Abstract:
An agricultural implement, such as a baler comprises a main frame and a hitch for attachment of the implement to a towing vehicle. The frame is supported on a bogie comprising a pair of steerable wheels. A pair of hydraulic rams can block these wheels in a fore-and-aft position for reversing the baler or for preventing fluttering during road transport. Hydraulic circuitry, which is used for controlling functions of said implement, such as the retraction of a bale chuteor the operation of a bale eject apparatus can be used to actuate the rams. The rams are loaded by providing pressurized oil to the return line and using a non-return valve for making the oil flow to the guiding the said circuitry to the rams.

Description:
BACKGROUND OF INVENTION 
     1. Field of Art 
     The present invention relates to pull-type agricultural implements which are conceived for attachment to a pulling vehicle, and more particularly to implements having a pair of steerable wheels. 
     2. Description of Prior Art 
     Traditionally, agricultural tractors have been designed for low road speeds, not exceeding 25 km/h. However, more and more modern tractors are capable of attaining top speeds of 50 km/h without discomfort to the user or danger for the tractor structure. In practice however, the speed of the tractor still has to be limited because the implements attached to the tractor do not allow high speeds. This certainly is the case where no suspension is provided for the wheels of the implement. 
     Accordingly, adequate suspension systems have been fitted to pull-type implements, permitting road speeds in excess of 25 km/h for the whole tractor-implement combination. In one embodiment the implement has been provided with a kind of bogie which is attached by two sets of leaf springs to the frame of the implement. The bogie comprises four wheels mounted to a front and a rear axle. Such structure behaves satisfactorily during road travel, where large turns are to be made, but seriously hampers the operation in the field, where the implement sometimes must take very short turns. The second pair of wheels then seriously hampers the movement of the baler and may even deteriorate the earth on headlands. 
     In response thereto it has been suggested to make the rear wheels of the implement steerable such that they can adapt freely to the short turns. However, for road travel all wheels have to be held in a fixed position to keep the wheels from fluttering in an uncontrolled movement, especially at high speeds. Moreover, the free movement of the rear wheels may complicate the rearward movement of the implement, as the wheels tend to turn over and deviate the implement to the left or right. 
     Hence there is a need for means disabling the free movement of the steerable wheels. 
     SUMMARY OF INVENTION 
     According to one aspect of the present invention there is provided an agricultural implement, comprising a main frame and a hitch attached to the main frame for attaching the implement to a towing vehicle. There are a pair of steerable wheels supporting the main frame and a means for blocking the steerable wheels in a fore-and-aft direction. The hydraulic circuitry for controlling functions of the implement comprises a feed line and a return line for connection to a hydraulic pump and an oil tank respectively, the connection enabling normal operation of said functions. Finally the circuitry comprises a means for actuating said blocking means by providing hydraulic pressure from said pump to said return line. 
     According to another aspect of the present invention, there is provided a method for blocking steerable wheels on an agricultural implement. The implement having a main frame, a hitch attached to the main frame for attachment of the implement to a towing vehicle and a pair of steerable wheels supporting the main frame. There is a means for blocking the steerable wheels in a fore-and-aft direction consisting of hydraulic circuitry for controlling functions of the implement. The circuitry comprising a feed line and a return line for connection to a hydraulic pump and an oil tank, respectively. The method comprising the step of actuating said blocking means by providing hydraulic pressure from said pump to said return line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the present invention will now be described in further detail, by way of example, with reference to the following drawings. 
     FIG. 1 is a side elevational view of a rectangular baler, having a frame mounted to a bogie having fixed and steerable wheels. 
     FIG. 2 is a top view of the bogie of FIG. 1, showing a pair of hydraulic rams for blocking the steerable wheels. 
     FIG. 3 is a side elevation view of the bogie of FIG.  2 . 
     FIG. 4 is a cross sectional view of one of the rams of FIG.  2 . 
     FIG. 5 is a hydraulic scheme, illustrating the operation of the blocking rams. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     It will be appreciated that the present invention will be described with reference to a rectangular baler, but that the invention is not limited thereto and that it readily can be adapted to other kinds of wheeled agricultural equipment which are adapted for attachment to a towing vehicle. 
     The terms “front”, “rear”, “forward”, “rearward”, “left” and “right” used throughout this description are determined with respect to the normal direction of travel of the machine in operation. However they are not to be construed as limiting terms. 
     FIG. 1 shows an agricultural baler  10  comprising a frame  11  which is equipped with a forwardly extending tongue  12  provided with hitch means (not shown) at its front end for coupling the baler  10  to a towing vehicle such as an agricultural tractor. A conventional pick-up assembly  14  lifts windrowed crop material off the field as the baler  10  is traveled thereover and delivers such material into the front end of a rearwardly and upwardly curved, charge-forming feeder duct  16 . The duct  16  communicates at its upper end with an overhead, fore-and-aft extending baling chamber  18  into which crop charges are loaded by a cyclically operating stuffer mechanism  20 . A continuously operating packer mechanism  22  at the lower front end of the feeder duct  16  continuously feeds and packs material into the duct  16  as to cause charges of the crop material to take on and assume the internal configuration of the duct  16  prior to periodic engagement by the stuffer  20  and insertion up into the baling chamber  18 . Each action of the stuffer  20  introduces a “charge” or “flake” of crop material from the duct  16  into the chamber  18 . 
     A plunger  24  reciprocates in a fore-and-aft direction within the baling chamber  18  under action of a pair of pitman rods  25  which are linked to the crank arms  26  of a gearbox  27  driven by a shaft  29  which is connected to the PTO shaft of the tractor. The reciprocating plunger  24  pushes each new charge introduced into the baling chamber  18  rearwardly and forms the subsequent charges into a package of crop material, which is pushed by the plunger  24  toward a rearmost discharge aperture  28  of the chamber  18 . 
     The baling chamber  18  comprises at least one movable wall portion  30  of which the position can be adjusted to vary the cross section of the aperture  28 . The position of the wall portion  30  is controlled by a pair of actuators in the form of hydraulic cylinders  31  (only one shown in FIG. 1) which are installed between the frame  11  and the wall portion  30 . Reduction of the cross section increases the resistance to rearward movement of the crop packages and hence the density of the crop material contained therein. Similarly an increase in cross section will reduce the resistance to the movement and the density of the newly formed packages. 
     Each package is securely bound in its final compacted form by a tying mechanism  32  before leaving the confines of the baling chamber  18 . The length of each bale produced by the baler  10  can be adjustably predetermined by conventional means not shown. 
     The baler is equipped with bale discharge means  36  in the form of a bale chute, mounted to the rear of the frame  11 , adjacent the discharge aperture  28  of the baling chamber  18 . The completed bale is received thereon and sustained thereby at least until the rear end of the bale has completely left the confines of the baling chamber  18 . The discharge means  36  embrace a front chute portion  37  and a rear chute portion  38 . The front portion  37  is attached by a pair of pivot pins  43  to the rear end of the baler frame  11 . In turn, the rear portion  38  is mounted via a pair of pivot pins  46  to the rear end of the front chute portion  37 . 
     The bale discharge means  36  can be moved into a transport position by means of a hydraulic cylinder  74 , which is mounted below the front chute portion  37 , between a support  75  welded to the rear end of the baler frame  11 , and a lever arrangement  76 , affixed to the front and rear chute portions  36 ,  37 . As shown in FIG. 5, the cylinder  74  is linked via a manually operated valve  77  on the left hand side of the baler frame  11  to hydraulic circuitry  78  of the baler, comprising a pressure line  79  and return line  83 ,  80 . The one line  79  has a pressure connection  81  and the other  80  a return connection  82  for coupling the lines  79 ,  80  to corresponding lines of the hydraulic circuit of the tractor, comprising a hydraulic pump and an oil tank. 
     Hydraulic valve  77  can be operated to pivot the rear chute portion  38  upwardly about pivot pins  46  at an angle of 90° to the front chute portion  37  and then to pivot both portions  37 ,  38  upwardly and forwardly about pivot pins  43  until the rear chute portion rests on a cradle  92  on top of the baling chamber  18 . 
     The baler  10  further is equipped with a system for removing completed bales from the baling chamber  18 , even when no fresh crop material is introduced in the front area of the baling chamber to be engaged by the plunger  24 . The system comprises a pair of longitudinally arranged slats (not shown) equipped with pivotable tines (equally not shown) which are arranged below the baling chamber  18 . A hydraulic double-acting cylinder  60  (FIG. 5) can be actuated to raise the tines into the baling chamber through slots in the bottom wall thereof. In this position the tines are operable to engage the bottom of the bale in the chamber  18 . A further double-acting cylinder  61  is operable to reciprocate the slats. Both cylinders  60 ,  61  are linked to the circuitry  78 , wherein an orifice  62  makes cylinder  60  receive priority oil flow when line  63  is pressurized by actuation of a valve  65 , which links line  63  to pressure line  79 . The cylinders  60 ,  61  raise the tines and force the slats and tines rearwardly, thereby driving the bale out of the baling chamber  18 . In this condition, return oil from both cylinders can flow back to return line  80  via line  64  and valve  65 . When the valve  65  is reversed, pressurized oil flows through line  64  to the rod ends of the cylinders  60 ,  61  to retract the tines and pull the slats forwardly to their home positions. Repeated actuation of the valve  65  drives the bale completely out of the baling chamber  18 . 
     The maximum pressure in the hydraulic circuitry  78  is defined by the pressure relief valve  86 , installed between the pressure line  79  and the return line  83 . 
     The baler frame  11  is mounted to the mounting plates  101  of a bogie  100 , shown in FIGS. 2 and 3. The bogie comprises two sets of leaf springs  103 , attached to the mounting plates  101 , a front axle  107  equipped with two fixed front wheels  102 , and a rear axle  108  with two steerable rear wheels  104 . The latter are rotatably mounted to the axle  108  by means of king pins  105  which can be pivoted about substantially vertical axes. A connection rod  106  ensures equal and simultaneous movement of the king pins  105 . The rear wheels  104  are not actively steered; they adapt freely to the path followed by the towing vehicle and the front wheels  102 . As such they allow sharp turns of the baler without “digging” of the rear wheels  104  into the earth. 
     The rear beam  108  of the bogie  100  is provided with two extendable blocking rams  110 , shown in further detail in FIG.  4 . Each ram has a cylindrical body  111 , which is mounted in a transverse direction along the beam  108 . The body  111  has a chamber which contains a rod  112  provided with a head  113  directed to the hub of the steerable wheel  104 . A spring  114  mounted inside the body  111  exerts an inward force on a foot  115  of the rod  112 . A port  116  links the chamber of the ram  108  to a line  119  branched to the return line  80  of the circuitry  78  (FIG.  5 ). 
     When no hydraulic pressure is applied to the rams  110 , the springs  114  ensure that the heads  113  do not engage the wheels  104 , such that they are still free to pivot about the axes of the king pins  105 . When pressurized oil is fed to the rams  110 , the rods  112  will be urged outwardly against the force of the springs  114 . They contact one or other of the rear wheels  104  and force it outwardly to a fore-and-aft direction. The rams  110  pivot the rear wheels until the rod feet  115  contact shoulders  117  inside body  111 . In this position, the rear wheels  104  are in alignment with the front wheels  102 . 
     As shown in FIG. 5, both rams  110  are connected via branch line  119  to the return line  80  of the baler circuitry  78 . The branch line  119  has a manually controlled shut-off valve  120 . During normal operations, the valve  120  is open for permitting remote control of the rams  110 . A non-return valve  121  is disposed between the sections  83  and  80  of the return line, permitting free flow of oil from the control valves  65 ,  77  to the return connection  82 . 
     When the baler  10  is operated in the field, it is not necessary to block the rear wheels  104  of the bogie  100 . The valve  120  is opened and the return connection  82  is linked to the return line of the tractor circuitry, draining oil to the oil tank. No pressurized oil is available at the ports  116  and the springs  114  of the rams  110  keep the ram heads  113  in their retracted position, such that the wheels  104  can adapt to the movement of the baler  10 . The pressure connection  81  receives pressurized oil from the tractor for possible actuation of the bale eject cylinders  60 ,  61  or the bale chute cylinder  74 . 
     Free pivotment of the rear wheels  104  is not always desired: e.g. it may be required to block them on order to stabilize the towed baler  10  during road transport. This can be accomplished easily by reversing the direction of the oil flow at connections  81  and  82 . By providing pressurized oil at return connection  82 , non-return valve  121  is forced to its closed position, thereby cutting line  80  from line  83 . Pressure builds up in the chambers of the rams  110  and urges ram heads  113  outwardly. In this manner the wheels  104  are blocked, such that they cannot flutter when the baler  10  is driven at high speeds during road transport. It is also advantageous to block the wheels  104  when driving the baler  10  along a slope or hill-side in order to keep the baler on track behind the tractor. Furthermore, blocking is required when the baler has to be driven rearwardly: otherwise the free rear wheels  104  would turn and deviate the baler  10  to the left or the right. 
     When one wants to block the wheels  104  during a longer period and/or while no continuous hydraulic pressure is available, the pressurized rams  110  may be held in place by locking the shut-off valve  120 . 
     When the valve  120  is opened, the rams  110  can be retracted immediately by linking the return connection  82  to the return line of the tractor circuitry. The control of the rams  110  can be realized advantageously by having connections  81 ,  82  linked to hydraulic circuitry comprising a valve of the same type as valves  65  and  77 , i.e. with four ports and three positions. Such valve in the tractor circuitry enables immediate switching between a locked and an unlocked condition of the rear wheels  104 . 
     It will be appreciated the invention is not limited to the described embodiment, but readily can be used in other types of pull-type agricultural equipment, such as carts, forage wagons, mowers, etc. It is also envisageable to connect the branch line  119  to the return line of other hydraulic circuitry, e.g. of the system controlling the position of the cylinders  31  for adjustment of the bale density. 
     It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is illustrated in the drawings and described in the specification.