shut off the recirculation blower. Shutting off the recirculation blower stops the incoming air flow through the fresh air filter, further enhancing the purging effect. 
   The following applies to the type of fixed cab air recirculation system containing one or more blowers dedicated to pressurizing the cab. This type of fixed system may contain a duct between the fresh-air filter and the pressurizer blower (“fresh air duct”). This type of fixed system would incorporate a path directly from the cab interior to the fresh air duct. Depending on the shape and location of this duct, relative to that of the cab enclosure, the path could simply be comprised of two adjacent openings. One opening would be on the enclosure, while one would be in the fresh air duct. 
   An alternative would be to have a separate duct (“bypass duct”) connecting the cab enclosure to the fresh air duct. In either case, air flow between the cab enclosure and the fresh air duct would be normally prevented by a valve (“bypass valve”). When a bypass duct exists, the bypass valve would be located within, or at either end of, said duct. Otherwise, the bypass valve would be located at or near to the adjacent openings. In either case, the bypass valve would automatically open when the cab is in the purge mode, i.e., when cab door is opened. The air pressure pulse created by the cab door closure causes air to flow through the bypass valve, into the fresh air duct, and onward through the fresh air filter. The bypass valve is triggered by the same purge control signal sources as is the variable recirculation device listed above (dome light, engine oil pressure, etc.). This signal can also shut off the pressurizer blower when in the purge mode. With this design, if the pressurizer blower is shut off when the cab door is opened, the recirculation blower continues to run and supply air flow to the heater and air conditioner evaporator core. This design has the additional advantage of reducing the possibility that the air conditioner evaporator fins freeze with condensate. 
   For a fixed cab air recirculation system containing no dedicated pressurizer blower, the purge control signal would simply shut off the blower(s) until after the cab door is closed to further enhance cab filter purging. 
   For increased purging effectiveness, compatible with any of these systems, the same signal could also open any or all of the air discharge louvers/vents. 
   These and other objects are obtained by providing a variable air circulation system for the cab enclosure of an off-highway vehicle. The system provides for adjustment of the ratio between fresh air circulation and recirculation of cab air. Fresh air is introduced into the cab through a fresh air inlet having a fresh air filter therein. The air inlet leads to a circulation conduit. When a cab door is opened, the recirculation vent is opened. When the door is closed, the air pulse created in the cab is effective, through the recirculation vent, to dislodge dust and dirt from the filter. The dust and dirt falls outside the cab. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, including its construction and method of operation, is illustrated more or less diagrammatically in the drawings, in which: 
       FIG. 1  is a schematic illustration of a fixed cab air HVAC system with dedicated pressurizer blower(s) for an off road vehicle cab incorporating an automatic cab air filter purge system embodying features of the invention; 
       FIG. 2  is a schematic illustration of a variable or fixed cab air HVAC system without dedicated pressurizer blower(s) for an off road vehicle cab incorporating an automatic cab air filter purge system embodying features of the invention; 
       FIG. 3  is a schematic illustration of the purge control  75 ; and 
       FIG. 4  is a schematic illustration of the purge control  175 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, and particularly to  FIG. 1 , the cab of an off-highway vehicle is seen generally at  10 . The cab  10  comprises a cab body  11  including a roof  12  supported on a pair of cab front posts  15 , between which a front windshield  17  is mounted. The roof  12  is supported at its back by cab rear posts  19 . 
   Between front and rear cab posts  15  and  19  on at least one side of the cab body  11 , is a cab access door  22 . Access to the cab  10  for the operator is provided through the door  22 , which is hinged at  23 , and the door is normally closed to provide a substantially dust tight enclosure  25  for the operator. 
   Modern off-highway vehicles generally have HVAC systems. Such a system conventionally takes one of two forms; either a fixed fresh air/recirculated air system or a variable fresh air/recirculated air system. A fixed fresh air/recirculated air system may or may not be equipped with a dedicated pressurizer blower(s). The cab  10  illustrated in  FIG. 1  depicts a fixed air system  30  with a dedicated pressurizer blower  61 . 
   The fixed air system  30  in the cab  10  is mounted in the cab roof  12  between the outer roof shell  32  and the inner headliner  34 . The system  30  distributes a combination of fresh air and recirculated air through a distribution plenum  41  over the windshield  17 . It takes in fresh air through a fresh air inlet port  43  formed in the roof  12  under a rear overhang  45  of the roof. As one of skill in the art would understand, the inlet and outlet can be positioned in other locations, those shown in the figures being the most effective for a cab of the general design depicted. 
   The system  30  comprises a recirculation blower  47  mounted over the plenum  41 ; the blower  47  is connected by an air conduit  48  to a heating and air conditioning core housing  52  adjacent to the blower. 
   The heating and air conditioning core housing  52  is connected, through a main air conduit  55  in the roof  12  above the headliner  34 , with the pressurizer blower  61 . The pressurizer blower  61  is, in turn, connected by a fresh air duct  63  to the fresh air inlet port  43 . Mounted over the inlet port  43 , between it and the duct  63 , is a cab fresh air filter  65 . 
   In the headliner  34 , connected to the conduit  55 , is a recirculation air louver  67 . Also, in the headliner  34 , above the rear posts  19 , is a fresh air bypass valve  70 . According to the invention, the bypass valve  70  is opened and closed by a purge control  75  to place the enclosure  25  of the cab  10  in communication with the fresh air duct  63  and, as such, with the air filter  65 . 
   The purge control  75  includes, in the embodiment illustrated (see  FIG. 3 ), a dome light circuit  77  in the cab enclosure  25 . When the operator opens the door  22 , a door-actuated switch  76  closes and current is directed to the dome light circuit  77 , which includes a dome light  78 . According to the invention, the dome light circuit  77  is also connected to an actuator  79  for the normally closed bypass valve  70 . Opening of the cab door  22  causes, according to the invention, the actuator  79  to open the bypass valve  70 . 
   The dome light circuit  77  is also connected to a relay  83  for the pressurizer blower  61 . Current in the circuit  77  activates the relay  83 , shutting off the blower  61 . The recirculation blower  47  may continue to run so that the HVAC core receives air flow. 
   When the operator closes the door  22 , an air pressure pulse is created in the enclosure  25 . This causes air to flow through the by-pass valve  70  into the fresh air duct  63  and outwardly through the filter  65 . Dust and dirt are dislodged outwardly. The dome light circuit  77  is subsequently opened, causing both the actuator  79  and the relay  83  to revert to their normal states. The result is a closing of the bypass valve  70  and resumption in operation of the blower  61 . According to the invention, for this type of HVAC system, when the door  22  is opened, the purge control  75  may also open any or all air discharge louvers/vents  71 . 
   Referring now to  FIG. 2 , the cab of another off-highway vehicle is seen generally at  110 . The cab  110  includes a body  111  having a roof  112  supported on a pair of cab front posts  115 , between which a front windshield  117  is mounted. The roof  112  is supported at its back by cab rear posts  119 . Between front and rear cab posts  115  and  119  is a cab access door  122 . The door  122  is hinged at  123 , and the door is normally closed to provide a substantially dust tight enclosure  125  for the operator. 
   The cab  110  illustrated in  FIG. 2  is equipped with a variable or fixed air HVAC system  130 , without a dedicated pressurizer blower. The variable air system  130  in the cab  110  is also mounted in the cab roof  112  between the outer roof shell  132  and the inner headliner  134 . The system  130  distributes a combination of fresh air and recirculated air through a distribution plenum  141  over the windshield  117 . It takes in fresh air through a fresh air inlet port  143  formed in the roof  112 , under a rear overhang  145  of the roof. 
   The system  130  comprises a blower  147  mounted over the plenum  141 . The blower  147  is connected by an air conduit  148  to a heating and air conditioning core housing  152  adjacent to the blower. 
   The heating and air conditioning core housing  152  is connected, through a main air conduit  155  in the roof  112  above the headliner  134 , with the fresh air inlet port  143 . Mounted over the inlet port  143 , between it and the conduit  155 , is a cab fresh air filter  165 . 
   In the headliner  134 , connected to the conduit  155 , is a recirculation air louver  167 . The louver  167  may be allowed to move incrementally between fully open and fully closed positions. This movement may be accomplished manually, or automatically by means of an electronic control system (e.g., an ATC system). In the latter case, the purge control ( FIG. 4 ) may be a part of, or work closely with, the electronic control system. 
   When the HVAC system  130  is set for maximum recirculation/minimum fresh air, the fresh air filter  165  life is generally extended. 
   Both systems, fixed and variable, may use pressurization as described with reference to blower  61 . Further, if used, the pressurization may be selectively activated or deactivated as an operational function of the controls. The inclusion or non-inclusion of an ATC is an additional variable that adds to the overall design flexibility afforded by the invention disclosed and claimed herein. 
   The purge control includes, in the embodiment illustrated (see  FIG. 4 ), a dome light circuit  177  in the cab enclosure  125 . When the operator opens the door  122 , a door-actuated switch  176  closes and current is directed to the dome light circuit  177 , which includes a dome light  178 . According to the invention, for an HVAC system without dedicated pressurizer, this circuit is connected to an actuator  179  for the recirculation louver(s)  167 . Opening the cab door  122  causes the actuator  179  to fully open the recirculation louver(s)  167 , for as long as the door remains open. The signal may also, according to the invention, activate a relay  183 , automatically shutting off the recirculation blower  147  until the cab door is again closed. 
   When the operator closes the door  122 , an air pressure pulse is created in the enclosure  125 . This causes air to flow through the recirculation louver(s)  167  and outwardly through the filter  165 . Dust and dirt are dislodged outwardly. The dome light circuit  177  is subsequently opened, causing the actuator  179  and, optionally, the relay  183  to resume their normal states. The result is that the recirculation louver(s)  167  reverts to its normal setting, based on current cab conditions. If the blower  147  was shut off (optional), it now also resumes operation. 
   The drawings show optional additional actuators  79 A and  179 A which could be used to control second louvers or bypass valves in alternative system embodiments employing such second components. It is, however, possible to control more than one louver or bypass valve with a single actuator, such as  79  or  179 . 
   According to the invention, for this type of HVAC system, when the door  122  is opened, the purge control may also automatically open any or all air discharge louvers/vents  171 . 
   A time delay device  180  is provided to delay the time period between closure of the cab door and turning on the blower  147 . 
   It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the inventions. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown.