Patent Publication Number: US-2023151571-A1

Title: Plow assembly

Description:
TECHNICAL FIELD 
     The present application relates to a plow for a vehicle, and more particularly to a plow with a movable wing and a plow movable with respect to a vehicle. 
     BACKGROUND 
     There are a variety of conventional plow constructions for vehicles. One type of conventional plow configuration is a back-blade style of plow having a main snow plow blade and wings attached to a side edge of the main snow plow blade. The back-blade style of plow may be mounted to a rear of a plow vehicle, and may include conventional wings that provide a larger plow face in use while being stowable for travel on the road. Another type of plow is a front-blade plow, where the plow may be mounted to the front of a plow vehicle. The front-blade plow may also include conventional wings like the back-blade plow. 
     In conventional plows with wings, the wings may be rotated in a limited manner about a single axis defined by the side edge of the main snow plow blade, where the wing is limited to rotation from a stowed position proximal to the sides of the plow vehicle to a position parallel to the main snow plow blade. This configuration, as mentioned above, allows a plow operator to position the wings proximal to the sides of the plow vehicle in order to operate the vehicle on a municipal road and within the lane constraints of the municipal road. Conventionally, once the vehicle arrives at the site to be plowed, the operator actuates the wings of the plow to a position parallel to the main snow plow blade or a fully extended position, forming a plow face or plow area that is greater than would otherwise be possible without failing to comply with the lane constraints of a municipal road. 
     In practice, the conventional plow with the wings in the fully extended position is likely to encounter an obstruction at least once during the operational life of the plow. Driveways and parking lots can include obstructions that are concealed by snow that the plow operator cannot see. As a result, the conventional plow may include control arms and springs coupled between the plow vehicle mount and the plow that allow the plow to tilt in response to encountering an obstruction. This tilting action can prevent damage to the plow in response to encountering the obstruction; however, the plow control arms and springs are limited in degree of titling action provided to a single axis 
     SUMMARY OF THE DESCRIPTION 
     The present disclosure is directed to a snow plow having a wing that is rotatably coupled to a side of a primary plow, and configured to rotate about a first axis substantially parallel to the side of the primary plow. A portion of the wing is operable to rotate about a second axis that is non-parallel to the first axis, where the portion is operable to rotate upward about the second axis relative to the ground in response to the wing encountering an obstruction. 
     In one embodiment, the snow plow includes a primary plow and a first wing. The primary plow may include first and second sides opposite each other with a blade disposed between the first and second sides. The blade may be operable to contact a ground surface to facilitate moving snow. 
     In one embodiment, the first wing is rotatably coupled to the first side of the primary plow via a first connection, and configured to rotate about a first axis substantially parallel to the first side of the primary plow. The first wing may include a main wing portion operable to rotate about a second axis that is non-parallel to the first axis, where the main wing portion is operable to rotate upward about the second axis relative to the ground in response to the first wing encountering an obstruction. 
     In one embodiment, the first wing may include a secondary portion operably coupled to the first side of the primary plow via the first connection. The secondary portion may be connected to the main wing portion via a lower connector and an upper connector. The lower connector may include a pivotable connection to the secondary portion and a fixed connection to the main wing portion, thereby enabling the main wing portion to rotate about the pivotable connection, wherein the pivotable connection defines the second axis. 
     In one embodiment, the upper connector includes first and second springs that oppose each other in compression, where a position of equilibrium between the first and second springs corresponds to a primary operating position of the first wing relative to the primary plow, wherein the first spring enables upward rotation of the main wing portion in response to the first wing encountering an obstruction that exerts an upward force on the main wing portion. 
     In one embodiment, the upper connector includes a hydraulic actuator operable to rotate the main wing portion upward and downward about the second axis in response to respective retraction and extension of the hydraulic actuator. 
     In one embodiment, the hydraulic actuator is operably coupled to an adjustable relief valve configured to enable the hydraulic actuator to retract in response to application of force on the main wing portion in a direction perpendicular to the second axis and greater than a threshold trip force. 
     In one embodiment, a first wing blade is rotatably coupled to the first wing such that the first wing blade is able to rotate upward in response to the first wing blade encountering an obstruction that exerts a sufficient force on the first wing blade (e.g., a force greater than a threshold force). 
     In one embodiment, a hydraulic actuator is operably coupled to the first wing blade to control the wing and enable it to rotate upward in response to encountering an obstruction or in response to a command from an operator. 
     The present disclosure is also directed to a receiver that movably couples the snow plow to the mounting device attached to the plow vehicle. In one embodiment, the receiver may be coupled to at least one hydraulic actuator and movably coupled to a receiver interface extending from the surface of the snow plow. As the hydraulic actuator(s) move the receiver interface in and out of the receiver, the distance proximally and distally between the snow plow and the plow vehicle changes. 
     These and other advantages and features of the invention will be more fully understood and appreciated by reference to the description of the current embodiment and the drawings. 
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited to the details of operation or to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention may be implemented in various other embodiments and of being practiced or being carried out in alternative ways not expressly disclosed herein. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. Further, enumeration may be used in the description of various embodiments. Unless otherwise expressly stated, the use of enumeration should not be construed as limiting the invention to any specific order or number of components. Nor should the use of enumeration be construed as excluding from the scope of the invention any additional steps or components that might be combined with or into the enumerated steps or components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a representative view of a snow plow in accordance with one embodiment. 
         FIG.  2    shows a representative view of the snow plow of  FIG.  1   . 
         FIG.  3    shows a perspective view of a snow plow in accordance with one embodiment. 
         FIG.  4    shows an enlarged view of  FIG.  1    in accordance with one embodiment. 
         FIG.  5    shows an alternative embodiment of the snow plow in accordance with one embodiment. 
         FIG.  6    shows an alternative embodiment of the snow plow in accordance with one embodiment. 
         FIG.  7    shows a control system of the snow plow in accordance with one embodiment. 
         FIG.  8    shows a control system of the snow plow in accordance with one embodiment. 
         FIG.  9    shows a perspective view of a snow plow in accordance with one embodiment. 
         FIG.  10    shows a rear perspective view of a portion of the snow plow of  FIG.  9   . 
         FIG.  11    shows a method of operation for an actuator of a snow plow in accordance with one embodiment. 
         FIG.  12    shows another rear perspective view of a portion of the snow plow of  FIG.  9   . 
         FIG.  13    shows a top view of a system for moving a snow plow proximally and distally with respect to a vehicle in accordance with one embodiment. 
         FIG.  14    shows various modes of operation in accordance with one embodiment. 
         FIG.  15    depicts a snow plow in accordance with an alternative embodiment. 
         FIG.  16    shows a side view of the snow plow of  FIG.  15   . 
         FIG.  17    shows a side view of the snow plow of  FIG.  15    in accordance with one embodiment. 
         FIG.  18    shows another side view of the snow plow of  FIG.  15    in accordance with one embodiment. 
         FIG.  19    shows another side view of the snow plow of  FIG.  15    in accordance with one embodiment. 
         FIG.  20    shows another side view of the snow plow of  FIG.  15    in accordance with one embodiment. 
         FIG.  21    shows a top view of the snow plow of  FIG.  15   . 
         FIG.  22    shows a rear perspective view of a portion of the snow plow of  FIG.  15   . 
         FIG.  23    shows a method of operation in accordance with one embodiment. 
     
    
    
     DESCRIPTION 
     A snow plow for a vehicle is shown in  FIGS.  1 - 3   , and is generally designated  100 . The snow plow  100  is described herein in several embodiments as being a back-blade type of plow disposed proximal to a rear of a vehicle  10 . The snow plow  100  is further described in several embodiments as a front-blade type of plow mounted to the front of the vehicle  10 . However, it is to be understood that the present disclosure is not so limited. The snow plow  100  includes a primary plow  120  having a longitudinal axis  103  and first and second respective sides  122 ,  222 . The primary plow  120  may include a mold board  124  and a blade  126  operable to displace snow or other debris from a ground surface, such as a driveway or parking lot. It is to be understood that the present disclosure, although described in conjunction with a snow plow, is not limited to a snow plow configured primarily for displacing snow. For instance, the snow plow  100  in an alternative embodiment may be configured as a general plow or blade (e.g., a bulldozer blade) for primarily moving debris or objects other than snow (e.g., snow removal may be an incidental function of the general plow or blade). 
     In the illustrated embodiments of  FIGS.  1 - 3   , the blade  126  of the primary plow  120  may be a wearable component that can be replaced as the edge of the blade  126  wears away. Example types of blades include a polymer-based blade, such as a polyurethane blade or a rubber-based blade, and a metal blade, such as heat treated steel. The blade  126  may be attached to the mold board  124  in a fixed position such that the blade  126  is stationary. Alternatively, the blade  126  may be attached to the mold board  124  in a trippable configuration, such that the blade  126  remains generally stationary in use until an obstruction is encountered that exerts a force on the blade  126  that is greater than a threshold trip force, at which point the blade  126  may move (e.g., rotate relative to a bottom edge of the mold board  124 ) in order to yield to the obstruction. 
     The mold board  124  in the illustrated embodiment may be shaped or configured in a variety of ways, depending on the application. For instance, the mold board  124  in the illustrated embodiment of  FIG.  3    provides a planar surface for pushing snow. However, the mold board  124  may be configured differently, such as having a curved surface for facilitating rolling the snow off the snow plow  100 . 
     The snow plow  100  described herein in conjunction with several embodiments includes a first wing  110  including a main wing portion  112  movable about 1) a first axis  101  and 2) a second axis  102 . The snow plow  100  may include a second wing  210  configured in a manner that mirrors the first wing  110 . Components of the second wing  210  that are similar to the first wing  110  are designated with a  200  series reference number—e.g., the second wing  210  includes a main wing portion  212  similar to the main wing portion  112  of the first wing  110 . Accordingly, for purposes of disclosure, the descriptions of the components of the first wing  110  are not substantially duplicated to describe corresponding components of the second wing  210 . 
     In one embodiment, movement of the main wing portion  112  about the second axis  102  may occur in response to encountering an obstruction that exerts an upward force on the main wing portion  112 , such that the main wing portion  112  may rotate about the second axis  102  in response to the encounter with the obstruction in order to prevent substantial damage to the snow plow  100  due to the encounter. 
     In one embodiment, the main wing portion  112  may be rotated about the first axis  101  backward and forward between positions B and F, shown in the illustrated embodiment of  FIG.  2   . As an example, the main wing portion  112  may be rotated in front of or behind the longitudinal axis  103  of the primary plow  120 . Positions B and F may vary from application to application. For instance, in the illustrated embodiment, position B corresponds to a position of approximately +90° relative to the longitudinal axis  103  of the primary plow  120  shown in  FIG.  2   , and position F corresponds to a position of approximately −90° relative to the longitudinal axis  103  of the primary plow  120 . With respect to the second wing  210 , in the illustrated embodiment, position F corresponds to an angle of approximately −90°, and position B corresponds to an angle of approximately +90°. In the illustrated embodiment, the angles for the positions F and B for the second wing  210  are similar to the angles for the positions F and B for the first wing  110 , but the range of movement for the second wing  210  is different from the range of movement for the first wing  110 . 
     Positions F and B correspond to the limits of movement of the main wing portion  112 , and may vary depending on the application. It is to be understood that an operator may position the main wing portion  112  at a location between positions F and B in use (e.g., to plow an area or to travel). For instance, the operator may position the main wing portion  112  at an angle of 20° in use, and then move the main wing portion  112  to position B for travel. It is also noted that the operator may position the main wing portion  112  of the first wing  110  at an angle different from the position of the main wing portion  212  of the second wing  210 . For instance, the operator may position the main wing portion  212  of the second wing  210  at an angle of +200° (or) −160° about the first axis  201 , and position the main wing portion  112  of the first wing  110  at an angle of −20° about the first axis  101 , thereby positioning one wing forward of the longitudinal axis  103  and the other wing aft of the longitudinal axis  103 . 
     In one embodiment, regardless of the longitudinal axis  103  or the position and configuration of the primary plow  120 , position B may correspond to an angle about the first axis  101  that disposes the first wing  110  in a stowed position such that the main wing portion  112  is generally proximal to and parallel to a side of the vehicle to which the snow plow  100  is mounted. This way, with the first wing  110  in the stowed position, the snow plow  100  may fit within the width constraints imposed by a municipal road for travel thereon. 
     The first wing  110  may include a secondary wing portion  116  pivotably coupled to the primary plow  120  to facilitate rotation of the first wing  110  about the first axis  101 . The secondary wing portion  116  may be pivotably coupled to the primary plow  120  via a joint  117 , which may be defined by a hinge and pin configuration that is provided between the first side  122  and the secondary wing portion  116  and that allows rotation of the first wing  110  about the first axis  101 . The secondary wing portion  116  may be moved via an actuator  114  (e.g., a hydraulic actuator) capable of extending and retracting to rotate the first wing  110  between positions F and B about the first axis  101 . 
     In an alternative embodiment, the actuator  114  may be operable to allow the first wing  110  to pivot toward position B in response to encountering an object that exerts a force greater than a tripping threshold. For instance, the actuator  114  may be configured to retract in response to a force that is applied on the first wing  110  in a direction normal or perpendicular to the first axis  101  and that is greater than the tripping threshold. In this way, the first wing  110  may be configured to yield in response to encountering an obstruction. Example configurations for retracting an actuator  114  in response to an obstruction are described herein, and may be implemented in conjunction with the actuator  114 ; however, it is to be understood that any type of tripping mechanism may be implemented in conjunction with the first wing  110  to facilitate yielding in response to encountering significant obstructions. 
     The first wing  110  may include a wing blade  119 , similar in some respects to the blade  126  of the primary plow  120 . For instance, the wing blade  119  may be a wearable blade capable of being replaced when considered appropriate. The wing blade  119  may also be made of material similar to the blade  126  of the primary plow  120 , such as being made of a polymer or metal material. In the illustrated embodiment, the wing blade  119  may be coupled to a mold board portion  111  of the main wing portion  112  in a stationary manner (e.g., via fasteners). Alternatively, similar to an alternative embodiment of the blade  126 , the wing blade  119  may be coupled to the mold board portion  111  in a manner that allows the wing blade  119  to pivot relative to the bottom edge of the mold board portion  111  in response to encountering an objection that applies a force on the wing blade  119  that exceeds a threshold tripping force. The threshold may be determined based on a variety of factors, including, for instance, a target amount of force for moving debris, strength of the snow plow  100  and the first wing  110 . 
     The main wing portion  112  of the first wing  110  in the illustrated embodiment of  FIG.  1    is operable to rotate about the second axis  102 . The main wing portion  112  may be pivotably coupled to the secondary wing portion  116  such that the main wing portion  112  may rotate about the second axis  102  between positions U and D shown in the illustrated embodiment of  FIG.  1   . Positions U and D may be determined based on target operating conditions. For instance, position U may be determined to be approximately 6 inches of rise with respect to the ground surface or the bottom edge of the blade  126  of the primary plow  120 . Six inches in this example is considered sufficient displacement in order to yield to an obstruction encountered in a driveway or parking lot without significant damage to the snow plow  100  or vehicle  10 . It is noted that position U described herein corresponds to an upper limit of movement of the main wing portion  112 . The main wing portion  112  may be positioned lower than the upper limit corresponding to position U. 
     The obstruction may be encountered in a variety of ways. For instance, when the first wing  110  is rotated about the first axis  101  at −90° in the position F, the toe of the first wing  110  may be susceptible to encountering an object. If such an object is encountered in this position, the first wing  110 , as discussed herein, may rotate upward about the second axis  102 . Such object may take the form of a curb or parking lot divider. 
     In an alternative example, the first wing  110  may be rotated about the first axis  101  at 0° between positions F and B, and an obstruction may be encountered by the wing blade  119  that applies an upward force on the first wing  110 . Such a force, if above a threshold force, may cause the main wing portion  112  to rotate upward as discussed herein. 
     Turning to position D, the main wing portion  112  may pivot downward relative to the second axis  102  to position D, which may vary depending on the application. In the illustrated embodiment, position D corresponds to approximately 3 inches of downward displacement with respect to the bottom edge of the blade  126  of the primary plow  120 . Similar to position U, position D is considered limited with respect to movement of the main wing portion  112 , such that the main wing portion  112  may be positioned between positions U and D. Position D, in one embodiment, may be determined based on the possible extent of wear to the wing blade  119  (e.g., the difference between a new wing blade  119  and a wing blade  119  that is considered to need replacing) and degree of terrain variation to be encountered by the main wing portion  112 . 
     In one embodiment, undulations or unevenness in a driveway or parking lot may be encountered by the first wing  110 . The main wing portion  112  may be biased toward position D, such that contact between the wing blade  119  and the ground is maintained to the extent the undulations are within the range between positions U and D. 
     The connector  150  between the main wing portion  112  and the secondary wing portion  116  of the first wing  110  is shown in further detail in the illustrated embodiment of  FIG.  4   . The connector  150  may include an upper connector  140  and a lower connector  130 . The lower connector  130  may include a plate  132  fixedly connected to the main wing portion  112  and pivotably connected to the secondary wing portion  116 , enabling the main wing portion  112  to pivot or rotate about the second axis  102 . 
     In the illustrated embodiment, the upper connector  140  of the connector  150  may be configured to substantially prevent movement of the main wing portion  112  relative to the secondary wing portion  116  in a direction parallel to the second axis  102 . The upper connector  140 , on the other hand, may be configured to allow rotation of the main wing portion  112  relative to the secondary wing portion  116  with respect to the second axis  102 . 
     The upper connector  140 , in the illustrated embodiment, includes first and second springs  142 ,  144  and a linkage  141 . The linkage  141  may be connected to an anchor  148  of the secondary wing portion  116  and may be operable to slide within a slot of a spring interface  147  of the main wing portion  112 . 
     The first and second springs  142 ,  144  may be configured to act against each other in compression with a balanced position corresponding to a target position of the lower edge of the wing blade  119  being generally parallel with the lower edge of the blade  126  of the primary plow  120 . The first spring  142  may compress relative to an anchor  148  of the secondary wing portion  116  and a spring interface  147  of the main wing portion  112 , enabling the main wing portion  112  to rotate upward to position U in response to a force applied upward on the main wing portion  112  that is greater than a threshold force (which depends at least in part on the stiffness of the first spring  142 ). In the illustrated embodiment, the second spring  144  may operate in compression between a floating anchor  146  and the spring interface  147 , enabling the first spring  142  to urge the main wing portion  112  toward position D but not further than position D. That is, at position D, the first and second springs  142 ,  144  may be in equilibrium, where, in operation and in contact with the ground, the main wing portion  112  may be disposed between positions U and D, and where, in a raised position where the snow plow  100  is lifted off the ground, the main wing portion  112  may rotate to position D. The first spring  142  and second spring  144  in this relationship may operate to urge the wing blade  119  toward the ground to maintain contact between the ground and the wing blade  119  (despite wear). 
     It is noted that in the illustrated embodiments of  FIGS.  1 ,  2 , and  4   , the main wing portion  112  is shown with a gap between the sides  113 ,  115  that increases in size from the lower connector  130  to the upper connector  140 . In this configuration, the side  113  of the main wing portion  112  may move closer to the side  115  of the secondary wing portion  116  as the main wing portion  112  moves toward position U and the first spring  142  is compressed. Alternatively, as depicted in the illustrated embodiment of  FIG.  5   , a first wing  110 ′ is provided similar in some respects to the first wing  110  with several exceptions, including a main wing portion  112 ′ having a side  113 ′ that is proximal to the side  115 ′ of the secondary wing portion  116 ′ such that, with the bottom edge of the main wing portion  112 ′ being substantially parallel to the bottom edge of the secondary wing portion  116 ′, the gap between the sides  113 ′,  115 ′ is substantially the same from between the lower and upper connectors  130 ′,  140 ′. The upper part of the main wing portion  112 ′, proximal to the upper connector  140 ′, may move behind or in front of the secondary wing portion  116 ′ as the main wing portion  112 ′ rotates about the second axis  102 . 
     In an alternative embodiment, depicted in the illustrated embodiment of  FIGS.  6  and  7   , a first wing  110 ″ is provided similar in some respects to the first wing  110 ,  110 ′ with several exceptions. The first wing  110 ″ may include a main wing portion  112 ″ with a mold board portion  111 ″ and a wing blade  119 ″, similar to the main wing portion  112 , mold board portion  111  and wing blade  119 . The first wing  110 ″ may include a lower connector  130 ″ and an upper connector  140 ″ that form part of the connector  150 ″ that couples the main wing portion  112 ″ to the secondary wing portion  116 ″. The lower connector  130 ″ may be similar to the lower connector  130 , including a plate  132 ″ that facilitates rotation of the main wing portion  112 ″ about the second axis  102 . 
     The upper connector  140 ″ in the illustrated embodiments of  FIGS.  6  and  7    may be an actuator  145 ″ connected to an anchor  148 ″ of the secondary wing portion  116 ″ and an anchor  146 ″ of the main wing portion  112 ″. The actuator  145 ″ may be operable to extend or retract to rotate the main wing portion  112 ″ about the second axis  102 . In one embodiment, the actuator  145 ″ may be configured to automatically retract in response to application of force above a threshold trip force on the main wing portion  112 ″ along an axis perpendicular to the second axis  102  (e.g., an upward force on the wing blade  119 ″ that occurs in response to encountering an object). Optionally, the actuator  145 ″ may be configured to extend to rotate the main wing portion  112 ″ into contact with the ground (within the limit of position D) in response to withdrawal of the force that was above the threshold force. Additionally, or alternatively, the actuator  145 ″ may be configured to operate as a type of spring retracting and extending in response to a force less than the threshold trip force in a more controlled, gradual, or slower manner than in retraction in response to a force greater than the threshold trip force. 
     In the illustrated embodiment of  FIG.  7   , the actuator  145 ″ is a hydraulic actuator having a cylinder side coupled to the anchor  148 ″ and a rod side coupled to the anchor  146 ″. A control system  300  may be operable to direct operation of the actuator  145 ″, and may include a directional control valve  302  that, in conjunction with the pilot operated check valves  308 , enables an operator to extend or retract the piston of the actuator  145 ″ based on the position of the directional control valve  302 . The directional control valve  302  is shown in the illustrated embodiment with a manual actuator; however, the present disclosure is not so limited. The directional control valve  302  may be operated via an electromechanical controller. 
     In operation, the directional control valve  302  positioned to connect the pump side to the cap-end of the actuator  145 ″ and the rod-end to the tank reservoir. The pilot actuated check valves  308  may allow the hydraulic fluid to flow from the pump  310  such that the rod extends, causing the anchor  146 ″ to rotate the main wing portion  112 ″ downward toward position D. The relief valve  312  may divert fluid to the tank reservoir in response to the rod of the actuator  145 ″ dead heading or encountering resistance above a threshold. After the operator has extended the actuator  145 ″ to a target position, the directional control valve  302  may be positioned to a neutral position, causing the pilot actuated check valves  308  to close in order to maintain pressure within the actuator  145 ″ to maintain the extended position of the actuator  145 ″. 
     In the illustrated embodiment, the control system  300  includes an adjustable relief valve  306  configured to crack and allow fluid to flow from the cylinder-side of the actuator  145 ″ to the tank reservoir in response to pressure greater than a threshold pressure. The threshold pressure may be determined based on an adjustment of the adjustable release valve  306 , and may be configured to correspond to a target threshold trip force for the actuator  145 ″. In response to the adjustable relief valve  306  opening, the cylinder side and the rod side of the actuator  145 ″ may float, allowing the rod to retract into the cylinder in response to continued application of force above the threshold trip force. This mode of operation may enable the actuator  145 ″ to allow the main wing portion  112 ″ to move toward position U in response to application of force above the threshold trip force. After such a force is withdrawn, the operator or control system  300  may direct the actuator  145 ″ to re-extend for using the first wing  110 ″ to move snow. 
     An alternative embodiment of the control system is shown in  FIG.  8   , and designated  300 ′. The control system  300 ′ may include pilot actuated check valves  308 ′, a pump  310 ′, a relief valve  312 ′, and a directional control valve  302 ′ similar to the correspondingly referenced components of the control system  300 . The adjustable relief valve  306 ′ in the illustrated embodiment is operable to divert fluid from the cylinder-side of the actuator  145 ″ to the tank, allowing the actuator  145 ″ to retract in response to application of force greater than the threshold trip force. The directional control valve  302 ′ may be left in a position to extend the rod of the actuator  145 ″ such that after the force is removed, the rod is extended to an operating position. 
     In the illustrated embodiment of  FIG.  8   , the rod-side flow path includes a check valve and a restrictor  305 ′ operable to allow fluid flow into the rod-side more quickly than out of the rod-side. This configuration may enable the actuator  145 ″ to retract more quickly than it extends. 
     The snow plow  100  may be coupled to the vehicle  10  in a variety of ways, as discussed herein. The snow plow  100  in the illustrated embodiment of  FIG.  3    is coupled to the vehicle via a hitch system  12 . The hitch system  12  may interface with the snow plow  100  to enable removable coupling between the vehicle  10  and the snow plow  100 . As discussed herein, the snow plow  100  is shown coupled to the rear of the vehicle  10 ; however, the present disclosure is not so limited. The snow plow  100  may be coupled to the front of the vehicle  10  via a hitch system or vehicle connection system configured to facilitate such a connection to the front of the vehicle  10 . An example hitch system for the snow plow  100 , in one embodiment, is described in U.S. Pat. No. 10,150,428, entitled ADAPTABLE HITCH SYSTEM, filed Feb. 19, 2018, issued Dec. 11, 2018, to Weihl—the disclosure of which is hereby incorporated by reference in its entirety. An example connection system for the snow plow, in one embodiment, is described in U.S. Patent Application 62/940,590, entitled PLOW ASSEMBLY LINKAGE, filed Nov. 26, 2019, to Weihl—the disclosure of which is hereby incorporated by reference in its entirety. 
     I. Front Plow 
     In an alternative embodiment, a snow plow  1000  is a front-blade plow. One embodiment of the snow plow  1000  as a front-blade plow mounted to the front of the vehicle  10  is depicted in  FIG.  9   . The snow plow  1000  may be similar to the snow plow  100  described above with the primary exception of its mounting position on the vehicle  10 . However, the snow plow  1000  has some differences from one or more embodiments described herein. The snow plow  1000  may be coupled to a vehicle support  1412  via a plow support  1380 . 
     In one embodiment, the snow plow  1000  may include a primary plow  1120  coupled to the plow support  1380 . The snow plow  1000  may also include a first wing  1110  and a second wing  1210 . The first wing  1110  may be rotatably coupled to the primary plow  1120  on a first side  1122  via a joint  1117 . The joint  1117  may vary from application to application, and is depicted as a hinge and pin configuration but the disclosure is not so limited. The joint  1117  allows the first wing  1110  to rotate about an axis  1101  to position F and position B as described with respect to  FIG.  2   . However, position F and position B may not be at the same angular positions as described above and may vary based on the application. Rotation about the axis  1101  allows the first wing  1110  to rotate toward the vehicle  10  to position B, which may allow the vehicle  10  to fit within a standard vehicle lane while travelling. The first wing  1110  can also rotate away from the vehicle  10  to position F. The first wing  1110  may be rotated by an actuator  1114 , which is described below with reference to  FIG.  10   . In the illustrated embodiment a limiter  1135  is provided to contact a surface  1139  of the first wing  1110  at one or more limit positions to prevent further movement. In the illustrated embodiment, the limiter may be configured to interface with the first wing  1110  at positions F and B to prevent further rotation outside the range between F and B. 
     Components of the second wing  1210  that are similar to the first wing  1110  are designated with a  1200  series reference number—e.g., the second wing  1210  may rotate about an axis  1201  similar to how the first wing  1110  may rotate about an axis  1101 . Accordingly, for purposes of disclosure, the descriptions of the components of the first wing  1110  are not substantially duplicated to describe the corresponding components of the second wing  1210 . 
     The first wing  1110  may include a main wing portion  1112  and a wing blade  1119 . The wing blade  1119  may be fixedly connected to the main wing portion  1112 , or the wing blade  1119  may be able to rotate upwards, for example in response to a change in contour of the ground or encountering debris or an obstruction that exerts a force greater than a tripping threshold. In one embodiment, the wing blade  1119  may include a pivot portion  1118  and a sliding portion  1121 . In the depicted embodiment, the sliding portion  1121  includes a fastener seated within or captured by a channel or slot to allow the wing blade  1119  to move upward in response to an upward force (e.g., a tripping force or the ground in response to a change in surface contour), while maintaining a coupling between the sliding portion  1121  and the main wing portion  1112 . The wing blade  1119  may rotate about the pivot portion  1118  such that the sliding portion  1121  moves from position L to position H. The position L may correspond to a position lower than a ground contacting plane  1125  defined by the blade  1126  of the primary plow  1120 , and position H may correspond to a position higher than this ground contacting plane  1125  defined by the wing blade  1119 . In use, the position of the sliding portion  1121  of the wing blade  1119  may be between position L and H with the wing blade  1119  contacting the ground. The position of the sliding portion  1121  may vary as the contour of the ground changes. As described herein, the sliding portion  1121  of the wing blade  1119  may be biased toward the ground such that, as the snow plow  1000  travels along the ground and the ground contour lowers relative to a current position of the sliding portion  1121 , the sliding portion  1121  may lower toward position L to follow the contour of the ground. Conversely, the sliding portion  1121  may lift toward position H as the ground contour rises as the snow plow  1000  travels over the ground and the height of the ground near the sliding portion  1121  is different from the height of the ground near the pivot portion  1118 . The bias force may vary from application to application, and may be determined selectable, in operation, installation, or the design stage, or a combination thereof, to enable the sliding portion  1121  of the wing blade  1119  to substantially maintain contact of the wing blade  1119  with the ground and to allow upward movement in response to changes in ground contour and/or an encounter with an obstruction. 
     In one embodiment, a distal portion  1131  of the wing blade  1119  distal from the pivot portion  1118  may be angled, (e.g., sloped or ramped) or curved, which may allow the distal portion  1131  to engage a potential obstruction and cause the wing blade  1119  to pivot upward toward H in response to encountering the obstruction. For instance, the angled or curved construction of the distal portion  1131  may direct an obstruction under the wing blade  1119  toward a bottom portion of the main blade  1126  so that the plow  1000  ride over the obstruction. 
     The wing blade  1119  in the illustrated embodiment pivots about an area proximal to the pivot portion  1118 , such that the pivot portion  1118  is near to or aligned with the plane of the adjacent segment&#39;s blade (e.g., main blade  1126 ). In response to the distal portion  1131  encountering an obstruction, the distal portion  1131  may begin to ride over the obstruction, causing the wing blade  1119  to pivot upward toward position H, and allowing the entire undersurface of the wing blade  1119  to ride over the obstruction. In this circumstance, because the undersurface of the wing blade  1119  leads to the pivot portion  1118  near or aligned with the plane of the blade  1126  (e.g., a main blade), the wing blade  1119  may raise the blade  1126  to clear the obstruction. As described herein, a movable component capable of pivoting in accordance with one or more embodiments described in conjunction with the wing blade  1119  may be incorporated into any segment of a plow construction, including segments of a V-blade. And although the wing blade  1119  is shown operable to pivot relative to an area proximal to a connection to another segment of a plow, it is to be understood that the wing blade  1119  may pivot relative to an area distal from a connection to another segment of the plow. 
     The distance from position L to position H may vary depending on the application. In one example, the distance from position L to position H may be six inches, with L being two inches lower than the ground contacting plane  1125 , and H being four inches higher than the ground contacting plane  1125 . Six inches in this example is considered sufficient displacement in order to yield to an obstruction encountered in a driveway or parking lot without significant damage to the snow plow  1000  or vehicle  10 , or to follow changes in the contour of the ground while maintaining contact with the ground. It is noted that position H described herein corresponds to an upper limit of movement of the wing blade  1119 . Depending on the strength of the tripping force exerted on the wing blade  1119  and the changes in contour of the ground, the sliding portion  1121  might not move all the way up to position H. 
     The wing blade  1119  and the blade  1126  are wearable components of the snow plow  1000 , generally meaning that the ground contacting surfaces of the wing blade  1119  and the blade  1126  wear away in response to repeated contact with the ground. Because the sliding portion  1121  of the wing blade  1119  is biased downward, in one embodiment, despite wear of the wing blade  1119  or the blade  1126 , or both, the sliding portion  1121  may be operable to maintain contact with the ground. 
     The distance L may vary as the wing blade  1119  wears away near the sliding portion  1121  and the pivot portion  1118  of the wing blade  1119 . For instance, as the main blade  1126  wears, the pivot portion  1118  of the wing blade  1119  may wear as well, raising the ground contacting plane  1125  over time relative to a new set of blades. The sliding portion  1121  may or may not wear at the same rate as the pivot portion  1118  and the blade  1126 . However, because the sliding portion  1121  may raise and lower, despite changes in the ground contacting plane  1125 , the sliding portion  1121  may be operable to maintain contact with the ground. If the sliding portion  1121  wears away in this configuration, the amount of allowable travel (e.g., L, H, or both) may vary. The sliding portion  1121  may wear such that L, H, or both, are considered insufficient, such as the upward movement capability of H becomes insufficient to allow the sliding portion  1121  to move upward to track changes in ground contour or to move in response to encountering an obstruction. In this case, the wing blade  1119  may be replaced along with one or more other blades of the snow plow  1000 . 
     In one embodiment, the wing blade  1119  may be referred to as the main wing portion and the main wing portion  1112  may be described as a secondary portion of the wing blade  1119 . For instance, the first wing  1110  and a similarly configured second wing  1210  may be incorporated into the snow plow  1000  described herein, with the wing blade  1119  of the first wing  1110  being the main wing portion of the snow plow  1000  that is capable of pivoting, and the main wing portion  1112  of the first wing  1110  being the secondary portion of the snow plow  1000  that is coupled to a first side of the primary plow of the snow plow  1000 . The wing blade  1119  may rotate about a second axis between position L and position H similar to rotation of the main wing portion  112  of  FIGS.  1 - 6    being allowed about the axis  102  between position U and position D. The main wing portion  1112  may be rotatably coupled to the primary plow  1120  similar in rotation of the secondary wing portion  116  of  FIGS.  1 - 6    relative to a first side of the primary plow  120  about the axis  101 . 
     Turning to the illustrated embodiment of  FIG.  10   , a rear perspective view of a portion of the snow plow  1000  is shown.  FIG.  10    shows the rear of the first wing  1110  and the primary plow  1120 . In one embodiment, the wing blade  1119  may move from position L to position H based on movement of an actuator  1145 . In the depicted embodiment, the actuator  1145  is a hydraulic actuator having a cap side  1147  coupled to the main wing portion  1112  and a rod side  1148  coupled to an anchor  1146 . The anchor  1146  is coupled to the wing blade  1119  and operable to move the wing blade  1119 . In the depicted embodiment, the cap side  1147  of the actuator  1145  is filled with a compressible gas (e.g., nitrogen gas), which biases the rod toward an extended position, which is downward in the illustrated embodiment. An amount of hydraulic fluid on the rod side  1148  of the actuator  1145  may be selectively changed, e.g., by increasing or decreasing the fluid pressure on the rod side  1148 . The hydraulic fluid pressure on the rod side  1148  may be transitioned to a float mode in which the hydraulic fluid is neither increasing or decreasing the fluid pressure on the rod side  1148 . In this float mode, the compressible gas may extend the actuator  1145  until sufficient resistance is met from either the ground by the wing blade  1119  or a mechanical limit of extension of the actuator  1145 . 
     In one embodiment, the cap side  1147  of the actuator  1145  may include an accumulator (e.g., a reservoir or tank) for the compressible gas. The accumulator may be integrated into the cap side  1147  of the actuator  1145  or may be external to the actuator  1145 . By providing compressible gas on one side of the actuator  1145 , a hydraulic coupling to this side of the actuator  1145  can be left out or absent from the hydraulic system. As a result, in one embodiment, the actuator  1145  may be coupled to only one hydraulic hose  1149  or a single hydraulic coupling. The greater the number of hydraulic hoses and couplings, the greater the complexity of the system, for installation, operation, and maintenance. With fewer hydraulic hoses and couplings in accordance with one embodiment, the installation time and maintenance time of the snow plow  1000  may be reduced, and operation can be more robust. Conventional hydraulic systems require more complicated control as operation requires that hydraulic fluid is pushed to one side of the cylinder while simultaneously being removed from the other. One embodiment according to the present disclosure may not rely on simultaneous control of fluid on the rod side  1148  and the cap side  1147  of the actuator  1145 . 
     Although the present disclosure is described in conjunction with the cap side  1147  including a compressible gas and biasing the actuator  1145  toward an extended position, the present disclosure is not so limited. Alternatively, the rod side  1148  may include a compressible gas (optionally coupled to an external accumulator), and the cap side  1147  may be coupled to a hydraulic system for controlling the amount of hydraulic fluid in the cap side  1147 . This alternative construction may be configured with the compressible gas on the rod side  1148  biasing the actuator  1145  toward a contracted position. As described herein, the actuator  1330  is configured in this manner to facilitate tilting of a top portion of the snow plow  1000  forward about an axis of rotation in response to the blade  1126  encountering an obstruction. 
     In one embodiment, in response to the wing blade  1119  encountering a sufficient force to overcome the bias of the actuator  1145  (e.g., a tripping force or a change in ground contour), the compressible gas of the cap side  1147  of the actuator  1145  may operate as a spring and allow the rod to move upwards therefore moving the wing blade  1119 . In response to a force sufficient to overcome the spring force (e.g., the bias force) of the compressed gas, more hydraulic fluid may flow into the rod side  1148  of the actuator  1145  while the compressible gas compresses (optionally, compressing in an external accumulator). If the force is no longer present, the compressible gas may expand from the accumulator (internal and/or external) back to the cap side  1147  of the actuator  1145 , biasing the rod downwards or to an extended position and moving the wing blade  1119  to maintain contact with the ground. The fluid on the rod side  1148  may be forced back to the tank of the hydraulic system by the compressible gas with the force no longer being present. The compressible gas may keep or maintain the sliding portion  1121  of the wing blade  1119  in contact with the ground (or at a set position) even while the other portions of the wing blade  1119  wear away, and even in cases where other portions of the wing blade  1119  are worn such that they are no longer in contact with the ground. It is to be understood that the actuator  1145  is one example of a tripping mechanism, ground follow mechanism, or bias mechanism to a set position, or any combination thereof, and that any type of tripping mechanism, ground follow mechanism, or bias mechanism may be used in conjunction with the wing blade  1119  to facilitate yielding in response to encountering a tripping force and/or in response to forces that overcome the bias force of the actuator  1145 . The hydraulic fluid on the rod side  1148  in this example may be provided in a float mode that allows the fluid to readily pass into and out of the rod side  1148  in response to movement of the actuator  1145 . 
     A control method for the control system in accordance with one embodiment for operation of the actuator  1145  is shown in  FIG.  11   . The method  1300  is focused generally toward operation of a system configured to retract and extend the wing blade  1119 . The control system may be configured to direct operation of one or more other actuators in a similar manner. 
     In addition to the operation of the actuator  1145  described in conjunction with tripping in response to an obstruction and/or moving based on changes in the ground contour, a control system may be operable to direct operation of the actuator  1145 . The control system may provide manual control, electromechanical control, or a combination of the two, over the plow. An operator may control the position of the snow plow  1000  by signaling the control system to control the hydraulic fluid in the system, such as by extending or retracting the lift actuator  1416 . If an operator directs the snow plow  1000  to move upward, for example to raise the snow plow  1000  for stacking or transport, the operator may signal (e.g., provide user input) to the control system to supply more hydraulic fluid to the rod side of the actuator  1416 , thus causing the rod to retract. The supply of hydraulic fluid to the rod side of the actuator  1416  may also be fluidly coupled to the rod side  1148  of the actuator  1416 , such that, in response to providing hydraulic fluid under pressure to the rod side of the actuator  1416 , the actuator  1145  for the wing blade  1119  retracts first (compressing the gas) until a mechanical limit of retraction is reached, and then the lift actuator  1416  raises and retracts. Steps  1320 ,  1322 ,  1324 . 
     Conversely, if the operator provides a signal to the control system to lower the snow plow  1000 , the system may supply hydraulic fluid to the cap side of the lift actuator  1416  under pressure and may cause the lift actuator  1416  to extend, and displace fluid from the rod side of the lift actuator  1416  under pressure. Step  1302 ,  1304 ,  1306 . Because the actuator  1145  is fluidly coupled to the rod side of the lift actuator  1416 , this pressure on the rod side of the lift actuator  1416  may maintain the position of the actuator  1145  in the retracted position (with the gas in a compressed state). After the lift actuator  1416  is fully extended such that the snow plow  1000  contacts the ground (or the mechanical limit of the lift actuator  1416  is reached), the pressure on the rod side of the lift actuator  1416  (due to supply of fluid to the cap side) may subside and the actuator  1145  may extend because the compressed gas in the actuator  1145  is no longer under pressure from fluid on the rod side  1148  of the actuator  1145 . Step  1308 ,  1310 . In this way, the actuator  1145  may automatically extend in response to the snow plow  1000  contacting the ground, and may automatically retract just prior to the snow plow  1000  being raised off the ground. 
     In other words, at a start  1302 , the rod of the actuator  1416  may be disposed in a retracted position with the plow in an up position (for stacking or transport). The hydraulic pressure on the rod side of the actuator  1416  may also be provided to the rod side  1148  to compress the gas on the cap side  1147  of the actuator  1145 , maintaining the wing blade in an up position proximal to position H. 
     At step  1304 , the control system may receive a directive from the operator to lower the snow plow  1000 . Hydraulic fluid may be provided to the lift actuator  1416  under pressure to cause the lift actuator  1416  to extend. In response, hydraulic fluid may be evacuated from the lift actuator  1416  under pressure, maintaining the actuator  1145  in a retracted position. After the lift actuator  1416  extends the plow to the ground position, pressure on the rod side  1148  of the actuator  1145  may subside, allowing the compressed gas to extend the actuator  1145  to move the wing blade  1119  into contact with the ground. Step  1310 . The compressed gas may bias the wing blade  1119  toward ground contact, and may allow the wing blade  1119  to move upward automatically in response to changes in the ground contour and/or engagement with an obstruction. Steps  1312 ,  1314 ,  1316 ,  1318 . 
     The wing blade  1119  may move upward automatically based on presence of an upward force greater than a bias force provided by the compressible gas. The upward force may be provided by a trip condition, such as a force provided in response to the wing blade  1119  encountering an object. Alternatively, the upward force may be provided by a change in contour of the ground that is not seen by the primary plow  1120  (e.g., the ground contacting plane  1125  of the primary plow  1120  is substantially unchanged, but the ground near the sliding portion  1121  of the wing blade  1119  is rising). Step  1312 . 
     If the force encountered by the wing blade  1119  does not overcome the bias force, the wing blade  1119  may remain substantially stationary. The bias force may vary as a function of the position of the wing blade  1119 . Because the gas in the actuator  1145  is compressible, the bias force provided by gas may increase as the gas pressure rises in response to upward displacement of the rod of the actuator  1145 . If the wing blade  1119  has encountered a force exceeding the bias force, the control system may provide hydraulic fluid to the rod side  1148  of the actuator  1145  and the pressure of the compressible gas may increase. Step  1314 . As a result, the rod may retract and therefore move the sliding portion  1121  of the wing blade  1119  upward. In the illustrated embodiment, the sliding portion  1121  of the wing blade  1119  can move no farther upward than position H, which may be set by a physical configuration of the first wing  1110  (e.g., a stop or the actuator  1145 ). In one embodiment, the sliding portion  1121  may not move to position H in response to the upward force, and instead may move toward position H but not all the way to position H because the upward force may balance with the increasing bias force (due to compression of the gas) prior to the wing blade  1119  reaching position H. 
     Depending on the magnitude of upward force, the sliding portion  1121  (and consequently the wing blade  1119 ) may move to any position between position L and position H. If the upward force is removed or reduced, the sliding portion  1121  may move toward position A (between L and H), and hydraulic fluid on the rod side  1148  may be returned from the actuator  1145  to the hydraulic system. Step  1318 . As mentioned herein, position A may correspond to a ground contact position, or position A may be above the ground such that there is a space between the wing blade  1119  and the ground. 
     If the wing blade  1119  has not encountered an upward force that overcomes the bias force, and the control system has received a signal from an operator to request to move the snow plow  1000  upward, the control system may direct the wing blade  1119  and the snow plow  1000  to move upward. If the control system has not received a signal requesting the wing blade  1119  move upward or downward, the control system may continue to maintain the actuator  1145  at position A, waiting for either an upward force that exceeds the bias force or an operator providing a signal to move the wing blade  1119 . 
     If the control system has received a signal from an operator requesting to move the snow plow  1000 , the control system may determine if the signal pertains to an upward movement request. Step  1320 . If the operator has requested upward movement, the hydraulic system may push hydraulic fluid to the rod side of the lift actuator  1416 . Step  1322 . In one embodiment, in response to additional hydraulic fluid on the rod side of the lift actuator  1416  and the actuator  1145 , the pressure of the compressible gas may increase, while the rod retracts and the wing blade  1119  moves upward toward position H. After the actuator  1145  can retract no further, the pressure on the rod side of the lift actuator  1416  may cause the lift actuator  1416  to retract. 
     In the embodiment depicted in  FIG.  10   , an actuator  1114  is provided to operably rotate the first wing  1110  about the first axis  1101  between the F and B positions noted in conjunction with  FIG.  2   . The actuator  1114  may be a hydraulic actuator with its rod coupled to a bracket  1134  and its cylinder coupled to the back of a mold board  1124  of the primary plow  1120 . As the rod retracts and extends, the rod actuates the bracket  1134  to rotate the first wing  1110  about the axis  1101 . In the illustrated embodiment, the actuator  1114  may have hydraulic fluid on both the rod side and the cap side of the cylinder. Alternatively, the cap side of the actuator  1114  may include compressible gas operable to bias the actuator  1114  toward an extended position, but operable to allow the first wing  1110  to move toward position B in response to encountering a force that overcomes the bias force of the actuator  1114  (e.g., encountering an obstruction). Alternatively, the rod side of the actuator  1114  may include a compressible gas operable to bias the actuator  1114  toward the retracted position B, and hydraulic fluid may be supplied or removed from the cap side to position the actuator  1114  at position F or between position F and B, compressing the gas on the rod side of the actuator  1114 . In this configuration, if the first wing  1110  encounters an obstruction as the vehicle is being backed up (e.g., backing up while the first wing  1110  encounters a light post), the actuator  1114  may automatically extend and allow the first wing to rotate toward position F. 
     It is to be understood that any of the actuators described herein with compressible gas may be positioned in this manner by supplying or removing hydraulic fluid on the side opposite of the compressible gas, or allowed to float such that the compressible gas biases the actuator to a mechanical limit of the actuator and/or the plow portion coupled to the actuator. 
     An operator may use the control system to rotate the first wing  1110  in accordance with the operator&#39;s directive in operation. When the control system adds hydraulic fluid to the cap side of the actuator  1114  and removes hydraulic fluid from the rod side of the actuator  1114 , the rod extends and the first wing  1110  rotates about the axis  1101  away from the vehicle  10  to the requested position up to position F. When the control system adds hydraulic fluid to the rod side of the actuator  1114  and removes hydraulic fluid from the cap side of the actuator  1114 , the rod retracts and the first wing  1110  rotates around the axis  1101  toward the vehicle  10  to the requested position up to position B. The extent to which the first wing  1110  can rotate in either direction around the axis  1101  may depend on the application. The second wing  1210  rotates in a similar manner but may have a different range of rotation than the first wing  1110 , e.g., position F for the second wing  1210  may not correspond to position F for the first wing  1110 . 
     In an alternative embodiment, the actuator  1114  may be operable to allow the first wing  1110  to pivot toward the vehicle  10  up to position B in response to the snow plow  1000  encountering an object that exerts a force greater than a tripping threshold or bias threshold. For example, the actuator  1114  may be configured to retract the rod in response to a force that is applied on the first wing  1110  in a direction normal or perpendicular to the first axis  1101  and that is greater than the tripping threshold. In this way, the first wing  1110  may be configured to yield in response to encountering an obstruction thus potentially limiting damage to the first wing  1110  and the snow plow  1000 . While the actuator  1114  is used in this example, it is to be understood that any type of tripping mechanism may be implemented in conjunction with the first wing  1110  to facilitate yielding in response to encountering significant obstructions, including compressed gas on one-side of the actuator  1114 . 
     In  FIG.  12   , another view of the rear of the snow plow  1000  of  FIG.  9    is shown.  FIG.  12    focuses on the primary plow  1120 . In the illustrated embodiment, two actuators  1330  are shown and are connected to the rear of the primary plow  1120  on the rod side and at an angle. On the cylinder side, the actuators  1330  are attached to a plow interface  1340 , about which the primary plow  1120  may pivot. The plow interface  1340  is secured to the rear of the primary plow  1120  in a pivotable manner, such that the primary plow may pivot about a longitudinal axis  1103  parallel to a forward face of the primary plow  1120  (e.g., parallel to the mold board  1124 ). The actuators  1330  may extend and retract to rotate the primary plow  1120  about this longitudinal axis  1103 . The actuators  1330  may be coupled to the mold board  1124 , as depicted in the illustrated embodiment, and can be secured to the primary plow  1120  by any suitable means, including removable pins. 
     In the illustrated embodiment, the actuators  1330  are hydraulic actuators with compressible gas on the rod side of the actuator  1330  and hydraulic fluid on the cap side of the actuator  1330  such that the rod is retracted and biased inward by the compressible gas on the cap side. The rod side of the actuator  1330  may include an accumulator, integral or external to the actuator  1330 , filled with the compressible gas. The actuators  1330  may be operable in a manner similar to the actuator  1145 , with the exception of the actuator  1330  being configured to extend instead of retract in response to a threshold force whereas the actuator  1145  may be retracted in response to a threshold force. For example, with the snow plow  1000  in the down position with the hydraulic fluid in float mode for the rod side of the lift actuator  1416 , force applied to the bottom of the mold board  1124  may apply longitudinal force on the actuator  1330  to compress the compressible gas in the actuator  1330  and cause the actuator  1330  to extend until a mechanical limit is reached. In response to the blade  1126  encountering an obstruction, the actuator  1330  may extend compressing the gas. 
     If the primary plow  1120  encounters a tripping force (e.g., in response to the main blade  1126  of the primary plow  1120  encountering an obstruction), the compressible gas may operate in a spring-like manner, allowing the actuators  1330  to extend as the gas further compresses. If the actuators  1330  are coupled to external accumulators, gas in the rod side and the accumulator may compress and hydraulic fluid may float supplied to the cap side of the actuator  1330  such that the rod extends. As the rod extends, the primary plow  1120  rotates about a longitudinal axis  1103  such that a blade  1126  of the primary plow  1120  moves toward the vehicle  10  while the upper edge of the primary plow  1120  moves away from the vehicle  10 . If the tripping force occurred because the primary plow  1120  encountered an obstruction, this tripping behavior may reduce or minimize damage to the primary plow  1120  and the snow plow  1000 . After the tripping force is no longer present, the compressible gas expands in the rod side of the actuator  1130  and at least a portion of the hydraulic fluid on the cap side of the actuator  1130  may be returned to the hydraulic system, such that the rod of the actuator  1130  retracts. 
     The actuators  1330  can also be controlled by the control system in a manner similar to method  1300 , with the exception of the actuators  1330  being biased toward a retracted position and the forces and positions pertaining to the position of the actuators  1330  instead of the actuator  1145 . In one embodiment, an operator can direct the control system to extend or retract the actuators  1330  to rotate the primary plow  1120  respectively forward or back about the longitudinal axis  1103 . To rotate the primary plow  1120  forward, the control system may provide hydraulic fluid to the cap side of the actuators  1330  (via supply of fluid to the fluidly coupled rod side of the lift actuator  1416 ) further compressing the compressible gas as the rod extends (optionally extending to its maximum length). 
     In one embodiment, the actuators  1330  (or any actuator described herein) may be replaced with a coupler configured similar to the actuator  1145 . The coupler in this configuration may include compressible gas on a rod-side or a cap-side that biases the coupler respectively to a retracted position or an extended position. Extension or retraction may be mechanically limited by the coupler itself (e.g., full extension or retraction) or by a mechanical stop provided by the snow plow  1000 . The coupler may extend or retract in a direction opposite the bias direction, thereby compressing the gas provided in the coupler. This extension or retraction may allow the snow plow  1000  to move in response to an applied force greater than the bias force provided by the compressed gas in the coupler. As an example, in the case of the actuator  1330  being provided with compressible gas on a rod side of the actuator  1330 , the coupler may be biased toward a retracted position by compressible gas. In response to the blade  1126  of the snow plow  1000  encountering an obstruction, the coupler may extend (compressing the gas further) and allow the snow plow  1000  to yield or move in response to the obstruction. After the obstruction or an applied force is no longer present, the coupler may retract to the bias position. This type of coupler may be used in place of conventional springs provided to allow a conventional plow to tilt forward in response to the plow hitting an obstruction. It is further noted that a coupler having compressible gas in accordance with one embodiment may avoid multiple of such conventional springs, with a more compact configuration and may further be adjustable by changing the pressure of the compressible gas. It is further noted that the coupler in one embodiment of the present disclosure, in contrast to a conventional extendable spring configuration for a plow, can be configured with a bias force for extension or retraction. 
     In the illustrated embodiments, one or more actuators (or a coupler) may include compressible gas (internal and/or external). The compressible gas may be provided to an actuator via a valve  1133 ,  1137  (e.g., a Schrader valve). The pressure of the compressible gas in an actuator can be varied via the valve, allowing adjustment of a bias force of the actuator. 
     In the illustrated embodiment of  FIG.  12   , the snow plow  1000  is coupled to a vehicle support  1412  in a pivotal manner relative to first and second vehicle couplings  1414 . The vehicle support  1412  may be removably coupled to the frame of the vehicle  10 , in accordance with one or more embodiments described herein, including the configuration described in connection with the snow plow  2000 . The plow support  1380  may be raised and lowered relative to the vehicle support  1412  by a lift actuator  1416 , which is coupled to the plow support  1380  via lift coupling  1418 . For instance, the lift actuator  1416  may be extended to lower the snow plow  1000  into contact with the ground, and the lift actuator  1416  may be retracted to raise the snow plow  1000  for transportation. As described herein, first and second actuators  1370  may extend and retract to move the snow plow  1000  proximal to and distal from the vehicle  10 . In a transport mode, the first and second actuators  1370  may retract the snow plow  1000 , the lift actuator  1416  may raise the snow plow  1000 , and the actuator  1114  may move the wings to the B position, such that the snow plow  1000  is close to the vehicle, clears the ground, and fits within lane constraints of the road. 
     The first and second vehicle couplings  1414  and a coupling of the lift actuator  1416  opposite the lift coupling  1418  may be disconnected by an operator to remove the plow support  1380  and the snow plow  1000  from the vehicle support  1412 . Alternatively, the snow plow  1000  may be removed from the vehicle  10  via a vehicle support  1412  configured similar to the vehicle support  2412  described herein, and operated to disconnect from a vehicle mount  112 . 
     The snow plow  1000  is described herein in conjunction with one or more actuators or couplers having compressible gas to bias the actuator or coupler toward a retracted or extended position and to allow extension or retraction in response to an applied force. It is to be understood that the snow plow  1000  is not so limited. An external spring or spring-like component may be provided in conjunction with one or more actuators or couplers to bias toward a retracted or extended position and facilitate extension or retraction in response to an applied force. For instance, a compressible spring may be provided in conjunction with the actuator  1370  to bias the actuator  1370  and the plow toward the O position. In response to the plow encountering an obstruction or a force applied toward position I, the compressible spring may enable the plow and the actuator  1370  to retract. 
     In the illustrated embodiments of  FIGS.  12  and  14   , the snow plow  1000  and the blade  1126  may be lifted off the ground by retraction of the lift actuator  1416 . The angle of the snow plow  1000  relative to the longitudinal axis  1103  may be varied by the actuators  1330 . With this arrangement, the forward position and height of the snow plow  1000  and blade  1126  can be controlled while also maintaining an angle of the snow plow  1000  relative to the longitudinal axis  1103 . In the illustrated embodiment, in response to lifting the snow plow  1000  to a raised position, the actuators  1330  may extend due to pressure in the hydraulic system and tilt the snow plow forward in a raised position. 
     In an alternative embodiment, the angle of the snow plow  1000  may be controlled separately from the position of the lift actuator  1416 . For instance, the angle of the snow plow  1000  may be kept in a generally vertical manner by extending or retracting the actuators  1330  based on the forward position and height of the snow plow  1000  determined by the lift actuator  1416  and the first and second actuators  1370 . 
     By controlling the angle of the snow plow  1000  in conjunction with the height and forward position, the snow plow  1000  can be maneuvered to comply with road width limitations, avoid contact between the wings  1112 ,  1212  and the ground (particularly the tips of the wings  1112 ,  1212  as depicted in  FIG.  14   ). Additionally, the snow plow  1000  can be transitioned among various modes of operation, including a plow mode with the snow plow  1000  in contact with the ground, a stacking mode in which the snow plow  1000  is raised for pushing and stacking snow above the ground, and a transportation mode in which the snow plow  1000  is stowed for travel. In these various modes, despite changes in height and forward position of the snow plow  1000  relative to the vehicle, the angle of the snow plow  1000  may be adapted to be generally vertical (or another angle in accordance with operator directive). 
     To rotate the primary plow  1120  backward, the control system may remove hydraulic fluid or remove pressure from the cap side of the actuator  1330  so that the compressible gas can further retract the rod. Depending on the height of the primary plow  1120  and the first and second wings  1112 ,  1212 , and the position of the first or second wings  1112 ,  1212  relative to the B and F positions, the primary plow  1120  may be limited in rotating backward around the longitudinal axis  1103  because the first wing  1110  and the second wing  1210  may come into contact with the ground. Contact in this manner may cause wear or damage to the wing blades  1119 ,  1219 . The angle of the primary plow  1120  and/or the height of the wing blades  1119 ,  1219  may be adjusted as the height of the primary plow  1120  is varied by retraction of the lift actuator  1416 , as shown for example in the transition to the plow mode depicted in  FIG.  14   . The positions of the actuators shown in  FIG.  14    for the various modes of operation may or may not correspond to the maximum retraction or extension of the actuators, depending on the application. 
     The position of the snow plow  1000  may be obstructed from the driver&#39;s view by portions of the vehicle  10 . For instance, from his or her position in the cabin of the vehicle  10 , the driver may be unable to see the position of the snow plow  1000  over the hood of the vehicle  10 . To facilitate visibility, the snow plow  1000  may include one or more visibility markers  1020 . The visibility markers  1020  may be attached to the outer edges of the primary plow  1120 , the first wing  1110 , and the second wing  1210 . The visibility markers  1020  allow a driver of the vehicle  10  to more easily see the position of the snow plow  1000 . 
     In the illustrated embodiment, the vehicle support  1412  may be removably coupled to the frame of a vehicle  10 , via a vehicle mount  112 . The snow plow  1000  may be releasably coupled to the vehicle  10  via coupling between the vehicle support  1412  and the vehicle mount  112 . The snow plow  1000  can be retrofitted for a range of mounting configurations for the vehicle  10  and is not limited to the vehicle support  1412 . 
     In one embodiment, the plow support  1380  of the snow plow  1000  comprises a receiver  1350 , which may be configured to support a receiver interface  1360 . The plow support  1380  may removably attach to the vehicle support  1412 . The receiver  1350  of the plow support  1380  and the receiver interface  1360  may allow the snow plow  1000  to move proximally and distally relative to the vehicle  10 . As shown in  FIG.  13   , the receiver  1350  is coupled to the plow support  1380 , and the plow support  1380  is attached to the vehicle support  1412 . Alternatively, the receiver  1350  may be coupled directly to the vehicle support  1412 . In the depicted embodiment, the receiver  1350  defines an opening configured to receive a receiver interface  1360  and the receiver interface  1360  is movably coupled to the receiver  1350 . For example, the receiver interface  1360  may be a protrusion or a shank. As depicted, the receiver interface  1360  forms part of the plow interface  1340  and extends from the rear surface of the primary plow  1120 . In an alternative embodiment, the receiver interface  1360  may be a separate component from the plow interface  1340  and may not be coupled to the plow interface  1340 . In another alternative embodiment, the receiver interface  1360  may be a separate component from the plow interface  1340  but may be coupled to the plow interface  1340 . In one embodiment, the receiver  1350  and the receiver interface  1360  are operable to restrict movement in directions perpendicular to a longitudinal axis of the receiver  1350  such that movement is substantially prevented in directions perpendicular to the longitudinal axis. 
     The receiver  1350  may be coupled to at least one actuator  1370  via the plow interface  1340 . The actuators  1370  may be coupled to the plow support  1380  on the cylinder side and to the plow interface  1340  on the rod side. In an alternative embodiment, the actuators  1370  may be directly coupled to the receiver  1350  on the cylinder side, directly coupled to the mold board  1124  on the rod side, or both. As depicted, the actuators  1370  are hydraulic actuators with hydraulic fluid on both the rod side and compressed gas on the cap side of the cylinder. The actuators  1370  may be biased in the extended position via compressed gas on the cylinder side of the actuators  1370 , and operative to retract in response to a force greater than the bias force of the actuators  1370  (e.g., in response to the snow plow  1000  encountering an obstruction.) The actuators  1370  may be controlled by providing hydraulic fluid under pressure to the rod side of the actuators  1370  to retract the actuators  1370 . If pressure is removed from the rod side of the actuators  1370 , the actuators  1370  may extend until mechanically limited based on expansion of the compressible gas. 
     In an alternative embodiment, the receiver  1350  may attach to the primary plow  1120  and the receiver interface  1360  may attach to the plow support  1380 . The actuator  1370  may be mounted with the rod side attached to the plow interface  1340  (as shown) or the plow support  1380 . 
     An operator can control the distance between the snow plow  1000  and the vehicle  10  by directing the control system to move the snow plow  1000  between position O and position I. In response to receiving a command from an operator to move the snow plow  1000  toward position I, the control system may supply hydraulic fluid to the rod side of the actuator  1370 , further compressing compressible gas on the cylinder side of the actuator  1370 . In the illustrated embodiment, the actuators  1370  include external accumulators  1371  coupled to the cylinder side and capable of storing compressible gas in conjunction with the cylinder side of the actuators  1370 . The external accumulator  1371  may facilitate greater length of travel for the actuator  1370  relative to a configuration without the external accumulator  1371 , providing gas of sufficient pressure throughout the range of motion of the actuator  1370  and sufficient bias force to retract in response to an obstruction but not in response to pushing snow or debris. In an alternative embodiment, the actuators  1370  may not include compressible gas on the cylinder side, and may be actuated by hydraulic fluid in a push-pull coordinated manner on the cylinder side and rod side. 
     Movement toward position I causes the receiver interface  1360  to slide further into the receiver  1350 . Position I is the closest the snow plow  1000  can be moved to the vehicle  10  proximally, and may vary from application to application depending on the construction. Position I may be the position of the snow plow  1000  when the rods of the actuators  1370  are fully retracted. 
     Alternatively, or additionally, position I may be the position of the snow plow  1000  when the receiver interface  1360  is fully seated in the receiver  1350 . In another embodiment, position I may be the position of the snow plow  1000  when the receiver interface  1360  contacts a back edge of the receiver  1350 , which may or may not be the point at which the receiver interface  1360  is fully covered by the receiver  1350 . 
     If the control system receives a command from an operator to move the snow plow  1000  toward position O, the control system may withdraw hydraulic fluid to the rod side of the actuator  1370 . This causes the rods to extend and the receiver interface  1360  to slide out of the receiver  1350 . Position O may correspond to the farthest the snow plow  1000  can be disposed from the vehicle  10  distally. In one embodiment, position O is reached when the rods of the actuators  1370  are fully extended. In one embodiment, the rods are  14 ″ long. Additionally, or alternatively, position O may be the position of the snow plow  1000  when the end of the receiver interface  1360  reaches the end of the receiver  1350 . In one embodiment, position O is selected to substantially prevent overextension of the actuators  1330 . For example, if the cylinder side of the actuators  1330  is coupled to the plow support  1380  rather than the plow interface  1340 , position O may be selected to be more proximal to the vehicle  10  in order to prevent overextension of the actuators  1330 . 
     As described herein, the actuators  1370  may have compressible gas on the cap side of the cylinder and hydraulic fluid on the rod side of the cylinder such that the rod is biased in the extended position. Thus, the primary plow  1120  is biased at position O. When the primary plow  1120  comes into contact with a force above a tripping threshold or overcomes a bias force of the actuators  1370 , the actuators  1370  may operate in a spring-like manner, and hydraulic fluid is provided to the rod side of the cylinder and the compressible gas compresses further in the cylinder side and the external accumulator  1371  such that the rod of each actuator  1370  retracts and moves the primary plow toward position I. The primary plow  1120  may move all the way to position I or may move to some position between position O and position I depending on the strength of the obstruction force. This allows the primary plow  1120  to yield when encountering an obstruction which may prevent or reduce damage to the snow plow  1000 . When the obstruction force is no longer present, hydraulic fluid may be withdrawn from the rod side of the actuator  1370  (e.g., automatically in response to pressure from the gas) and the compressible gas may expand such that the actuators  1370  are once again biased toward the extended position and the primary plow  1120  returns to position O or a position between  0  and I at which the operator has selected for operation. 
     If the vehicle  10  with the snow plow  1000  is travelling from place to place, it can be configured in a transport mode as depicted in the illustrated embodiment of  FIG.  14   . The snow plow  1000  can be in a variety of positions during transport mode. For example, the primary plow  1120  may be tilted forward about the longitudinal axis  1103  and the first wing  1110  and the second wing  1210  may be rotated around the axes  1101 ,  1201  back toward the vehicle  10 . This lifts the blade  1126  off the ground and keeps it behind the primary plow  1120  while driving such that the blade  1126  is not the first point of contact if the snow plow  1000  comes into contact with an obstruction. The control system may move the snow plow  1000  to this position by adjusting the length of the lift actuator  1416 , the actuators  1330 , the actuators  1370 , and the actuators  1114 ,  1214 . To tilt the primary plow  1120  forward, the control system supplies hydraulic fluid to the cap side of the actuators  1330  further compressing the compressible gas. This causes the rods of the actuators  1330  to extend, pushing the top edge of the primary plow  1120  forward and consequently tilting the blade  1126  toward the vehicle  10 . To move the first wing  1110  and the second wing  1210  backwards, the control system removes hydraulic fluid from the cap side of the actuators  1114 ,  1214  and supplies hydraulic fluid to the rod side of the cylinders of the actuators  1114 ,  1214 , which causes the rods to retract. As the rods retract, the first wing  1110  is rotated about the axis  1101  toward the vehicle  10  and the second wing  1210  is rotated about the axis  1201  toward the vehicle  10 . As the primary plow  1120  tilts forward, the outer edge of the first wing  1110  and the second wing  1210  and the wing blades  1119 ,  1219  lift off the ground and rotate toward the vehicle  10 . This may provide a safer transport mode because all blades are rotated back toward the vehicle  10 . 
     There are applications where controlling the distance of the snow plow  1000  relative to the vehicle  10  is useful. For example, when parking the vehicle  10 , an operator may want to move the snow plow  1000  closer to the vehicle  10  in order to allow the vehicle  10  to better fit into a parking space. An operator may want the snow plow  1000  to be further away from the vehicle  10  when plowing in order to minimize blowback of the snow onto the vehicle  10  or to provide less clearance between the snow plow  1000  and the vehicle  10  when the snow plow  1000  is actuated to its transport mode. The closer the snow plow  1000  is to the vehicle  10  during transport, the closer the center of gravity of the vehicle  10  and the snow plow  1000  is to the vehicle&#39;s center of gravity without the snow plow  1000 , and the more even the weight of the system is distributed over the wheels. 
     Although a moveable portion (e.g., a wing blade  1119 ) is described in conjunction with a wing  1110  relative to a primary plow  1120 , it is to be understood that the present disclosure is not so limited. The snow plow  1000  may include any number of segments, such as two segments that form the primary plow  1120  capable of forming a V-configuration (e.g., a V plow). As another example, the snow plow  1000  may include four segments, including two segments that form a V-configuration and two wings respectively coupled to one of the two segments that form the V-configuration. Any segment of the snow plow  1000  may include a movable portion configured according to one or more embodiments described herein. For instance, a V-plow may include wing blades  1119  capable of rotating upward and downward relative to a pivot point to follow the ground contour and/or move in response to encountering an obstruction. In another example, with a four segment plow, each segment may include a rotatable or movable portion capable of following the ground. 
     II. Alternative Front Plow 
     Another alternative embodiment a snow plow in the form of a front-blade plow is shown in  FIGS.  14 - 22    and generally designated  2000 . The front-blade plow is similar to the snow plow  1000  described herein with several exceptions. For instance, the snow plow  2000  may be mounted to the front of the vehicle  10  as depicted in  FIG.  14   , and may be coupled to a vehicle support  2412  via a plow support  2380 . The vehicle support  2412  may be removably coupled to a vehicle mount  112 , which is attached to the vehicle  10 . In other words, the snow plow  2000  may be mounted to the front of the vehicle  10  via the vehicle supports  2412  and the vehicle mounts  112 . 
     It is noted that the snow plow  2000  in the illustrated embodiment includes many components configured in a manner similar to components of the snow plow  1000 , with several exceptions as described herein. For purposes of disclosure, components of the snow plow  2000  are designated with a  2000  series reference number, and similar components of the snow plow  1000  are designated with a  1000  series reference number. 
     The vehicle mount  112 , in the illustrated embodiment of  FIGS.  14 - 20   , is attached to a frame of the vehicle  10 . The vehicle mount  112  may be installed at the time of manufacture or by a third party in a retrofit of the vehicle  10 . 
     The vehicle mount  112  in the illustrated embodiment may include a guide slot  114  operable to receive and guide a lower pin  2415  to a lower receiver  116 , which may be in the form of a hook operable to support and maintain a position of the lower pin  2415 . The vehicle mount  112  may include an upper receiver  118  operable to receive a moveable upper pin  2419 , which can be moved via a handle  2421 , which is depicted in the illustrated embodiment of  FIG.  18   , and which is spring loaded to return the upper pin  2419  into the upper receiver  118  if present. 
     As described herein, the vehicle support  2412  along with the snow plow  2000  may be removably coupled to the vehicle mount  112 . For purposes of disclosure, a sequence of steps for decoupling the vehicle support  2412  from the vehicle mount  112  is described with respect to  FIGS.  18 - 20   . Coupling the vehicle support  2412  to the vehicle mount  112  may be conducted in the reverse. 
     Starting with  FIG.  18   , a coupling block B may be provided beneath the plow support  2380 . The handle  2421  may be operated to remove the upper pin  2419  from the upper receiver  118 , enabling removal of the lower pin  2415  from the lower receiver  116 . After the upper pin  2419  has been removed from the upper receiver  118 , the lift actuator  2460  may be contracted to rotate the vehicle support  2412  via rotatable coupling  2414  between the vehicle support  2412  and the plow support  2380 . With the plow support  2380  being supported by the coupling block B, and with the upper pin  2419  removed from the upper receiver  118 , retraction of the lift actuator  2460  may cause the lower pin  2415  to disengage from the lower receiver  116  of the vehicle support  112 . The guide slot  114  may guide the lower pin  2415  in disengaging from the lower receiver  116  and ultimately from the vehicle supports  112 , as shown in the illustrated embodiment of  FIG.  20   . 
     As seen in the illustrated embodiment of  FIG.  18   , the vehicle support  2412  may include a receiver plate  2423  spaced apart from a main body  2425  of the vehicle support  2412  to define a gap therebetween that is operable to receive the upper receiver  118  and the lower receiver  116  of the vehicle mounts  112 . The ends of the main body  2425  and the receiver plates  2423  that are proximal to the vehicle  10  may be angled away from the upper receiver  118  and the lower receiver  116 , facilitating and guiding receipt of the upper receiver  118  and lower receiver  116  between the main body  2425  and the receiver plates  2423  as the vehicle mount  112  and the vehicle supports  2412  are moved into proximity to each other for coupling therebetween. 
     As described herein, the snow plow  2000  is similar to the snow plow  1000  in many respects. For instance, the snow plow  2000  may include a primary plow  2120  coupled to the plow support  2380 , similar respectively to the primary plow  1120  and the plow support  1380 . The snow plow  2000  may also include a first wing  2110  that may be rotatably coupled to the primary plow  2120  on a first side  2122  via a joint  2117 . The first wing  2110 , the first side  2122 , and the joint  2117  may also be similar respectively to the first wing  1110 , the first side  1122 , and the joint  1117 . The joints  2117  may allow the first wing  2110  to rotate about an axis  2101  to a position F and a position B. Positions F and B may vary depending on the application, as described herein, and rotation about the axis  2101  may allow the first wing  2110  to rotate toward the vehicle to position B and to rotate away from the vehicle  10  to position F. The second wing  2210  may be similar to the first wing  2110 , with components similar to the  2100  series reference numbers being designated with a  2200  series reference number. 
     The first wing  2110  may include a main wing portion  2112  and a wing blade  2119 . The wing blade  2119  may be fixedly connected to the main wing portion  2112 , or the wing blade  2119  may be able to rotate upwards, for example in response to a change in contour of the ground or encountering debris or an obstruction that exerts a force greater than a tripping threshold. 
     In one embodiment, the wing blade  2119  may include a pivot portion  2118  and a sliding portion  2121 . In the depicted embodiment, the sliding portion  2121  includes a fastener seated within or captured by a channel or slot to allow the wing blade  2119  to move upward in response to an upward force (e.g., a tripping force or the ground in response to a change in surface contour), while maintaining a coupling between the sliding portion  2121  and the main wing portion  2112 . The wing blade  2119  may rotate about the pivot portion  2118  such that the sliding portion  2121  moves from position L to position H. The position L may correspond to a position lower than a ground contacting plane  2125  defined by the blade  2126  of the primary plow  2120 , and position H may correspond to a position higher than this ground contacting plane  2125  defined by the wing blade  2119 . 
     In use, the position of the sliding portion  2121  of the wing blade  2119  may be between position L and H with the wing blade  2119  contacting the ground. The position of the sliding portion  2121  may vary as the contour of the ground changes. As described herein, the sliding portion  2121  of the wing blade  2119  may be biased toward the ground such that, as the plow  2000  travels along the ground and the ground contour lowers relative to a current position of the sliding portion  2121 , the sliding portion  2121  may lower toward position L to allow the wing blade  2119  to follow the contour of the ground. Conversely, the sliding portion  2121  may rise toward position H as the ground contour rises with the plow travelling over the ground and the height of the ground near the sliding portion  2121  being different from the height of the ground near the pivot portion  2118 . The bias force may vary from application to application, and may be determined selectable, in operation, installation, or the design stage, or a combination thereof, to enable the sliding portion  2121  of the wing blade  2119  to substantially maintain contact of the wing blade  2119  with the ground and to allow upward movement in response to changes in ground contour and/or an encounter with an obstruction. 
     In the illustrated embodiment of  FIG.  16   , another view of the rear of the snow plow  2000  is shown.  FIG.  12    focuses on the primary plow  2120 , and depicts two actuators  2330  connected to the rear of the primary plow  2120 . On the rod side of the actuators  2330  and at an angle, the actuators  2330  are coupled to the primary plow  2120  in a pivotal manner. On the cylinder side of the actuators  2330 , the actuators  2330  are attached to a plow interface  2340 , about which the primary plow  2120  may pivot. It is to be understood that the actuators  2330  may be coupled to the primary plow  2120  and the plow interface  2340  in a different manner, such as, for example, with the rod side of the actuators  2330  coupled to the plow interface  2340 . 
     The plow interface  2340 , in the illustrated embodiment, is secured to the rear of the primary plow  2120  in a pivotable manner, such that the primary plow may pivot about a longitudinal axis  2103  parallel to a forward face of the primary plow  2120  (e.g., parallel to the mold board  2124 ). The actuators  2330  may extend and retract to rotate the primary plow  2120  about this longitudinal axis  2103 . The actuators  2330  may be coupled to the mold board  2124 , as depicted in the illustrated embodiment, and can be secured to the primary plow  2120  by any suitable means, including removable pins. 
     In the illustrated embodiment, the actuators  2330  are hydraulic actuators, similar to the actuators  1330 , with compressible gas on the rod side of the actuator  2330  and hydraulic fluid on the cap side of the actuator  2330  such that the rod is retracted and biased inward by the compressible gas on the rod side, e.g., with the hydraulic fluid on the cap side being in a float state. The rod side of the actuator  2330  may include an accumulator  2331 , integral or external to the actuator  2130 , filled with the compressible gas. The actuators  2330  may be operable in a manner similar to the actuator  2145 , with the exception of the actuator  2330  being configured to extend instead of retract in response to application of a threshold force. It is noted that the hydraulic system, as described herein, may be transitioned from a float state to an active state that involves one or more of retracting the lift actuator  2416 , extending the actuators  2330 , retracting the actuators  2145  operable to raise and lower the wing blades  2119 , and retracting the actuators  2370 . Transitioning back to a float state may allow the compressible gas to do the reverse, including one or more of extending the lift actuator  2416 , retracting the actuators  2330 , extending the actuators  2145  operable to raise and lower the wing blades  2119 , and extending the actuators  2370 . The compressible gas associated with each of these actuators may bias portions of the snow plow  2000  toward one or more biased positions, which can be overcome by application of force such as contact with the ground or an obstruction. 
     In one embodiment, one or more actuators may be operable to control movement of different parts of the snow plow  2000 , including different types of components in different movements (such as the lift actuator  2145 , actuators  2330 , actuators  2370 , and the actuators  2145 ). Such one or more actuators may operate in conjunction with each other to provide freedom of movement for the snow plow  2000  in multiple directions for components of the snow plow  2000  in response to encountering an obstruction. In other words, different longitudinal axes may be provided for a plurality of actuators that move in response to encountering an obstruction. For example, in response to the mold board  2124  of the snow plow  2000  encountering an obstruction, the lift actuator  2416  may retract, the actuators  2330  may extend, and the actuators  2370  may retract. This movement of the lift actuator  2416 , the actuators  2330 , and the actuators  2370  may be enabled via compression of gas provided in the respective actuators. In this way, multiple components of the snow plow  2000  may yield or move in response to a portion of the snow plow  2000  encountering an obstruction. 
     In another example, if the primary plow  2120  encounters a tripping force (e.g., in response to the main blade  2126  of the primary plow  2120  encountering an obstruction), the compressible gas may operate in a spring-like manner, allowing the actuators  2330  to extend as the gas further compresses. If the actuators  2330  are coupled to external accumulators, gas in the rod side and the accumulator may compress within the external accumulator and hydraulic fluid may be supplied to the cap side of the actuator  2330  as the rod extends. As the rod extends, the primary plow  2120  may rotate about the longitudinal axis  1103  such that the blade  2126  of the primary plow  2120  moves toward the vehicle  10  while the upper edge of the primary plow  2120  moves away from the vehicle  10 . If the tripping force occurred because the primary plow  1120  encountered an obstruction, this tripping behavior may reduce or minimize damage to the primary plow  2120  and the snow plow  2000 . Although, in this example, the actuators  2330  are described as extending in response to the snow plow  2000  encountering an obstruction force, additional or alternative actuators of the snow plow  2000  may extend or retract in response to the snow plow  2000  encountering an obstruction. For instance, in addition to extension of the actuators  2330 , the lift actuator  2416  and/or the actuators  2370  may retract in response to the snow plow  2000  encountering the obstruction. 
     In the illustrated embodiment, the snow plow  2000  may include a hydraulic system  2420 , similar to the hydraulic system described herein in conjunction with the snow plow  1000 . The hydraulic system  2420  may be hydraulically coupled to the actuators of the snow plow to control movement thereof. The hydraulic system  2420  may include a single hydraulic coupling for each of the actuators of the snow plow  2000  (or a subset thereof), including the lift actuator  2416 , the actuators  2330 , the actuators  2370 , and the actuators  2345 . The single hydraulic coupling may be operable to control supply of fluid to one side of the actuators, while the other side of the actuators may be filled with compressible gas (which is optionally in gaseous communication with an accumulator). In one embodiment, the actuators having a single hydraulic coupling (e.g., the lift actuator  2416 , the actuators  2330 , the actuators  2370 , and the actuators  2345 ) may be controlled together via a hydraulic valve operable to control supply of hydraulic fluid to all of these actuators simultaneously. In one embodiment, the single hydraulic couplings may define branch circuits that are linked to a source hydraulic circuit, for which hydraulic fluid is controlled by the hydraulic valve. In other words, the hydraulic couplings for the one or more of the lift actuator  2416 , the actuators  2330 , the actuators  2370 , and the actuators  2345  may all form part of the same hydraulic circuit, for which hydraulic fluid is controlled by the hydraulic valve. With this configuration, hydraulic actuation of the lift actuator  2416 , the actuators  2330 , the actuators  2370 , and the actuators  2345  may be conducted simultaneously, such as to transition the snow plow  2000  from an operable position to a transport position, at which the primary plow  2120  is raised relative to the ground, the wing blades  2119 ,  2219  are raised to position H relative to the ground, and the primary plow  2120  is tilted forward about the longitudinal axis  2103 . In one embodiment, because the primary plow  2120  is tilted forward about the longitudinal axis  2103  and the wing blades  2119 ,  2219  are raised to position H, the wings  2110 ,  2210  may be rotated to position B, via control by the hydraulic system  2420 , in a manner that provides ground clearance for travel and maintains a left to right width of the vehicle  10  that fits within a standard lane size of the road. 
     The actuators  2330  in the illustrated embodiment are respectively coupled to the rear of the primary plow  2120  via an upper mount and to the plow interface  2340  via a lower mount. The upper mount may include first and second upper plates spaced apart to receive an upper end portion of the actuator  2330 . The first upper plate may include a plurality of apertures that are respectively axially aligned with a corresponding plurality of apertures disposed in the second upper plate. The apertures may accept a pin or bolt that rotatably couples to an upper end portion of the actuator  2330  to the upper mount. 
     The apertures of the first and second upper plates may be spaced relative to each other to enable coupling of the actuator  2330  to the upper mount at a plurality of positions. For example, the plurality of positions of the upper mount may enable coupling the upper end portion of the actuator  2330  at different positions, some closer to the longitudinal axis  2103  and some farther from the longitudinal axis  2103 . The lower mount for the actuators may be similar in some respects to the upper mount, including first and second lower plates spaced apart to receive a lower end portion of the actuator  2330 . The first and second lower plates may each include a plurality of apertures that are axially aligned and provide for multiple coupling positions for the actuator  2330 . The plurality of apertures of the lower mount may enable coupling the lower end portion of the actuator  2330  at different positions, some closer to the longitudinal axis  2103  and some farther from the longitudinal axis  2103 . 
     In practice, it is noted that the mounting position of the actuator  2330  relative to the plow interface  2340  and the primary plow  2120  may be varied or adjusted to configure the snow plow  2000  for use with a particular truck. For instance, a height of one vehicle  10  may be different from the height of another vehicle  10 . The mounting positions of the actuators  2330  may be adjusted to set the angle of the primary plow  2120  (and the angles of the first and second wings  2110 ,  2210 ) relative to the ground. 
     An upper end of the actuator  2330  may be mounted via a pin to one of a plurality of available positions provided by the upper mount, and the lower end of the actuator  2330  may be mounted via a pin to one of a plurality of available positions provided by the lower mount. By selecting upper and lower mounting positions for the actuator  2330 , an installer or maintenance worker can tune the snow plow  2000  to the ground (e.g., an angle of the snow plow relative to the ground and the truck), enabling different truck configurations without changing the mounting iron (e.g., the vehicle mount  112  and/or vehicle support  2412 ) or construction thereof. For instance, the installer or maintenance worker may select sets of holes from the upper and lower mounts for the actuator  2330  for setting both the length and angle of the actuator  2330  relative to the primary plow  2120  and the plow interface  2340 . 
     In one embodiment, a geometry of the snow plow  2000  relative to the truck and the ground may vary over time (e.g., as one or more blades wear). A maintenance worker may adjust the upper position or lower position, or both, of the actuator  2330  relative to the upper and lower mounts in order to re-adjust the position of the primary plow  2120  with respect to the ground and the truck. For instance, the upper end portions of the actuators  2330  may be moved to sets of apertures that are 2 inches farther from the longitudinal axis  2103 , and the low end portions of the actuators  2330  may be moved to sets of apertures that are 0.5 inches closer to the longitudinal axis. 
     In the illustrated embodiment, the angle of the primary plow  2120  relative to the ground and truck may affect the angle of the axes  2101 ,  2201  of the first and second wings  2110 ,  2210  relative to the ground. This angle may affect the available travel and pivot angle of the wing blades  2119 ,  2219  between positions H and L. As the main blade  2126  wears, a portion of the wing blades  2119 ,  2219  proximal to the axes  2101 ,  2201  may wear, potentially causing the distal portion  2131 ,  2231  of the wing blades  2119 ,  2219  to rise toward position H despite less wear than the portion of the wing blades  2119 ,  2219  proximal to the axes  2101 ,  2201 . This movement toward position H may limit the amount of upward travel of the wing blades  2119 ,  2219  that is available in response to encountering an obstruction. 
     To account for the effects of blade wear, including the limiting of available movement toward position H for the wing blades  2119 ,  2219 , the mounting locations of the actuators  2330  may be adjusted to change the angle of the primary plow  2120  relative to the ground. For instance, the mounting locations of the actuators  2330  may be adjusted to pivot an upper portion of the primary plow  2120  away from the vehicle  10 , thereby angling the axes  2101 ,  2201  to provide a greater amount of travel for distal portions  2131 ,  2231  of the wing blades  2119 ,  2219  between position H and the ground (despite wear of the main blade  2126 ). In other words, by adjusting the mounting locations of the actuators  2330  and the angle of the axes  2101 ,  2201 , despite wear of the main blade  2126 , an operating position of the wing blades  2119 ,  2219  may be re-adjusted to be similar to the operating position of the wing blades  2119 ,  2219  prior to the blade wear and enabling a similar amount of travel (e.g., 3 inches of upward motion) between the operating position and position H in response to encountering an obstruction. In the illustrated embodiment, each of the actuators  2114  of the snow plow  2000 , in the illustrated embodiment, may be coupled to the hydraulic system  2420  via first and second hydraulic couplings, enabling the hydraulic system to actively control an angular position of each of the wings  2110 ,  2210  between the F and B positions. 
     The operation of the compressible gas and hydraulic system  2420  in conjunction with the snow plow  2000  is similar in many respects to the operation of the compressible gas and hydraulic system of the snow plow  1000 . In one embodiment, the snow plow  2000  may be configured such that the lift actuator  2416 , as depicted in the illustrated embodiment of  FIG.  16   , may be provided with compressible gas on one side of the lift actuator  2416 . The compressible gas in the illustrated embodiment may be provided on the cylinder side of the lift actuator  2416 , optionally in conjunction with an accumulator  2417 , and biasing the lift actuator  2416  to an extended position if the hydraulic fluid on the rod side of the lift actuator  2416  is allowed to float or return to the tank. With the snow plow  2000  positioned in an operable position, the bias of the lift actuator  2416  may provide downforce on the plow support  2380  to bias the primary plow  2120  and the wings  2110 ,  2210  toward the ground. With the ground contour changing as the snow plow  2000  is driven over the ground, the lift actuator  2416  may vary in length via compression of the compressible gas on the cylinder side of the lift actuator  2416 . In other words, the changes in ground height may overcome the bias force of the lift actuator  2416  (or downforce of the lift actuator  2416 ), allowing the primary plow  2120  and the wings  2110 ,  2210  to follow the contour of the ground. 
     In the illustrated embodiment, the accumulator  2417  is depicted as being coupled directly to the lift actuator  2416 . It is to be understood that the accumulator  2417  may be separate from the lift actuator  2416 , and directly fluidly coupled to the lift actuator  2416 . It is also to be understood that the accumulator  2417  regardless of whether the accumulator  2417  is mounted directly to or separate from the lift actuator  2416 , the accumulator  2417  may be indirectly fluidly coupled to the lift actuator  2416 . For instance, the accumulator  2417  may be indirectly fluidly coupled to the lift actuator via a pneumatic valve  2413  as described herein. In one embodiment, the accumulator  2417  may be integrated with a structural component of the snow plow  2000  to form a structural integrated accumulator—e.g., the accumulator  2417  may be provided by an internal space of a structural tubular member of the snow plow  2000 . More specific to this example, the accumulator  2417  may be provided by the cross member of the vehicle support  2412  to which the upper portion of the lift actuator  2416  is coupled. A Schrader valve may be mounted to a flange that forms a seal with an internal cavity of this cross member, which is depicted in the illustrated embodiment of  FIG.  16   . A gas line may also be coupled to the structural integrated accumulator, where the gas line may be directly coupled to the lift actuator  2416  or indirectly via a pneumatic valve  2413 . In the indirect configuration, another gas line may couple the pneumatic valve  2413  directly to the lift actuator  2416 . 
     A method of operation in accordance with one embodiment is shown in  FIG.  23    and generally designated  3000 . As described herein, the lift actuator  2416  may be operable to raise and lower the snow plow  2000 , and the method  3000  is described in conjunction with operation of the lift actuator  2416  by the hydraulic system  2420 . The method  3000  is not limited to operation with the lift actuator  2416 . The method  3000  may be implemented in conjunction with any type of actuator, including any one or more of the actuators described herein. 
     A control system may be provided in conjunction with the hydraulic system  2420  to control operation of the lift actuator  2416  according to one embodiment of the method  3000 . The control system may be integrated with control aspects of the hydraulic system  2420  in the illustrated embodiment; however, it is to be understood that the control system may be separate. 
     The control system may include any and all electrical circuitry and components to carry out the functions and algorithms described herein. Generally speaking, the control system may include one or more microcontrollers, microprocessors, and/or other programmable electronics that are programmed to carry out the functions described herein. The control system may additionally or alternatively include other electronic components that are programmed to carry out the functions described herein, or that support the microcontrollers, microprocessors, and/or other electronics. The other electronic components include, but are not limited to, one or more field programmable gate arrays (FPGAs), systems on a chip, volatile or nonvolatile memory, discrete circuitry, integrated circuits, application specific integrated circuits (ASICs) and/or other hardware, software, or firmware. Such components can be physically configured in any suitable manner, such as by mounting them to one or more circuit boards, or arranging them in other manners, whether combined into a single unit or distributed across multiple units. Such components may be physically distributed in different positions, or they may reside in a common location. When physically distributed, the components may communicate using any suitable serial or parallel communication protocol, such as, but not limited to, CAN, LIN, FireWire, I2C, RS-232, RS-485, and Universal Serial Bus (USB). 
     The control system for the method  3000  may operate a pneumatic valve  2413  disposed between the accumulator  2417  and the lift actuator  2416 , and more specifically between the accumulator  2417  and a lift actuator reservoir  2411  of the lift actuator  2416 . The pneumatic valve  2413  may optionally include an orifice that restricts flow of gas from the accumulator  2417  to the lift actuator reservoir. Additionally, with the pneumatic valve  2413  including such an orifice, a second pneumatic valve may be disposed in parallel with the pneumatic valve  2413  and configured to selectively provide unrestricted flow of gas between the accumulator  2417  and the lift actuator reservoir  2411 . For instance, the pneumatic valve  2413  with a restricting orifice may be operated for timed control in accordance with steps  3004  and  3008  described herein, and the second pneumatic valve may be operated for control with full pressure in accordance with steps  3004  and  3006 . 
     The lift actuator reservoir  2411  may be configured to contain compressible gas. Compressible gas may be added to or removed from the lift actuator reservoir  2411  in accordance with the method  3000 . For instance, the control system may operate the pneumatic valve  2413  to provide compressible gas from the accumulator  2417  to the lift actuator reservoir  2411 , and compressible gas may be transferred from the lift actuator reservoir  2411  via a check valve  2418 . 
     The check valve  2418  may limit a pressure of the lift actuator reservoir  2411  to be less than or equal to the pressure of compressible gas in the accumulator  2417 . 
     In the illustrated embodiment, from step  3006  to step  3012 , the pneumatic valve  2413  may be closed and hydraulic fluid may be provided from the hydraulic system  2420  to the lift actuator  2416  via operation of a hydraulic valve  2423  in order to retract the lift actuator  2416 . In this sequence, with a starting pressure of the lift actuator reservoir  2411  being pressure p, the same as the pressure p of the accumulator  2417 , the decrease in volume of the lift actuator reservoir  2411  due to application of hydraulic pressure causes the pressure in the lift actuator reservoir  2411  to rise. The check valve  2418  may open to limit pressure in the lift actuator reservoir  2411  such that, at the retracted position, the pressure of the lift actuator reservoir  2411  is substantially the same as the pressure p of the accumulator  2417  despite the change in volume of the lift actuator reservoir  2411 . In this sequence, because the initial pressure of the lift actuator  2411  is p or nearly the same as the pressure p of the accumulator  2417 , the pressure in the lift actuator reservoir  2411  may exceed the pressure p soon after hydraulic pressure is applied to the lift actuator  2416 , such that the open check valve  2414  may open soon after hydraulic pressure is applied to the lift actuator  2416 . 
     In other sequences, such as a transition from an extended position with a pressure in the lift actuator reservoir  2411  being less than the pressure p of the accumulator  2417  (e.g., from step  3008  to step  3012  and then to step  3002 ), the pressure of the lift actuator reservoir  2411  may cause the check valve  2418  to open midway between the retracted and extended position or closer to the retracted position. 
     In one embodiment, at step  3010 , the pressure of the lift actuator reservoir  2411  at the extended position may correspond solely to a change in volume of the lift actuator reservoir  2411  due to movement from the retracted position to the extended position. In other words, as depicted in the illustrated embodiment, from steps  3002  to step  3004  and to step  3010 , the pneumatic valve  2413  may be kept closed such that the pressure change in the lift actuator reservoir  2411  corresponds to a change in volume and not a change in amount of compressible gas. As a result, retraction of the lift actuator  2416  from the extended position to the retracted position may return a pressure of the lift actuator reservoir  2411  to a pressure p similar to or the same as the pressure p of the accumulator  2417  without opening the check valve  2418 . 
     The lift actuator reservoir  2411  in the illustrated embodiment is variable in size, depending on the position of the lift actuator  2416 . As an example, the volume of the lift actuator reservoir  2411  with the lift actuator  2416  in a retracted position (e.g., step  3002 ) is less than a volume of the lift actuator reservoir  2411  with the lift actuator  2416  in an extended position (e.g., step  3006 ). As a result, a pressure of compressible gas in the lift actuator reservoir  2411  may be varied based on a position of the lift actuator  2416 , timing of operation of the pneumatic valve  2413  for supply of compressible gas at pressure p to the lift actuator reservoir  2411 , and operation of the check valve  2418  to limit pressure 
     Starting at step  3002 , with the lift actuator  2416  in a retracted position, the hydraulic system  2420  may operate a hydraulic valve  2428  to transition from applying hydraulic pressure to a float mode to allow the lift actuator  2416  to begin extending to the extended position. Step  3004 . Depending on the configuration, a transition to float mode for the hydraulic system  2420  may be sufficient to enable extension of the lift actuator  2416  (or another actuator described herein) due at least in part to a weight of the plow  2000  coupled to the lift actuator  2416 . An increase in pressure of the lift actuator reservoir  2411  via opening the pneumatic valve  2413  may also facilitate extension of the lift actuator  2416 . 
     During or after extension of the lift actuator, the pneumatic valve  2413  may be opened to control a pressure of the lift actuator reservoir  2411 . Depending on a pressure of the lift actuator reservoir  2411 , as described herein, a bias force F d  may be present for biasing the lift actuator  2416  toward the extended position. In the context of the lift actuator  2416 , the bias force F d  may correspond to downforce applied on the plow  1000  toward contact with the ground. 
     At step  3010 , as described herein, the control system may keep the pneumatic valve  2413  in a closed position as the hydraulic system  2420  transitions to a float mode and allows the lift actuator  2416  to extend. The pressure of the lift actuator reservoir  2411  in this configuration may be significantly less than the pressure p of the accumulator  2417  due to the increase in size of the lift actuator reservoir  2411 . For instance, the pressure of the lift actuator reservoir  2411  may decrease from a pressure p of  600  psi in the accumulator  2417  to a pressure of  100  psi in the lift actuator reservoir  2411  with the lift actuator  2416  at full extension. This configuration may provide little or no bias force F d  toward extension (e.g., little or no downforce applied to the plow  2000 ). With little or no bias force F d , and the hydraulic system  2420  in a float mode, the lift actuator  2416  may enable the plow  2000  to raise and lower without substantial downforce applied to the plow  2000  toward contact with the ground. 
     At step  3006 , as described herein, the control system may maintain the pneumatic valve  2413  in an open position to enable gaseous communication between the accumulator  2417  and the lift actuator reservoir  2416 . As a result, a pressure of the lift actuator reservoir  2416  may substantially correspond to a pressure p of the accumulator  2417  present at step  3002 . The volume of the accumulator  2417  may be substantially larger than the volume of the lift actuator reservoir  2416 , so that transfer of compressible gas from the accumulator  2417  to the lift actuator reservoir  2416  has a reduced or de minimus effect on pressure p of the accumulator  2417  and the overall system. 
     In the illustrated embodiment, at step  3006 , the bias force F d  toward extension of the actuator  2416  is a function of the pressure p of the lift actuator reservoir  2411 . This bias force Fd may be the maximum allowable by the system, and may provide downforce with respect to the snow plow  2000  and the ground. If an obstruction is encountered that counters and exceeds the downforce, the lift actuator  2416  may retract as the compressible gas is compressed and the pressure in the accumulator  2417  and the lift actuator reservoir  2411  increases. In response to the obstruction force, the gas may compress until the lift actuator  2416  bottoms out or full retracts or until compression of the gas generates a bias force Fd that is in equilibrium with the obstruction force applied on the lift actuator  2416 . After the obstruction force recedes, the compressible gas may extend the lift actuator  2416  back toward extension to bias the snow plow  2000  toward the ground. 
     In an alternative embodiment of step  3006 , the control system may open the pneumatic valve  2413  to pressurize the lift actuator reservoir  2416  in the fully extended position at pressure p of the accumulator  2417 . However, at this stage, the control system may close the pneumatic valve  2413  so that the lift actuator reservoir  2411  is not coupled to the accumulator  2417  via the pneumatic valve  2413 . The lift actuator  2416  in this configuration may apply a bias force F d  similar to that described above in conjunction with step  3006  and the pneumatic valve  2413  being maintained in an open position. However, in response to encountering an obstruction force that exceeds the bias force F d , gas in the lift actuator reservoir  2411  may begin to compress and open the check valve  2418 , bleeding or transferring gas from the lift actuator reservoir  2411  to the accumulator  2417 . After the obstruction force recedes, the check valve  2418  may be closed, the lift actuator  2416  may extend but the bias force toward extension may be less because the pressure in the lift actuator reservoir  2411  deceases due to expansion in the volume of the lift actuator reservoir  2411 . 
     In the illustrated embodiment, at step  3008 , the lift actuator  2416  may be extended. The control system may operate the pneumatic valve  2413  to control a pressure of the lift actuator reservoir  2411 . The control system may open the pneumatic valve  2413  during extension of the lift actuator  2416  or after extension of the lift actuator  2416 . The pressure of the lift actuator reservoir  2411  may be controlled in accordance with a duration (e.g., a length of time) of activation of the pneumatic valve  2413  (e.g., 0.5 s, 1.0 s, 1.5 s, 2.0 s). For instance, the control system may be configured to open the pneumatic valve for 0.5 s to raise the pressure of the lift actuator reservoir  2411  from 100 to 200 psi (relative to step  3010 ) with the lift actuator  2416  in the extended position. This configuration provides an open loop type of control of the pressure in the lift actuator reservoir  2411 . In one embodiment, an operator may direct the control system to open the pneumatic valve  2413  to increase the pressure in the lift actuator reservoir  2411  in order to increase a downforce on the plow  2000 . The operator may bump or actuate the pneumatic valve  2413  one or more times until a pressure is achieved to the satisfaction of the operator. 
     Alternatively, a sensor may be provided that provides sensor output indicative of a pressure of the lift actuator reservoir  2411 . The control system may be operable to receive this sensor output and to control the pneumatic valve  2413  based on the sensor output to control a pressure of the lift actuator reservoir  2411  according to a target pressure selected by the system and/or an operator. 
     By controlling the pressure of the lift actuator reservoir  2411  (e.g., open loop or closed loop), the control system can control the amount of bias force F d  generated by the lift actuator  2416  toward the extended position. In other words, a system in accordance with one embodiment may provide variable downforce or down pressure with respect to the snow plow  2000  and the ground. 
     At step  3008 , if an obstruction force exceeds the bias force F d , the lift actuator  2416  may retract until the lift actuator  2416  is fully retracted or an equilibrium is satisfied between the increase in pressure and resulting increase in bias force F d  and the obstruction force. If the pressure in the lift actuator reservoir  2411  exceeds the pressure p of the accumulator  2417 , the check valve  2418  may open to bleed or transfer gas from the lift actuator reservoir  2411  to the accumulator  2417  so that the pressure of the lift actuator reservoir  2411  does not significantly exceed the pressure p of the accumulator  2417 . After the obstruction force is removed, the lift actuator  2416  may extend, and depending on whether the check valve  2418  opened, the bias force F d  may be the same or less than before the obstruction was encountered. The control system may be automatic or in response to input from an operator opening the pneumatic valve  2413  to supply compressible gas to the lift actuator reservoir  2411 . 
     As described herein, the method  3000  may involve the hydraulic system  2420  transitioning from a float mode to a pressure mode to supply hydraulic fluid to the lift actuator  2416  under pressure and retract the lift actuator  2416 . The pressure in the lift actuator reservoir  2411  may be limited to the pressure p of the accumulator  2417  by the check valve  2418 . It is noted that the operation of the hydraulic system  2420  and the control system in accordance with the method  3000  may be based at least in part on input or directive from the operator (e.g., a directive to lower or raise the snow plow  2000 .). Directional terms, such as “vertical,” “horizontal,” “top,” “bottom,” “upper,” “lower,” “inner,” “inwardly,” “outer” and “outwardly,” are used to assist in describing the invention based on the orientation of the embodiments shown in the illustrations. The use of directional terms should not be interpreted to limit the invention to any specific orientation(s). 
     The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. For example, and without limitation, any individual element(s) of the described invention may be replaced by alternative elements that provide substantially similar functionality or otherwise provide adequate operation. This includes, for example, presently known alternative elements, such as those that might be currently known to one skilled in the art, and alternative elements that may be developed in the future, such as those that one skilled in the art might, upon development, recognize as an alternative. Further, the disclosed embodiments include a plurality of features that are described in concert and that might cooperatively provide a collection of benefits. The present invention is not limited to only those embodiments that include all of these features or that provide all of the stated benefits, except to the extent otherwise expressly set forth in the issued claims. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular. Any reference to claim elements as “at least one of X, Y and Z” is meant to include any one of X, Y or Z individually, and any combination of X, Y and Z, for example, X, Y, Z; X, Y; X, Z; and Y, Z.