Abstract:
An air cleaner assembly includes a housing having an outer wall defining an air flow inlet, an air flow outlet and a hollow interior section. The housing is openable for service access to the interior section. A serviceable and selectively removable filter cartridge is positioned in the housing. The filter cartridge includes filter media surrounding an open central interior. A pulse jet distribution arrangement communicates with the interior of the housing and includes a device configured to direct a pulse of compressed gas into the interior of the filter cartridge. An evacuation valve arrangement is mounted to the housing to receive ejected dust from the filter cartridge and direct the received ejected dust out of the housing. The valve arrangement includes a frame, a blocking element mounted for reciprocation in relation to the frame and a biasing element for urging the blocking element into a closed position.

Description:
[0001]    The instant application is a continuation-in-part of U.S. application Ser. No. 13/832,519 which was filed on Mar. 15, 2013 and is still pending. That application is a continuation-in-part of U.S. application Ser. No. 13/748,406, which was filed Jan. 23, 2013 and is now abandoned. That application was, in turn, a continuation of U.S. application Ser. No. 12/924,352, filed Sep. 24, 2010 and issued on Feb. 26, 2013 as U.S. Pat. No. 8,382,870. The subject matter of each of the patent and the several applications is incorporated hereinto by reference in its entirety. 
         [0002]    This disclosure relates to a self-cleaning air filter, and, in particular, a self-cleaning air filter for vehicles and motorized equipment. 
     
    
     BACKGROUND 
       [0003]    Operating in dusty environments has long been a problem for equipment and vehicles. The respiration of dusty and contaminated air greatly hinders performance and can damage the vehicle or equipment&#39;s engines. Even though vehicles and equipment have filter elements that filter the inlet air flow, in extremely dusty environments, these filter elements quickly become caked with dust and debris, which retards and stops the air flow through the filter element to the engine. Consequently, these filter elements must be frequently cleaned to remove the deeply imbedded dust which penetrates into the filter element or the entire filter element must be replaced to ensure the proper operation of the equipment and vehicles. In extremely dusty environments, the demand of constantly cleaning and/or replacing filter elements comes at a significant cost of time and money. 
         [0004]    A technique commonly referred to as “pulse jet” or “reverse pulse” self-cleaning has been used in industrial and large scale air filtration systems. Reverse pulse self-cleaning involves periodically releasing a quick burst (“pulse”) of compressed air into the filter element, which expands through the filter element in the opposite direction of the normal airflow through the filter element. The rapidly expanding compressed air pulse passing out of the filter element dislodges the dust cake collected on the outside of the filter element, as well as some dust which has penetrated into the element pleat. While effective for industrial and large scale air filtration systems, reverse pulse self-cleaning, heretofore, has been inoperable for small air filtration systems, such as those for vehicles and other types of motorized equipment. Reverse pulse self-cleaning works in industrial and large scale air filtration systems because of the sheer volume of the filter housing and the volume of the filter housings in relation to the volume of the filter elements. 
         [0005]    In industrial and large scale applications, multiple arrays of filter elements are disposed within large volume filter housings. These filter housings are spacious enough that the compressed air pulse can propagate through the filter elements to effectively clean them before energy of the pulse dissipates within the filter housing and the pressure differential equalizes returning the system to its normal filtering operation. 
         [0006]    In small scale applications, such as for vehicles and motorized equipment, where space is limited, the filter housings lack the volume in relation to the volume of the filter elements to make reverse pulse self-cleaning operable or effective. In such applications, a single filter element is typically disposed within the limited confines of the filter housing. The filter housings provide little volume around the filter element within which a compressed air pulse can expand and dissipate. Consequently, an expanding compressed air pulse almost instantly equalizes the pressure differential between the inside and outside of the filter element within the filter housing, which prematurely terminates the expansion of the pulse through the filter element. As a result, the effectiveness of the pulse jet self-cleaning action is lost or greatly reduced. 
         [0007]    One issue with cleaning such filters with a compressed air pulse is that adequate air pressure must be exerted through the filter in order to remove or dislodge the dust cake collected on the outside of the filter element. It would therefore be advantageous to provide a pulse jet distribution arrangement which is capable of distributing the air pulse at an adequate pressure so as to dislodge the particulates from the exterior surface of the filter. 
       BRIEF SUMMARY 
       [0008]    In one embodiment the present disclosure relates to an air cleaner assembly comprising a housing including an outer wall defining an air flow inlet, an air flow outlet and a hollow interior section. The housing outer wall includes a side wall. The housing is openable for service access to the hollow interior section. A serviceable filter cartridge is positioned in the housing hollow interior section. The filter cartridge is selectively removable from the air cleaner housing, with the filter cartridge comprising filter media surrounding an open central interior. A pulse jet distribution arrangement communicates with the hollow interior section of the housing. It includes a device configured to direct a pulse of compressed gas into the open central interior of the filter cartridge. An evacuation valve arrangement is mounted to receive ejected dust from the filter cartridge and is adapted to direct the received ejected dust out of the air cleaner housing. The valve arrangement comprises a frame, a blocking element mounted for reciprocation in relation to the frame and a biasing element for urging the blocking element into a closed position. 
         [0009]    In another embodiment of the present disclosure, a self-cleaning air filter assembly which is connected to an associated compressed air source comprises a housing defining a chamber located therein and a hollow filter element disposed within the chamber such that an interior volume is defined within the filter element and an exterior volume is defined between the filter element and an interior wall of the housing. During a filtering cycle, a negative pressure differential between the interior volume and the exterior volume draws airflow inward through the filter element. During a self-cleaning cycle, a positive pressure differential between the interior volume and the exterior volume forces air flow outward through the filter element. A nozzle is configured to direct a pulse of compressed gas into the interior volume of the filter element. A valve in communication with the housing and connected to an associated compressed air source is provided for selectively releasing a pulse of compressed air into the nozzle whereby dust is dislodged from the exterior surface of the filter element into the housing chamber. A vent is mounted to the housing over an opening therein for venting the pulse of compressed air from the housing. The vent comprises a frame, a blocking element mounted for reciprocation in relation to the frame and a biasing element for urging the blocking element into a closed position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The drawings illustrate several embodiments of the present disclosure, in which: 
           [0011]      FIG. 1  is a perspective view, partially broken away, of an air cleaner assembly including an air filter according to a first embodiment of the present disclosure; 
           [0012]      FIG. 2  is an enlarged partial exploded view of the air filter of  FIG. 1  showing a pressure relief valve and a portion of a housing; 
           [0013]      FIG. 3  is an exploded perspective view of the pressure relief valve of  FIG. 2 ; 
           [0014]      FIG. 4  is an assembled side elevational view of the pressure relief valve of  FIG. 3 ; 
           [0015]      FIG. 5  is an end elevational view of the pressure relief valve of  FIG. 4 ; 
           [0016]      FIG. 6  is a side sectional view of the air filter of  FIG. 1  shown during a normal filtering cycle; 
           [0017]      FIG. 7  is a side sectional view of the air filter of  FIG. 6  shown during a cleaning cycle; 
           [0018]      FIG. 8  is a partial perspective view of an exemplary application of the air cleaner assembly of  FIG. 1  used in a typical military style vehicle; 
           [0019]      FIG. 9  is a simple schematic view of the air filtration system using the air cleaner assembly of  FIG. 1 ; 
           [0020]      FIG. 10  is a flow chart of a method for controlling a pulse valve employed for cleaning the air filter of  FIG. 1 ; 
           [0021]      FIG. 11  is a graph illustrating differential pressure across the air filter of  FIG. 1  over the life of the air filter when the method of  FIG. 10  is employed; 
           [0022]      FIG. 12  is an enlarged view of a portion of the plateaued region of  FIG. 11 ; 
           [0023]      FIG. 13  is a graph representing a model relating the extent of clogging to pulse interval; 
           [0024]      FIG. 14  is an end elevational view of another embodiment of air cleaner assembly according to the present disclosure; 
           [0025]      FIG. 15  is a side elevational view in cross section of the air cleaner assembly of  FIG. 14  along lines  15 - 15 ; 
           [0026]      FIG. 16  is a front elevational view of a nozzle according to the prior art; 
           [0027]      FIG. 17  is a cross sectional view of the nozzle of  FIG. 16  along lines  17 - 17 ; 
           [0028]      FIG. 18  is a side elevational view of a nozzle according to the present disclosure; 
           [0029]      FIG. 19  is a front elevational view of the nozzle of  FIG. 18 ; 
           [0030]      FIG. 20  is an enlarged cross sectional view of the nozzle of  FIG. 19  along line  20 - 20 ; 
           [0031]      FIG. 21  is a graph illustrating inches of water restriction versus hours of operation comparing the prior art nozzle of  FIGS. 16 and 17  and the nozzle illustrated in  FIGS. 18-20 ; 
           [0032]      FIG. 22  is a front elevational view of a nozzle according to still another embodiment of the present disclosure; and 
           [0033]      FIG. 23  is a rear elevational view of a nozzle according to a further embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIGS. 1-13  illustrate an embodiment of an air cleaner assembly including a self-cleaning air filter according to the present disclosure, which is designated generally as reference numeral  10 . As shown, air filter  10  includes a tubular filter element  20  disposed within a cylindrical filter casing  30 . Filter element  20  is of conventional design and function having a tubular sidewall of pleated filter material, which collects dust and debris as air passes through. Filter element  20  is typically constructed of a blend of cellulose and synthetic fibers. Further, a synthetic fine fiber coating is typically applied to the surface of the media. Other constructions are, however, contemplated. For example, filter element  20  can be constructed of all synthetic fibers rather than conventional paper. Filter element  20  is axially centered within filter casing  30 . The tubular sidewall of filter element  20  is inset from the casing sidewalls defining an open space  13  around the outside of the filter element. The tubular sidewall also defines an open interior space  15  within filter element  20 . Filter casing  30  has an open end enclosed by a removable lid  38 . Lid  38  allows filter element  20  to be replaced as desired. Lid  38  is secured to casing  30  by connecting rod  39 , which extends axially through filter element  20 . Filter casing  30  includes an exterior surface  32  and an inlet port  34 , through which dust laden air  100  from the atmosphere enters one end (the “inlet end”) of air filter  10  and an outlet port  36  through which clean filtered air  104  exits the opposite end (the “outlet end”) of the air filter. As shown, inlet port  34  extends tangentially from the casing sidewall at the inlet end of filter casing  30  and an outlet port  36  that extends axially from the casing bottom  33  at the outlet end of casing  30 . Outlet port  36  allows for connection to the air intake and fuel induction system of a combustion engine by a hose, pipe or duct, although air filter  10  can be integrally mounted to the engine&#39;s air intake and fuel injection systems as desired. 
         [0035]    A pulse valve  40  is mounted to the side of outlet port  36  and operably connected to a compressed air source  60 . Pulse valve  40  releases short blasts or pulses of compressed air from the compressed air source within filter element  20 , which facilitates the self-cleaning action of air filter  10 . In one embodiment, pulse valve  40  is a conventional solenoid type control valve where a solenoid (not shown) actuates a diaphragm (not shown) to open and close the valve. Pulse valve  40  is mounted to the side of outlet port  36 . An elbow  44  connects the output of pulse valve  40  to a nozzle head  46 , which is centered along the longitudinal axis of filter casing  30 . Nozzle head  46  includes a conical deflector  48 , which deflects the pulse of compressed air radially through filter element  20 . Pulse valve  40  is under the control of an electronic control module  42 , which actuates the solenoid to open and close the valve at predetermined intervals. Control module  42  is electrically powered by any available internal or external power source, but is generally powered using the electrical power source found in the equipment or vehicle. Control module  42  may include processing circuitry  37 , memory  39  and an I/O interface  41  for connection to other control system sensors and devices. The processing circuitry generally includes a suitable general purpose computer processing circuit, such as a microprocessor and its associated circuitry. The processing circuit is operable to carry out the operations attributed to it herein. Within the memory are various program instructions. The program instructions are executable by the processing circuit and/or any other components of the control module  42  as appropriate. If desired, one or more of the components of the control module  42  may be provided as a separate device, which may be remotely located from the other components of the control module. 
         [0036]    In some embodiments, control module  42  controls pulse valve  40  based on flow through air filter  10 . In that regard, control module  42  receives measurements of parameters that can be used to measure air flow, or estimate air flow, through air filter  10  from one or more sensors  43 ,  45 . Such parameters can include, for example, one or more of a) air pressure at inlet port  34 ; b) air pressure at the outlet port  36 ; c) air flow at the inlet port; and d) air flow at the outlet port. One or more sensors  43 ,  45  can include, for example, one or more of air flow sensors (e.g., pitot tubes and/or anemometers) and air pressure sensors (e.g., vacuum transducers). Also, one or more sensors  43 ,  45  can be used independently or concurrently. In one embodiment, a first vacuum transducer  43  measures air pressure at inlet port  34  and a second vacuum transducer  45  measures air pressure at outlet port  36 . Received parameter measurements are applied to a model relating the parameters to pulse rate to determine how to control pulse valve  40 . Pulse valve  40  is then controlled to pulse in accordance with the determination. One such model is described in connection with  FIGS. 10-13 , discussed below. 
         [0037]    Further, in some embodiments, control module  42  can interface with external systems and/or devices over SAE J1939/CAN OPEN protocols using I/O interface  41 . Using these protocols, control module  42  can be programmed and/or configured. For example, user-defined constants used in the model can be set using these protocols. As another example, the model can be configured and/or specified using these protocols. 
         [0038]    Air filter  10  also includes a spring loaded pulse pressure vent (PPV)  50 , which vents the compressed air pulse from filter casing  30  during the self-cleaning cycle of air filter  10 . PPV  50  also acts as a vent for the dust removed during cleaning to be blown out of the housing. PPV  50  vents the over-pressure on the outside of filter element  20  from the compressed air pulse so that a pressure differential is maintained between the inside and outside of the filter element so that the cleaning action is maintained through the cleaning cycle. PPV  50  also acts as a vent for the dust removed during cleaning to be manually blown out of filter casing  30 . PPV  50  is mounted between the inlet and outlet ends of filter casing  30  within an opening  35  in the casing sidewall. PPV  50  includes an annular mounting pad  52 , which is securely seated within opening  35  of filter casing  30 . A plurality of spacers or posts  53  extending from mounting pad  52  suspend a cover plate  54  over opening  35 . A helical spring  56  biases a rigid diaphragm with a pliable seal  58  against mounting pad  52  to hold PPV  50  closed sealing filter casing  30 . Spring  56  is selected so that PPV  50  opens at a predetermined positive pressure within filter casing  30 . 
         [0039]    During the normal filtering cycle ( FIG. 6 ), the operation of the combustion engine creates a negative pressure differential between the inside and outside of filter element  20 , which draws the airflow through air filter  10 . Dust laden air from the atmosphere enters air filter casing  30  through inlet port  34 . The dust laden air surrounds filter element  20  in area  13  and is drawn inward through the filter element  20  where dust and debris collect on the outside of the filter element. The now “filtered” air exits air filter  10  to the engine through outlet port  36 . As shown, PPV  50  is closed during the normal filtering cycle. 
         [0040]    During the cleaning cycle ( FIG. 7 ), pulse valve  40  releases a short powerful blast of compressed air (the “compressed air pulse”) into filter element  20 , which dislodges dust and debris  102  from the filter element into area  13  thereby providing the self-cleaning action of air filter  10 . Nozzle head  46  directs the compressed air pulse onto the deflector  48 , which projects the compressed air pulse outward radially into the filter element. The compressed air pulse creates a high pressure wave that expands outward radially through filer element  20  as it moves along the length of filter element  20  from the outlet end to the inlet end. The high pressure wave created by the compressed air pulse briefly inverts the pressure differential between the inside and outside of filter element  20  and temporarily reverses the direction of air flow through filter element  20  thereby providing the cleaning action. In releasing the compressed air pulse, pulse valve  50  opens only for a brief duration generally 5-10 milliseconds. The cleaning cycle is maintained only as long as the positive pressure differential between the inside and outside of the filter element can be maintained. Consequently, the cleaning cycle lasts less than a few tenths of a second. 
         [0041]    During the brief cleaning cycle, the over pressure of the compressed air pulse expanding through filter element  20  immediately opens PPV  50 . PPV  50  opens once the internal air pressure of filter casing  30  reaches its predetermined pressure. PPV  50  opens to vent the compressed air pulse to the atmosphere thereby maintaining the now positive pressure differential between the inside and the outside of filter element  20 . Venting the compressed air pulse to the atmosphere sustains the cleaning action for the entire duration of the pulse and allows the high pressure wave of the compressed air pulse to traverse the length of the filter element providing an efficient cleaning of the entire filter element. Without PPV  50  venting the compressed air pulse to the atmosphere, the pressure differential between the inside and outside of filter element  20  would quickly equalize within the confined space of filter casing  30  thereby interrupting the cleaning action provided by the compressed air pulse. Once the compressed air pulse has been vented from filter casing  30 , the positive pressure differential is lost and the vacuum draw from the outlet port  36  quickly reestablishes the negative pressure differential between the inside and outside of the filter element, whereby the air flow direction through air filter  10  reverts back and the normal filtering cycle is reestablished. 
         [0042]    In certain embodiments, air filter  10  forms part of an integrated air filtration system in equipment or vehicles powered by any internal combustion engine that operates in environments with extremely high contents of dust, sand and other particulate in the atmosphere. By way of example only and for simplicity of illustration and explanation,  FIGS. 8 and 9  illustrate the application of air filter  10  to an air filtration system of a military type vehicle  2 . In other embodiments, the air filtration system and the air filter may take other forms and be adapted for the desired application within the scope of this invention. 
         [0043]      FIG. 8  depicts air filter  10  mounted to vehicle  2  outside of the engine compartment. The compressed air source (not shown in  FIG. 8 ) is typically mounted to the vehicle undercarriage or within the engine compartment, which contains an engine  4 . It should be noted that in other applications, air filter  10  and the compressed air source may be located in any available space and suitable location on, in or outside of the vehicle or equipment as desired for the particular application. 
         [0044]      FIG. 9  depicts a schematic of air filter  10  incorporated into an air filtration system of vehicle  2 . Pulse valve  40  is connected to compressed air source  60  by air line  72 . Another airline  74  supplies compressed air source  60  with filtered and dried air from outlet port  36  of air filter  10  thereby ensuring that the volume of compressed air supplied back to pulse valve  40  is contaminant and moisture free. A hose, pipe or duct  70  connects outlet port  36  of air filter  10  to the engine&#39;s air intake and fuel injection system  6 . 
         [0045]    Compressed air source  60  supplies the volume of clean dry compressed air to air filter  10  from which the compressed air pulse is released within filter element  20  to facilitate the self-cleaning action. The necessary volume and pressure of the compressed air supplied from the compressed air source is determined by several factors, including, but not limited to the volume and configuration of air filter  10 , the type of filter element  20 , the volume and properties of dust within the inlet airflow, and the frequency of the air filter&#39;s cleaning cycle. Air filter  10  can be connected to any suitable and available compressed air source, whether specifically dedicated to supplying the air filter or one presently existing in the equipment or vehicle application that is available to supply the air filter. As shown, compressed air source  60  includes a compressor unit  62 , a storage tank  64 , a compressed air dryer  66  and moisture drain switch  68 . Compressed air source  60  may also include other ancillary components (not shown), such as, but not limited to, compressed air filters, water purge valves, pressure gages and switches, hoses, lines, clamps and fittings. Generally, the components which make up the compressed air source  60  are of conventional design well known in the art. Compressor unit  62 , storage tank  64  and other components of compressed air source  60  are selected so that the compressed air source supplies air filter  10  with the volume of clean, dry compressed air necessary for generating the required compressed air pulse within the air filter. 
         [0046]    One skilled in the art will note that this invention enables the use of reverse pulse self-cleaning in small scale applications, such as for vehicles and motorized equipment. The pulse pressure vent compensates for the filter casing&#39;s small confined volume where the compressed air pulse is normally dissipated in large industrial systems by venting the compressed air pulse from the casing. The pulse pressure vent opens at a preset positive pressure so that the compressed air pulse vents to the atmosphere once it passes through the filter element. The pulse pressure vent maintains the positive pressure differential between the inside and outside of the filter element, which sustains the cleaning action during the cleaning cycle. Without the pulse pressure vent, the compressed air pulse would almost instantly expand within the confined volume of the filter casing and equalize the pressure differential between the inside and the outside of the filter element abruptly terminating the cleaning action before the pulse could clean the entire filter element. Venting the compressed air pulse through the pulse pressure vent allows the pressure wave of the pulse to travel the length of the filter element and the energy in the pulse to effectively dislodge dust from the filter element. The vent also provides an egress path from the filter casing for the dust and debris during the cleaning cycle. The pulse pressure vent can be readily adapted for filter housings of any size, configuration or capacity in a variety of vehicle, equipment and other applications. In addition, the pressure setting, size, configuration and location of the pulse pressure valve between the inlet and outlet ends of the filter casing is selected so that the compressed air pulse can be vented as the pulse travels the length of the filter element, thereby ensuring the entire area of the filter element will be cleaned. 
         [0047]      FIGS. 10-13  illustrate a flowchart of a method  100  by which control module  42  controls pulse valve  40  to clean air filter  10 . Method  100  can be implemented as program instructions stored in memory  39  of control module  42  and executed by processing circuitry  37  of control module  42 . The flowchart spans from a beginning-of-life  102  of air filter  10  to an end-of-life  104  of the air filter. Beginning-of-life  102  corresponds to the point in the life cycle of air filter  10  when the air filter has not been used or is clean. End-of-life  104  corresponds to the point in the life cycle of air filter  10  when the air filter is no longer performing according to specification or is otherwise unsuitable for continued air filtering. 
         [0048]    Referring to  FIG. 10 , at beginning-of-life  102  of air filter  10 , a current differential air pressure ΔP ACT  across inlet port  34  and outlet port  36  is measured  106  during normal operation of the vehicle. In one embodiment, to measure differential pressure ΔP ACT , an air pressure IP ACT  at inlet port  34  during normal operation of the vehicle is measured using first vacuum transducer  43  and an air pressure OP ACT  at outlet port  36  during normal operation of the vehicle is measured using second vacuum transducer  45 . Thereafter, the difference between the two pressures is calculated to determine differential pressure ΔP ACT =OP ACT −IP ACT . In another embodiment, differential pressure ΔP ACT  is estimated from pressure IP ACT . 
         [0049]    To estimate differential pressure ΔP ACT , pressure IP ACT  is measured using first vacuum transducer  43 . Further, an air pressure OP HI  at outlet port  36  and an air pressure IP HI  at inlet port  34  are determined when the vehicle engine is at full load or high idle and air filter  10  is new and clean. Thereafter, the ratio between pressure IP ACT  and pressure IP HI  is determined: 
         [0000]    
       
         
           
             
               
                 IP 
                 ACT 
               
               
                 IP 
                 HI 
               
             
             . 
           
         
       
     
         [0000]    The ratio is applied to scale a differential air pressure ΔP HI =OP HI −IP HI  across air filter  10  when the vehicle engine is at full load or high idle and air filter  10  is new and clean is determined: 
         [0000]    
       
         
           
             Δ 
              
             
                 
             
              
             
               P 
               HI 
             
              
             
               
                 
                   IP 
                   ACT 
                 
                 
                   IP 
                   HI 
                 
               
               . 
             
           
         
       
     
         [0000]    This scaled differential pressure corresponds to an estimate of differential pressure ΔP ACT . Pressure IP m , pressure OP HI  and differential pressure ΔP HI  can be determined at beginning-of-life  102  of air filter  10  or determined from another air filter of the same type as air filter  10  at the beginning-of-life of the other air filter. 
         [0050]    After measuring differential pressure ΔP ACT , a determination  108  is made as to whether differential pressure ΔP ACT  exceeds a threshold T. If differential pressure ΔP ACT  fails to exceed threshold T, differential pressure ΔP ACT  is measured  106  again and determination  108  is repeated. Optionally, the re-measurement can be delayed by a predetermined amount of time (e.g., one minute). Until threshold T is exceeded, pulse valve  40  is disabled and cleaning is disabled. 
         [0051]    Threshold T is typically set at a level that allows an optimal amount of dust to build up in air filter  10  before cleaning of the air filter can begin. This recognizes that, generally, in dust collection and self-cleaning, some amount of dust on air filter  10  is desirable for maximum cleaning efficiency. Typically, the optimal amount of dust increases pressure differential ΔP HI  by 2-4 inches water column. Alternatively, threshold T can be set to allow more or less than an optimal amount of dust to build up, or to allow cleaning to begin immediately. 
         [0052]    While not necessary, threshold T is typically based off pressure differential ΔP HI  and a caking factor CA F . Caking factor CA F  is a constant entered into the control module  42  that specifies an air pressure increase above pressure differential ΔP HI  when the vehicle engine is at full load or high idle and air filter  10  is new and clean. Caking factor CA F  is typically set to achieve the optimum amount of dust buildup for filtration. Threshold T at full load or high idle is the summation of differential pressure ΔP HI  and caking factor CA F . However, when not at full load or high idle, differential pressure ΔP HI  and caking factor CA F  need to be scaled to determine threshold 
         [0000]    
       
         
           
             T 
             = 
             
               
                 ( 
                 
                   
                     ( 
                     
                       
                         IP 
                         ACT 
                       
                       
                         IP 
                         HI 
                       
                     
                     ) 
                   
                    
                   Δ 
                    
                   
                       
                   
                    
                   
                     P 
                     HI 
                   
                 
                 ) 
               
               + 
               
                 
                   ( 
                   
                     
                       ( 
                       
                         
                           IP 
                           ACT 
                         
                         
                           IP 
                           HI 
                         
                       
                       ) 
                     
                      
                     
                       CA 
                       F 
                     
                   
                   ) 
                 
                 . 
               
             
           
         
       
     
         [0000]    As should be appreciated, the scaling is done as described above to estimate differential pressure ΔP ACT . 
         [0053]    With reference to  FIG. 11 , an example graphical representation of pressure differential ΔP ACT  over the life of air filter  10  is illustrated. The vertical axis corresponds to pressure differential ΔP ACT  (e.g., in inches water column) and the horizontal axis corresponds to the life of air filter  10  (e.g., in hours). As can be seen, pressure differential ΔP ACT  gradually increases before plateauing. The level at which pressure differential ΔP ACT  stops gradually increasing is defined by threshold T. 
         [0054]    Once differential pressure ΔP ACT  exceeds threshold T, an optimal differential air pressure ΔP OPT  across air filter  10  at the current load is calculated  110 . In some embodiments, differential pressure ΔP OPT  is the same as threshold T. In that regard, differential pressure ΔP OPT  is typically equal to 
         [0000]    
       
         
           
             
               ( 
               
                 
                   ( 
                   
                     
                       IP 
                       ACT 
                     
                     
                       IP 
                       HI 
                     
                   
                   ) 
                 
                  
                 Δ 
                  
                 
                     
                 
                  
                 
                   P 
                   HI 
                 
               
               ) 
             
             + 
             
               
                 ( 
                 
                   
                     ( 
                     
                       
                         IP 
                         ACT 
                       
                       
                         IP 
                         HI 
                       
                     
                     ) 
                   
                    
                   
                     CA 
                     F 
                   
                 
                 ) 
               
               . 
             
           
         
       
     
         [0000]    As should be appreciated, differential pressure ΔP OPT  varies as engine load changes (i.e., as the revolutions per minute (RPM) of the engine changes). For example, a reduction in RPM results in a reduction of differential pressure ΔP OPT . After calculating differential pressure ΔP OPT , the difference between differential pressure ΔP ACT  and differential pressure ΔP OPT  is calculated as a clogging factor CL F =ΔP ACT −ΔP OPT , as illustrated in  FIG. 12 .  FIG. 12  shows an enlarged view of a portion of the plateaued region of  FIG. 11 . The vertical axis corresponds to pressure differential ΔP ACT  and the horizontal axis corresponds to the life of air filter  10 . 
         [0055]    The foregoing calculated clogging factor CL F  by down scaling differential pressure ΔP HI  and clogging factor CA F . In some embodiments, clogging factor CL F  can instead be calculated by upscaling differential pressure ΔP ACT  as follows: 
         [0000]    
       
         
           
             
               CL 
               F 
             
             = 
             
               
                 
                   ( 
                   
                     
                       IP 
                       HI 
                     
                     
                       IP 
                       ACT 
                     
                   
                   ) 
                 
                  
                 Δ 
                  
                 
                     
                 
                  
                 
                   P 
                   ACT 
                 
               
               - 
               
                 Δ 
                  
                 
                     
                 
                  
                 
                   P 
                   HI 
                 
               
               - 
               
                 
                   CA 
                   F 
                 
                 . 
               
             
           
         
       
     
         [0056]    Clogging factor CL F  is input into a model relating clogging factor CL F  to the pulse interval for cleaning pulses to calculate the current pulse interval. The model includes upper and lower bounds on the pulse interval, such as two minutes and one hour, respectively. Further, the model can include upper and lower bounds on clogging factor CL F , which correspond to the lower and upper bounds on the interval, respectively. Typically, as clogging factor CL F  increases, the pulse interval decreases, and vice versa. If clogging factor CL F  is less than its lower bound, the pulse interval will be the greatest allowed pulse interval (e.g., one hour). Similarly, if clogging factor CL F  is greater than its upper bound, the pulse interval will be the smallest allowed pulse interval (e.g., two minutes). The model is suitably defined by a user of control module  42 , for example, by defining lower and upper bounds for clogging factor CL F  and the pulse interval. 
         [0057]      FIG. 13  illustrates a linear model relating clogging factor CL F  to the pulse interval for cleaning pulses. The vertical axis corresponds to clogging factor CL F , and the horizontal axis corresponds to the pulse interval spacing in time units. As illustrated, the pulse interval increases linearly as clogging factor CL F  increases and decreases linearly as clogging factor CL F  decreases. In some embodiments, the model may be exponential. 
         [0058]    In some embodiments, the model adds a scaling factor to increase the pulse interval for low engine loads (e.g., low engine RPM). Namely, flow rate through air filter  10  decreases as engine load decreases. Through testing, it has been found that the optimal pulse interval for low engine loads does not necessarily correspond to the optimal pulse interval for higher engine loads. The pulse intervals at low engine loads are too high. Hence, a scaling factor can be added for lower engine loads to decrease the pulse interval. For example, the scaling factor can increasingly decrease the interval as engine load decreases. 
         [0059]    After calculating the pulse interval, pulse valve  40  is pulsed  112  according to the pulse interval to clean air filter  10 . A determination  114  is then made as to whether air filter  10  has reached end-of-life  104 . So long as air filter  10  has not reached end-of-life  104 , differential pressure ΔP ACT  is measured  116  again and the foregoing is repeated starting from calculating  110  differential pressure ΔP OCT . Optionally, the re-measurement can be delayed by a predetermined amount of time (e.g., one minute). If air filter  10  has reached end-of-life  104 , a user of control module  42  can be notified by, for example, one or more of a light, audible alarm, display readout, or by interface to the vehicle computer and a display location of the vehicle manufacturer&#39;s choice. 
         [0060]    End-of-life  104  can be determined in any number of ways. For example, end-of-life  104  can be a predetermined time duration from beginning-of-life  102 . As another example, end-of-life  104  can be the time point at which differential pressure ΔP ACT  is no longer controllable at the maximum pulse frequency (i.e., lowest pulse interval). This can be determined through historical analysis of previous pulse intervals used with pulse valve  40 . If the smallest pulse interval was previously used with pulse valve  40 , and a predetermined amount of time has elapsed, with no improvement in clogging factor CL F , differential pressure ΔP ACT  is no longer controllable.  FIG. 11  illustrates this uncontrolled differential pressure P ACT  can be monitored for signs that end-of-life  104  is reached. 
         [0061]    In view of the foregoing, differential pressure ΔP ACT  is actively controlled by changing the pulse interval to maintain differential pressure ΔP ACT  as close to differential pressure ΔP OPT  as possible. As clogging factor CL F  increases, the pulse interval of air valve  40  decreases. Eventually, clogging factor CL F  should start to fall again, whether this is due to the increased pulse frequency or simply an environment with light dust loading. The pulse frequency will then decrease until clogging factor CL F  increases again. In some instances, clogging factor CL F  continues to increase due to an extremely dusty environment or air filter  10  reaching end-of-life  104 . 
         [0062]    Further, in view of the foregoing, method  100  estimates flow or a percentage of full flow without utilizing a flow sensor. It is done with independent vacuum transducers. Advantageously, the vacuum transducers provide simplicity, reliability, and cost reduction as compared to approaches which directly measure air flow with an anemometer or a pitot tube. However, it is to be appreciated that direct measurements of air flow can be employed with the approach described herein. Flow can be directly measured using, for example, a pitot tube or an anemometer 
         [0063]    When employing direct measurements of flow with method  100 , differential pressure is replaced with the direct measurement of flow at inlet port  34 . Further, the above described ratios are replaced with the ratio of flow F ACT  during normal operation of the vehicle and flow F HI  when the vehicle engine is at full load or high idle and air filter  10  is new and clean: 
         [0000]    
       
         
           
             
               
                 F 
                 ACT 
               
               
                 F 
                 HI 
               
             
             . 
           
         
       
     
         [0000]    To illustrate, optimal flow F OPT  can be calculated as 
         [0000]    
       
         
           
             
               
                 F 
                 ACT 
               
               + 
               
                 ( 
                 
                   
                     ( 
                     
                       
                         F 
                         ACT 
                       
                       
                         F 
                         HI 
                       
                     
                     ) 
                   
                    
                   
                     CA 
                     F 
                   
                 
                 ) 
               
             
             , 
           
         
       
     
         [0000]    and clogging factor CL F  can be calculated as F ACT −F OPT . 
         [0064]    With reference now to  FIGS. 14 and 15 , another embodiment of a cleaner assembly includes a filter  120  which may be tubular or cylindrical. In other words, it has a hollow interior. The filter is disposed within a cylindrical housing  130 . The housing includes an inlet port  134  which may be located adjacent one end, the distal end, of the housing and an outlet port  136  which may be located adjacent another end, the proximal end, of the housing. The housing itself is cylindrical in nature with a hollow interior. The distal end of the housing  130  is closed by a lid  138 . A connecting rod  139  extends centrally in the housing and mounts at one end to the lid  138 . Another end of the connecting rod  139  mounts to a nozzle  150 . 
         [0065]    With reference also now to  FIGS. 18-20 , the nozzle comprises a housing  152  including an inlet end  154  which is open and an outlet end  156  which is generally closed so as to define a hollow interior  158 . The interior includes a threaded section  160  which accommodates a threaded end of a conduit  161  ( FIG. 15 ). The nozzle comprises a longitudinal axis  162  and a central opening  164  through the outlet end  156  which is aligned with the longitudinal axis  162 . Also provided are at least two side openings  168 . As best seen in  FIG. 19 , the side openings  168  can be generally arcuate in nature, such that each of them extends at least 45 degrees around the circumference of a circle defined in the outlet end  156  encircling the central opening  164 . In the embodiment shown, three such openings  168  are provided. 
         [0066]    As is best seen in  FIG. 20 , the side openings extend at an angle α of approximately 22½ degrees from the longitudinal axis  162  of the nozzle. It should be apparent from  FIG. 20  that the hollow interior  158  includes an enlarged diameter section  172  located immediately adjacent to inlet ends of the side openings  168  and that the inlet ends comprise radiused inlets  174 . These allow for a relatively smooth flow of air through the nozzle. The outlet ends of the side openings  168  can be sharp and not radiused as shown in this embodiment. However, no air flows through the central opening  64 . Rather, it is threaded as at  176  in order to accommodate a threaded end of the connecting rod  139 . As is apparent from  FIG. 15 , the connecting rod mounts at one end to the nozzle  150  and at the other end to the filter  120  to retain it in place. 
         [0067]    With continued reference to  FIG. 15 , the housing  130  also includes a pulse pressure vent assembly  180 . This comprises a housing opening  182  which is surrounded by a plurality of posts or standoffs  186  to which is mounted a cover plate or stop  190 . Disposed between the opening  182  and the cover plate  190  is a biasing member  192 , such as a spring. The spring biases a blocking member  196  or diaphragm that selectively seals the housing opening  182 . As is evident from FIG.  14 , in one embodiment, the cylindrical housing  130  can include three such pressure vent assemblies  180 . These can be located equiangularly around the periphery of the housing  130 . However, other configurations, such as two or four vents, are also possible. Further, the angular locations of the vents does not need to be symmetrical. 
         [0068]    It has been found that the nozzle  150  illustrated in  FIGS. 18-20  is advantageous in relation to a prior art nozzle  210  of the type which is illustrated in  FIGS. 16 and 17 . The prior art nozzle  210  includes a housing  212  with an inlet end  214  and an outlet end  216  so as to define a hollow interior  218 . The hollow interior can include a threaded section  220 . The nozzle includes a longitudinal axis  222  along which lies a central opening  224 . The central opening is threaded as at  226 . Also provided are a plurality of side openings  228 , each of which is generally circular as best shown in  FIG. 16 . In the prior art, six or eight such side openings  228  can be provided in the housing  212 . The side openings  228  are also threaded as at  230 . The threading is believed to improve air flow through the side openings. It should be apparent from  FIG. 17  that the side openings are provided on a radiused face  236  of the nozzle. 
         [0069]    With reference now to  FIG. 21 , through testing, it has been found that a prior art nozzle similar to the one illustrated in  FIGS. 16 and 17  is disadvantageous from the standpoint that when employed in the air cleaner assembly illustrated in, e.g.,  FIGS. 14 and 15 , the nozzle does not clean the filter sufficiently so as to retard or minimize a restriction of the filter, i.e., a reduction in the filtration capability of the filter, by a buildup of dirt and dust on the exterior periphery of the filter. Put another way, the restriction encountered during filtration, even after pulse cleaning the filter using the prior art nozzle is significantly larger than is the restriction encountered when employing the nozzle of  FIGS. 18-20  and when using the same pulse duration and pressure of air in the same filter housing to clean the identical filter. The prior art nozzle tested had six threaded side holes which were at an angle of about 22½ degrees to a longitudinal axis of the nozzle. This nozzle, while it had good dispersion, did not release enough pressurized air to adequately clean the filter. The restriction of the filter, namely, dirt and dust build up on the exterior periphery of the filter, was such that it made it difficult for the filter to allow enough air flow through it to supply the internal combustion engine with an adequate amount of air. Such restriction becomes significant as early as 10 hours into the operation of the air cleaner assembly and is very pronounced at 20 hours or more. In contrast to the almost exponential increase in the restriction of the filter attempted to be cleaned with the prior art nozzle of  FIGS. 16 and 17 , the nozzle of  FIGS. 18-20  is capable of repeatedly cleaning the same filter so that the restriction of the filter does not increase significantly as the hours of operation of the air cleaner assembly passes 60, 80 or even 100 hours. 
         [0070]    Pulse volume testing performed on the prior art nozzle indicates that the relative energy released through this nozzle is not acceptable to effectively dislodge the dust from the filter element. Therefore, it was determined that increasing the open area of the nozzle was called for and, hence, arcuate shaped openings in the nozzle were developed. The angle of trajectory and the coverage area of the nozzle relative to the filter element appears to be advantageous at 22½ degrees in relation to the longitudinal axis of the nozzle. 
         [0071]    It has been found that the prior art nozzle did not allow an adequate amount of pressurized air to flow at a high enough pressure to fully clean the filter. Although the dispersion of pressurized air to the interior periphery of the filter was adequate, the air pressure was inadequate. In order to increase the energy of the air exiting the nozzle so as to effectively pulse clean the cylindrical filter, arcuate apertures have been employed. It has been found that the lesser the number of openings, the better. Although testing data may be needed to confirm this, it would appear that the maximum number of openings which could be employed, while still providing air at a high enough pressure, would be four. Such a nozzle may prove useful on a large diameter cylindrical filter element that is very long. On the other hand, perhaps just two longer arcuate openings in the nozzle would be advantageous, because they would allow for slightly more open area at the outlet end of the nozzle. It is also believed that larger nozzles may allow for an increase in angular slot length, although it is believed that reducing the number of slots or arcuate openings would probably have a greater effect in increasing the throughput of air through the nozzle. 
         [0072]    If four arcuate openings were employed, each opening could be on the order of 45 degrees. Thus, the four openings together would constitute a minimum of 180 degrees around the circumference of a circle centered on the openings. Four slots would decrease the open area percentage at the outlet end of the nozzle but would increase air velocity. Thus, a design with four slots might work better on filter elements which are longer. The nozzle illustrated in, e.g.,  FIG. 19  comprises three 60 degree openings, again amounting to a minimum of 180 degrees around the circumference of a circle. 
         [0073]    In the embodiment of the nozzle shown in  FIGS. 18-20 , the slot entrance area of each nozzle is 0.108 inches squared. However, the exit area is 0.161 inches squared. This occurs because the size of the aperture in the nozzle increases from the entrance end to the exit end, thus, increasing the area of the opening and the measured width thereof. 
         [0074]    Pulse cleaning of a filter is effective due to several factors. These include the pressure of the air, the direction and angle of dispersion, the volume of the air and the velocity of the air. In the chart of  FIG. 21 , it can be seen that the nozzle of  FIGS. 18-20  adequately performs with the specific size and shape of the filter element illustrated at  FIG. 15 . That filter has a length of about 12.75 inches, an internal diameter of about 5.1 inches and an external diameter of about 9.1 inches, and hence a thickness of 2 inches. The filtration material of the filter used was Hollingsworth and Vose number FA6900NWFR. A planar filtration material was employed in a pleated filter arrangement. The results shown in  FIG. 21  will change if a different size or shape is provided for the filter element and also if its thickness is changed or if the filtration material used is different, even if the air pressure and nozzle shape are kept constant. 
         [0075]    In another embodiment of the present disclosure, as illustrated in  FIG. 22 , a nozzle  250  could be provided with a plurality of arcuate openings  252  (three in number in this embodiment), wherein each opening extends at an angle β of approximately 84 degrees at an outlet end  256  of the nozzle. It is believed that the larger sized openings  252  are advantageous from the perspective that they will allow an increased amount of pressurized air to flow at the outlet end of the nozzle. In this embodiment, therefore, about 252 degrees of open area are provided at the outlet end of the nozzle with the metal material of the nozzle at that surface constituting only 108 degrees of the circumference of a circle centered on the nozzle openings  252 . 
         [0076]    With reference now to  FIG. 23 , in accordance with still another embodiment of the present disclosure, a nozzle  270  can include a central opening  274  and a set of side openings  278 , each having a filleted entrance as at  280 , such that the openings lie adjacent to each other. In this embodiment, the peripheral openings almost touch each other, thereby providing the nozzle  270  with a yet further enlarged set of openings to more easily allow a flow of pressurized air when pulse cleaning a cylindrical filter. It appears that maintaining nozzle integrity is not an issue for concern with regard to the sizes of the arcuate slots for the nozzle disclosed herein. Rather, geometry is the limiting factor. The slots begin at a smaller diameter and gradually increase toward the exit of the nozzle. Thus, the inlet side of each slot in the nozzle can only have so much open area so that the filleted entrance is not compromised. The maximum size is illustrated in  FIG. 23 . 
         [0077]    As to the diameter of the nozzle which can be used in an air cleaning environment, the nozzle diameter is going to control the cleaning area which needs to increase if the filter element gets larger. Since the nozzle is located in this embodiment in the outlet area of the air filter, it does block some of the outlet&#39;s flow area (see  FIG. 15 ). Thus, the maximum diameter of the nozzle must be small enough that it does not cause significant restriction in the air outlet for the air which has been cleaned by the filter. In order to minimize such a restriction on nozzle diameter, one could increase the diameter of the outlet tube. However, the outlet tube diameter is often dictated by the size of the engine, meaning that this option may be limited. One way of addressing that issue would be to make the outlet tube have a larger diameter in the area where the nozzle lies and, downstream from the nozzle, taper down the diameter of the outlet tube to an appropriate size to match the size necessary for the engine in question. 
         [0078]    At this point, applicants have not performed much experimental testing to better understand the effect of changing the number of openings in the nozzle or changing their size. However, it has been determined that to increase the energy conveyed by the pulsed air, arcuate openings of a minimum size are necessary in order that the cylindrical filter be adequately cleaned during pulse cleaning so that dirt built up on the exterior surface of the filter does not result in an unwanted increase in the restriction to flow through the filter during filtration after ten or twenty hours of use. 
         [0079]    The disclosure has been described with reference to several embodiments. Obviously, modifications and alterations will occur to others upon a reading and understanding of this disclosure. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims and the equivalents thereof.