as required , detailed embodiments of the present invention are disclosed herein ; however , it is to be understood that the disclosed embodiments are merely exemplary of the invention , which may be embodied in various forms . therefore , specific structural and functional details disclosed herein are not to be interpreted as limiting , but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure . without limitation on the possible orientations of the tow frame embodying the present invention , front and back generally mean with respect to the direction of travel , i . e . towards the top of the page in fig1 and 2 and to the left in fig3 and 4 . referring to the drawings in more detail , the reference numeral 15 generally designates a tow frame embodying the present invention . the tow frame 15 may be drawn by , for example , a tow vehicle such as a tractor 20 . the tow frame 15 may be utilized to pull a variety of different implements , including first ( middle ), second ( left side ) and third ( right side ) seed drills 21 , 22 and 23 . the seed drills 21 , 22 and 23 may comprise , for example , john deere model no . 9300 grain drills , which are available from deere & amp ; company of moline , ill . such seed drills are used for planting row crop seed and may include front gauge wheels 24 , shoes 25 for opening the earth to receive the seed deposits , and press wheels 26 for closing the earth over the planted seeds . seed boxes or hoppers 27 are located above the shoes 25 . seed dispensing mechanisms ( not shown ) are normally provided for metering desired quantities of seeds into the open furrows in the field . seed drills are also available which dispense fertilizer to facilitate seed germination . the drills 21 , 22 and 23 may be provided with hydraulic piston - and - cylinder units 28 for raising and lowering between lowered field positions ( fig3 ) with their shoes 25 embedded in the ground and raised transport positions ( fig4 ) with their shoes 25 disengaged . although a specific type of shoe drill is shown for use with the tow frame 15 of the present invention , it will be appreciated that various other types of implements , including other types of planters , can be drawn by tow frames embodying the present invention . for example , planters are available with disks for opening the ground slots or furrows in lieu of the shoes 25 . the planters and their various components are selected to maximize yield for various crops and field conditions . the tow frame 15 of the present invention generally comprises a yoke subframe 31 , a primary or central subframe 32 and a pair of wing subframes 33 . the yoke subframe 31 includes a tongue 35 mounting a hitch 36 at a front end 37 thereof for attachment to the tractor 20 . an a - frame 38 extends rearwardly from the tongue 35 and includes a pair of rearwardly - diverging side legs 39 terminating at side leg rear ends 40 and a center leg 41 , which may comprise an extension of the tongue 35 , terminating at a center leg rear end 42 . the primary subframe 32 includes a front , transverse , tubular drawbar 45 with opposite ends 46 . the drawbar 45 may be pivotally connected to the yoke subframe 31 , for example by three clevis - type hinge assemblies 47 each including a transverse hinge pin 48 extending along a horizontal , transverse pivotal axis located slightly in front of and extending in parallel relation with respect to the drawbar 45 . the yoke and primary subframes 31 , 32 are thus adapted to flex with respect to each other . a pair of side members 51 extend rearwardly from the drawbar 45 , each side member 51 including a front end 52 fastened to a respective drawbar opposite end 46 and a rear end 53 mounting a t - flange 54 which is perpendicular to the side member 51 . a pair of double - clevis hinge brackets 57 are each mounted on a respective side member t - flange 54 . each hinge bracket 57 includes a generally vertical front plate 58 which is fastened , for example by bolting , to a respective t - flange 54 . upper and lower pairs of horizontal clevis plates 59 are fastened to and extend rearwardly from the front plate 58 . the clevis plate pairs form upper and lower clevis receivers 60 , 61 . a vertical back plate 62 is mounted , for example by welding , on the clevis plates 59 and may be positioned in parallel , spaced relation rearwardly from the front plate 58 for attachment , for example by bolts 63 , to the first seed drill 21 . each wing subframe 33 includes a proximate end 67 pivotally connected to a respective hinge bracket 57 and a distal end 68 . each wing subframe 33 further includes a swing arm or proximate member subassembly 69 comprising upper and lower swing arm beams or tubes 71 , 72 with proximate end sleeves 73 , 74 pivotally received in the hinge bracket clevis upper and lower receivers 60 , 61 respectively and forming the wing subframe proximate end 67 . a hinge pin subassembly 78 includes a plate 79 fastened ( e . g . bolted ) to the topmost clevis plate 59 and a wing subframe hinge pin 85 extending through the clevis plates 59 and the sleeves 73 , 74 . the swing arm tubes 71 , 72 terminate at outer ends 75 , 76 respectively . the swing arm tubes 71 , 72 extend substantially parallel to each other for most of the lengths of the swing arms 69 and are separated by spacers 77 . at their outer ends 75 , 76 the swing arm tubes 71 , 72 converge . each lower swing arm tube 72 mounts a locking assembly 80 in proximity to its outer end 76 , the locking assembly 80 comprising a pair of lock bars 81 fastened above and below the lower swing arm tube 72 . the lock bars 81 project inwardly ( with the swing arm 69 folded alongside a respective side member 51 ) from the swing arm lower tube 72 and include diverging ends 82 with locking pin receivers 83 . each locking assembly 80 includes a locking pin 84 adapted for selective placement in the locking pin receivers 83 on the inside of a respective side member 51 whereby the side member 51 is releasably captured between the locking pin 84 on the inside , the lock bars 81 above and below , and the juxtaposed lower swing arm tube 72 on the outside in a field or working configuration ( fig8 and 9 ). alternatively , the lock bars 81 may project from the side members 51 and lockably receive the lower swing arm tubes 72 . each swing arm 69 mounts a respective wing a - frame 87 including a distal extension member 88 with inner and distal ends 89 , 90 and a diagonal brace member 91 , also with inner and distal ends 92 , 93 . the extension and brace member inner ends 89 , 92 may be pivotally connected to the swing arm lower tubes 72 , for example , by clevis - type hinge assemblies 94 defining horizontal , aligned pivotal axes extending in parallel relation slightly outwardly from the swing arm lower tubes 72 . each wing a - frame 87 is thus articulated with respect to the primary subframe 32 about such aligned pivotal axes of the hinge assemblies 94 . with the wing subframe 33 in its field or working position , each extension member 88 forms approximately a right angle with respect to a respective swing arm 69 , and each brace member 91 extends diagonally from a respective hinge assembly 94 located between the swing arm lower tube ends 74 , 76 to the extension member distal end 90 at the wing subframe distal end 68 . at the wing subframe distal end 68 , the extension and brace member distal ends 90 , 93 may be connected by a gusset plate 95 . a wing hitch assembly 96 is provided at each wing subframe distal end 68 for hitching to a respective second or third implement 22 , 23 . the actuating system 34 includes a pair of piston - and - cylinder units 100 each having inner and outer ends 101 , 102 . a respective clevis - type hinge assembly 104 mounts each piston - and - cylinder unit inner end 101 to the drawbar 45 and includes upper and lower plates 105 , 106 for releasably clamping to the drawbar 45 with bolts 107 . the locations of the hinge assemblies 104 are thus slidably adjustable along the drawbar 45 . the piston - and - cylinder unit outer ends 102 are likewise pivotally and adjustably connected to the swing arm upper tubes 71 by clevis type hinge assemblies 110 . the hinge assemblies 110 may be located between the swing arm upper tube proximate ends 73 and the wing brace member inner ends 92 , and their positions are slidably adjustable along the swing arm upper tubes 71 . a pair of hydraulic lines 115 extend from a source of hydraulic fluid pressure , which may be provided on the tractor 20 , and communicate with the piston - and - cylinder units 100 . although double - acting ( extendable and retractable ) hydraulic piston - and - cylinder units 100 are shown , other types of linear actuators may be provided . for example , single - acting hydraulic or pneumatic units could be employed . further , jack assemblies with telescoping tubes reciprocated by screw - threaded rods are available from barker manufacturing company of battle creek , mich . the threaded rods are driven by electric motors which could draw power from the electrical system of the tractor 20 . the tow frame 15 is shown in a field configuration in fig1 and 5 with the wing subframes 33 extending laterally from the primary subframe 32 . in this configuration the lock assemblies 80 secure the swing arms 69 to the primary subframe side members 51 . the tow frame 15 is articulated about a transverse pivotal axis extending through the hinge assemblies 47 in front of the drawbar 45 whereby relative rotation is permitted between the yoke and primary subframes 31 , 32 . the tow frame 15 is also articulated about longitudinal pivotal axes that extend through the hinge assemblies 94 whereby the wing a - frames 87 are relatively pivotable with respect to the swing arms 69 . thus , the tow frame 15 is designed in operation to conform to various field conditions , for example unlevel ground conditions , whereby the implements 21 , 22 and 23 may normally be in position for effectively working the field . implements of various widths may be used in conjunction with tow frames 15 embodying the present invention . with the tow frame 15 in its field configuration , the combined widths of the implements 21 , 22 and 23 provide a total , field - working width which is approximately three times the width of an individual implement . although such a maximum width potential is highly desirable for efficient operation , the width of the tow frame 15 in its field configuration may exceed a practical width which could be conveniently transported on a roadway or driven into a barn or other storage building . to facilitate transporting and storing the tow frame 15 and the implements 21 , 22 and 23 , the tow frame 15 may be relatively easily folded from its field configuration ( fig1 and 5 ) to a transport configuration ( fig2 and 6 ). folding is accomplished by removing the locking pins 84 from the locking assemblies 80 and extending the piston - and - cylinder units 100 whereby the wing subframes 33 pivot with respect to the primary subframe 32 about respective pivotal axes that extend vertically through the hinge assemblies 56 . with the tow frame 15 in a transport configuration , the hinge assemblies 56 are substantially longitudinally aligned with the wing hitch assemblies 96 . thus , when the tow frame 15 is pulled , the wing subframes are primarily placed in tension . the piston - and - cylinder units 100 may be closed against fluid flow therethrough in their extended positions to assist in retaining the wing subframes 33 in their transport positions , but when the tow frame 15 is pulled straight in a forward direction little or no force is exerted on the piston - and - cylinder units 100 because of the aforementioned alignment of the hinge assemblies 56 and the wing hitch assemblies 96 . by thus aligning the hinge assemblies 56 and the wing hitch assemblies 96 , most of the force associated with pulling the second and third implements 22 , 23 is transmitted to the hinge assemblies 56 as a pulling force in a direction directly rearward . with the tow frame 15 in its transport configuration ( fig2 ), its overall width , including the second and third implements 22 , 23 , is about two - thirds of its overall width with the implements 21 , 22 and 23 in their field configurations ( fig1 ). the tow frame in its transport configuration is thus better adapted for travel over roadways and also for placement in storage facilities . if a further width reduction is desired , one of the second or third implements 22 , 23 can be unhitched and the corresponding wing a - frame 87 folded upwardly out of the way . the resulting assemblage may thus assume an overall width somewhat less than that of the assemblage with all three implements 21 , 22 , 23 and the tow frame 15 in a tow configuration . it is to be understood that while certain forms of the present invention have been illustrated and described herein , it is not to be limited to the specific forms or arrangement of parts described and shown .
a tow frame for agricultural implements , such as seed drills , is provided . the tow frame includes a primary subframe for attaching to a tow vehicle and to an agricultural implement . a pair of wing subframes are hingedly mounted on opposite sides of the primary subframe . second and third implements may be coupled to the wing subframes . the tow frame is foldable between a field configuration with the implements substantially transversely aligned and a transport configuration with the wing subframes folded rearwardly whereby the second and third implements are each positioned partly behind the first implement .