Abstract:
An agricultural vehicle is described having a chassis and a cab mounted on the chassis. A suspension system for reducing the accelerations transmitted from the vehicles tires or tracks through the frame, into the cab, and ultimately through to the operator is provided. By reducing the accelerations, the ride quality is greatly improved, allowing operators to operate a vehicle for longer periods of time without excessive fatigue.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Various aspects of the present invention relate to a suspension system linkage arrangement for an agricultural vehicle having a cab resiliently supported on the chassis of the vehicle. 
         [0003]    2. Description of Related Art 
         [0004]    The ride quality and operator comfort of a work vehicle is adversely affected by vibrations or movement transmitted from the frame or chassis of the vehicle to the operator&#39;s cab. As the cab typically is built separately from, and later mounted on, the frame, and because the cab is separate from the frame, movement of the frame may be transmitted through and amplified by the connections between the cab and the frame. 
         [0005]    As the work vehicle travels across a surface, movement of the frame/chassis induces the operator&#39;s cab to pitch, roll and bounce. Movement of the cab can be particularly severe in agricultural and construction equipment vehicles (e.g., tractors, combines, backhoes, cranes, dozers, trenchers, skid-steer loaders, etc.), because such vehicles typically operate on off-road surfaces or fields having a high level of bumpiness. 
         [0006]    Operator comfort may also be adversely affected by the operation of various systems on a work vehicle. In particular, operation of various work vehicle systems can cause forces to be applied to the chassis of the vehicle which, in turn, are transmitted to the cab. Examples of these forces include: draft forces exerted on the hitch of an agricultural tractor by an implement (e.g., a plow), which can cause the cab to pitch; normal forces applied to a work vehicle as the vehicle turns in response to a steering device, which can cause the cab to roll; clutch forces generated when a work vehicle clutch (e.g., a main drive clutch; four-wheel drive clutch) is engaged or disengaged, which can cause the cab to pitch; gear shift forces generated when a transmission of a work vehicle is shifted, which can cause the cab to pitch; braking forces generated as brakes of a work vehicle are operated, which can cause the cab to pitch; and acceleration forces generated when a speed actuator changes the speed of a work vehicle which can cause the cab to pitch. 
         [0007]    The movement of the cab caused by surface bumps and the operation of vehicle systems cause both qualitative and quantitative problems. An operator of such a vehicle experiences increased levels of discomfort and fatigue caused by the vibrations. Productivity is decreased when an operator is forced to rest or shorten the work day, or is unable to efficiently control the work vehicle. The operator is also less likely to be satisfied with a work vehicle that provides poor ride quality. Under certain conditions, the frequency and magnitude of cab movement may force the operator to decrease driving speed, further decreasing productivity. 
         [0008]    It is common for the cab, or operator station, to be mounted directly on the chassis and to rely only on springing in the operator&#39;s seat to improve operator comfort. This, however, is not entirely satisfactory, and therefore the cab can be supported on rubber mounts that provide an improved degree of cushioning. 
         [0009]    Another known suspension system enables the cab to be resiliently mounted on the vehicle chassis. Stabilizer linkages are provided on the tractor fore and aft of the cab to limit the movement of the pivotal connection of the stabilizer linkages to the cab to essentially a vertical movement that lies in a vertical plane including the longitudinal centers of the vehicle chassis and the cab. A sway or yaw limiting mechanism as well as a pitch limiting mechanism are provided to limit the pitch and roll of the cab as it moves through the vertical plane relative to the vehicle chassis. 
         [0010]    The present invention improves upon the known cab suspension systems, and thus it is to such a system that the present invention is primarily directed. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    Briefly described, a suspension system for reducing the accelerations transmitted from the vehicles tires or tracks through the frame, into the cab, and ultimately through to the operator is provided. By reducing the accelerations, the ride quality is greatly improved, allowing operators to operate a vehicle for longer periods of time without excessive fatigue. 
         [0012]    An agricultural vehicle includes a chassis and a cab mounted on the chassis, wherein a suspension system of the vehicle comprises a linkage assembly including a first and second fore-aft linkage, and a lateral linkage. The fore-aft linkages restrain the front of the cab from moving fore-aft and laterally. The linkages enable the cab to move and down, through an arc shape, without restraint. To restrain rotational movement, the rear lateral linkage is provided. 
         [0013]    In exemplary embodiments, the linkages are Watts linkages, being a relatively short, double arm lever rotatably mounted, and two relatively long levers extending in opposite directions from the ends of the double arm lever to fixed pivot points. All pivoting points are free to rotate in a vertical plane. It is advantageous for the shorter lever to be vertical and the two longer levers to be substantially horizontal when the vehicle is at rest on a level surface. 
         [0014]    The terms “fore”, “aft” and “transverse” as used herein are all referenced to the longitudinal centerline of the chassis with the vehicle moving in a forward direction. The term “vertical” refers herein to the direction perpendicular to the forward wheel axle, i.e., the normal to the plane of contact of the wheels with the ground. The terms “pitch”, “yaw” and “roll” are likewise referenced to the longitudinal axis of the chassis, roll being rotation of the cab about a longitudinal axis, pitch about a transverse axis and yaw about a vertical axis. 
         [0015]    These and other objects, features and advantages of the present invention will become more apparent upon reading the following specification in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0016]      FIG. 1  illustrates a perspective view of a suspension system, in accordance with an exemplary embodiment of the present invention. 
           [0017]      FIG. 2  illustrates a perspective view of the suspension system carrying a cab, in accordance with an exemplary embodiment of the present invention. 
           [0018]      FIG. 3  illustrates another perspective view of the suspension system carrying the cab, in accordance with an exemplary embodiment of the present invention. 
           [0019]      FIG. 4  illustrates a perspective view of a bottom portion of the cab carried by the suspension system, in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Referring now in detail to the figures,  FIG. 1  illustrates a perspective view of a suspension system  10  for a cab  100  ( FIGS. 2-4 ). The suspension system  10  comprises a linkage assembly  20 , including a first fore-aft linkage  22 , and second fore-aft linkage  24 , and a lateral linkage  26 . 
         [0021]    The suspension system  10  communicates between the first chassis section  12  and the second chassis section  14  of the tractor, providing suspension control of damping members  30 , one  32  located at the front of the first chassis section  12 , and two  34 ,  36  located at the rear of the first chassis section  12  and in communication with the second chassis section  14 . 
         [0022]    The first chassis section  12  of the tractor thus is supported by the three damping members  30 , preferably hydraulic cylinders, each acting independently. The linkage assembly  20  uses the set of three linkages  22 ,  24 ,  26  to restrain the cab. The two fore-aft linkages  22 ,  24  are attached at the rear to the second chassis section  14  of the tractor, and at the front to the first chassis section  12 . The linkages  22 ,  24  meet in the front at a single point P. The linkages are attached to the first chassis section  12  and the second chassis section  14  with rod end bearings allowing some movement as the first chassis section  12  moves. 
         [0023]    The fore-aft linkages  22 ,  24  restrain the front of the first chassis section  12  from moving fore-aft and laterally. The linkages  22 ,  24  further enable the cab  100  to move and down, through an arc shape, without restraint. To restrain rotational movement, the rear lateral linkage  26  is provided. 
         [0024]    It is desirable that the linkages  22 ,  24  be as close as possible to horizontal at the mid-stroke of the cylinders. As the linkages  22 ,  24  move up and down, the movable end of the linkage attached to the cab  100  moves in an arc. The arc actually forces the cab fore-aft. The amount of movement is dependent on how close to horizontal the linkages are in mid-stroke and their length. The longer the linkages  22 ,  24  are, the larger the arc diameter; therefore, the cab  100  moves fore-aft less. The closer to horizontal they are the lower the fore-aft movement. Notably, the same situation also applies to the rear linkage. 
         [0025]    For example, at the mid-stroke of the first chassis section  12 , the linkages  22 ,  24 ,  26  can lie in a plane generally horizontal. This arrangement of the linkage assembly  20  can minimize unwanted fore-aft, lateral and rotational movement of the first chassis section  12  as it moves up and down. 
         [0026]    In one embodiment, the linkages  22 ,  24 ,  26  are Watts linkages, to further minimize fore-aft, lateral and rotational movement. In such an embodiment, the aft end of the first chassis section  12  would be able to move up and down relative to the first chassis section  12 , but prevented from moving from side to side. In other words, the linkage allows pitching of the cab  100  relative to the first chassis section  12 , but prevents yaw. A Watts link has a pivot point in its center, and a rod that runs to each side therefrom. This design eliminates the side to side motion of a panhard rod. 
         [0027]    The damping members  30  can comprise a low rate mechanical or air spring in parallel with an active device such as an hydraulic actuator. Alternatively, an active air spring could be used alone. 
         [0028]    The present linkage assembly  20  can be combined with other passive, semi-active or active suspension systems to improve ride quality and operator comfort. Such systems include vibration isolators mounted between the chassis and cab or seat. Passive systems use passive vibration isolators (e.g., rubber isolators, springs with friction, or viscous dampers) to damp vibrations with different isolators used to damp different frequencies. Rubber isolators can be used, for example, to damp high frequency vibrations and air bags used to damp low frequency vibrations. Performance of passive systems, however, is limited due to design compromises needed to achieve good control at resonance frequencies and good isolation at high frequencies. 
         [0029]    Semi-active systems achieve control and isolation between the chassis and the cab by controlling a damper to selectively remove energy from the system in response to movement of the cab sensed by sensors. 
         [0030]    Active systems use sensors to sense cab movement and a controller to generate control signals for an actuator, which applies a force to the cab to cancel vibrations transmitted to the cab by the chassis. The power needed to apply the force is supplied by an external source (e.g., hydraulic pump). 
         [0031]    In an exemplary embodiment, the suspension system attenuates both low and high frequency vibrations between the chassis and cab. Attenuation of high frequency vibrations can decrease acoustic noise in the cab, decrease fatigue, and decrease vibration-induced mechanical faults. Attenuation of low frequency (e.g., less than 20 Hz) vibrations can decrease operator fatigue and improve vehicle operability. The attenuation of low frequency vibrations is particularly important because the resonant frequencies of the human body are typically below 20 Hz. For example, the human abdomen resonates at frequencies between 4-8 Hz, the head and eyes resonate at frequencies around 10 Hz, and the torso at 1-2 Hz. The actual frequency may vary with the particular individual. 
         [0032]    Aspects of the cab  100  are illustrated in  FIGS. 2-4 . Specifically, aspects of the cab  100  being carried on the chassis sections  12 ,  14  are illustrated.  FIG. 2  shows the cab  100  carried by the suspension system  10 .  FIG. 3  illustrates a connection point  105 , where a front of the cab  100  is mounted to the suspension system  10 . A bottom portion of the cab  100  is illustrated in  FIG. 4 .  FIG. 4  illustrates connection points  110 ,  115 ,  120  where a rear of the cab  100  is mounted to the suspension system  10 . 
         [0033]    Numerous characteristics and advantages have been set forth in the foregoing description, together with details of structure and function. While the invention has been disclosed in several forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions, especially in matters of shape, size, and arrangement of parts, can be made therein without departing from the spirit and scope of the invention and its equivalents as set forth in the following claims. Therefore, other modifications or embodiments as may be suggested by the teachings herein are particularly reserved as they fall within the breadth and scope of the claims here appended.