Abstract:
A stabilization and leveling system for an industrial vehicle of a type comprising a frame and at least one axle which is pivotally connected to the frame. The system comprises a linear actuator pivotally connected between the frame and the axle. The linear actuator includes a lock mechanism and a lock override system. The linear actuator is freely extendable and retractable when the lock mechanism is in a non-actuated condition, such that the axle is freely tiltable relative to the frame, and locked against free extension and retraction upon actuation of the lock mechanism, thereby preventing free movement of the linear actuator and resultant free tilting of the axle relative to the frame. The lock override system is actuable to override the lock mechanism to extend or retract the linear actuator to permit controlled tilt of the axle when it is locked.

Description:
BACKGROUND  
         [0001]    The present invention relates to an axle stabilization system for an industrial vehicle. More particularly, the present invention relates to an axle stabilization and leveling system for an industrial vehicle having a frame pivotally mounted on an axle such that the axle is tiltable relative to the frame.  
           [0002]    In many industrial vehicles, for example, forklifts, telescopic material handlers, cranes, and excavators, the vehicle frame is typically pivotally mounted to at least one of its axles such that those axles are tiltable relative to the frame. One of the axles, typically the front axle, is either fixed relative to the frame or pivotal with a controlled leveling system associated therewith to allow an operator to controllably level the frame relative to that axle. Such a leveling system generally includes at least one hydraulic cylinder connected to the vehicle hydraulic system and positioned between the frame and the front axle. The operator commands extension or retraction of the cylinder to controllably tilt the axle and thereby level the frame. The hydraulic cylinder does not permit any free movement and only extends or retracts in response to operator commands.  
           [0003]    As for the other axle, typically the rear axle, it has generally been allowed to freely pivot and thereby tilt in response to ground contours or centrifugal forces during turning to provide the vehicle with greater comfort and driving stability. However, under various use or loading conditions, the rear axle tilting may cause the vehicle to become less stable.  
           [0004]    The prior art discloses the use of various rear axle stabilizer systems that include one or more lockable hydraulic cylinders connected to the vehicle hydraulic system and positioned between the frame and the rear axle. The cylinders are generally open to allow free cylinder movement and corresponding free axle tilt. However, in response to various operating conditions, one or both cylinders are locked to rigidly fix the connection between the frame and the rear axle thereby eliminating free tilting. For example, U.S. Pat. Nos. 4,393,959 (Acker), 4,705,295 (Fought), 6,129,368 (Ishikawa), and 6,131,918 (Chino) each disclose systems including two hydraulic cylinders, one on each side of the pivot joint. Ishikawa further discloses a system utilizing a single hydraulic cylinder. In each of these prior art designs, once a predetermined condition is detected, the cylinders lock to rigidly fix the position of the axle. If the operator attempts to level the front of the vehicle using the leveling system while the rear axle is locked, the leveling command may be prevented, the vehicle may contort front to rear, or one of the rear tires may lift off the ground due to the rigidity of the rear axle.  
         SUMMARY  
         [0005]    The present invention relates to a stabilization and leveling system for an industrial vehicle of a type comprising a frame and at least one axle which is pivotally connected to the frame such that it is tiltable relative to the frame. The stabilization system comprises a linear actuator pivotally connected between the frame and the axle. The linear actuator includes a lock mechanism and a lock override system. The linear actuator is freely extendable and retractable when the lock mechanism is in a non-actuated condition, such that the axle is freely tiltable relative to the frame, and locked against free extension and retraction upon actuation of the lock mechanism, thereby preventing free movement of the linear actuator and resultant free tilting of the axle relative to the frame. The lock override system is actuable to override the lock mechanism to extend or retract the linear actuator to permit controlled tilt of the axle when it is locked. The linear actuator is preferably self-contained such that it is independent of the vehicle hydraulic supply, thereby allowing easier installation, particularly in field installations, and reduces the actuator&#39;s susceptibility to failure based on malfunction of the vehicle hydraulic system.  
           [0006]    The stabilization system further comprises a sensor system, configured to sense one or more vehicle parameters, and a controller. The controller is associated with the sensor system, the lock mechanism, and the lock override system and is configured to actuate the lock mechanism upon receipt of a signal from the sensor system indicating a predetermined vehicle parameter condition exists. The controller is also configured to actuate the lock override system upon receipt of a command to actuate such. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0007]    [0007]FIG. 1 is a side elevation of an illustrative industrial vehicle.  
         [0008]    [0008]FIG. 2 is a rear elevation of an illustrative axle and frame assembly incorporating a linear actuator in accordance with the present invention.  
         [0009]    [0009]FIG. 3 is plan view in partial section of a preferred embodiment of the linear actuator of the present invention.  
         [0010]    [0010]FIG. 4 is a schematic representation of the linear actuator of FIG. 3 associated with a control system.  
         [0011]    [0011]FIG. 5 is a schematic representation of the linear actuator of FIG. 3 in a free flow condition.  
         [0012]    [0012]FIG. 6 is a schematic representation of the linear actuator of FIG. 3 in a closed flow condition.  
         [0013]    [0013]FIG. 7 is a schematic representation of the linear actuator of FIG. 3 in a leveling bypass condition.  
         [0014]    [0014]FIG. 8 is a side elevation of the industrial vehicle of FIG. 1 with its boom elevated. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    The preferred embodiments of the present invention will now be described with reference to the drawing figures where like numerals represent like elements throughout. Reference to orientation, for example, front, rear, left, right, is to provide descriptive clarity only and is not intended to be limiting. The present invention may be utilized in conjunction with either vehicle axle and on either side of the vehicle.  
         [0016]    Referring to FIGS. 1 and 2, an illustrative industrial vehicle  10  is shown. The vehicle  10  generally comprises a frame  12  pivotally connected to front and rear axles  14 ,  16  at respective pivot unions  26 . The pivot unions  26  allow the axles  14 ,  16  to tilt relative to the frame  12  as indicated by the arrows in FIG. 2. The illustrated vehicle  10  is of a type having a telescoping material handling boom  24 , but the present invention may be utilized in conjunction with other types of vehicles. A controlled leveling system (not shown) may be associated with the front axle  14 . The linear actuator  50  of the present invention is pivotally mounted between the frame  12  and rear axle  16  at pivot points  20  and  22 . As explained above, the distinction between front and rear is immaterial to the present invention. The controlled leveling system could be associated with the rear axle  16  and the linear actuator  50  of the present invention associated with the front axle  14 . However, since the controlled leveling system is typically associated with the front axle  14 , such orientation is utilized hereinafter to simplify the description.  
         [0017]    Referring to FIGS. 3 and 4, the preferred linear actuator  50  is a fluid actuator, for example, a hydraulic actuator. The preferred actuator  50  comprises a cylinder  52  having a primary fluid housing  54  and a reservoir chamber  56 . A moveable piston  58  is positioned in the primary fluid housing  54  such that it defines first and second chambers  62  and  63 . A piston rod  60  connected to and moveable with the piston  58  extends from the cylinder  52 . A closed fluid loop  64  provides fluid passage between the chambers  56 ,  62  and  63 . A primary fluid loop  66  interconnects the first and second chambers  62  and  63  and a secondary fluid loop  68  interconnects the primary fluid loop  66  with the reservoir chamber  56 .  
         [0018]    Operation of the closed fluid loop  64  of the preferred linear actuator  50  will be described with reference to FIG. 4. Extension and retraction of the piston rod  60  are generally controlled via the primary fluid housing  54  and primary fluid loop  66 . The reservoir chamber  56  and the secondary fluid loop  68  provide a backup system. The secondary loop  68  is interconnected with the primary fluid loop  66  via a pressure relief valve  82  and a check valve  84 . The pressure relief valve  82  is configured such that it will allow fluid flow from the primary loop  66  to the reservoir chamber  56  only upon the existence of a predetermined, generally undesirably high level of pressure in the primary loop  66 . The check valve  84  is configured such that it will only allow fluid to flow from the receiver chamber  56  to the primary loop  66  upon the existence of a predetermined, generally low level of pressure, for example, a vacuum condition, in the primary loop  66 . As such, under normal operating conditions, the primary loop  66  operates independent of the secondary loop  68  and reservoir chamber  56 . As such, if desired, for example, if reliability is less of a consideration, the linear actuator  50  could be made without the reservoir chamber  56  and secondary loop  68 . Alternatively, although it is preferred that the linear actuator  50  be self contained, the reservoir chamber  56  and secondary loop  68  could be replaced by the vehicle&#39;s hydraulic system to provide the desired backup system.  
         [0019]    The primary loop  66  preferably includes a plurality of valves  70 - 80  which control fluid flow through the loop  66  and thereby control actuation of the linear actuator  50 . Lock valve  70  is a bi-direction valve which allows fluid to freely flow in both directions between the first and second chambers  62  and  63 . A suitable valve is the Sterling Solenoid Cartridge Valve, 10.4 ohm coil, 14 watts @ 12 vdc. The preferred embodiment includes two oppositely directing uni-directional leveling valves  74  and  78 , which are generally closed to fluid flow, positioned in the primary loop  66 . Suitable valves are Hydra-Force Solenoid Cartridge Valves, 9.8 ohm coil, 15 watts @ 12 vdc. With the leveling valves  74 ,  78  generally closed to fluid flow, the lock valve  70  controls general fluid flow through the loop  66 . When the lock valve  70  is open to fluid flow, as illustrated in FIG. 5, fluid is free to flow between the first and second chambers  62  and  63 . This allows free movement of the piston  58  and piston rod  60  and thereby free tilting of the axle (not shown). When the lock valve  70  is closed to fluid flow, fluid generally cannot flow between the first and second chambers  62  and  63 , and therefore, the piston  58  and piston rod  60  are fixed, thereby locking the axle (not shown). If lock override is not desired, for example, if the vehicle does not include a front controlled leveling system, the leveling valves may be omitted.  
         [0020]    A throttle  73  and restrictor valve  72  are preferably included in the loop  66  to reduce the likelihood of a sudden fluid flow upon opening of the lock valve  70 . A suitable restrictor valve is a Hydra-Force Solenoid Cartridge Valve, 9.8 ohm coil, 15 watts @ 12 vdc. The restrictor valve  72  is generally open to fluid flow such that fluid generally flows unrestricted through the lock valve  70 . However, the control system  100  (not shown) is configured to close the restrictor valve  72  to fluid flow for a given amount of time, for example, five seconds, when the lock valve  70  is opened. With the restrictor valve  72  closed, fluid encounters the throttle  73 , thereby restricting flow for the given time to allow the loop  66  to normalize.  
         [0021]    Referring to FIG. 4, each leveling valve  74 ,  78  provides a controllable, uni-directional bypass in the primary loop  66 . As such, each leveling valve  74 ,  78  permits controllable overriding of the lock valve  70 . As illustrated in FIG. 7, one of the leveling valves  74 ,  78  may be actuated to open a one-way fluid path between the chambers  62  and  63  even though the lock valve  70  is closed to fluid flow. In the illustrated example, leveling valve  74  is actuated to allow fluid to flow from chamber  62  to chamber  63 . The resultant change in fluid pressure in this example causes the piston  58  and rod  60  to retract. With the actuator  50  positioned as shown in FIG. 2, the retraction would cause the frame  12  to level from right to left with respect to the axle  16 . Each leveling valve  74 ,  78  preferably has an associated pressure relief valve  76 ,  80 . Each relief valve  76 ,  80  is configured to prevent flow through its bypass loop until the pressure in that bypass loop reaches a minimum value. As such, the relief valve  76 ,  80  creates fluid resistance to leveling for more controlled leveling.  
         [0022]    While the preferred linear actuator  50  is a fluid actuator, other actuators, including mechanical actuators, may be used. For example, the actuator could include a notched rod engaged by a toothed wheel. The wheel would be generally free rotating, but would be locked against free rotation to lock the actuator. The wheel could then be driven in a desired direction to overcome the locked condition. Alternatively, the rod could be driven by a lockable, driveable belt arrangement.  
         [0023]    Referring to FIGS. 4 and 8, interaction between the linear actuator  50  and vehicle operation will be explained in further detail. The vehicle is provided with a control system  100  which preferably includes a controller  102  and a plurality inputs  104  and outputs  106 . The inputs  104  are preferably associated with various vehicle components and provide the controller  102  with a plurality of signals indicating various vehicle parameters or operator commands. The controller  102  processes the signals and sends necessary outputs  106  to control the various components of the linear actuator  50 . As illustrated, the controller  102  may also send output commands to other vehicle components, for example the front axle frame level enable control (FLE) or the front axle frame level speed control (FLS). In such a manner, the linear actuator  50  leveling function can be coordinated with the front frame leveling system.  
         [0024]    In the preferred embodiment, the inputs  104  include: a boom position sensor (BPS), configured to sense whether the boom  24  is positioned within a given range; a brake system sensor (BSS) configured to sense whether the park brake or service brake is applied; a frame attitude sensor (FAS) configured to determine the extent the frame  12  is tilting to the left or to the right; and a frame level input (FLI) configured to receive commands from the operator to level the frame  12  left or right. In the preferred embodiment, the controller  102  is configured to actuate the lock valve  70  upon receipt of a signal that the boom  24  is positioned within the given range and also a signal that one of the brakes is applied. The controller  102  is further configured to actuate the respective leveling valve  74 ,  78  upon receipt of a frame level command, provided the frame  12  is not already tilting beyond a given angle in the commanded direction. Although the frame leveling valves  74 ,  78  in the preferred embodiment will not have an impact when the lock valve  70  is open, the controller  102  can be configured to address such. For example, the controller may be configured to: not send a leveling command unless the lock valve  70  is closed; send the leveling command irrespective of the lock valve  70  condition, realizing that the leveling valve  74 ,  78  will not impact on the linear actuator if the lock valve  70  is open; or lock the lock valve  70  upon receipt of the leveling command.  
         [0025]    The above controller inputs and outputs are only illustrative of the preferred control configuration. It is understood that numerous inputs, including and in addition to the above, may be chosen as well as numerous permutations as to the controller output.