Patent Publication Number: US-6336784-B1

Title: Frame leveling speed control system for an extendible boom vehicle

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates to boom-type vehicles, and more particularly to a frame leveling speed control arrangement for a boom-type vehicle. 
     A boom-type vehicle such as an extendible boom forklift typically includes a boom pivotably mounted to a frame. Hydraulic cylinders are interposed between the boom and the frame for moving the boom between its raised and lowered positions. The frame carries a set of wheels, and one or more frame leveling cylinders are interposed between the frame the wheels for leveling the frame when it is desired to raise the boom. 
     It is an object of the present invention to provide a system for insuring that a brake is applied when the boom reaches a predetermined angle relative to the frame. It is a further object of the invention to provide relatively slow movement of the frame leveling cylinder when the boom reaches a predetermined position relative to the frame. A still further object of the invention is to provide a system for preventing movement of the vehicle and for providing controlled movement of the frame leveling cylinder when the boom attains a predetermined angle relative to the frame. 
     In accordance with one aspect of the invention, a boom-type vehicle includes a frame carrying a set of ground-engaging wheels, and a frame leveling arrangement interposed between the frame and the wheels for leveling the frame relative to the ground. A boom is pivotably mounted to the frame, and a position sensing arrangement is interposed between the boom and the frame for sensing the angle of the boom relative to the frame. The frame leveling arrangement includes a leveling speed control responsive to the position sensing arrangement for enabling the leveling arrangement to operate at a first speed of operation when the angle of the boom relative to the frame is below a predetermined threshold, and to operate at a second speed of operation less than the first speed when the angle of the boom relative to the frame is above the predetermined threshold. A hydraulic cylinder arrangement is preferably interconnected between the boom and the frame for providing pivoting movement of the boom relative to the frame. The position sensing arrangement may be in the form of a movable member interconnected with the boom and movable in response to the movement of the boom relative to the frame, and a sensing member mounted to a portion of the cylinder arrangement interconnected with the frame, such that the position of the movable member relative to the sensing member changes according to the angle of the boom relative to the frame. The movable member may be in the form of a rod having a first end pivotably interconnected with the boom and a second end spaced therefrom. The sensing member may be in the form of a proximity switch operable to detect the second end of the rod when the angle of the boom relative to the frame reaches the predetermined threshold. The frame leveling arrangement may be in the form of a hydraulic cylinder arrangement interconnected between the frame and the wheels. The leveling speed control features a shiftable flow restricting arrangement interconnected with the hydraulic cylinder arrangement. The shiftable flow restricting arrangement may be in the form of a flow restrictor in the flow path of the hydraulic frame leveling cylinder arrangement and a check valve which is shiftable in response to actuation of the proximity switch to direct fluid flow through the flow restrictor when the angle of the boom relative to the frame reaches the predetermined threshold. 
     In accordance with another aspect of the invention, a boom-type vehicle includes a frame carrying a set of ground-engaging wheels, and a brake mechanism interconnected with the wheels for selectively preventing rotation of the wheels relative to the frame. A frame leveling arrangement is interposed between the frame and the wheels for leveling the frame relative to the ground. A boom is pivotably mounted to the frame, and a position sensing arrangement is interposed between the boom and the frame for sensing the angle of the boom relative to the frame. A brake actuator is responsive to the position sensing arrangement for automatically applying the brake mechanism when the angle of the boom relative to the frame exceeds a predetermined threshold. The position sensing arrangement is preferably as summarized above, and the brake actuator is responsive to actuation of the proximity switch for automatically applying the brake mechanism. 
     In a particularly preferred embodiment, the position sensing arrangement is interconnected with both the brake actuator and the leveling speed control arrangement. In this manner, the brake mechanism is automatically applied when the boom attains a predetermined angle relative to the frame and, simultaneously, the leveling speed control arrangement is operable to restrict fluid flow to and from the frame leveling cylinder arrangement for reducing the speed of operation of the frame leveling cylinder arrangement. This combination of automatic brake actuation and leveling speed control insures that the vehicle remains stationary and the frame can only be leveled at a relatively slow speed when the boom is at or above a certain angle relative to the frame. 
     The invention also contemplates a method of operating a boom-type vehicle, substantially in accordance with the foregoing summary. 
     Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings illustrate the best mode presently contemplated of carrying out the invention. 
     In the drawings: 
     FIG. 1 is an isometric view of a boom-type vehicle, in the form of an extendible boom forklift, incorporating the subject matter of the present invention; 
     FIG. 2 is a partial isometric view showing the upper rear end of the boom-type vehicle of FIG. 1, with the boom in a lowered position relative to the frame; 
     FIG. 3 is a view similar to FIG. 2, showing the boom in a raised position relative to the frame; 
     FIG. 4 is a schematic view illustrating the brake actuator in accordance with the present invention, as incorporated into the extendible boom vehicle of FIG. 1; and 
     FIG. 5 is a hydraulic circuit diagram illustrating the leveling speed control mechanism in accordance with the present invention, incorporated into the extendible boom vehicle of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a vehicle in the form of an extendible boom forklift  10  generally includes a frame or chassis  12  and a boom assembly  14  mounted to chassis  12 . Chassis  12  includes a central frame member  15  extending in a longitudinal front-rear direction. A pair of front ground-engaging wheels are carried by a front axle assembly mounted toward the forward end of central frame member  15 , and a pair of rear ground-engaging wheels  20  are mounted toward the rearward end of central frame member  15 . A cab  22  is mounted between front wheels  18  and rear wheels  20  on one side of central frame member  15 , and a drive train is mounted on the side of central frame member  15  opposite cab  22 . 
     A pair of uprights  24  are mounted to central frame member  15  toward its rearward end, rearwardly of cab  22  and wheels  20 . A pair of lift cylinders  26  are located one on either side of frame  16 , and each lift cylinder  26  is connected to chassis  12  via a pivot connection which pivotably secures the cylinder end of the lift cylinder  26  to chassis  12  for movement about a substantially horizontal pivot axis. A pair of slave cylinders  30  are also located one on either side of chassis  12 , and the cylinder end of each slave cylinder  30  is connected to chassis  12  via a pivot connection which provides pivoting movement of the slave cylinder  30  about a substantially horizontal pivot axis. 
     Boom assembly  14  generally includes an outer boom member  32  and an intermediate boom member  34  which is received within an internal passage defined by outer boom member  32  for telescoping inward and outward movement relative to outer boom member  32 . Boom assembly  14  further includes an inner boom member received within an internal passage defined by intermediate boom member  34  and mounted for axial inward and ouward telescoping movement relative to intermediate boom member  34 . A nose section  36  is mounted to the forward end of the inner boom member, and is located forwardly of the forward end of chassis  12 . A drive arrangement provides inward and outward movement of intermediate boom member  34  and the inner boom member to which nose section  36  is mounted, in a manner as is known. 
     A tool mounting assembly  38  is pivotably mounted to the lower end of nose section  36 , and a tilt cylinder (not shown) is interposed between nose section  36  and tool mounting assembly  38 . Tool mounting assembly  38  includes an arrangement for releasably engaging a tool with boom assembly  14  through nose section  36 . As shown in the drawings, the tool is in the form of a fork assembly  42 , although it is understood that any other tool as desired can be mounted to tool mounting assembly  38 . 
     Boom assembly  14  includes a mounting structure  44  toward its rearward end. Lift cylinder  26  is engaged with mounting structure  44  via a pivot connection  46 , and slave cylinder  30  is connected to mounting structure  44  via a pivot connection  48 . A pivot shaft  50  is operable to pivotably mount boom assembly  14  to uprights  24  through mounting structure  44 . Boom assembly  14  is pivotable about a pivot axis defined by the longitudinal axis of pivot shaft  50 . 
     With the arrangement as described above, boom assembly  14  is operable to lift a load located forwardly of chassis  12  utilizing the tool, such as fork assembly  42 , mounted to the forward end of boom assembly  14  forwardly of front wheels  18 . Extension of lift cylinders  26  functions to pivot boom assembly  14  upwardly about pivot shaft  50  to lift the load carried by the tool, such as fork assembly  42 , and likewise retraction of cylinders  26  functions to lower the load by allowing boom assembly  14  to pivot downwardly about pivot shaft  50 . 
     In a manner as is known, the rear axle assembly, to which rear wheels  20  are mounted, is pivotable relative to central frame member  15  to provide oscillating movement of wheels  20  relative to chassis  12  as forklift  10  travels over uneven terrain. A stabilizing cylinder assembly  52  is interposed between central frame member  15  and the rear axle assembly, to cushion shocks which would otherwise be experienced by central frame member  15  and the components mounted thereto, such as cab  22  and boom assembly  14 , during such oscillating movement of wheels  20  relative to central frame member  15 . In FIG. 1, stabilizing cylinder  52  is shown as being located at the left side of forklift  10 . 
     In a similar manner, the front axle assembly, to which front wheels  18  are mounted, is pivotable relative to central frame member  15  to provide oscillating movement of wheels  18  as forklift  10  travels over uneven terrain. A frame leveling cylinder (not shown) in FIG. 1 is located at the right side of forklift  10  and is interconnected between central frame member  15  and the front axle assembly. In a manner as is known, the frame leveling cylinder is utilized to level chassis  12  relative to wheels  18  and  20  when forklift  10  is parked on uneven terrain and boom assembly  14  is to be raised and extended to place a load carried by fork assembly  42  onto an elevated surface. In accordance with a conventional operation, stabilizing cylinder  52  is automatically locked in position upon actuation of the frame leveling cylinder to fix the position of rear wheels  20  relative to central frame member  15 , and operation of the leveling cylinder, located between the front axle assembly and central frame member  15 , is operable to move chassis  12  to a level position. 
     FIGS. 2 and 3 illustrate a position sensing arrangement interposed between boom assembly  14  and central frame member  15  for detecting when the angle of boom assembly  14  relative to chassis  12  reaches a predetermined threshold. Referring to FIG. 2, the position sensing arrangement includes a rod  54  mounted to a plate  56  through a pivotable mounting arrangement  58 . Plate  56  is one of a pair of such plates mounted to the underside of boom assembly  14 , and the rod of one of slave cylinders  30  is pivotably mounted to and between the plates such as  56 . Rod  54  extends through a guide member  60  mounted to the cylinder end of slave cylinder  30 . A proximity switch  62  is also mounted to the cylinder end of slave cylinder  30 , below guide member  60 . 
     FIG. 3 illustrates boom assembly  14  raised relative to central frame member  15  by operation of lift cylinders  26 . Such movement of boom assembly  14  results in extension of slave cylinders  30 , which causes rod  54  to be moved within guide member  60  along with the rod of slave cylinder  30 . That is, rod  54  moves along with the rod of slave cylinder  30 , and guide member  60  functions to maintain the longitudinal axis of rod  54  parallel to the longitudinal axis of slave cylinder  30 . When boom assembly  14  attains a predetermined angle relative to central frame member  15 , the end of rod  54  reaches proximity switch  62 , which is then actuated to in turn initiate the brake actuator mechanism and the frame leveling speed control of the present invention. In a representative embodiment, the predetermined angle of boom assembly  14  relative to central frame member  15  may be 60°, although it is understood that any angle as desired could be selected. 
     FIG. 4 is a partial schematic diagram of the electrical system of forklift  10  interconnected with proximity switch  62 . As shown in FIG. 4, the electrical system includes a parking brake switch  64  and a relay  66 . In turn, relay  66  is interconnected with a level speed control solenoid  68 , a parking brake actuator solenoid  70 , and a pair of stabilizing cylinder solenoids  72 . In operation, when proximity switch  62  is opened by movement of the end of rod  54  over proximity switch  62 , proximity switch  62  functions to actuate relay  66  and to simultaneously actuate parking brake switch  64  to engage the parking brake of forklift  10 . Alternatively, manual actuation of parking brake switch  64  by the operator functions to actuate relay  66 . When this occurs, power is supplied to level speed control solenoid  68  and power is cut off to parking brake solenoid  70  and stabilizing cylinder solenoids  72 . 
     FIG. 5 illustrates a portion of the hydraulic circuit of forklift  10  containing level speed control solenoid  68  and stabilizing cylinder solenoids  72 . Level speed control solenoid  68  is interconnected in a frame leveling valve, shown schematically at  74 , and controls the position of a level speed control valve  75 . Level speed control valve  75  is connected in a line  76 , which in turn is connected to a three-position four-way leveling frame control valve  78  through a line  80 . A flow restrictor  82  is positioned in branch line  80 . 
     Level speed control valve  75  is spring-biased toward a normal flow position, as shown in FIG.  5 . Upon actuation of level speed control solenoid  68  as described above, level speed control valve  75  is forced to a check position, in which the flow of fluid in line  76  is cut off and fluid is supplied to frame leveling valve  78  through line  80  and flow restrictor  82 . When this occurs, a reduced flow of fluid is supplied to the frame leveling cylinder, shown in FIG. 5 at  84 , thereby slowing the speed of leveling of forklift  10  when boom assembly  14  is above the predetermined angle relative to central frame member  15 . Illustratively, flow restrictor  82  may provide approximately a 90% reduction in fluid flow to frame leveling cylinder  84 . 
     As noted previously, power to stabilizing cylinder solenoids  72  is cut off when boom assembly  14  is above the predetermined angle relative to central frame member  15 . When this occurs, a pair of stabilizing cylinder control valves  86 , (FIG.  5 ,) are spring-biased from a flow position, which provides normal operation of stabilizing cylinder  52 , to a check position, as shown in FIG. 5, which combines with check valves  88  to prevent fluid from flowing into or out of stabilizing cylinder  52 . This functions to lock stabilizing cylinder  52  in position so as to prevent movement of stabilizing cylinder  52  when leveling cylinder  84  is being operated in response to leveling control valve  78 . 
     With this system, movement of boom assembly  14  to a predetermined angle relative to central frame member  15  automatically results in application of the parking brake of forklift  10 , locking of stabilizing cylinder  52  and actuation of level speed control valve  75  to restrict the flow of fluid to frame leveling cylinder  84 , to prevent movement of fork lift  10  and to provide slow frame leveling when boom assembly  14  is raised above the predetermined angle. In addition, stabilizing cylinder  52  is locked and level speed control valve  75  is actuated upon manual engagement of the vehicle&#39;s parking brake, regardless of the position of boom assembly  14  relative to central frame member  15 . 
     Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.