Abstract:
In the operation of work machines of the type required to carry heavy loads over uneven ground conditions, it is oftentimes desirable to provide the work machine with a way to automatically maintain the chassis in a substantially horizontal condition. The present invention provides a work machine having a chassis and at least one elongate member having a first end rotatably coupled with the chassis. Also provided is a controller and a position sensor coupled to at least one of the elongate members which generates a position signal indicative of an orientation of the elongate member relative to the chassis and relays the position signal to the controller. The controller, in response to the position signal, determines an actual height of the chassis from the position signal and adjusts the actual chassis height to conform to a controller-inputted desired chassis height.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a suspension leveling system and, more specifically, to a suspension leveling system thereof for maintaining the chassis of a work machine substantially horizontal during operation.  
         BACKGROUND  
         [0002]    Work machines of the type used to remove downed timber from timber harvest areas oftentimes must navigate across rough terrain consisting of uneven ground slopes and obstacles such as stumps, downed timber and rocks. For certain work machines such as the forwarder which are required to traverse this type of terrain while transporting heavy loads it becomes important to maintain the load in a substantially horizontal orientation so as to prevent tipping of the work machine.  
           [0003]    A prior art example of a method of automatically adjusting a body of a tractor to a horizontal position can be found can be found in U.S. Pat. No. 6,131,919 which issued on Oct. 17, 2000 to Lee et al. Although the arrangement and corresponding method taught by Lee et al. may be adequate for its intended purpose, it fails to teach an arrangement and method thereof for ensuring that all of the wheels of the work machine remain in contact with the grounds surface.  
           [0004]    The subject invention is directed at overcoming one or more of the problems as set forth above.  
         SUMMARY OF THE INVENTION  
         [0005]    In one aspect of the present invention, a work machine is provided. The work machine includes a chassis and at least one elongate member having a first end rotatably coupled to the chassis. Also provided is a controller and a position sensor coupled to at least one of the elongate members which generates a position signal indicative of an orientation of the elongate member relative to the chassis and relays the position signal to the controller. The controller, in response to the position signal, determines an actual height of the chassis from the position signal and adjusts the actual chassis height to conform to a controller-inputted desired chassis height.  
           [0006]    In another aspect of the present invention, a method of stabilizing the chassis of a work machine of the type having at least one elongate member having a first end rotatably coupled with the chassis is provided. The method comprises the steps of: providing a controller; providing a position sensor coupled to at least one of the elongate members; the position sensor generating a position signal indicative of an orientation of the elongate member relative to the chassis and relaying the position signal to the controller; and the controller, in response to the position signal, determining an actual height of the chassis from the position signal and adjusting the actual chassis height to conform to a controller-inputted desired chassis height. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a diagrammatic side elevation view of a work machine embodying the principles of the present invention;  
         [0008]    [0008]FIG. 2 is a diagrammatic illustration of a control circuit for use with the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0009]    With reference now to the Figures, shown in FIG. 1 is a work machine  100  embodying the principles of the present invention. The work machine  100  includes a cab portion  101  and a first trailer portion  102  hingedly coupled to the cab portion  101  at articulation joint  105 . As should be apparent, the articulation joint  105  allows the cab portion  101  and first trailer portion  102  to be articulable relative to each other about a vertical axis  106  with articulation preferably being provided in a conventional manner such as by the use of hydraulic cylinders  109 . A second trailer portion  110  is preferably hingedly coupled to the first trailer portion  102  at articulation joint  113 , thereby allowing for relative articulation of the first and second trailer portions  102 , 110  about a vertical axis  114 . As should be appreciated by those skilled in such art, such an arrangement allows for tighter turning radii than otherwise would be possible for a single trailer having the same effective length as the combined first and second trailers portions  102 , 110 .  
         [0010]    The cab portion  101  along with the first and second trailer portions  102 , 110  collectively define a chassis of the work machine  100  which is shown generally at  117 . A bunk assembly  118  is pivotally attached to the chassis  117  and is defined by a central beam  121  and a plurality of posts  122  attached thereto on each side of the chassis  117  and extending upwardly therefrom. The bunk assembly  118  therefore defines an open bunk area  123  for retaining a load, for example logs, therein. A conventional gate  125  may also be attached to the central beam  121 . A work implement, preferably comprising a crane  126 , is pivotally attached to the chassis  117  and is used for placing the logs within the bunk area  123 .  
         [0011]    A plurality of ground engaging members, preferably comprising six tires  129  (three shown), are coupled with the chassis  117  by use of corresponding elongated members or arms  130 ,  130 ′,  130 ″ (three shown) each having a first end  131  and a second end  132 . Each arm  130 , 130 ′, 130 ″ is rotatably coupled with the chassis  117 , typically via an axle (not shown), at the first end  131  and coupled to a tire  129  at the second end  132 , and each is controlled by a respective suspension cylinder  133 , 133 ′, 133 ″. As will be explained in more detail below, the suspension cylinders  133 , 133 ′, 133 ″ comprise a part of a control circuit  134  which is used to adjust the vertical orientation of the tires  129  relative to the chassis  117  in order to maintain the bunk assembly  118  substantially horizontal as the work machine  100  traverses uneven terrain. It is to be understood that although only three arms  130 , 130 ′, 130 ″ and respective suspension cylinders  133 , 133 ′, 133 ″ are shown, the work machine  100  described herein also includes three corresponding suspension cylinder/arm arrangements on the other side of the work machine  100 . Furthermore, motive devices, preferably comprising hydraulic motors with one shown generally at  135 , may be coupled to the second end  132  of each arm  130 , 130 ′, 130 ″ and are used to impart a motive force to each tire  129 .  
         [0012]    Shown in FIG. 2 is the control circuit  134  of the present invention. The control circuit  134  utilizes a programmable microprocessor or controller  201  which mimics the manual controls so as to maintain the chassis  117  in a substantially horizontal orientation as the work machine  100  traverses uneven terrain. The control circuit  134  includes a plurality of position sensors  202 , preferably comprising potentiometers, coupled to preferably each of the six arms  130 , 130 ′, 130 ″. Each of the position sensors  202  generates a position signal indicative of the orientation of a corresponding arm  130 , 130 ′, 130 ″, relative to the chassis  117 , which is sent to the controller  201 . In addition, a roll sensor  205 , preferably comprising a pendulum or other like gravity operated device, is coupled to the cab portion  101  or other location on the chassis  117  and generates an orientation signal indicative of the transverse pitch of the work machine  100  which is also sent to the controller  201 . As used herein, “transverse pitch” means the slope of the ground&#39;s surface from one longitudinal side of the work machine  100  to the other longitudinal side.  
         [0013]    Control circuit  134  includes a valve assembly  206  which is conventional for the type of work machine  100  described herein and so will not be discussed in any detail greater than necessary to explain the present invention. For the work machine  100  of the type described herein, the valve assembly  206  typically includes four solenoid operated three way directional control valves (not shown) which route hydraulic fluid to the suspension cylinders  133 , 133 ′, 133 ″, via pump  209 , and back to the reservoir  210  in response to inputs from either the controller  201  or manual controls (not shown). A plurality of primary conduits  213   a - d  conveys hydraulic fluid to and from the suspension cylinders  133 , 133 ′, 133 ″. A plurality of locking devices, preferably comprising lock valves  214 , are in fluid communication with primary conduits  213   a  and  213   d  and are used to selectively lock one or more of the suspension cylinders  133 , 133 ′ or  133 ″ in place. Pressure sensors  215  may also be included and are used to sense pressure acting on each suspension cylinder  133 , 133 ′ and  133 ″ and relaying the pressure information to the controller  201  via suitable leads  218 .  
       INDUSTRIAL APPLICABILITY  
       [0014]    With reference to the drawings and in operation, the controller  201  is programmed with an algorithm to assist in maintaining the chassis  117  in a substantially horizontal position as the work machine  100  traverses uneven terrain, thereby relieving the operator of this task. Two modes of operation are possible with the present invention: (1) a MANUAL mode allowing for manual control of the orientation of the work machine  100 ; and (2) AUTO mode which automatically processes the position and orientation signal inputs received from the respective sensors  202 , 205  so as to maintain the chassis  117  in the aforementioned substantially horizontal position.  
         [0015]    As the name implies, MANUAL mode allows the operator to manually control the orientation of the work machine  100  relative to the horizontal via the conventional valve assembly  206 . Possible orientations include raising and lowering the work machine  100 , tilting the work machine  100  forward and back, and rolling the work machine  100  left and right. In addition, by manually locking one or more of the lock valves  214  and directing the chassis  117  to lower, the unlocked tiers(s)  129  can be raised off of the ground&#39;s surface.  
         [0016]    When placed in the AUTO mode, the control circuit  134 , via the programmed algorithm, seeks to mimic what would otherwise be manual inputs by the operator. Upon receiving the aforementioned position and orientation signals, the controller  201  is programmed to seek a dead band of ride height and pitch angle based upon ground slope (e.g., obtains an average slope) from which the chassis  117  is placed in the desired horizontal position. By providing the controller  201  with the aforementioned programming, a work machine  100  with increased stability may be achieved. More precisely, the aforementioned algorithm prevents the tires  129  from reaching their respective limits of travel. For example, if a tire  129  encounters a depression or protrusion which is deeper or higher than the length of the respective arm, for example arm  130 , the remaining arms  130 ′, 130 ″ are controlled to either lower the chassis  117  to ensure that the tire  129  encountering the depression remains in contact with the ground&#39;s surface, or raise the chassis  117  to ensure that the remaining tires  129  remain in contact with the ground&#39;s surface.  
         [0017]    Furthermore, when the work machine  100  encounters a transverse slope, the roll sensor  205  relays the transverse orientation of the work machine  100 , relative to the horizontal, to the controller  201  via the orientation signal. The controller  201  then compares the actual transverse orientation of the work machine  100  with the programmed transverse orientation limit. If the actual transverse orientation exceeds the aforementioned transverse orientation limit, the controller directs all the tires  129  (via the suspension cylinders  133 , 133 ′, 133 ″) on the lowermost side of the work machine  100  to raise and/or all of the tires  129  on the highest side of the work machine  100  to lower. As should be appreciated by those of ordinary skill in such art, while operating in the AUTO mode the operator may still use the manual controls to manually change the transverse pitch of the work machine  100 . However, while in AUTO mode, the aforementioned algorithm overrides the manual controls to prevent the work machine  100  from exceeding the pre-determined transverse orientation limit.  
         [0018]    Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.