Abstract:
A skidder having a diesel engine coupled to a multiple gear ratio transmission driving a pair of wheel sets for a skidder. The diesel engine is controlled by an operator manipulated foot pedal or hand lever to control the power output and ultimately the maximum skidder ground speed. A controller is provided to pre-select the maximum gear into which the transmission may be placed to ultimately limit the maximum ground speed of the skidder so that the operator sets the forward speed in a binary fashion by depressing the foot pedal or hand operated device to a maximum output condition.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a skidder and more specifically to a propulsion system for such skidder. 
       BACKGROUND OF THE INVENTION 
       [0002]    In industrial vehicles known as skidders have been in use for many years serving the function of pulling felled trees from a logging site to a landing where they can be conveyed to a facility for processing the wood. Skidders originally involved vehicles having a chain connected to the log to drag it out of the logging site but have evolved to skidders where they have grapple hooks to physically hold the felled timber to carry it out. Skidders have been developed to enhance operator efficiency, safety and productivity in spite of the arduous duty cycles demanded of skidders. 
         [0003]    One of the problems with skidders is that they must operate over a highly irregular terrain, caused mainly by the stumps of logs or trees that have already been felled. The terrain created by the tree stumps is so severe that it becomes extremely difficult for the operator of a skidder to navigate it over the tree stumps to the landing where logs would be carried away in volume. Current skidders use manual transmissions with clutches and other mechanisms so that the operator, in addition to compensating for severe inputs to the steering mechanism, must shift gears to provide a practical speed through the field to the landing where the logs are delivered. This activity requires that the operator free a hand to shift the gear mechanism thus leaving only one hand on the steering mechanism. The problem of maintaining a proper speed is exacerbated by the fact that the operator is jostled so that the only way to maintain any sort of control is to depress the power lever or throttle to the floor so that the operator can be held in place in the operator seat in the cab. 
         [0004]    Another problem with skidders is that the prime mover, or internal combustion engine, used to power the skidder also drives a hydraulic pump that powers various actuators employed to, among other tasks, grapple the log to be transported. It is essential that the engine RPM be high enough to provide sufficiently quick actuator response time to ease the burden on the operator while keeping the ground speed at an appropriate level in light of the terrain. 
         [0005]    What is needed therefore is a propulsion system that reduces the adverse requirements on the operator of such skidder vehicles. 
       SUMMARY OF THE INVENTION 
       [0006]    In one form, the invention is a skidder propulsion system having a prime mover providing a rotary output with a maximum governed RPM. A multiple gear ratio transmission is coupled to and receives the output from the prime mover. The transmission provides a rotary output to at least one set of wheels for the skidder. A device is provided for controlling the output of the prime mover up to the maximum governed RPM. A controller is provided for pre-selecting at least one of a maximum gear for the transmission and the governed maximum RPM of the prime mover to select a maximum skidder ground speed in response to movement of the output controlling device to a maximum output condition. 
         [0007]    In another form, the invention is a skidder that includes a frame and a plurality of wheel sets mounted on the frame to enable ground movement. A prime mover providing a rotary output with a maximum governed RPM is mounted in the frame. A multiple gear ratio transmission is coupled to and receives the output from the prime mover. The transmission provides a rotary output to at least one set of the wheels for the skidder. An operator station is mounted to the frame and has a foot operated controller for varying the output of the prime mover up to the maximum governed RPM. A controller is provided for pre-selecting at least one of a maximum gear for the transmission and the governed maximum RPM of the prime mover so that a maximum skidder ground speed is maintained in response to movement of the foot operated controller to a maximum output condition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a side view of a skidder showing a schematic representation of the skidder propulsion system elements. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    Referring now to  FIG. 1 , there is shown a skidder  10  having a frame  12  supporting a pair of wheel sets  14  and  16 . Wheel sets  14  and  16  have appropriate mechanisms for differential application of torque to the wheels facing  FIG. 1  and the wheels on the opposite side. Many different forms may be provided for steering, but in the skidder shown in  FIG. 1 , an articulated joint  18  is provided between the wheel set  14  and the wheel set  16 . The wheel sets  14  and  16  ultimately receive their rotary torque input from a prime mover  20 , shown schematically. Prime mover  20  may be any one of a number of devices to provide a controllable rotary torque output, but the usual type of prime mover  20  for this type of vehicle is a compression ignition for diesel engine. The diesel engine  20  operates on the principle that the heat of compression of air is sufficiently great to ignite a fuel charge that has been injected into individual cylinders in an appropriate quantity and timing to produce a desired power output. 
         [0010]    A fuel system (not shown) for the prime mover  20  receives control inputs from an ECM  22  via appropriate control interconnections  24 . The ECM  22  in current diesels uses sensors and other control inputs (not shown to simplify the understanding of the present invention) to operate the prime mover  20  at an appropriate RPM and torque output as demanded by an operator and modified for emissions or fuel economy considerations. The ECM  22  receives an input from an operator  26  via a foot actuated power lever  28 , commonly referred to as an accelerator pedal and an appropriate interconnection  29 , either mechanically or electrically. Alternatively, the power lever may be a hand operated lever or device. 
         [0011]    The prime mover  20  provides a rotary torque output to a transmission  30  via driveshaft  31 , indicated by a dashed line, that has a connection through appropriate output shafts represented by dashed lines  32  and  34  to wheel sets  14  and  16 . It should be apparent to those skilled in the art that in the mechanical connection  32  and  34  to wheel sets  14  and  16 . Appropriate differential mechanisms and braking mechanisms are employed in the wheel sets  14  and  16  to properly control the skidder  10 . 
         [0012]    The transmission  30  is a multiple gear ratio transmission having a plurality of forward and reverse ratios. Transmissions of the heavy duty type employ various hydromechanical and electrical methods for shifting gears and may utilize torque converters to allow the shifts to be smooth and efficient. The transmission  30  may be an automatic transmission having control and actuation mechanisms to change gears and uses a torque converter for startup and smooth gear changes. This type of transmission may also employ lockup mechanisms under certain conditions. 
         [0013]    Another type of transmission  30  may be employed for skidder  10  is a semi-automatic transmission in which the gear ratio changes are made automatically, but a master clutch is used in place of a torque converter. 
         [0014]    The transmission  30  may have any number of forward and reverse gear ratios. By way of non-limiting example, an automatic transmission may have  6  forward and three reverse gear ratios. The semi-automatic transmission may have  8  forward and  7  reverse gear ratios. 
         [0015]    Either type of transmission  30  is controlled by an ECM  36  through a control line  38  which provides various control functions to enable selection of the most appropriate gear ratio for the conditions experienced by the skidder  10 . The ECM  36  receives an input from an operator control mechanism  40  via line  42  to pre-select the maximum gear the transmission  30  would go into, in response to operator input via a lever  44 . Operator control mechanism  40  may take many different forms, but, as shown, may be a mechanism that enables step-up or step-down incremental gear selections by movement of the operator lever  44 . In another form shown by dashed line  45 , operator control mechanism  40  may include a multiple position switch, push-button or dial to achieve the selection of the maximum attainable gear. The ECM  36  may be set up to a default maximum gear ratio, for example 6 th  gear, thus enabling the operator  26  to bump up or down from that gear selection. The ECM  36  may also be programmed to remember previous maximum gear selections to set those as the default upon startup of the skidder  10 . 
         [0016]    In addition to selection of the maximum gear for transmission  30 , the maximum governed RPM of prime mover  20  may also be pre-selected by an appropriate control input to ECM  22 . 
         [0017]    The skidder  10  has a grapple assembly, generally indicated by reference character  46 , to secure a felled tree trunk to drag it out of the forest without have to leave the skidder to secure a chain to the tree as in earlier skidders. In addition, the skidder  10  may have a pusher blade  48  to move or carry branches or leaves out of the operating field. In addition, the skidder has a frame  50  surrounding the operator  26  to provide protection from falling debris. 
         [0018]    The skidder  10 , as stated previously, has a maximum ground velocity, usually governed by the terrain over which it is passing and the load, or size of a tree trunk it is carrying. With transmission  30  the operator  26  pre-selects a maximum gear attainable from transmission  30  by means of the lever  44 . When the skidder  10  moves forward, the usual operation for an operator, owing to the extremely rough and rugged terrain over which it passes is to push the foot pedal  28  to the floor or to push the hand operated lever to maximum output. This allows the transmission  30  to make appropriate gear selections according to a predetermined logic up into the maximum limited speed as set by the maximum governed RPM of the prime mover  20 . The ultimate result of this combination is that the operator selects the maximum ground speed in a binary fashion by pushing the hand lever to maximum or the foot pedal to the floor and is free to exert efforts to maintain the skidder  10  on a predetermined course, taking into consideration the terrain over which the skidder  10  passes. 
         [0019]    The selection of the maximum attainable gear ratio for transmission  30 , which has heretofore not been utilized in a commercial skidder, enables a significant increase in productivity and reduction in operator fatigue. 
         [0020]    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.