Abstract:
A towed implement is provided with ground support wheels mounted to its chassis by trailing wheel support arms and respective suspensions including lift cylinders with which are associated damping devices that operate in such a way as to prevent damage to a respective cylinder from rebounding forces resulting when the suspension is being returned to its operating position by the release of energy stored in spring arrangements of the suspension after being loaded by an obstacle engaging the associated wheel. In one embodiment, the spring arrangement includes a damping spring located between an end of the associated cylinder and piston, and in another embodiment, the spring arrangement includes a gas pressure reservoir which, by virtue the operation of a reversing link in the suspension, is loaded both when the wheel is caused to move in a first direction by engaging an obstacle, and when the wheel is moved in the opposite direction by the airborne wheel once past the obstacle.

Description:
FIELD OF THE INVENTION 
     The invention pertains to a towed implement with an undercarriage, at least one wheel suspension, a spring member and an adjusting device. 
     BACKGROUND OF THE INVENTION 
     DE-A-31 39 936 discloses a towed agricultural implement with an undercarriage, on the two lateral end regions of which one respective wheel suspension is arranged. Both wheel suspensions include a shaft in the region of their pivoting axis, and these shafts are connected such that they can be moved relative to one another by means of a spring-loaded, transverse swinging arm, namely on the ends that face one another. An adjusting device can be engaged with limit stops on the wheel suspensions in one direction in order to adjust the wheel suspensions in one direction. 
     EP-A1-0 149 870 discloses a towed mower in which an adjusting device and a spring member are connected in series. In one of the embodiments described in this publication, an adjusting cylinder acts upon a pivoted shaft that vertically pivots the wheel cranks on the respective end regions by means of braces in the form of gas springs formed by hydraulic cylinders coupled with gas accumulators. 
     The known suspension arrangements exhibit a problem which occurs when the mower encounters an obstacle, namely that the spring members need to absorb much energy and, after overcoming the obstacle, abruptly release the stored energy in case of low counter forces, for example when the wheel raises off the ground. This can lead to damage to the adjusting device, wherein the piston may, in particular, impact on the end of the cylinder housing or an inside shoulder and/or undergo damage to the sliding surface or the seals. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided an improved suspension arrangement for a towed implement. 
     An object of the invention is to provide a suspension arrangement for a towed implement wherein provision is made for damping the rebound of the stored energy so as to prevent damage to the hydraulic or pneumatic actuators. 
     A more specific object of the invention is to provide a suspension for a towed implement including damping arrangements using coil or disc springs, gas pressure reservoirs or rubber-like elements. 
     Yet a more specific object is to provide a suspension, as set forth in the foregoing objects, wherein the damping arrangements may include devices that are relatively inexpensive and readily available on the market such as a coil spring or disk spring that is arranged around a piston rod in a cylinder housing, or a caoutachouc mass in the form of a ring or the like could be inserted between the end of the cylinder housing and the piston; and/or a gas pressure reservoir could be connected to a second piston chamber. 
     Yet another object of the invention is to provide a second embodiment wherein the wheel suspension includes a reversing link which operates when pivoted in a first direction to direct forces such that a gas spring accumulator that is coupled to a hydraulic cylinder connected to the reversing link acts so as to cushion loads caused when the wheel passes over an obstacle and, when pivoted in a second direction by the force of a suspended wheel returning to its operating position, also acts to cushion this movement of the wheel. 
     These and other objects will become apparent from a reading of the ensuing description together with the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic left side elevational view of a towed implement equipped with a suspension constructed in accordance with a first embodiment of the present invention. 
     FIG. 2 is a schematic representation of an adjusting device with a spring member and a damping device constructed in accordance with the first embodiment of the invention. 
     FIGS. 3 through 6 are views of the adjusting device of FIG. 2 shown in respective first, second, third and fourth operating states. 
     FIG. 7 is a schematic representation of a second embodiment of the adjusting device incorporating a reversing link together with a spring member and a damping device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The towed implement  10 , shown in FIG. 1, includes an undercarriage  12 , wheels  14 , wheel suspensions  16 , a spring arrangement  18 , adjusting devices  20  and a working unit  24 . 
     The implement  10  is constructed in the form of a mower-conditioner that serves for cutting, processing and depositing stalk crops on the ground. While in operation, the implement  10  is towed over uneven terrain with a relatively high speed and constantly subjected to shocks that, in addition to the flexibility of the wheels  14 , need to be absorbed by the spring arrangement  18 . However, the invention is by no means limited to an implement of this type, but can also be used in other towed implements, e.g., balers, soil conditioning tools, saws, sprayers and the like. 
     The undercarriage  12  is essentially constructed in the form of a frame that has the shape of an upside-down “U” with vertical limbs  26  and a horizontal crossbeam  28 , in the intermediate space of which the working unit  24  is at least partially accommodated. The undercarriage  12  carries the working unit  24  in a fashion described in greater detail below, and together with the working unit can be adjusted to different elevations in reference to the ground. 
     A wheel  14 , that is conventionally provided with a pneumatic tire, is connected in the lower region of each limb  26 , such that it can be vertically pivoted, namely by means of the wheel suspension  16 , which includes a trailing link having its forward end pivotally coupled to the limb  26  and carrying at its rear end a spindle on which the wheel  14  is rotatably mounted. Thus, the undercarriage  12  is supported on the ground by the wheels  14 . 
     A holder or bracket  32  is situated in the upper region of each limb  26 . In addition, a bearing  36  located in a rear region of an upper longitudinally extending arm  38  forms part of a pivotal coupling of the arm  38  to the crossbeam  28 . Further, a bearing  40  forms part of a vertical pivotal axis about which a forward section of the tongue  22  is connected for pivoting horizontal relative to a rear section that is fixed to the cross beam  28 . Receivers  42  for springs  44  are also provided on each side of the crossbeam  28 . 
     Each wheel suspension  16  further includes a connection or bracket  46  located at the upper rear portion of the trailing link, and extending between the brackets  32  and  46  is an extensible and retractable motor  60  of the adjusting device  20 . The motor  60 , which is constructed in the form of a single-action hydraulic motor that is pressurized to effect its extension, can also be considered to form part of the wheel suspension  16 . A lower suspension link  52  cooperates with the upper link  38  to form a four-bar linkage and has its rear end coupled to the trailing link by a pivot pin  50 , and has its forward end coupled to a lower rear region of the working unit  24 . 
     The spring member arrangement  18  includes a gas pressure reservoir  56  that acts as a spring element. Although the gas pressure reservoir  56  is common to both motor operators  60  forming part of the adjusting device  20  in FIG. 2, it would also be conceivable to provide a gas pressure reservoir  56  for each of the motor operators  60 . The gas pressure reservoir  56  is connected to a shared supply line  30  for both motor operators  60  which ends in a generally known three position, three way hydraulic valve  34  and makes it possible to receive the pressure medium from a pump  62  or to release a pressure medium into a reservoir  64  by means of this hydraulic valve  34 . The hydraulic valve  34 , the pump  62  and the reservoir  64  are schematically shown in FIG. 2, for simplicity, with it to be understood that they replace a generally known hydraulic system that, however, is significantly more complicated to realize. The control of the motor operators  60  is accomplished remotely from the towing vehicle (not shown). The gas pressure reservoir  56  has such dimensions that its gas cushion is not compressed when the motor operator  60  is extended, and is subjected to the system pressure. The gas cushion is only compressed when the implement  10  more or less abruptly encounters an obstacle and the motor operators  60  are subjected to shocks. 
     Referring now also to FIGS. 3-6, it can be seen that a damping device  48  is incorporated in each of the operators  60 . Specifically, each operator  60  includes a cylinder housing  66  and a piston  68  with a piston rod  70  which is able to slide in the cylinder housing  66 . One end of the cylinder housing  66  is closed and connected to a supply line  30 , wherein the other end of the cylinder housing is closed by a plate  72 , through which the piston rod  70  extends. The cylinder housing  66  is connected to the undercarriage  12  in a pivoted fashion by the holder  32 . Except for the supply line  30 , no other hydraulic fluid connections are provided. 
     The damping device  48  is constructed in the form of a simple helical compression spring that is situated in the piston rod chamber of the cylinder housing  66  between the piston  68  and the plate  72  and surrounds the piston rod  70  with a certain amount of play. An annular disc  74  is arranged on the damping device  48 , namely on its side that faces the piston  68 . This annular disk  74  serves for achieving a superior contact between the damping device  48  and the piston  68  and contains a not-shown seal on its outer circumference which decelerates its movement along the inner wall of the cylinder housing  66  and thus prevents the damping device  48  from moving freely and developing undesirable noises. However, the annular disk  74  is not absolutely imperative for the function of the damping device  48  and can also be omitted. 
     FIGS. 3-6 respectively illustrate different operating states of the implement. Specifically, in FIG. 3, the state shown is that which occurs in the mowing mode, i.e., the motor operators  60  are retracted, the gas pressure reservoir  56  assumes a neutral position and the damping device  48  is not stressed. FIG. 4 shows the state in which the motor operators  60  are extended in order to raise the implement  10  into its transport position. The piston  68  contacts the damping device  48  such that its stroke is stopped. In FIG. 5, the situation shown is that which occurs when the implement  10  moves over an obstacle and the wheel suspension  16  is subjected to a shock that cannot be absorbed solely by the pneumatic tires of the wheels  14 . In this case, the wheel  14  becomes airborne and the gas cushion in the gas pressure reservoir  56  is compressed and the piston  68  is able to move into the cylinder housing  66 . Although this is not imperative, the stress on the damping device  48  can be relieved. The pressure in the motor operator  60  significantly increases above the system pressure. Once the obstacle has been passed over, the state becomes that shown in FIG. 6 wherein the motor operator  60  is once again extended while being subjected to a less intense stress because the wheel  14  in question does not contact the ground. Since the gas pressure reservoir  56  is now able to abruptly release and may even generate an internal vacuum, the piston  68  impacts on the damping device  48  and is decelerated. This damping prevents the plate  72  from being damaged. 
     Referring now to FIG. 7, there is shown a second embodiment of the invention. Specifically, there is shown a damping device  48 ′ that includes a reversing element  76 , a brace or strut  78  and the gas pressure reservoir  56 . This damping device  48 ′ does not require a separate damping element, but rather is able to utilize the gas pressure reservoir  56  due to the change in direction caused by the reversing element  76 . The motor operator  60  in this embodiment is also constructed in the form of a single-acting hydraulic cylinder, wherein the arrangement in this embodiment is chosen such that the end of the cylinder housing  66  is situated on the bottom and the piston rod  70  extends upward. However, this is not absolutely imperative for the invention. The bracket  32  is situated in the lower end region of the limb  26  in this embodiment. Although only one motor operator  60  and only one bracket  32  are illustrated, these components are actually provided on both sides. 
     The reversing element  76  is constructed in the form of an essentially L-shaped or V-shaped, pivoted arm with two limbs, with an end of one limb containing a bearing  80  connected to the piston rod  70 , with the second limb having an end containing a bearing  82  connected to an upper end of the brace  78 , and with a bearing  84  located in the reversing element  76  between the bearings  80  and  82  and connecting the reversing element  76  to a holder or bracket  86  constructed of a single member or parallel, fork-like members fixed to the undercarriage  12  or its limb  26 , respectively. If a straight line is drawn through the bearings  80  and  82 , the bearing  84  is always situated laterally of this straight line, namely on the side that faces the motor operator  60 . 
     The brace or strut  78  extends between a bearing  88  on the bracket  46  in the upper rear region of the wheel suspension  16  and the bearing  82  on the reversing element  76 . The brace  78  may even be provided with a spring in order to additionally dampen shocks. 
     The function of the embodiment shown in FIG. 7 is as follows. Specifically, the undercarriage  12  is supported on the ground by the wheels  14 , wherein an essentially rigid connection that contains the motor operator  60  arranged in a pivoted fashion on the limb  26 , the reversing element  76 , the brace or strut  78  and the wheel suspension  16  counteracts a downward movement of the undercarriage. 
     Leaving aside the elasticity that is inherent to each component, only the gas pressure reservoir  56  performs a spring function. This means that the gas cushion of the gas pressure reservoir  56  is more or less compressed when the wheels  14  move over a rock or similar uneven terrain or obstacle. In such instances, the wheel suspension  16 , according to FIG. 7, is pivoted in the counterclockwise direction, the strut  78  is raised and the reversing element  76  is also pivoted about the bearing  84  in the counterclockwise direction. Due to this pivoting movement, the piston rod  70  presses into the cylinder housing  66  and compresses the gas cushion in the gas pressure reservoir  56 . 
     As soon as the obstacle is passed over and the force acting upon wheel suspension  16  decreases such that the gas pressure reservoir  56  is able to release, the compressed gas extends the piston rod  70  and the reversing element  76  is pivoted in the clockwise direction until the central longitudinal axis of the piston rod  70  and a line drawn through the bearings  80 ,  84  are situated congruently or in alignment with each other. In this case, the piston  68  has not yet reached the plate  72  but is also prevented from additionally extending by being located on center with the pivot points established by the bearings  80  and  84 . If the wheel  14  and the wheel suspension  16  are able to additionally pivot in the clockwise direction, e.g., because the wheel  14  “hangs in the air”, the piston rod  70  with the bearing  80  is moved over center relative to the bearing  84  and now causes the piston rod  70  to be pressed inward against the pressure in the gas reservoir  56 . This means that an additional downward movement is counteracted by a spring action. The distance of the bearing  80  from the bearings  82  and  84  can be chosen differently in order to vary the power transmitting ratio. 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.