the agricultural mower to which the present invention is applied is a towed , trailed , or drawn mower . this is in contrast to a tractor - mounted mower . towed mowers have different suspension needs than do mounted mowers , as towed mowers are supported by the ground , independent of the tractor . referring now to the drawings wherein like reference numerals correspond to the same or similar parts throughout the drawings , the present invention includes a system for suspending a header 6 from a fixed - frame agricultural mower using hydraulic cylinders 14 and an accumulator 40 . ( a fixed - frame , for the purposes of this document , including the claims , is herein defined as a frame that does not articulate linearly relative to a ground - engaging wheel axle .) the header 6 , in turn , supports a cutter bar 9 . in a first embodiment , shown in fig1 - 4 , a fixed - frame , towed mower 1 is equipped with two one - way hydraulic suspension cylinders 14 located at the outer edges of the frame 15 and supporting the header 6 via pivoting links 42 . the pitch control hydraulic cylinder 13 controls the orientation of the cutter bar 9 in relation to the ground , known as pitch , while the tongue swing cylinder 17 is used to control the orientation of the tongue 2 in relation to the frame 15 . fig3 illustrates the hydraulic circuits , including the tongue circuit for controlling tongue swing cylinder 17 , with a first tractor remote valve , and the header circuit for controlling the pitch control cylinder 13 and hydraulic suspension cylinders 14 with a second tractor remote valve . the header circuit provides three functions including control of header tilt , flotation , and lift . the flotation is provided by a hydro - pneumatic accumulator 40 used to exchange volumes of hydraulic fluid with the lift / flotation cylinders . this function is necessary when the header 6 is lowered , to allow the header 6 to follow the terrain , which occurs in the first embodiment when the lift / flotation cylinders 14 are retracted , wherein they cooperate with the accumulator 40 . an upper pressurized gas chamber of the hydro - pneumatic accumulator 40 is under pressure . the pressure is shared with a lower chamber of the hydro - pneumatic accumulator 40 , open to the hydraulic system . the header circuit also includes a take - up cylinder 41 and a valve 39 . the take - up cylinder 41 controls the oil volume displaced for lifting and lowering the header . the valve 39 may be a manually operated ball valve that can be opened to allow flow , or closed to block flow . the valve 39 may alternatively be a solenoid operated valve capable of allowing flow when a solenoid is energized , and blocking flow then a solenoid is de - energized . the present invention is not limited to these types of valves . the functions of the valve 39 are described below . in operation the towed mower 1 is hydraulically connected to a tractor ( not shown ) which provides a source of oil and is used to pump oil into the mower hydraulic systems to perform a variety of functions including : 1 ) to control the position of the mower 1 relative to the tractor , the cylinder 17 , as controlled by the first tractor remote valve 85 is extended or retracted , thereby changing the orientation of the tongue 2 relative to the frame 15 ; 2 ) to control the position of the header 6 relative to the ground , the second tractor remote valve 87 is moved to one extreme position which will cause the header 6 to lift , and when moved to the other extreme position will cause the header 6 to lower , and when left in the middle position will hold the header 6 in a set position ; 3 ) charging the lift / flotation circuit . charging of the lift / flotation circuit is necessary in order to insure that the take - up cylinder 41 , a component of the mower hydraulic system , yet not strictly speaking a part of the suspension system , is properly filled with oil . the lift / flotation cylinders 14 and the tractor remote valve 87 can be directly connected or isolated by means of the valve 39 . in the first embodiment , as illustrated in fig4 , the valve 39 is set in a manifold at the base of the take - up cylinder 41 . charging is completed by allowing oil to flow through the valve 39 , when opened , through the lines to the take - up cylinder 41 , while first allowing air to escape at the take - up cylinder , and then to fully extend that cylinder , while also purging air out of the lines between the valve 39 and the lift / flotation cylinders 14 and the pressure gage 60 . the tractor remote valve 87 is held in the position to force oil to the circuit until the lift / flotation cylinders 14 are in the extended position , and the header 6 is lifted to the transport position shown in fig2 a . after this first step of the charging procedure , the valve 39 is locked , isolating the lift / flotation cylinders 14 from direct connection to the tractor hydraulics . in the present embodiment for a fixed - frame mower 1 as in fig1 , 2 a and 2 b , the accumulator 40 is biased so as to act like a compressive spring by plumbing it to the extend port of the lift / flotation cylinders 14 , most clearly shown in fig3 and 4 . thus , during this first step of the charging procedure , the tractor lifts the cutter bar 9 and pressurizes the accumulator 40 . to complete the charging procedure the tractor remote valve 87 is opened to the tractor hydraulic fluid reservoir so that it does not force oil through the remote valve 87 . this allows the oil to flow from the take - up cylinder 41 to the tractor hydraulic reservoir . then the valve 39 is opened , either manually or electronically by the operator , to allow gravity to work against the accumulator 40 to lower the cutter bar 9 to the ground . the hydraulic system pressure can be viewed on a pressure gauge 60 so that the operator can bleed the valve 39 to allow the cutter bar 9 to press against the ground with appropriate pressure . this is done by pre - determining mower model - specific values for hydraulic system pressure at which the operator can close the valve 39 to maintain . the bias of the accumulator 40 to lift the cutter bar 9 keeps the cutter bar 9 from digging into the ground surface , yet is sufficiently small to allow gravity to press the cutter bar 9 against the surface and maintain continuous contact . this property of the cutter bar 9 is herein defined for the purposes of this document , including the claims , as “ float .” oil in the mower hydraulic system will constantly be seeking to occupy volume so as to obtain equilibrium pressures throughout the system . if the take - up cylinder valve 39 is locked , oil flow is restricted to flowing between the suspension cylinders 14 and the accumulator 40 . thus , with the valve 39 locked , the cutter bar 9 cannot be lifted or lowered via the tractor hydraulic system but only by the exchange of oil between the cylinders 14 and accumulator 40 as would be caused by variations in the force the ground exerts on the cutter bar 9 due to ground surface irregularity while mowing . as the mower passes over uneven ground , the ground exerts changing forces on the cutter bar ( s ) 9 . the oil can flow between the cylinders 14 and the accumulator 40 to constantly maintain system pressure so that good contact between the cutter bar 9 and the ground is maintained . in the first embodiment for a fixed - frame mower , the suspension cylinders 14 are attached to a pivoting link 42 such that extending the cylinders 14 causes the header 6 to lift , while retracting the cylinder 14 lowers the header 6 to the ground . in an alternative embodiment , valuable to mowers which may have separate configurations for transport and mowing , a single one - way suspension cylinder 14 may be used as shown in fig5 a - 5 d . this cylinder 14 could pivotally connect , for instance , to a main frame 15 and a rear sub - frame 62 where the main frame 15 is fixed and the rear sub - frame 62 is allowed to lift , lower , or roll about an axis parallel to a direction of travel . in fig5 a , the rear sub - frame 62 maintains its orientation to the ground by a four - bar linkage comprising an upper link set 12 and a lower link set 11 . the four - bar linkage is described more fully in u . s . patent application ser . no . 11 / 927 , 866 , filed oct . 30 , 2007 , and is hereby incorporated by reference herein in its entirety . the rear sub - frame 62 is pivotally attached to a front sub - frame 10 , to which the header 6 is ultimately attached . the rear sub - frame 62 is a link within the four - bar linkage , and the orientation of the sub - frame 62 is dictated thereby . the front sub - frame 10 may be permitted to pivot relative to the rear sub - frame 62 in order to orient the header 6 in an appropriate position for operation or transport . swing arm cylinders 65 are provided on both sides of the agricultural mower 1 to pivot the tool bars 9 relative to the front sub - frame 10 . in this second embodiment , the hydraulic system works by the same principles as in the first embodiment . however , the single cylinder 14 attached to the mower 1 as stated is configured to lift the sub - frame 10 , 62 by retracting and to lower the sub - frame 10 , 62 by extending . in this embodiment the accumulator 40 is plumbed to the retract port of the cylinder 14 , as clearly illustrated in fig5 c and 5 d . 2 ) using the tractor as the power source , pressurize the mower hydraulic system . the sub - frame / header 6 will rise to a maximum height due to full retraction of the take - up cylinder 41 and to fully stroking the cylinders 14 . 5 ) crack the valve 39 slowly to bleed excess pressure until the appropriate pressure is read from the gauge . the appropriate pressure will be established for each individual towed mower 1 model on which the present invention is incorporated . 6 ) lock the valve 39 at an appropriate pressure . the cutter bars 9 will contact the ground with the hydraulic suspension of the present invention giving it the appropriate amount of contact pressure . the mower 1 is operational . as an alternative to step 2 , using the tractor as the power source . . . , the pressure to the mower hydraulic system may be provided from the gas side of the accumulator 40 . pressurized air , nitrogen , carbon dioxide , argon , helium , or any other appropriate gas may be used to effect this pressurization . the embodiments of the novel suspension system herein described may be utilized for any implement making use of a floating header . the invention is not intended to be limited to agricultural mowers . the above embodiments are the preferred embodiments , but this invention is not limited thereto . it is , therefore , apparent that many modifications and variations of the present invention are possible in light of the above teachings . it is , therefore , to be understood that within the scope of the appended claims , the invention may be practiced otherwise than as specifically described .
a suspension system for fixed - frame , towed agricultural implements having at least one floating head . a hydraulic cylinder is used for both lift and suspension of the floating head . a hydraulic accumulator provides expansion room for hydraulic fluid to move in and out of the hydraulic cylinder during suspension .