Abstract:
An apparatus and method for controlling positions of an implement and a marker associated with a work vehicle. The apparatus includes a hydraulic circuit coupled to a first cylinder that governs the position of the marker, a first valve coupled to a second cylinder that governs the position of the implement and also coupled to a first port of the circuit, and a second valve coupled to a second port of the circuit. The circuit is configured to isolate the first port of the circuit from secondary pressure supplied to the second port by way of the second valve, and further configured to isolate the primary port of the circuit from primary pressure supplied to the first port by way of the first valve. The primary pressure influences movement of both the marker and the implement, while the secondary pressure influences movement of the marker only.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not applicable. 
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     FIELD OF THE INVENTION 
     The present invention relates to a system and method for controlling the position of an implement associated with a work vehicle (such as an agricultural work vehicle such as a tractor or a planter pulled by a tractor) and the position(s) of one or more markers attached to the implement. More particularly, the present invention relates to a system and method for controlling the positions of an implement and one or more markers by which it is possible to both provide coordinated positioning in which the markers and implement move together and independent positioning in which the markers and implement can be moved independently of one another. 
     BACKGROUND OF THE INVENTION 
     It is known for agricultural work vehicles, such as tractors or combines or other agricultural harvesting machines, to tow implements that perform (or include tool bar(s) that perform) one or more functions, such as plowing, planting or seeding, fertilizing, and harvesting in a field. Also, it is known for agricultural work vehicles to employ one, two or more markers that typically are extendable beyond the perimeter of the work vehicle and create markings by, for example, gouging furrows in the field adjacent to the vehicle. Such markers are typically attached to the implement towed by the work vehicle, although they may be attached to the work vehicle itself. Since an agricultural work vehicle typically traverses a field in a systematic row-by-row format, the markers often are used to create markings in the field to indicate to the operator of the vehicle a path for the next row. Markers are often, though not necessarily, installed in pairs on both sides of an agricultural work vehicle. Also, some agricultural work vehicles include more than one marker that can extend from a given side of the vehicle. For example, an agricultural work vehicle can include both inner and outer markers, where the outer markers are employed to provide markings at relatively larger distances from the work vehicle, and the inner markers are employed to provide markings at relatively smaller distances from the work vehicle. 
     With respect to most agricultural work vehicles, it is necessary for the work vehicles to have the capability of raising and lowering the implements (or tool bars of the implements) and markers with respect to the work vehicles and the ground. For example, a typical agricultural work vehicle proceeding through a field in a row-by-row manner must turn around at the end of each row in order to proceed down the successive row. While turning around, it is sometimes appropriate to raise the implement (or the tool bar of the implement) towed by the agricultural work vehicle some distance above the ground to prevent the implement from acting upon (or damaging) the ground or crops outside the lines of the rows. Similarly, it is common that the markers attached to an implement of a work vehicle be raised some distance above the ground while the work vehicle is turning around to prevent improper marking, damage to the ground or crops, or damage to the markers themselves that might occur if the markers encountered obstacles such as fences, trees, and boulders. 
     Often it is necessary not only that the markers themselves be raised but also that the implementation of the markers be changed while the work vehicle is turning around. For example, while it may be appropriate to utilize markers on both sides of a work vehicle as it first enters and makes its initial crossing of a field so as to create row markings on both sides of the work vehicle, implementation of markers on both sides of the work vehicle is no longer appropriate once it has completed its first row. Instead, it is then appropriate to utilize a marker only on one side of the work vehicle so that, as the vehicle proceeds down one of the two paths marked during its initial crossing of the field, a new row marking parallel to the previous row markings is created only in that section of the field that has not yet been traversed by the work vehicle. Insofar as a work vehicle needs to turn around regularly as it advances row-by-row through a field, it is appropriate to alternate the implementation of the markers used to create row markings so that new row markings are always created in that section of the field that has not yet been traversed by the work vehicle. 
     Because it is often appropriate for the markers and implement/tool bar of an agricultural work vehicle to raised and lowered at the same time, some conventional agricultural work vehicles actuate the raising and lowering of their markers and implements/tool bars using the same hydraulic valve. Such a single-valve system is simple and inexpensive to install on an agricultural work vehicle. However, in some agricultural work vehicles, it is desirable to have the capability of controlling the raising and lowering of markers independently of the raising and lowering of the implements/tool bars. For example, in the case of planters, it often is desirable to have the capability of raising and lowering markers, for reasons such as those discussed above (e.g., to avoid damage to the markers), without simultaneously raising and lowering the implements/tool bars of the planters, which would interrupt the planting operation. Some conventional planters, as well as other conventional agricultural work vehicles that need to provide such independent control of the markers and implements/tool bars, provide such independent control through the use of two (or more) different hydraulic valves for separately actuating the different devices. 
     Although such conventional systems employing multiple hydraulic valves allow for independent control of the markers and implements/tool bars, the systems can be difficult to manually operate. In particular, in situations where an operator desires coordinated movement of both the markers and implements/tool bar, the operator must manually actuate both (or all) of the hydraulic valves in order to obtain the desired functional adjustments. Such simultaneous actuation of multiple valves can require considerable attention and coordination on the part of the operator. Therefore, while the use of multiple hydraulic valves in a conventional agricultural work vehicle allows for independent control of the markers and implement/tool bar, it complicates achieving simultaneous movement of the markers and implement/tool bar that would otherwise be simple to achieve in agricultural work vehicles employing only a single hydraulic valve. 
     Accordingly, it would be advantageous if a new system and method were developed for implementation in an agricultural work vehicle that made it possible to control the positions of the vehicle&#39;s markers and implement/tool bar both simultaneously and independently of one another. In particular, it would be advantageous if, by way of such a new system and method, it was possible for an operator to achieve simultaneous raising and/or lowering of both the markers and the implement/tool bar of an agricultural work vehicle without having to simultaneously, manually actuate multiple different hydraulic valves, yet also possible to achieve independent control of the markers and implement/tool bar. 
     These and other aspects of the invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made therefore, to the claims herein for interpreting the scope of the invention. 
     SUMMARY OF THE INVENTION 
     In particular, the present invention relates to an apparatus for controlling positions of at least a portion of an implement and a first marker, both of which are associated with a work vehicle. The apparatus includes a hydraulic circuit coupled to a first cylinder that governs the position of the first marker, a first hydraulic valve coupled to a second cylinder that governs the position of the portion of the implement and also coupled to a first port of the hydraulic circuit, and a second hydraulic valve coupled to a second port of the hydraulic circuit. The hydraulic circuit is configured to isolate the first port of the hydraulic circuit from secondary hydraulic pressure supplied to the second port by way of the second hydraulic valve, and further configured to isolate the primary port of the hydraulic circuit from primary hydraulic pressure supplied to the first port by way of the first hydraulic valve. The primary hydraulic pressure is capable of producing changes in the positions of both the portion of the implement and the first marker in a coordinated manner, and the second hydraulic pressure is capable of producing changes in the position of the first marker independently of the position of the portion of the implement. 
     The present invention further relates to a work vehicle assembly that includes at least one marker that is capable of being raised and lowered at least in part by way of a first hydraulic cylinder, a component of the work vehicle assembly that is capable of being raised and lowered at least in part by way of a second hydraulic cylinder, and a hydraulic circuit having first and second ports and further coupled to the first hydraulic cylinder. The work vehicle assembly further includes a hydraulic fluid pressure source, a hydraulic fluid reservoir, and first and second control valves, each of which is coupled between a respective one of the first and second ports and both of the hydraulic fluid pressure source and the hydraulic fluid reservoir, where the first control valve additionally is coupled to the second hydraulic cylinder. The hydraulic circuit includes means for isolating the first port from secondary hydraulic pressure applied to the second port by way of the second control valve, and for isolating the second port from primary hydraulic pressure applied to the first port by way of the first control valve. Additionally, the primary hydraulic pressure communicated by way of the first control valve is capable of producing changes in the positions of both the first and second hydraulic cylinders, and the secondary hydraulic pressure communicated by way of the second control valve is capable of producing changes in the position of the first hydraulic cylinder but not the second hydraulic cylinder. 
     The present invention additionally relates to a method of controlling positions of at least one portion of an implement and at least one marker on a work vehicle assembly. The method includes providing primary hydraulic pressure by way of a first control valve to both a first cylinder and a first port of a hydraulic circuit that in turn is coupled to a second cylinder, where the first and second cylinders respectively govern the positions of the portion of the implement and the at least one marker, respectively, and where the providing of the primary hydraulic fluid adjusts the positions of both the portion of the implement and the at least one marker. The method further includes preventing the primary hydraulic pressure from being communicated, while it is being provided to the first port of the hydraulic circuit, to a second port of the hydraulic circuit, and providing secondary hydraulic pressure by way of a second control valve to the second port of the hydraulic circuit, where the providing of the secondary hydraulic pressure adjusts the position of the at least one marker. The method additionally includes preventing the secondary hydraulic pressure from being communicated, while it is being provided to the second port of the hydraulic circuit, to the first port of the hydraulic circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective side elevation view of an exemplary agricultural work vehicle assembly that includes a tractor towing an implement having a tool bar and left and right marker assemblies including outer and inner markers; 
     FIG.  2 ( a ) is a fragmentary side elevation view of the right marker assembly shown in FIG. 1, where the marker assembly is shown with both the outer marker and inner marker in lowered positions; 
     FIG.  2 ( b ) is a fragmentary side elevation view of the right marker assembly shown in FIG. 1, where the marker assembly is shown with the outer marker in a raised position and the inner marker in a lowered position; 
     FIG.  2 ( c ) is a fragmentary side elevation view of the right marker assembly shown in FIG. 1, where the marker assembly is shown with each of the outer marker and inner marker in raised positions; and 
     FIG. 3 is a schematic diagram of an exemplary hydraulic system for allowing both simultaneous and independent control of the markers of the right and left marker assemblies and the implement/tool bar of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The figures and corresponding text below describe several exemplary embodiments of the invention. However, it should be understood that the present disclosure is only exemplary of the invention and is not intended to be limiting and that the claims below should be referred to for a full understanding of the scope of the invention. 
     Referring to FIG. 1, the present invention relates to work vehicles such as agricultural work vehicles that employ one or more markers that can be raised or lowered with respect to the ground and an additional implement (or toolbar of an implement) that also can be raised or lowered with respect to the ground. In the embodiment shown in FIG. 1, an exemplary work vehicle, in this case an agricultural work vehicle, is shown to be a tractor  10  that tows a planter  20 . The tractor  10  can, for example, be a MX Series Magnum tractor manufactured by CNH Global NV of Racine, Wis., while the planter can be, for example, a Pivot-Transport planter also manufactured by CNH Global NV. As shown, the planter  20  towed behind the tractor  10  includes left and right marker assemblies  30 ,  40  that are attached to left and right sides  50 ,  60  of the planter respectively. Each of the left and right marker assemblies  30 ,  40  has outer and inner markers  151 ,  161 , and  51 ,  61 , respectively (see also FIG.  2 ). Additionally, the planter includes a toolbar  70  that is attached to the remainder of the planter  20  (the planter can also be termed an implement). 
     In accordance with the present invention, each of the markers  151 ,  161 ,  51  and  61  and the toolbar  70  can be raised and lowered with respect to the ground. In FIG. 1, the right outer marker  51  is shown to be in a raised position, while the left outer and inner markers  151 ,  161  are shown to be in lowered positions. In addition to the toolbar  70 , the planter  20  additionally includes several other components that are known in the art, including a plurality of hoppers  80  and a liquid fertilizer tank  90 . The toolbar  70  can include a variety of elements including, for example, seed discs, furrow opening and closing mechanisms, and press wheels, as are known in the art. 
     Although FIG. 1 shows the tractor  10  and planter  20 , the present invention is intended to apply to any agricultural or other work vehicles that include one or more markers, as well as include a toolbar, implement or other device, where it is necessary to be able to raise and lower all of these devices. Although the planter  20  is shown to be towed by the tractor  10 , the present invention also is intended to be applicable to any agricultural or other work vehicle on which one or more raisable/lowerable marker(s) and toolbar/implement are employed, regardless of whether all of these components are positioned on a single vehicle portion, or on multiple vehicle portions (e.g., where one marker is on the tractor, another marker is on a towed device other than the planter, and the toolbar/implement along with possibly yet another marker are on the planter itself.) The present invention further would relate to a work vehicle having only a single marker assembly, e.g., a right marker assembly, or having more than two marker assemblies, as well as to a vehicle on which one or more of the marker assemblies had only a single marker, or more than two markers. 
     Referring to FIGS.  2 ( a )- 2 ( c ), the right marker assembly  40  is shown in three positions, namely, a first position in which each of the right outer and inner markers  51 ,  61  is in its lowered position (FIG.  2 ( a )), a second position in which the outer marker is raised but the inner marker is lowered (FIG.  2 ( b )), and a third position in which each of the outer and inner markers is raised (FIG.  2 ( c )). As shown, the right marker assembly  40  includes a shoulder hinge  42  by which the marker assembly  40  is connected to the right side  60  of the planter  20 . In addition to the shoulder hinge  42 , the right marker assembly  40  includes an upper arm portion  43 , an elbow hinge  44 , a lower arm portion  45 , a wrist hinge  46 , and an outer extension  47 , which are connected to one another in succession. The right outer marker  51  is formed primarily by elements  44 - 47  and is supported by the right inner marker  61 , which is formed primarily by elements  42  and  43 . Marking devices such as marking rings can be coupled to an outer tip  48  of the outer extension  47  and to an outer end  58  of the upper arm portion (see FIG. 1 for an exemplary marking ring  49 ). 
     The right inner marker  61  is actuated by a right inner marker cylinder  62  while the right outer marker  51  is actuated by a right outer marker cylinder  52  (see FIGS.  2 ( a ) and  2 ( b )). As shown, when the outer marker cylinder  52  is expanded, this causes the lower arm portion  45  to raise. Because the outer extension  47  is hingedly connected to the lower arm portion  45  by the wrist hinge  46 , the outer extension falls due to gravity as the lower arm portion  45  is raised such that the lower arm portion  45  and the outer extension  47  retract in upon one another as shown in FIG.  2 ( b ). Conversely, when the right outer marker cylinder  52  is retracted, the lower arm portion  45  is lowered. Because a lever  41  attached to the outer extension  47  proximate the wrist hinge  46  is hingedly coupled to a pull  53  that in turn is coupled to the outer end  58 , the outer extension  47  swings outward as the lower arm portion  45  is forced outward, and thus the right outer marker  51  becomes fully extended as shown in FIG.  2 ( a ). 
     FIGS.  2 ( a ) and  2 ( b ) show the right inner marker  61  in its lowered position. That is, the right inner marker  61  can remain in its lowered position regardless of whether the right outer marker  51  is lowered or not. As shown in FIGS.  2 ( a ) and  2 ( b ), the right inner marker  61  is lowered when the right inner marker cylinder  62  is retracted. However, as shown in FIG.  2 ( c ), when the right inner marker cylinder  62  is extended, the upper arm portion  43  becomes raised and the right inner marker  61  therefore is raised. As is evident from FIG.  2 ( c ), when the right inner marker  61  is in its raised position, the right outer marker  51  must also be in its raised position. Although not shown in FIGS.  2 ( a )- 2 ( c ), the left marker assembly  30  in the present embodiment has a similar design to that of the right marker assembly and, in particular, the outer and inner markers  151 ,  161  of the left marker assembly are actuated by a left outer marker cylinder  152  and a left inner marker cylinder  52 , respectively (see FIG.  3 ). 
     Referring to FIG. 3, components of a hydraulic system  100  capable of being implemented on the tractor  10  and the planter  20  to raise and lower the markers  51 ,  61 ,  151  and  161  and the toolbar  70  is shown. In particular, the hydraulic system  100  includes a pump  110  that is powered by an engine  120  of the tractor  10 , and that is hydraulically coupled to a reservoir  130  from which it receives hydraulic fluid. The hydraulic fluid is then communicated to first and second toolbar cylinders  140 ,  142  that govern the raising and lowering of left and right halves of the toolbar  70 , to the left and right outer marker cylinders  152  and  52 , respectively, and to the left and right inner marker cylinders  162  and  62 , respectively, by way of first and second control valves  170  and  172 , and a control circuit  174 . The right inner and outer marker cylinders  62 ,  52  are those discussed above with reference to FIGS.  2 ( a )- 2 ( c ) while the left inner and outer marker cylinders  162 ,  152 , though not shown with reference to FIG. 1 or  2 ( a )- 2 ( c ), serve the same purposes with reference to the left marker assembly  30  as marker cylinders  62  and  52  serve with reference to the right marker assembly  40 . In FIG. 3, the control valves  170 ,  172  are shown to be located on the tractor  10  so that the valves can be actuated by a tractor operator (e.g., using control levers within a cab of the tractor), while the control circuit  174  is shown to be located on the planter  20 ; however, the exact positioning of these components can vary depending upon the embodiment. 
     As shown, the first control valve  170  specifically governs the provision of hydraulic fluid and hydraulic fluid pressure to ports S and R of the control circuit  174 , while the second control valve  172  specifically governs the provision of hydraulic fluid and hydraulic fluid pressure to ports S 1  and R 1  of the control circuit. Each of the first and second control valves  170 ,  172  has four possible positions or states, namely: a raise position in which hydraulic fluid is directed from the pump  110  to a respective one of the ports S, S 1  and from the a respective one of the ports R, R 1  to the reservoir  130 ; a lower position in which hydraulic fluid is directed from the pump  110  to a respective one of the ports R, R 1  and from a respective one of the ports S, S 1  back to the reservoir; a neutral position in which fluid flow between the corresponding ports S, R or S 1 , R 1  and the pump and reservoir is precluded; and a float position in which both of the ports S, R or S 1 , R 1  corresponding to the control valve are coupled to the reservoir  130 . As shown, each of ports S, R, S 1 , and R 1  is a port of the control circuit  174 . In addition, the port S is coupled to head portions  144  of each of the toolbar cylinders  140  and  142 , while the port R is coupled to rod portions  146  of each of those cylinders. Consequently, whenever the first control valve  170  is switched to the raise position, hydraulic fluid flow is provided to the head portions  144  of the cylinders  140 ,  142 , which causes the cylinders to expand and thus raises the left and right halves of the toolbar  70 . (In alternate embodiments, only one cylinder can be used to raise the toolbar  70  or a portion thereof or another movable element, or more than two cylinders can be used to raise more than two segments of the toolbar or other movable elements.) However, when the first control valve  170  is switched to the lower position, hydraulic fluid flow is directed to the rod portions of the cylinders  140 ,  142  and thus causes the toolbar  70  to be lowered. Further, when the first control valve is in the neutral position, hydraulic fluid flow cannot occur to or from the first and second toolbar cylinders  140 ,  142  from or to the pump or reservoir  110 ,  130 , and consequently the position of the toolbar  70  is locked. Additionally, when the first control valve  170  is in the float position, the toolbar  70  can lower under the influence of gravity as fluid is passed from the head portions  144  of the toolbar cylinders  140 ,  142  to the rod portions  146  (because the rod portions are smaller in cross-section than the head portions due to the presence of the rods therewithin, some of the fluid leaving the head portions also is directed toward the reservoir  130 ). 
     The hydraulic fluid pressure provided to the ports S and R as determined by the first control valve  170 , in addition to being provided to the cylinders  140  and  142 , also is provided to the control circuit  174 . Based upon the status of the control circuit  174 , the hydraulic fluid pressure provided to the ports S and R additionally can determine the upward and downward positioning of the right and left outer and inner marker cylinders  52 ,  62 ,  152  and  162  which govern the positioning of the corresponding right and left outer and inner markers  51 ,  61 ,  151  and  161 , respectively. Although, depending upon the status of the control circuit  174 , the hydraulic fluid provided to the ports S and R can influence the positions of these marker cylinders  52 ,  62 ,  152 , and  162 , in accordance with the present embodiment of the invention, the hydraulic fluid provided to the ports S 1  and R 1  as determined by the control valve  172  also can influence the positions of these marker cylinders. That is, the actuation of the marker cylinders  52 ,  62 ,  152  and  162  and positioning of the markers  51 ,  61 ,  151  and  161  based upon the actuation of those cylinders can be governed either by way of the first control valve  170 , in which case some or all of the marker cylinders can be actuated simultaneously with the actuation of the toolbar cylinders  140 ,  142 , or by way of the second control valve  172 , in which case some or all of the marker cylinders can be actuated independently of any actuation of the toolbar cylinders  140 ,  142 . To prevent interaction between the hydraulic pressure provided by the two control valves  170 ,  172 , the control circuit  174  serves to isolate the ports S 1 , R 1  from hydraulic fluid pressure being provided at the ports S, R and serves to isolate the ports S, R from hydraulic fluid pressure being provided at the ports S 1 , R 1 . 
     As shown in FIG. 3, the control circuit  174  includes first and second pilot operated check valves  176 ,  178 , first and second conventional check valves  180  and  182 , and first and second pilot-to-close check valves  184  and  186 . The first pilot operated check valve  176  is connected between the port S and a first intermediate node  188 , while the second pilot operated check valve is connected between the port R and a second intermediate node  190 . Further, the first conventional check valve  180  is coupled between the first intermediate node  188  and the port S 1 , while the second conventional check valve  182  is coupled between the second intermediate node  190  and the port R 1 . Except as discussed below with respect to check valves  176  and  178 , each of the check valves  176 ,  178 ,  180 , and  182  are configured and positioned so as to only allow hydraulic fluid to flow through each respective check valve toward its respective intermediate node, and not from its respective intermediate node back to the corresponding one of the ports S, R, S 1  and R 1 . For example, the first conventional check valve  180  is configured and orientated to allow hydraulic fluid to flow from port S 1  to the first intermediate node  188 , but not in the opposite direction. 
     While the first and second conventional check valves  180 ,  182  are designed to always prevent hydraulic fluid from flowing from the intermediate nodes  188 ,  190  to ports S 1  and R 1 , and to only allow hydraulic fluid to flow from the ports S 1  and R 1  to the intermediate nodes  188  and  190 , respectively, the first and second pilot operated check valves  176  and  178 , while normally being closed to prevent hydraulic fluid flow from the intermediate nodes  188 ,  190  to the ports S and R, can be operated in certain situations to allow hydraulic fluid to flow in that reverse direction. As shown, a first pilot line  192  is coupled between the first pilot operated check valve  176  and the port R, while a second pilot line  194  is coupled between the second pilot operated check valve  178  and the port S. Consequently, when hydraulic fluid pressure at the port S exceeds a certain minimum threshold, the second pilot operated check valve  178  enters an alternate state in which it allows hydraulic fluid to flow from the second intermediate node  190  to the port R. Similarly, when the hydraulic fluid pressure at the port R exceeds a certain minimum threshold, then the first pilot operated check valve  176  enters an alternate state in which it allows hydraulic fluid to flow from the first intermediate node  188  to the port S. 
     Further referring to FIG. 3, a third pilot line  196  couples the first pilot-to-close check valve  184  to the port S, while a fourth pilot line  198  couples the second pilot-to-close check valve  186  to the port R. The first pilot-to-close check valve  184  is coupled in parallel with the first conventional check valve  180  between the port S 1  and the first intermediate node  188 , and the second pilot-to-close check valve  186  is coupled in parallel with the second conventional check valve  182  between the second intermediate node  190  and the port R 1 . Each of the pilot-to-close check valves  184 ,  186  is designed to normally allow hydraulic fluid to flow in either direction between its respective port S 1 , R 1  and its respective intermediate  188 ,  190 . However, when hydraulic pressure at the port S exceeds a minimum threshold, the first pilot-to-close check valve  184  prevents hydraulic fluid from flowing from the first intermediate node  188  back to the port S 1 . Similarly, when the hydraulic fluid pressure at the port R exceeds a certain minimum threshold, then the second pilot-to-close check valve  186  prevents hydraulic fluid from flowing from the second intermediate node  190  back to the port R 1 . 
     Further as shown in FIG. 3, head portions  157  of each of the right and left outer marker cylinders  52 ,  152  are coupled to the first intermediate node  188  by respective right and left solenoid valves  202 ,  204  (which also are included as part of the control circuit  174  as shown in FIG.  3 ), and by a two-way restriction orifice  206  and a one-way restriction orifice  207 . The restriction orifices  206 ,  207  are coupled in series with one another and the respective solenoid valves  202 ,  204  between the first intermediate node and the head portions of the respective cylinders  52 ,  152 . Each of the solenoid valves  202 ,  204  can be set in one of two positions, a first position in which fluid flow is unrestricted by the solenoid valve and a second position in which fluid can only flow through the solenoid valve towards its respective marker cylinder and not away from its cylinder. The restriction orifices  206 ,  207  allow fluid flow both from the first intermediate node  188  to the solenoid valves  202 ,  204  and from the solenoid valves  202 ,  204  to the first intermediate node; however, the restriction orifices limit the rates at which fluid can flow. While the two-way restriction orifice  206  restricts flow in both directions, the one-way restriction orifice  207  serves only to restrict flow occurring toward the cylinders  52 ,  152 . 
     Additionally as shown, respective head portions  208  of the respective right and left inner marker cylinders  62 ,  162  are coupled to the first intermediate node  188  by way of respective first and second solenoid valves  210 ,  212 , each of which can be set in either a first position in which all fluid flow through the respective solenoid valve is prevented and a second position in which fluid flow through the respective solenoid valve is unrestricted. Although not required, in the embodiment shown, the respective solenoid valves  210 ,  212 , are connected to the respective head portions  208  of the respective marker cylinders  62 ,  162  by respective one-way restriction orifices  211 , which restrict fluid flow toward the head portions but not away from the head portions. Further, respective rod portions  214  of the right and left inner marker cylinders  62 ,  162  are coupled to the second intermediate node  190 . In the present embodiment, these connections are made by way of respective two-way restriction orifices  216 , although such orifices need not be employed in every embodiment. 
     Given the design of the control circuit  174 , the inner and outer marker cylinders  62 ,  162 ,  52  and  152  can be actuated independently of the actuation of the toolbar cylinders  140 ,  142  if hydraulic fluid is applied at the ports S 1  and R 1  by way of the second control valve  172 , and also can be activated simultaneously with the toolbar cylinders  140 ,  142  if hydraulic fluid pressure is applied at the ports S and R by way of the first control valve  170 . In the case of simultaneous control, the first control valve  170  is adjusted to either the raise position or the lower position such that hydraulic fluid pressure from the pump  110  is communicated to the port S or to the port R, respectively. At such times, the second control valve  172  is typically in the float position, although this is not necessary. If the hydraulic fluid pressure is provided to the port S, the hydraulic fluid flows through the first pilot operated check valve  176  to the first intermediate node  188 , and in turn is provided to each of the solenoid valves  210 ,  212 ,  202 , and  204 . Consequently, the head portions  157  of the right and left outer marker cylinders  52 ,  152  receive hydraulic fluid, which tends to raise the outer markers  51 ,  151  and, additionally, if the solenoid valves  210 ,  212  are in their second positions such that fluid is communicable therethrough, hydraulic fluid is then provided also to the head portions  208  of the respective right and left inner marker cylinders  62 ,  162 , which causes the inner markers  61 ,  161  also to raise. 
     Further, as hydraulic fluid enters the head portions  208  of the inner marker cylinders  62 ,  162 , hydraulic fluid must exit those cylinders from the rod portions  216 , and fluid thus exiting the cylinders is returned to the second intermediate port  190 . Because the hydraulic fluid pressure at the port S is at a high level, the second pilot line  194  communicates this pressure to the second pilot operated check valve  178 , which causes that check valve to allow the fluid returning to the second intermediate port  190  to return to the reservoir  130  by way of the port R. Additionally, the third pilot line  196  communicates the pressure at the port S to the first pilot-to-close check valve  184 , which causes that valve to close and thus prevent fluid from flowing from the first intermediate node  188  to the port S 1 . Also, because the hydraulic pressure applied to the port S is applied to the head portions  144  of the toolbar cylinders  140 ,  142 , the toolbar  70  also tends to raise simultaneously as the markers are being raised. 
     Alternately, if the control valve  170  is put into the lower position such that the hydraulic fluid pressure from the pump  110  is applied to the port R, then hydraulic fluid flows through the first pilot operated check valve  178  to the second intermediate node  190 . Because the pressure at the port R is communicated by way of the pilot line  192  to the first pilot operated check valve  176 , that check valve allows hydraulic fluid to flow from the first intermediate node  188  to the port S and then further to the reservoir  130  by way of the first control valve  170 . Consequently, fluid from the head portions  157  of the left and right outer marker cylinders  52 ,  152  can flow through the solenoid valves  202 ,  204  (assuming that those solenoid valves are in the first position allowing unrestricted flow therethrough) and further through the restriction orifices  206 ,  207  back to the first intermediate node  188  and finally to the reservoir  130  by way of the port S. The outer markers  51 ,  151  corresponding to the outer marker cylinders  52 ,  152  are lowered at a controlled pace (despite the fact that they are lowered under the force of gravity) due to the restriction created by the restriction orifice  206 . If one or both of the solenoid valves  202 ,  204  are in their second position preventing flow away from the cylinders  52 ,  152 , then the corresponding markers  51 ,  151  are locked in place and cannot lower. Also, fluid does not flow from the port R to the port R 1  via the second pilot-to-close check valve  186  since the fourth pilot line  198  communicates the pressure of the port R to that check valve such that the valve precludes such flow. 
     Further, as fluid is provided to the second intermediate node  190  by way of the second pilot operated check valve  178 , the fluid is further directed to the rod portions  216  of the inner marker cylinders  62 ,  162 . If the solenoid valves  210  and  212  corresponding to the right and left inner marker cylinders  62 ,  162  are in their second, fluid-conducting positions, then hydraulic fluid is capable of leaving the head portions  208  of the cylinders and returning by way of the corresponding solenoid valves to the first intermediate node  188  and then, because the first pilot operated check valve  176  is open due to the pressure upon the first pilot line  192 , further able to return to the reservoir  130  by way of the port S. If either of the solenoid valves  210 ,  212  happens to be in its first (closed) state, then the corresponding marker cylinder  62  or  162  cannot vary in its position. Additionally, as hydraulic fluid pressure is applied to the port R, then that fluid pressure is again provided to the rod ends  146  of the toolbar cylinders  140  and  142 , and consequently the toolbar  70  lowers simultaneously with the lowering of the outer markers and/or inner markers as determined by the states of the solenoid valves  202 ,  204 ,  210  and  212 . 
     In certain embodiments, including the one shown in FIG. 3, a switch  218  (actuatable by the operator or also by a computer) governs the positions of the solenoid valves  202 ,  204 . In particular, the switch  218  allows an operator to alternate the solenoid valves&#39; positions so that, at a first time, the solenoid valve  202  is in its first position such that it is fully conducting while the solenoid valve  204  is in its second position at a second time, the solenoid valve  204  is in its first position while the solenoid valve  202  is in its second position, and so on. 
     Regardless of whether the second control valve  172  is in the neutral state when hydraulic fluid is provided to one or the other of the ports S and R, the circuit  174  nonetheless prevents hydraulic fluid from being communicated to either of the ports S 1  and R 1 . In particular, when the first control valve  170  is in the raise state such that hydraulic fluid pressure is provided to the port S, fluid nevertheless cannot be communicated from the first intermediate port  188  to the port S 1  by way of the first conventional check valve  180 , nor can hydraulic fluid be provided from that intermediate node to the port S 1  by way of the first pilot-to-close check valve  184 . Likewise, hydraulic fluid returning to the second intermediate node  190  cannot be provided to the port R 1  by way of either the second conventional check valve  182  or the second pilot-to-close check valve  186 . Likewise, when the first control valve  170  is in the lower position, such that hydraulic fluid pressure is provided to the port R, the conventional check valves  180 ,  182  and pilot-to-close check valves  184 ,  186  prevent fluid flow from the intermediate nodes  190 ,  188  toward the ports R 1  and S 1 . Thus, the ports S 1  and R 1  are isolated from the hydraulic fluid pressure provided at either of the ports S and R. 
     In the case where the first control valve  170  is in the neutral position but the second control valve  172  is in the raise position or the lower position, the outer marker cylinders  52 ,  152  and inner marker cylinders  62 ,  162  can be actuated independently of (e.g., without the actuation of) the toolbar cylinders  140 ,  142 . In particular, if the second control valve  172  is placed into the raise position, hydraulic fluid pressure is provided from the pump  110  to the port S 1 . The pressure at the port S 1  is initially provided to the first intermediate node  188  by way of both the first conventional check valve  180  and the first pilot-to-close check valve  184 . However, because the first conventional check valve  180  is spring-biased towards being closed, once some of the fluid initially moves from the port S 1  to the first intermediate node  188 , the first conventional check valve tends to close, thus preventing further fluid flow through that valve. Consequently, after initially flowing through both the first conventional check valve  180  and the first pilot-to-close check valve  184 , the fluid then continues to flow from the port S 1  to the first intermediate node  188  only by way of the first pilot-to-close check valve. Regardless of how the hydraulic fluid reaches the first intermediate port  188 , that fluid then proceeds toward each of the solenoid valves  202 ,  204 ,  210  and  212  and is capable of actuating the outer and inner marker cylinders  52 ,  152 ,  62 , and  162 , depending upon the states of those solenoid valves. When the solenoid valves  210  and  212  are in their second, fluid-communicating positions, fluid further returns from the rod ends  216  of the inner marker cylinders  62 ,  162  to the second intermediate node  190  and further returns to the port R 1  from that node by way of the second pilot-to-close check valve  186 . 
     Alternately, when the second control valve  172  is in the lower position such that hydraulic fluid pressure is provided to the port R 1 , hydraulic fluid flows first to the second intermediate node  190  by way of both of the second conventional check valve  182  and the second pilot-to-close check valve  186 , and then continues to flow to the second intermediate node by way of only the second pilot-to-close check valve. Depending upon whether the solenoid valves  210  and  212  are in the fluid communicating positions, hydraulic fluid may or may not flow toward the rod ends  216  of the inner marker cylinders  62 ,  162  and then return from the head ends  208  of those cylinders by way of the solenoid valves to the first intermediate node  188 . Further, depending upon whether the solenoid valves  202  and  204  are in their fluid communicating positions, fluid also may return to the first intermediate node  188  by way of the respective solenoid valve(s) and the restriction orifices  206 ,  207 . The fluid returning to the first intermediate node  188  then further can proceed out to the reservoir  130  by way of the port S 1  by way of the first pilot-to-close check valve  184 . Assuming that the first control valve  170  is either in the neutral position or the float position while all this is taking place, there is no significant hydraulic fluid pressure at the ports S and R, and consequently neither of the first and second pilot operated check valves  176 ,  178  are opened to allow fluid to flow from the intermediate nodes  188 ,  190  to the ports S and R. Thus, the actuation of the marker cylinders  52 ,  152 ,  62  and  162  can occur independently of (typically, without) any actuation of the toolbar cylinders  140 ,  142 . 
     The control circuit  174  shown in FIG. 3 is only one embodiment of several possible embodiments envisioned by the present invention. The control circuit  174  shown in FIG. 3 employs three pairs of different types of check valves  176  and  178 ,  180  and  182 , and  184  and  186  in order to allow for the outer markers  51 ,  151  to move up and down when in the lowered position to accommodate variation in the terrain encountered by the markers. That is, typically, when the inner and outer markers  51 ,  151 ,  61 ,  161  are in their lowered positions, the second control valve  172  is in the float position such that, as those markers need to vary in their position to account for variations in terrain, hydraulic fluid can freely flow back and forth to the marker cylinders  52 ,  152 ,  62  and  162  by way of the ports S 1  and R 1  and the pilot-to-close check valves  184  and  186 . However, in alternate embodiments, for example, embodiments in which the marker linkages themselves include compensation features that effectively allow the markers to float without necessitating any movement of hydraulic fluid in relation to the movement of those markers, then the pilot-to-close check valves  184  and  186  can be eliminated and the first and second conventional check valves  180  and  182  can be replaced with pilot operated check valves like the check valves  176  and  178 , with pilot lines coupling those respective new pilot operated check valves to the ports S 1  and R 1  (in alternating fashion, just as the pilot lines  192  and  194  couple the check valves  176  and  178  to the ports S and R.) 
     The present invention is also intended to encompass a variety of alternate embodiments that employ varying numbers and types of valves in place of or in addition to any of the valves  170 ,  172 ,  176 ,  178 ,  180 ,  182 ,  184 ,  186 ,  202 ,  204 ,  210  and  212 , so long as there are two isolated hydraulic actuation paths in which one of the paths actuates one or more marker(s) while another of the paths actuates those marker(s) plus an additional component such as a toolbar. 
     To apprise the public of the scope of this invention, the following claims are made: