Abstract:
A hitch control unit for use in a tractor comprises a housing that defines an arcuate surface having a tangentially extending slot. An arm extending through the slot is rotatably mounted in the housing and connected to a transducer to produce a signal indicative of the position of the arm along the slot. A stop movably mounted in the housing defines a reference position for the arm along the slot, and a finger-actuated wheel rotatably mounted in the housing allows the position of the movable stop along the slot to be adjusted. The wheel has an internally screw threaded bore and is mounted in the housing for rotation about an axis that extends parallel to the slot and the adjustable stop is connected to an arcuate rack in screw threaded engagement with the bore in the wheel.

Description:
BACKGROUND OF INVENTION 
     1. Field of Art 
     The present invention relates to a hitch control unit for use in a tractor. 
     2. Description of Prior Art 
     U.S. Pat. No. 5,231,892 discloses a hitch control unit for a tractor that comprises a housing having a pair of sidewalls joined to an outwardly convex cover wall formed with a fore-aft extending slot. An arm that can be moved manually along the slot is connected to a transducer, such as a potentiometer, that produces an output signal indicating the desired position of the implement mounted on the hitch of the tractor. An adjustable stop is movable by means of a thumb wheel along the slot and defines an abutment for the transducer arm. After the arm has been moved to raise the towed implement, for example while the tractor is performing a steering manoeuvre, it can quickly be returned to its position in abutment with the stop so that the towed implement can be returned to its original position. 
     The control knob on the end of the transducer arm, by which it is manipulated by the tractor operator, can be pivoted on the arm out of abutment with the adjustable stop to allow the arm to be moved intentionally past the stop when necessary. 
     In U.S. Pat. No. 5,231,892, the thumb wheel that adjusts the position of the movable stop is mounted on the housing for rotation about an axis parallel to the pivoting axis of the lever. This makes it necessary to use a complex linkage to couple the thumb wheel to the adjustable stop. Since the linkage includes meshing gears and a toothed thumb wheel, a smooth, infinite adjustment of the stop is not possible. As the thumb wheel moreover is spring loaded to restrain unwanted movement of the movable stop, the wheel always has to be pushed downward against the spring force and maintained in the downward position before rotational movement thereof becomes possible. 
     SUMMARY OF THE INVENTION 
     With a view to mitigating the foregoing disadvantage, the present invention provides a hitch control unit for use in a tractor. The unit comprises a housing having an arcuate surface having a tangentially extending slot. There is an arm extending through the slot and rotatably mounted in the housing. A transducer is connected to the arm to produce a signal indicative of the position of the arm along the slot. There is a stop movably mounted in the housing to define a reference position for the arm along the slot. Finally, an adjustment wheel is rotatably mounted in the housing to adjust the position of the movable stop. The adjustment wheel has an internally screw threaded bore and is mounted in the housing for rotation about an axis that extends parallel to the slot. The adjustable stop is connected to or formed integrally with an arcuate rack in screw threaded engagement with the bore in the adjustment wheel. 
     Another disadvantage of the unit of U.S. Pat. No. 5,231,892, is that the use of a pivotable control knob on the end of the transducer arm to allow the stop to be bypassed is costly to implement and inconvenient to operate. 
     In a preferred embodiment of the invention, the arm connected to the transducer is resiliently bendable in a direction transverse to the slot in the housing to allow it to be deflected around the abutment presented by the adjustable stop when it reaches the reference position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described further, by way of example, with reference to the accompanying drawings. 
     FIG. 1 is a perspective view from above of an assembled hitch control unit. 
     FIG. 2 is a view of the assembled hitch control unit as seen from one side. 
     FIG. 3 is a plan view from above of the assembled hitch control unit. 
     FIG. 4 is an exploded view of the hitch control unit. 
     FIG. 5 is a side view of the hitch control unit with the housing omitted. 
     FIG. 6 is a perspective view of the housing from below with only some of the components of the hitch control unit in position. 
     FIG. 7 is a schematic perspective view illustrating the operation of the adjustable stop. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The hitch control unit  10 , shown in its assembled state in FIGS. 1 to  3 , has a housing  12  formed with an arcuate upper surface containing an elongated slot  14 . The control of the height or position of a hitch is effected by sliding a control knob  16  along the slot  14 . Additionally, the hitch control unit  10  includes a rotatable numbered wheel  18  that can be manually turned through a second slot  19  in the housing  12  to act as a draft control. Draft and position control are well known modes of control of a tractor hitch and therefore need no further explanation. A switch  20  is set in an opening in the side of the housing  12  for rapid lowering and raising of the hitch. 
     As seen in FIG. 4, the knob  16  is mounted on an arm that extends radially from a hub  54 . The wheel  18  and the hub  54  are operatively connected to respective separate transducers  46   b  and  46   a  (being potentiometers in the illustrated embodiment of FIG. 4) that produce an electrical output indicative of their position. The unit  10  has an electrical connector  22  containing contacts connected to the transducers  46   a  and  46   b  and to the contacts of the switch  20  on the one hand to provide electrical power to the devices and on the other hand to collect output signals corresponding to the positions of the control knob  16  and of the wheel  18  and to the setting of the switch  20 . 
     It is sometimes desired to raise the hitch temporarily and then to return it to the same reference position. The setting of the reference position of the hitch is achieved by means of a finger operated adjustment wheel  24  that, as will be described in more detail below, moves a stop  26  parallel to the slot  14 . The stop  26  presents an obstruction to the movement of the control knob  16  along the slot  14  at the reference position set by turning the adjustment wheel  24 . The stop  26  limits the range of movement of the control knob  16  in the direction of lowering of the hitch but, if desired, by moving the control knob  16  to one side, it can be moved beyond the position of the stop. 
     The internal construction of the hitch control unit  10  will be described by reference to the exploded view of FIG.  4 . The unit  10  comprises the housing  12 , which is a one-piece plastics moulding (or eventually also could be a die cast element), and a support plate  40  on which the potentiometers  46   a ,  46   b  and the connector  22  are mounted. The potentiometers are of similar construction and are mounted one on each side of the support plate  40 . A bolt  42  near the centre of the support plate  40  defines the axis of rotation of the potentiometer  46   b  connected to the hub  54 , whereas a bolt  43 , provided upwardly offset from the bolt  42 , defines the axis of rotation of the potentiometer  46   a  connected to the wheel  18 . The axes of rotation need not be offset and the bolts  42 ,  43  could be replaced by a single shaft extending on both sides of the support plate  40  and defining a single pivot axis for both potentiometers  46   a ,  46   b . Each potentiometer comprises a body  46   a ,  46   b  that is respectively slid over the bolts  43 ,  42  and fixedly connected to the support plate  40 . Each potentiometer  46   a ,  46   b  furthermore comprises a two-winged slot  47  (only one of which is shown in FIG. 4) for receiving axial projections  48   a ,  48   b , eccentrically provided respectively on the wheel  18  and on the hub  54 . 
     The potentiometers  46   a  and  46   b  are of conventional design and comprise a wiper arm moveable along an internal track. Moving the knob  16  actuates the wiper arms of the potentiometers  46   a ,  46   b  and the wheel  18 , a movement that is transmitted through the axial projections  48   a ,  48   b  and the slots  47 . The ends of the track and the wiper arm are connected to contacts in the electrical connector  22  which is further connected to the contacts of the switch  20  inset into the side of the housing  12 . 
     The support plate  40  has opposite mounting faces onto which each potentiometer  46   a ,  46   b  is mounted. Around each potentiometer  46   a ,  46   b  there is mounted a friction disc  44   a  and  44   b  to which the draft control wheel  18 , respectively the hub  54  is frictionally coupled. Each of the friction discs  44   a ,  44   b  is radially constrained by a flange protruding from the support member  40  which together with features on the wheel  18  or the hub  54 , as the case may be, form a chamber within which the potentiometer resides thereby giving it greater protection. 
     More specifically, with reference to the wheel  18 , it comprises an internal, axially extending rim  49  building a housing for the potentiometer  46   a . In-between the wheel  18  and the support plate  40 , the friction ring  44   a  is provided for offering some resistance to rotational movement of the wheel  18 . A nut  50  fixes the wheel  18  onto the bolt  43  thereby clamping the ring  44   a  in-between the wheel  18  and the plate  40  with a desired force; this force being high enough to prevent unwanted movement of the wheel  18  eventually caused by vibrations of the tractor. A thrust spring (not shown) eventually also could be provided to maintain a constant force. 
     When the wheel  18  is rotated to adjust the desired draft force experienced by the tractor, the projections  48   a  rotate the wiper arm of the potentiometer  46   a  along the internal track thereby producing an electrical signal which is indicative of the position of the wheel  18 . Two radially extending stops  51 , of which only one is shown in FIG. 4, are provided angularly offset on the rim  49  and cooperate with an abutment stop  63  on the support plate  40  to limit the angular rotational motion of the wheel  18 . 
     As already mentioned, the control knob  16  is connected to the arm  52  that extends radially from the hub  54 . When the hub  54  is mounted by means of a nut  56  onto the bolt  42 , it builds a cup-like housing for the potentiometer  46   b . Comparable to the operation of the wheel  18 , as the knob  16  moves along the slot  14 , it rotates the hub  54  and through the axial projections  48   b , the wiper arm of the potentiometer  46   b  is moved along its resistive track. In so doing, electrical signals are produced to indicate the position of the knob  16 , which represents the desired position of the hitch relative to the tractor. 
     Channels (not shown) in the support plate  40  pass from each potentiometer chamber beneath the friction discs  44   a ,  44   b  to the main electrical connector  22  thereby allowing the wiring to pass out of the chamber. 
     The support plate  40  provides support and retention for the electrical connector  22  which can be easily fitted or removed without the need for any additional components due to features integral in the support plate  40 . 
     The support plate  40  is further formed with two brackets  61  that extend from it, one on each side of the adjustment wheel  24  to provide additional support and axial constraint. Mating formations are also formed on the support plate  40  and the housing  12  to locate the support plate  40  with respect to the housing thereby improving the overall accuracy of the unit between the potentiometers and the end stops in the housing. 
     To improve the tactile properties of the draft control unit, the adjustment wheel  24  is formed in two parts, the inner part being of a relatively hard plastics material and the outer part being of a rubber like material having better frictional properties. Similarly, the control knob  16  is fitted with a rubber like cap  16   a.    
     To facilitate manufacture, the outer part may be moulded over the inner part. Specifically for the draft control wheel  18 , the base part comprises numbers or a graduation scale slightly projecting therefrom. The base part then is moulded over with a material of contrasting colour, without however moulding over the graduation scale to leave it uncovered. This gives the draft control wheel  18  visual feedback of its position that will not wear under the extreme conditions in which an agricultural tractor is operated. 
     The present invention is concerned primarily with the manner of providing an adjustable stop  26  along the slot  14  and the manner in which this is achieved will now be described by reference to FIGS. 5 to  7 . 
     The stop  26  is formed as a projection from an arcuate rack  60  that acts as a lead screw. The arcuate rack  60  has a cruciform cross section with two radially extending limbs and two axially extending limbs. The axially extending limbs have serrated edges that act as a screw thread and are engaged in a matching thread within the inner part of the thumb wheel  24 . 
     The inner radially extending limb is received in a guide channel  62  that is mounted on the underside of the housing  12 . The guide channel  62  is itself arcuate and acts to trap the member  60  between itself and the underside of the housing  12 . The underside of the housing in turn is provided with an arcuate groove (not shown) to receive the outer radially extending limb of the rack  60 . As a result, as the wheel  24  is turned, the arcuate rack moves along an arc substantially parallel to the upper surface of the housing  12  and advances the stop  26  along the slot  14 . As best seen in FIG. 5, the guide channel  62  comprises a cantilevered portion which is formed such that it exerts a spring force upwards onto the inner radially extending limb of the rack  60 , to thereby create a slight frictional resistance between the rack  60  and its supporting structure. As such, the rack  60  is sufficiently braked against any unintended movement. 
     The arm  52  on which the control knob  16  is mounted, is flexible in the direction of the two small arrows in FIG.  4  and has a chamfered trailing edge  52   b  so that it is automatically deflected to one side when it is pushed against the stop  26 . 
     In operation, when the driver of the tractor wishes to raise the towed implement attached to the hitch, for example when carrying out a steering manoeuvre, the knob  16  is moved away from its reference position resting on the stop  26  to the fully raised position. After the steering manoeuvre has been completed, the operator moves the knob back towards the fully lowered position of the hitch but the knob  16  will meet resistance when its arm  52  collides with the stop  26 . Fine adjustment to this reference position can be made by moving the stop  26  using the finger operated wheel  24 . If the hitch is being slightly raised, then the movement of the stop  26  will automatically be transferred to the control knob  16 . Fine control in the opposite direction is effected by moving the stop  26  and then pushing the control knob up to the new position of the stop  26 . 
     If the hitch needs to be lowered temporarily for any reason beyond the position set by the stop  26 , then the stop  26  can be bypassed by pushing the control knob  16  to one side, bending its arm  52  away from the stop  26 . When the control knob  16  is subsequently pushed in the opposite direction past the stop  26 , the chamfered edge  52   b  of the arm  52  will act to deflect the arm  52  to one side so that it may ride over the stop  26 . 
     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 illustrated in the drawings and described in the specification.