HIGH VISIBILITY LIFT TRUCK AND COMBINED UPRIGHT AND CARRIAGE ASSEMBLY AND SIDESHIFT SYSTEM FOR A LIFT TRUCK

Abstract: A lift truck (10) includes an upright assembly (12) having first (16), second (18) and third (20) telescoping mast sections formed from pairs of laterally spaced and interconnected I-beam rails (40, 42 and 44, respectively). A carriage assembly (28) is mounted for movement on the third mast section. Rollers (54, 56) mount the mast sections and carriage assembly together. A drive assembly includes twinned actuating cylinders (58) for connecting the first and second mast sections. A first dead chain (88) connects the first and third mast sections. A second dead chain (92) connects the second mast section and the carriage assembly. A guide rod (96) is connected to the second dead chain and a guide sleeve (98) is mounted to the second dead chain, a guide sleeve (98) is mounted to the second mast section and a stop (100) is mounted on the end of the rod.

Description: HIGH VISIBILITY LIFT TRUCK AND COMBINED UPRIGHT AND CARRIAGE ASSEMBLY AND SIDESHIFT SYSTEM FOR A LIFT TRUCK Technical Field The present invention relates generally to the industrial vehicle field and more particularly, to a lift truck providing both extensive positive (upward above ground level) and negative (downward below ground level) lift capabilities such as required of, for example, "marina" type lifts. Background of the Invention Certain applications of lift trucks require an upright construction that is capable of providing both positive and negative lift from a ground or support level position. For example, such a lift truck is particularly useful for handling boats in and around marinas. The market for such a lift truck has significantly increased in recent years with ever more and more people owning and operating pleasure boats. In the marina setting, lift trucks may be utilized to both lower boats into and raise boat out of the water from an elevated dock or the like. Similarly, such lift trucks may be utilized to raise boats for positioning well above the ground in an overhead storage rack. Heretofore, lift truck designs have been developed for this purpose. One such representative design is disclosed in U.S. Patent 3,841,442 to Erickson et al assigned to the Assignee of the present invention. The lift truck disclosed in the Erickson et al patent includes outer, intermediate and inner, telescoping mast sections with a load carriage elevatable on the inner mast section. The lift truck also includes a pair of actuator cylinders and cooperating chains. These cylinders and chains are connected to the mast sections so that one cylinder and chain set is adapted to elevate the load carriage and the inner mast section above ground level. The other cylinder and chain set is adapted to lower below ground level the load carriage and inner and intermediate mast sections together as a unit in the outer mast section. While the lift truck disclosed in the Erickson et al patent allows positive and negative lift capabilities for effective utilization in a marina setting, it suffers from a number of distinct short¬ comings shared with other state of the art lift truck designs. More specifically, the tandem lift cylinder and chain sets required for positive and negative lift are mounted between the uprights of the masts significantly limiting and in many cases substantially blocking forward visibility. In effect, the reduced forward visibility substantially limits the ability of the lift truck operator to properly orient the forks when picking a boat up or placing a boat in a storage rack berth. Accordingly, a significant potential exists that a boat may be damaged while being picked- up, carried and/or placed with the lift truck. Other shortcomings of state of the art lift trucks include a relatively limited lifting capacity. This directly results from (1) the provision of separate actuator cylinder and chain sets for achieving positive and negative lift configurations; (2) the utilization of heavy gauge steel rails necessary to increase rigidity and (3) the forward location of the mast sections relative to the center axis of the lift truck. The weight of the cylinders and heavy gauge rails as accentuated by the forward placement requires the provision of a heavier, bulkier counterweight. The truck must also be made longer overall to provide a greater moment arm for the counterweight to be effective. Further a more powerful operating engine is also required to obtain the desired performance. Each of these requirements add substantially to the cost of lift trucks. Additionally, state-of-the-art marina lift trucks commonly utilize complicated fork structures and controls. Unfortunately, the fork structures typically require maintenance at relatively short intervals to insure reliable operation. Such maintenance is particularly required at ocean marinas due to the corrosive properties of saltwater environments. Additionally, the complicated controls require the individual to receive extensive training before the lift truck can be effectively operated. Even when fully familiar with the operation of the controls, the manipulation of multiple levers as now required on state of the art lift trucks requires additional time thereby reducing the productivity of even a skillful operator. Another problem typical of prior art lift truck designs relates to the need for an improved fork. Forks presently in use are typically constructed of steel for strength and include a protective cover on the upper surface to cushion and protect a boat hull from direct contact with the steel fork. It has been found, however, that such covers when pinched between the boat hull and the steel fork wear quickly and must be replaced after only a relatively short service life. Additionally, as the covers become worn they have a tendency to retain more and more water when manipulated to lift a boat from the water. Subsequently, when the boat is then positioned in an upper berth of a rack, -the water retained in the covers drips down onto underlying boats. This water often includes contaminants such as rust from the forks and grease or oil from the dock side water. These contaminants may stain the finish and/or furnishings of underlying boats to the dissatisfaction of the boat owners. As a result, customer relations of the marina operator may be adversely affected. From reviewing the above it is clear that a need exists for an improved lift truck providing positive and negative lift capabilities that is particularly adapted for operation in both coastal and inland marinas. Summary of the Invention Accordingly, it is a primary objective of the present invention to provide a lift truck having positive and negative lift capabilities overcoming the above-described limitations and disadvantages of the prior art. Another object of the present invention is to provide a lift truck of compact design including shorter overall length and height having a relatively wide upright assembly with a clear window for improved forward visibility allowing more efficient operation. Still another object of the present invention is to provide a lift truck with significantly enhanced lifting capacity over prior art designs. An additional object of the present invention is to provide a lift truck as well as a combined upright and carriage assembly that furnishes a delayed carriage lift so that the carriage is moved at a relatively low speed when in a negative configuration and at a higher speed when in a positive configuration. Advantageously, the lower speed of the negative configuration improves the stability of operation when the load being handled is partially obscured from sight. The higher speed of movement of the positive lift configuration serves to enhance productivity when the load is in clear sight and the greater speed of operation can be more easily controlled. Yet another object of the present invention is to provide an upright assembly for a lift truck exhibiting increased rigidity. This is achieved through the utilization of shorter rails and a roller configuration wherein at least three pair of rollers capture the nested rails of the upright over a wide span at all positions of operation. Still a further object of the present invention is to provide a carriage assembly including pivotally mounted forks with relatively widely spaced pivot points. The forks also include an inside strut arrangement that cooperates with the wide pivot points to significantly enhance the durability of the design. An additional object of the invention is to provide forks with a unique composite construction that are both light weight and durable. The forks include a curved upper surface member that reduces stress concentrations and spreads the load over a larger area of the load being handled. The forks also include jackets of rubber that are specially contoured to fit tightly and cushion the load on the forks. Still another object of the invention is to provide a hydraulic sideshifter circuit for a lift truck of relatively simple design fully responsive to a single operator control. Advantageously, the sideshifter circuit operates to fully coordinate the movement of both forks and prevent any possibility of passing a fork under the load. Additional objects, advantages, and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and the combinations particularly pointed out in the appended claims. To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, an improved lift truck is provided for transporting, lifting and lowering a load. The lift truck includes an upright assembly formed from first, second and third telescoping mast sections. A carriage assembly is mounted for movement along a path on the upright assembly and more particularly the third mast section. The carriage assembly includes forks for engaging and supporting the load. The lift truck also includes a drive assembly for both the upright assembly and carriage assembly. The drive assembly includes a combination of twinned telescoping, compound hydraulic cylinders and two sets of dead chains that serve to move the carriage assembly at a first relatively slow speed over the first portion of the movement path and at a second, relatively fast speed over the second portion of the movement path. The drive assembly is described in greater detail below. More particularly, the twinned hydraulic cylinders are mounted behind the mast sections where they are protected from damage from inadvertent contact or impact with other objects. Additionally, by mounting the cylinders behind the outer rails of the mast sections, a high visibility window is maintained between the rails providing the operator with excellent forward visibility for more efficient operation of the apparatus. Still more particularly, each of the mast sections comprises a pair of laterally spaced, interconnected telescopic I-beam rails. The second mast section is roller mounted in nested and overlapping relation with the first mast section. Similarly, the third mast section is roller mounted in nested and overlapping relation with the second mast section. The rollers support the second and third mast sections longitudinally and laterally for extensible telescoping movement. More specifically, a series of four pair of rollers are stub shaft mounted to the first mast section so as to engage the outer channel of the I- bea rails of the second mast section. Four rollers engage each rail. One pair of rollers is mounted adjacent the upper end,' one pair is mounted adjacent the lower end and two pair are mounted along a median portion of the first mast section. A similar roller arrangement is provided on the second mast section to support the third mast section. More particularly, four pairs of rollers are rotatably mounted on stub shafts to the rails of the second-mast section for engagement in the outer channels of the rails of the third mast section. One pair of rollers are mounted adjacent the upper end, one pair adjacent the lower end and two pairs along a median portion. Advantageously, the roller arrangement increases the rigidity of the upright assembly by providing multiple rail loading in all lift configurations. As a result the rails and carriage better resist deflection. Thus, bounce and twist are substantially eliminated during operation of the apparatus. Accordingly, it is much easier to position a load in a desired location such as a berth in a boat rack. This is particularly true where little clearance exists between the boat and the top, bottom and sides of the berth. The drive assembly allows control of the lift configuration of the combined upright and carriage assembly through manipulation of a single operator control. More particularly, the twinned actuating cylinders are positioned so as to extend between mounting brackets on a cross bar at the lower end of the first mast section and a tie bar at the upper end of the second mast section. A first pair of dead chains operatively connects the first and third mast sections. One dead chain is provided adjacent each side of the upright assembly. Each of the dead chains has one end anchored to a lower U-shaped tie of the first mast section and the other end anchored to a bracket on the third mast section. Additionally, each of the dead chains is played over a sheave mounted adjacent the top of the second, intermediate mast section. A lift linkage including a second pair of dead chains operatively connects the second mast section with the carriage assembly. One dead chain is provided adjacent each side of the upright assembly. Each of the dead chains has one end anchored to a bracket on the carriage assembly. Individual guide rods are connected to the opposite end of each chain. The two guide rods are freely received in a pair of cooperating guide sleeves mounted to the second mast section. A stop is provided at the end of each of the guide rods to abut and engage with the cooperating guide sleeves. When it is desired to lower or raise the upright and carriage assembly from any negative lift configuration, the guide rods slide freely through the guide sleeves. This action prevents relative movement between the carriage assembly and the third mast section. Consequently, the drive assembly functions to maintain the carriage assembly in its lowermost position on the third mast section at ground level and at any negative lift configuration. This insures that when the carriage assembly clears ground level all the mast sections will also clear ground level. Thus, the operator then knows that the lift truck may be moved to transport the load to a new location. Further, since the only relative movement at any negative lift configuration is between the first and second mast sections and the second and third mast sections, the load is being moved at a relatively slow 2-1 ratio for increased stability. In contrast, when the drive assembly is engaged to either raise or lower the upright and carriage assembly from any positive lift configuration, the stops at the ends of the guide rods are abutting and engaging the guide sleeves. Accordingly, the carriage assembly moves up or down relative to the third mast section in conjunction with up or down movement of the second mast section relative to the first mast section and up or down movement of the third mast section relative to the second mast section respectively. Accordingly, the carriage assembly moves at a 3-1 ratio in any positive lift configuration. This additional speed serves to increase productivity. In accordance with a further aspect of the present invention the carriage assembly includes a frame formed from a pair of transversely spaced, vertically extending lift brackets and a pair of vertically spaced horizontally extending upper and lower fork bars. Three pairs of rollers are mounted to the lift brackets with three rollers on each bracket engaging the opposing inner channels of the I- beam rails forming the third mast section. Forks for supporting a load are pivotally mounted to the frame at the upper fork bars by means of pivot pins. Additionally, a pair of actuators are provided for driving the forks about the pivotal mounting to any selected position. Each fork also includes an inwardly depending strut that has a rearwardly directed surface for bearing against the lower fork bar in any assumable fork position. Advantageously, these struts serve to rigidify the forks and substantially eliminate application of right angle forces to the pivotal mounting thereby significantly increasing both overall service life and intervals between maintenance. Each of the forks is of composite construction including a box beam foundation and curved upper surface support member. A jacket of rubber material, preferably reinforced with polyester cord is received over and around each fork. The jacket may be held in position on the fork by means of a band clamp adjacent the fork heel. Additionally, a skid plate is mounted beneath the heel of the forks to protect both the forks and particularly the covering jackets from damage through engagement with the ground. In accordance with yet another aspect of the present invention, a unique sideshifter circuit is provided for selectively shifting the forks of a lift truck to the left or right. The sideshifter circuit includes a single operator control that is connected to a directional control valve. Pressurized fluid is fed from the directional control valve through a valve housing operatively positioned in the feed line between the directional control valve and the fork actuators. The valve housing includes four piloted check valves and one shuttle check valve. Additionally, the valve housing includes two ports connected to the directional control valve with the shuttle valve connected across those ports. Lines are also provided for feeding fluid from the shuttle check valve to the piloted check valves. This fluid acts as a pilot signal to open those check valves. The valve housing also includes two actuator ports and two diverter ports with one piloted check valve controlling fluid flow through each of the actuator ports and diverter ports. One actuator port is connected to the rod end of one fork actuator with the other actuator port connected to the rod end of the other fork actuator. Similarly, one diverter port is connected to the base end of one fork actuator and the other diverter port is connected to the base end of the other fork actuator. Advantageously, the sideshifter circuit operates to shift the forks in a coordinated manner in the same direction and at the same speed. Thus, by the convenient manipulation of a single operator control the forks may be shifted to either the left or right as desired to align the forks with the load being picked up or to align the load for positioning in, for example, an overhead berth. The coordinated movement between the forks serves to minimize rocking of the load during shifting. Additionally, the movement insures that one fork is not passed under the load. In prior art designs this has been a prevalent problem. As a fork is passed under the load, the load becomes unstable. It should be appreciated that the sideshifter circuit serves to automatically stop movement of both forks when one of the forks reaches its limit of travel. This also prevents the inadvertent passing of one fork under the load under circumstances where this problem could not have been prevented in prior art designs. Advantageously, the described lift truck provides a number of benefits over prior art designs. The drive assembly for the combined upright and carriage assembly capably moves both the second and third mast sections into positive and negative lift configurations through operation of the twinned cylinders. By elimination of the need for a second cylinder and chain set for attaining a negative lift configuration as required in prior art designs, significant weight savings also result. Further, since both the intermediate and inner mast sections are movable into positive and negative lift configurations, the overall length of the individual mast sections may be reduced over prior art designs such as discussed above in the Erickson et al. Patent U.S. 3,841,442. These design features result in significant weight savings that in conjunction with the positioning of the load closer to the center axis of the truck serve to significantly increase lifting capacity of the present apparatus when compared with lift trucks of state-of-the-art design having similar weight and power. The reduction in the required counterweight and power requirements significantly enhances the efficiency of operation of the apparatus while also representing significant capital savings for the owner/purchaser. Still other objects of the invention will become readily apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention simply by way of illustration of one of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modifications in various, obvious aspects all without departing from the invention. Accordingly, the drawing and descriptions will be regarded as illustrative in nature and not as restrictive. Brief Description of the Drawing The accompanying drawing incorporated in and forming a part of the specification, illustrates several aspects of the present invention, and together with the description serves to explain the principles of the invention. In the drawing: Figure 1 is a perspective view of a lift truck of the present invention shown holding a boat in a carrying position wherein the operator has a clear view between the side rails of the upright assembly and beneath the bottom of the boat hull; Figure 2 is a perspective view of the lift truck wherein the upright is shown in a negative lift configuration engaging a boat at dockside; Figure 3 is a rear quarter perspective view of the combined upright and carriage assembly of the present invention particularly showing the drive assembly; Figure 3A is a schematical circuit diagram showing one circuit for controlling the operation of the main lift cylinders; Figure 4 is a side elevational view of the upright and carriage assembly in a full negative lift configuration showing the engagement of the rollers with the various mast sections; Figure 5 is a partially schematic, side elevational view similar to Figure 4 showing the upright and carriage assembly in a ground level configuration showing the roller engagement and the mounting of the upright assembly to the frame of the lift truck; Figure 6 is a side elevational view similar to Figures 4 and 5 showing the combined upright and carriage assembly in a full positive lift configuration once again showing the roller engagemen ; Figure 7 is an enlarged plan view of the upright assembly shown partially in section; Figure 8 is an exploded view showing the lift linkage connecting the carriage assembly and the intermediate mast section of the upright assembly; Figure 8A is a schematical view in detail showing the operation of the lift linkage including the guide rods and guide sleeves; Figure 9 is a fragmentary and partially sectional front elevational view showing the carriage assembly in a full positive lift configuration including the hydraulic hoses feeding the fork actuators; Figure 10 is view similar to figure 9 but showing the carriage assembly alone and demonstrating the relative pivotal movement of the forks; and Figure 11 is a schematical circuit diagram showing the sideshifter circuit for shifting the forks of the lift assembly of the present invention; Reference is now made in detail to the preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Detailed Description of the Invention Referring now to the drawing figures and particularly figures 1 and 2, the apparatus 10 of the present invention is shown. As described in greater detail below, the apparatus 10 provides both extensive positive (upward above ground level as shown in figure 1) and negative (downward below ground level as shown in figure 2) lift capabilities. Such capability is particularly suited for "marina" type lifts where it is necessary to lower boats into and raise boats out of the water from an elevated dock D. It should be appreciated, however, that the apparatus 10 of the present invention is adapted for uses other than those associated with a marina, that the marina setting is only being utilized as an example and that the broader aspects of the invention should not be limited thereto. As shown, the apparatus 10 includes an upright assembly 12. The upright assembly 12 is pivotally mounted to a truck T by means of pins 13 received in cooperating dual mounting brackets 14 mounted to the mast section 16 and a pair of mounting yokes Y on the truck frame. Thus, the upright assembly 12 is pivotally mounted in front of and adjacent the top of the front wheels W (see particularly figure 5) of the truck T. This mounting serves to move the upright assembly 12 and the load carried thereby back toward the front axle F and center axis of the truck T. As a consequence, a smaller counterweight may be utilized. Additionally, less of a moment arm is required for the counterweight and consequently the overall length of the truck T may be shortened. This advantageously serves to increase the overall maneuverability of the apparatus 10 and even allows closer spacing between boat berthing racks in a storage facility. As described in greater detail below in the section entitled "Combined Upright and Carriage Assembly", the upright assembly 12 includes first, second and third telescoping mast sections 16, 18, 20 respectively (see also figures 3 and 7) . These mast sections 16, 18, 20 are nested in overlapping relation to each other. Fore and aft tilting movement of the upright assembly 12 including the mast section 16,18, 20 is controlled by a pair of tilt cylinders 22 (one of which is shown) which are connected to opposite sides of the mast section 16 in a manner known in the art. The truck T is also of a type known in the art including an operator cab C. The cab C is mounted on a frame/chassis supported by ground engaging wheels W. The truck T is powered by a motor (not shown) such as a turbocharged diesel engine. A carriage assembly 28 is mounted for movement along a path on the mast section 20. As described in greater detail below in the section entitled "Combined Upright and Carriage Assembly" the carriage assembly 28 includes a pair of forks 30 pivotally mounted by means of pins 32 to an upper fork bar 34. The gap or distance between the forks 30 is controlled by a pair of actuators 36. By varying the space or gap, the forks 30 may be utilized to engage the hull of a boat B so that the boat may be lifted, transported and lowered as desired using the apparatus 10. As described in greater detail below, the individual mast sections 16, 18, 20 of the upright assembly 12 and the carriage assembly 28 are driven in a unique manner to provide positive and negative lift configurations utilizing a single drive cylinder. Preferably, the cylinder is twinned and mounted to the apparatus 10 so as to be nested directly behind the mast sections 16, 18 (see figure 3). Advantageously, in this way a substantially unobstructed view is provided between the outer rails of the mast sections 16, 18, 20. Hydraulic hoses H that feed the fork actuators 36 are routed within the upright assembly 12 to further improved visibility. Additionally, as described in greater detail below, the need for hose reels extending laterally outside the upright assembly 12 as provided for in prior art designs is eliminated. The resulting increased visibility allows the operator to more effectively guide the apparatus 10 and more accurately and better position the boat B on the forks 30 so as to allow placement in a rack berth. Further, by eliminating the hose reels and moving the hoses H within the upright assembly 12 where they are protected, the problem of snagging hoses on objects common to prior art designs is avoided. One possible circuit for controlling the operation of the cylinders 58 is shown in figure 3A. As shown, a single lift control lever 160 is operatively connected to a directional control valve 162 for selectively connecting a pressurized fluid source 118 and sump 120 to the cylinders 58. When the lever 160 is moved in a first direction, pressurized fluid is directed from the source 118 through the directional control valve 162 and the feed line 164 to the port 166 of the locking valve 168 at the base of each cylinder 58. From there, the fluid passes through the check valves 170 and 172 into the base of the cylinders 58 causing the cylinders to expand and raise the intermediate mast section 18 relative to the mast section 16. Simultaneously, fluid pressure is released from the pilot feed line 174 with fluid in the feed line 174 returning to the sump 120. When the lever 160 is moved in the opposite direction, pressurized fluid is directed from the source 118 through the directional control valve 162 into the pilot feed line 174. The resulting fluid pressure in the line 174 pilots the check valves 170 open. As a result, pressurized fluid is released from the cylinders 58 which then retract, lowering the intermediate mast section 18 relative to the mast section 16. More specifically, the fluid from the cylinders 58 bypasses the check valves 172 by flowing through the restrictor valves 176 which control the flow rate and, therefore, the rate of descent. The fluid passing through the restrictor valves 176 then passes through the check valves 170 held open by the pressurized fluid from the pilot feed line 174. Next, the fluid returns to the sump 120. A pressure relief valve 178 limits the pressure in the pilot feed line 174. As should be appreciated, unless a pilot signal is provided through the feed line 174 or the check valves 170 are manually opened through operation of the actuators 180, any lowering of the mast section 18 relative to the mast section 16 is prevented as flow of fluid from the cylinders 58 is blocked. Combined Upright and Carriage Assembly As described briefly above, the upright assembly 12 includes first, second and third mast sections 16, 18, 20 in telescoping relation to each other (see figure 7). Each mast section 16, 18, and 20 comprises a pair of laterally spaced interconnected telescopic I-beam rails 40, 42, 44 respectively. As best shown in figure 7, the rails 40, 42, and 44 are mounted in nested and overlapping relation to each other. Accordingly, the first or outer mast section 16 receives the second or intermediate mast section 18 which receives the third or inner mast section 20. More specifically, the pair of parallel transversely spaced I-beam rails 40 of the outer mast section 16 are secured together by upper and lower U- shaped ties 46 and a cross bar 48. The inner opposed channels of the rails 40 are arranged to receive the rails 42 of the intermediate mast section 18. A plurality of vertically spaced transverse tie bars 50 connect together the rear flanges of the I-beam rails 42. The inner opposed channels of the rails 42 are arranged to receive the rails 44 of the inner mast section 20. A plurality of vertically spaced transverse braces 52 connect together the rear flanges of the I-beam rails 44. The U-shaped ties 46, cross bar 48, tie bars 50 and braces 52 are arranged so that they pass inside of each other as required during positive and negative lift of the mast sections 16, 18, 20 as described below. Thus it should be appreciated that there is no interference between the braces of the mast sections during telescopic movement in either direction. As shown, intermediate mast section 18 is nested within outer mast section 16 in such a manner that the forward flanges of I-beam rails 42 are disposed outside of the forward flanges of the I-beam rails 40 and the rearward flanges of I-beam rails 42 are disposed within the channel forwardly of the rear flanges of the rails 40. The inner mast section 20 is nested within the intermediate mast section 18 in an identical manner. A first set of four pairs of rollers 54 are rotatably mounted on stub shafts to the web of the rails 40 of the first or outer mast section 16. The rollers 54 are suitably mounted to support the intermediate mast section 18 longitudinally and laterally for extensible telescoping movement relative to the outer mast section 16. More particularly, the rollers 54 extend through suitable cut-outs in the forward flange of the rails 40 and engage in the outer flanges of the I-beam rails 42 of the intermediate mast section 18. As should be appreciated, four rollers 54 are mounted to each I-beam rail 40 of the mast section 16 (see also figures 3, 4 and 6). One pair of rollers 54 is mounted adjacent the upper end, one pair is mounted adjacent the lower end and two pair are mounted along a median portion of the mast section 16. Advantageously, the arrangement of the rollers insures that at least three pair engage the intermediate mast section 18 at all times even when in the fully raised and fully lowered positions. A similar roller arrangement is provided on the intermediate mast section 18. More particularly, a second set of four pairs of rollers 56 are rotatably mounted on stub shafts to the web of the rails 42 of the intermediate mast section 18. The rollers 56 are suitably mounted to support the inner mast section.20 longitudinally and laterally for extensible telescoping movement relative to the intermediate mast section 18. More particularly, the rollers 56 extend through suitable cut-outs in the forward flanges of the rails 42 and engage ' in the outer flanges of the I- bearo rails 44 of the inner mast section 20. Four rollers 56 are mounted to each rail 42 of the mast section 18 with one pair of rollers mounted adjacent the upper end, one pair of rollers mounted adjacent the lower end, and two pairs of rollers mounted along a median portion. Here again, the arrangement of the rollers insures that at least three pairs of rollers engage the inner mast section 20 at any time even when in the fully raised or fully lowered position (again, see also figures 3, 4, and 6). If necessary, it should be appreciated that additional roller pairs may be mounted along the median portions of the mast sections 16, 18 to insure wide span, three point arrangement. Accordingly, the reference to four pairs of rollers 54 and 56 should only be considered exemplary of one possible roller arrangement. The arrangement of the rollers 54 insures that a relatively wide span is always maintained between the rollers 54 engaging the intermediate mast section 18. A similar wide span of engagement is maintained between the rollers 56 engaging the inner mast section 20 (see particularly figures 4 and 6) . Advantageously, the multiple points of engagement over a relatively wide span provide a more rigid structure that effectively minimizes play and reduces bounce, twisting and bending during operation of the apparatus 10. Accordingly, deflection at the front end of the boat B held on the forks 30 is significantly reduced. This allows the operator to position the boat with certainty in a rack berth and significantly reduces the potential for inadvertently damaging the hull by engagement with the rack. It should also be appreciated that the upright assembly 12 provides significant improvements in forward visibility. These allow the operator to more effectively and efficiently guide the operation of the apparatus 10 lending to significant increases in operator productivity. More particularly, the raising and lowering of the mast sections 18 and 20 as well as the carriage assembly 28 may be completed by simply actuating a single lever that controls the operation of the twinned telescoping compound hydraulic cylinders 58. As best shown in figure 3, the cylinders 58 are mounted so as to nest directly behind the rails 40, 42 of the mast sections 16, 18. Advantageously, the rails 40, 42 effectively serve to protect the cylinders 58 from inadvertent collision damage. Additionally, this positioning of the cylinders 58 serves to leave the space between the left and right hand rails of the mast sections 16, 18, 20 open for maximum forward visibility. In fact a visibility window approximately 40 inches wide between the innermost rails 44 is provided to aid the operator in guiding the apparatus 10. By eliminating the mounting of actuator cylinders between the rails of the upright assembly 12 and widening the overall assembly, it is also possible to mount the hydraulic hoses H that feed the fork actuators 36 within the assembly. As shown in figure 3, the hoses H (only one shown) are clamped to the outer surface of the mast section 16 between the cross bar 48 and the intermediate U-shaped tie 46. The hoses H are then routed through an opening in the side of the lower flange 47 of the tie 46 and fixed in a bracket (not shown) at the front face of the tie. From there, the hoses H are played over a pair of sheaves 60 mounted on stub shafts at the upper end of the intermediate mast section 18. The hoses H are then extended downwardly from the sheaves 60 and fixed to the lowermost cross brace 52 on the inner mast section 20. From there each of the hoses H extends through a tube 62 that is anchored to the intermediate and upper cross braces 52 of the inner mast section 20 (see figure 9: tube is not shown in figure 3 for clarity of presentation of other structure) . Each of the hoses H hangs down from the tube 62 and top cross brace 52 of the inner mast section 20 in a J-shaped loop with the distal end of the loop anchored to the upper fork bar 34 of the carriage assembly 28. From there, the hoses H feed the individual fork actuators 36. Advantageously, by routing the hoses H inside the upright assembly 12, hose reels and related plumbing are eliminated. Not only is the simplified structure of the present hose routing system less expensive to produce but it also is more reliable. More specifically, the hoses H are now maintained inside the upright assembly 12 and inside plastic tubes 62 where they are protected from damage and inadvertent snagging on objects. Carriage Assembly As indicated above, the carriage assembly 28 is mounted for relative movement along a path on the inner mast section 20. As best shown in figures 9 and 10 the carriage assembly 28 includes a frame comprising a pair of transversely spaced vertically extending lift brackets 66 and horizontally extending upper and lower fork bars 34 and 68 respectively. The lift brackets 66 and upper and lower fork bars 34, 68 are preferably formed from steel and secured together as by welding to form a rigid frame. A series of rollers 70 are stub shaft mounted to the lift brackets 66 (see also figure 8) . Preferably, three pairs of rollers 70 are utilized with three rollers mounted to each lift bracket 66. The rollers 70 are adapted to mesh in the inner channels of the I-beam rails 44 of the inner mast section 20 (see also figure 7) . The rollers 70 serve to support the carriage assembly 28 for relative movement within the inner channel portions by riding along the forward and rearward flanges of the I-beam rails 44. The forks 30 of the carriage assembly 28 are substantially L-shaped (see figures 4 and 9) . The shanks of the forks 30 are pivotally mounted at their proximal ends to the upper fork bar 34 by means of pins 32. A pair of actuators 36 mounted to the upper fork bar 34 provide control of the movement of the forks 30 about the pivot pins 32. More particularly, one actuating cylinder 36 includes an extensible rod 72 attached by means of a pivot pin to a flange 74 on one of the forks 30. Similarly, the other actuator cylinder 36 includes an extensible rod 72 mounted by means of a pivot pin to an inwardly extending flange 74 on the other fork 30. When the rods 72 are extended from the actuators 36, the forks 30 pivot outwardly in the direction of action arrows A (see figure 10) . Conversely, as the extensible rods 72 are retracted, the forks 30 move in the direction of action arrow B. It should be appreciated that the actuators 36 are independently operable to provide for independent movement of each fork 30 throughout the full range of allowed motion. The operating circuit for the actuators 36 is described in greater detail below in the section entitled "Sideshifter Circuit". Advantageously, it should be appreciated that the fork pivot points are widely spaced (ie. approximately 72" apart) . This wide stance insures that the shanks of the forks 30 are nearly vertical when carrying most boats. Accordingly, the pivot pins 32 are only loaded vertically in most instances. As a result, angular force moments along the pivot pin axis, that have a tendency to deform the pivot seals and expose the assembly to the corrosive salt water environment, are substantially eliminated. Improved durability results. As also shown in figures 9 and 10 an inwardly extending strut 76 is mounted to the shank of each fork 30. Each strut 76 includes a rearwardly directed surface for bearing against the lower fork bar 68. Preferably, the bearing surface is formed from a durable low-friction material such as nylon. As should be appreciated from reviewing the drawing figure, each strut 76 is designed so as to engage and bear against the lower fork bar 68 in all possible positions of the forks 30. This engagement insures that the forks 30 are rigidly supported and also enhances durability by substantially preventing the application of right angle forces axially along the pivot pins 32 when the forks are under load. Advantageously, the strut arrangement also allows capacity loads to be lifted even when the forks 30 are fully expanded. Consequently, the carriage assembly 28 can function as if it were nearly twelve feet wide and effectively support wide beam boats with utmost stability. As should be appreciated from viewing figure 9 showing the forks 30 in section, the horizontally extending leg of each fork 30 which supports the load includes a box beam foundation 78 and a curved upper surface support member 80. The curved support member 80 eliminates knife edge corner loading and provides a large contact surface with a boat hull. This serves to advantageously spread the load across a larger surface area of the hull so as to significantly reduce stress concentrations that could otherwise crack a fiberglass hull in larger, heavier boats. Preferably, both the box beam foundation 78 and upper surface support member 80 are formed from steel for sufficient strength. The box beams 78 and support member 80 are also sealed to prevent water entrance when submerged when, for example, being positioned below a boat to be raised from the water. The forks 30 are also gradually tapered from the heel, adjacent the shank, to the toe (see figures 4 and 10) . Preferably each fork has a ten foot bottom taper to approximately a four inch thickness at the toe. This taper makes it easier for the operator to remove boats from trailers and guide the forks 30 between a boat hull and a rack without damaging the rack. Further, this is accomplished without sacrificing the strength and stiffness needed at the heel to support large boats 30 to 35 feet in length. The forks 30 are covered with a durable non- marking rubber jacket 82 that fits snugly and may be easily replaced (see figures 4 and 9) . Preferably, the rubber jacket 82 is reinforced with polyester cord to provide a longer service life. The jacket 82 is slipped over the toe of a fork 30 and secured in position at the heel by means of a band clamp 84. Advantageously, the jacket material and the snug fit insure that a minimum amount of water is retained in the jacket 82. Accordingly, dripping that causes stains on underlying craft when positioning a boat in an upper berth of a rack is substantially reduced. Further, since the jacket 82 covers the entire periphery of the fork 30 on which it is received, the steel fork is protected from direct engagement not only with the boat hull but also the rack in which a boat is being placed. Accordingly, rack damage is minimized including the chipping and scraping of paint from the rack. This is significant as salt water dripping from overlying boats can quickly corrode the exposed steel surface of a rack. Rust from the rack may then drip onto underlying boats staining the finish and furnishings. Advantageously, the present fork design significantly reduces this problem. Periodically it is desirable to rotate the jackets 82 relative to the forks 30 to extend their service life. This may be achieved by simply loosening the associated band clamps 84 and utilizing the apparatus 10 to lift and place several boats B. As this is done, the engagement of the boats B with the forks 30 serves to rotate the jackets 82 and bring a new portion of the jackets into engagement with the hull of the boat B. Once the jackets 82 are rotated approximately 90 degrees, the band clamps 84 may be retightened to hold the jackets in their new position. In order to protect the jackets 82 from damage through engagement with the ground, a skid plate 86 of heavy steel is mounted beneath the heels of the forks 30. Operation of the upright and carriage assembly of the apparatus 10 of the present invention will now be described in detail. Drive Assembly As briefly mentioned above, the drive assembly of the present invention allows the operator to control the positioning of the movable mast sections 18, 20 and the carriage assembly 28 through manipulation of a single control lever 160 (see figures 3, 3A and 8). More particularly, the drive assembly operatively connects the mast sections 16, 18, 20 of the upright assembly 12 and the carriage assembly 28 together. The twinned telescoping actuating cylinders 58 operatively connect the outer and intermediate mast sections 16, 18. One end of each of the twinned cylinder 58 is mounted in a bracket on the cross bar 48 of the outer mast section 16 with the opposite end mounted in another bracket on the upper tie bar 50 of the intermediate mast section 18. A first flexible member or dead chain 88 operatively connects the stationary mast section 16 with the inner mast section 20. As shown, one dead chain 88 is provided adjacent each side of the upright assembly 12. Each of the dead chains 88 has one end anchored to the lower U-shaped tie 46 of the outer mast section 16 and the other end anchored to a bracket on the intermediate mast section 18. Each of the chains 88 is also played over a sheave 90 mounted adjacent the top of the intermediate mast section 18. A lift linkage including a second flexible member or dead chain 92 operatively connects the intermediate mast section 18 and the carriage assembly 28. Again, one dead chain 92 is provided adjacent each side of the upright assembly 12. Each dead chain 92 has one end anchored to a bracket 93 on the carriage assembly 28. Further, each dead chain 92 is played over a sheave 94 mounted adjacent the top of the inner mast section 20. In accordance with an additional feature of the present invention, a speed control governing movement of the carriage assembly 28 is built into the present design to insure maximum load control while optimizing productivity. More particularly, it should be appreciated by reviewing figures 3-6 and 8 that the ends of the second dead chains 92 that are mounted to the intermediate mast section 18 are formed by guide rods 96. The guide rods 96 are received for free sliding engagement within cooperating guide sleeves 98 mounted to an intermediate tie bar 50 of the mast section 18. A stop 100, in the form of a nut, is screwed onto threads at the distal end of each guide rod 96. Locking nuts 102 may be similarly threaded into position to engage the stop nut 100 and hold it in position. The function of the drive assembly, including the guide rods 96, guide sleeves 98, and stop nuts 100 will now be described in detail. In order to lower the upright assembly 12 and carriage assembly 28 from a ground level to negative lift configuration (ie. from the configuration shown in figure 5 to the configuration shown in figure 4) the actuating cylinders 58 are retracted. Accordingly, the cylinders 58 directly draw the intermediate mast section 18 downwardly relative to the stationary outer mast 16. As this is done, a gradually increasing length of the dead chains 88 is played out over the sheaves 90. This causes the inner mast section 20 to be gradually extended more and more downwardly from the intermediate mast section 18. The downward movement of the inner mast section 20 with respect to the intermediate mast section 18 causes a gradually increasing length of the second dead chains 92 to be played out over the sheaves 94. The relative position of the carriage assembly 28 on the inner mast section 20, however, remains unaltered. More specifically, as the carriage assembly 28 is lowered from the ground level position to a negative lift configuration, the guide rods 96 slide freely through the guide sleeves 98 (note action arrows C in figure 8 wherein the guide rods 96 move from the phantom line position at ground level to the full line position when fully lowered) . This essentially serves to disengage the dead chains 92 thereby preventing any relative movement of the carriage assembly 28 on the inner mast section 20. The same result occurs as the carriage assembly 28 is raised and returned to the ground level position (note action arrows D in figure 8 wherein the guide rods 96 move from the full line position when fully lowered to the phantom line position at ground level) . Accordingly, it should be appreciated that the carriage assembly 28 remains at the bottom of the inner mast section 20 at ground level and all negative lift configurations. When the upright assembly 12 and carriage assembly 28 are moved from the ground level position to the fully raised position (ie. from the position shown in figure 5 to the position shown in figure 6) the actuating cylinders 58 are extended. This directly results in the raising of the intermediate mast section 18 relative to the outer mast section 16. With the raising of the intermediate mast section 18, the length of the first dead chains 88 played out over the sheaves 90 is gradually shortened. This causes the inner mast section 20 to be extended and moved upwardly relative to the intermediate mast section 18. The relative movement of the inner mast section 20 in turn causes the length of the dead chains 92 played out over the sheaves 94 to be gradually shortened. Since the stop nuts 100 are in abutting engagement and capture the guide sleeves 98 at the ground level position and above (note phantom line position in figure 8) , the dead chains 92 are now engaged. As a result, the carriage assembly 28 is moved upward relative to the inner mast section 20 until it is fully extended in its uppermost position as shown in figure 6. Whether raising or lowering an article with the apparatus 10, a single operator control 160 is all that needs to be manipulated. Additionally, it should be appreciated that the drive assembly between the upright assembly 12 and carriage assembly 28 is effectively designed so that at ground level, the carriage assembly 28 is always in its lowermost position on the inner mast section 20. Thus, as soon as the carriage assembly 28 and particularly the forks 30 clear ground level, the operator is assured that each of the mast assemblies 18, 20 has also cleared ground level. Accordingly, the operator can quickly and easily confirm when the necessary clearance is present to allow him to back away from the dock D. In prior art designs where separate controls and cylinder and chain sets are required for extension and retraction of the mast assemblies and raising and lowering of the carriage assembly, this is not necessarily true. For example, depending on the particular manipulation of the controls, the situation can arise where the carriage assembly and the boat maintained on the forks is above ground level while one or more of the mast sections is still extended below ground level. Under these circumstances, any attempt to back away from the dock D meets with the engagement of the downwardly extended mast section into the front edge of the dock D. Such an impact could damage the dock D or mast section. Advantageously, this potential problem is avoided with the apparatus 10 of the present invention. Operating efficiency are also enhanced with the present design. Since the mast sections 18 and 20 are both being extended upwardly at the same time that the carriage assembly 28 is moving upwardly relative to the mast section 20, the speed of the upward movement of the boat is enhanced (resulting in a 3 to 1 ratio) . This is at a time when the boat is in the direct view of the operator and the additional speed can be more readily controlled to position the boat at the proper level for placing the boat in an overhead berth. In contrast, a slower relative speed of movement of the boat is provided when lowering the boat to a negative lift position below ground level. This is due to the fact that while the mast sections 18 and 20 are being lowered, there is no relative movement of the carriage assembly 28 on the inner mast section 20 (resulting in a 2 to 1 ratio) . The relatively slower movement of the boat when in a negative lift configuration advantageously allows the operator better control when lowering the boat over the dock edge down into the water. This is a significant advantage where the operator's vision is partially obscured by the boat and the dock itself. Further, it should be appreciated that reliable operation is insured through the provision of the twinned cylinders 58 and dual dead chains 88 and 92 that provide redundant load support. Sideshifter Circuit In accordance with an additional aspect of the present invention, the apparatus 10 may incorporate a unique sideshifter circuit 110, shown schematically in figure 11. More specifically, when using a lift truck to handle a variety of loads with differing shapes and sizes such as boats in a marina, it is desirable to be able to move each fork independently. This allows the operator to better position each of the forks around and under the boat. It is also desireable to be able to sideshift the boat while elevated in order to make minor lateral adjustments as the boat is set into place or to center the boat relative to the truck before transport. As indicated above, the forks 30 are pivotally mounted to the carriage assembly 28 by means of the pivot pins 32 received in the upper fork bar 34. A pair of actuator cylinders 36 having a base end mounted to the upper fork bar 34 and a rod end attached by means of brackets 74 to the forks 30 control the positioning of the forks. The left and right forks 30 may be independently positioned by manipulation of the control levers 112, 114 respectively. As shown, the control lever 112 is operatively connected to a directional control valve 116 that controls flow between a pressurized fluid source 118, the actuator 36 controlling the left fork 30 and a sump 120. Similarly, the control lever 114 is directly connected to a directional control valve 122. This control valve 122 controls flow between the pressurized fluid source 118 the actuator 36 connected to the right fork 30 and the sump 120. By manipulating the control levers 112 and 114 and hence the directional control valves 116 and 122, the rods of the actuators 36 may be independently and selectively retracted and extended to narrow or widen the spacing between the forks 30. In prior art lift truck designs, it is only possible to sideshift the forks utilizing the two control levers that independently control the left and right forks; that is control levers equivalent to the levers 112 and 114 described above. Convention dictates that when the two control levers are actuated in the same direction, the forks move together or apart depending on the direction of lever movement. Accordingly, when an operator wants to sideshift a load, he must use two hands to move the control levers equal distances in opposite directions. In order to keep the load from rocking, a great deal of training and skill is necessary to feather the levers as needed and maintain the load in position on the forks while laterally shifting the ioad the desired distance. Further, when one of the forks reaches its limit of travel, the operator must be careful and stop further movement of the other fork. This is because continued movement of the fork would cause it to begin to slide under the load. When this occurs, the load may become unstable. Advantageously, these problems are avoided utilizing the sideshifter circuit of the present invention. More particularly, a separate lever 124 operatively connected to a directional control valve 126 is provided for sideshif ing the load. As shown, the directional control valve 126 controls the flow of pressurized fluid between the pressurized fluid source 118, the two actuators 36 and the sump 120. More particularly, the sideshifter circuit includes a valve housing 128. The housing 128 includes a pair of control valve ports 130, 132 connecting the valve housing 128 to the directional control valve 126. A shuttle check valve 134 is connected across the ports 130, 132. A pilot fluid feed line 136 leads from the shuttle check valve 134 to four piloted check valves 138. The valve housing 128 also includes a pair of actuator ports 140, 142 connected to feed lines 144, 146, respectively, that provide communication with the rod ends of the actuators 36. More particularly, the port 140 is in communication with the rod end of the left fork actuator 36 while the port 142 is in fluid communication with the rod end of the right fork actuator 36. Additionally, the valve body 128 includes two diverter ports 148, 150. The diverter ports 148, 150 are connected to feed lines, 152, 154 respectively, that provide fluid communication between the diverter ports and the base ends of the actuators 36. More particularly, the diverter port 148 is in fluid communication with the base end of the right fork actuator 36 while the diverter port 150 is in fluid communication with the base end of the left fork actuator 36. One of the pilot operated check valves 138 controls flow through each of the actuator ports 140, 142 and diverter ports 148, 150. The check valves 138 prevent flow through the actuator ports 140, 142 and diverter ports 148, 150 unless piloted open by hydraulic pressure through the line 136 from the shuttle check valve 134. When the sideshift control lever 124 is moved in a first direction to position the forks 30 to the right, the directional control valve 126 directs fluid from the pressurized fluid source 118 to the port 130. The fluid flows from the port 130 through the valve housing 128 and out the port 140 where it is directed to the rod end of the left fork actuator 36. Flow is blocked in the opposite direction by the left fork . directional control valve 116 which is in the neutral position. Pressure developed in the port 130 is made available to the shuttle check valve 134. Valve 134 makes the pressure available through feed line 136 to pilot all four piloted check valves 138 open. As a result, fluid returning ' from the base end of the left fork actuator 36 is allowed to flow into the valve body 128 through the diverter port 150. The other potential flow path is blocked by the left fork directional control valve 116. The flow entering the port 150 is directed through the valve body 128 and the diverter port 148 to the base end of the right fork actuator 36. Fluid flow in the other direction is blocked by the right fork directional control valve 122. Due to the operation of the diverter ports 148, 150 of the valve body 128, return flow from the left fork actuator 36 has become the supply flow for the right fork actuator 36. Since the actuators 36 have equal areas both the left and right actuators are now operated at equal velocities. Further, since the forks 30 are of equal geometry, the forks 30 move together in the same direction at substantially the same speed in a coordinated fashion. Accordingly, load rocking is minimized. Flow returning from the rod end of the right actuator 36 is blocked by the right fork directional control valve 122 and thereby enters the valve body at the port 142. The flow then passes through the valve body 128 and out the port 132 with fluid returning through the directional control valve 126 to the sump 120. Similarly, when the sideshift control lever 124 is moved in the opposite direction to position the forks to the left, the sideshift directional control valve 126 directs fluid to the port 132. The fluid flows through the valve body 128 and the port 142 to the rod end of the right fork actuator 36. Pressure developed in the port 132 is made available to the shuttle check valve 134 which then directs that pressure through the pilot feed line 136 to the pilot operated check valves 138 which consequently open. Fluid returning from the base end of the right fork actuator 36 then enters the diverter port 148 and is directed through the valve body 128 and the diverter port 150 to the base end of the left fork actuator 36. Hence, return flow from the right fork actuator 36 becomes the supply flow for the left fork actuator 36. Accordingly, the forks 30 are moved in a coordinated fashion in the same direction at substantially the same speed. Flow returning from the rod end of the left fork actuator 36 enters the port 140 and passes through the valve body 128 and the port 130. From there the fluid is directed through the directional control valve 126 to the sump 120. Advantageously, it should be appreciated that if either fork actuator 36 reaches its limit of travel, fluid flow through both actuators stops. Accordingly, the forks 30 maintain their spacing under the boat B. Thus, the possibility of sliding a fork under the boat in these circumstances is eliminated. Consequently, the stability of the boat B on the forks 30 is assured. In summary, numerous benefits result from employing the concepts of the present invention. The apparatus 10 provides significantly enhanced lifting capacity over prior art designs. This is achieved through the provision of an upright assembly 12 having a series of three mast sections 16, 18, 20 supported by a unique roller arrangement so as to be particularly rigid. Since both the intermediate and inner mast sections 18, 20 may be extended in positive and negative lift configurations, the individual mast sections may be made shorter and, therefore, are lighter in weight. The mounting of the upright assembly 12 to the lift truck T also serves to move the weight of the upright assembly 12 and the load back toward the center axis of the lift truck. Further, the elimination of tandem drive systems required in the past to achieve both positive and negative lift configurations serves to further reduce system weight. The reductions in weight and the rearward shifting of the weight present toward the center axis reduce not only the counter weight and counterweight moment arm but also the overall power requirements. The unique design of (1) the upright assembly 12, including the wide space between the side rails; (2) the carriage assembly 28, including the unique sideshifting mechanism; (3) the pivoting forks that eliminate complicated mechanical slide mechanisms; (4) the routing of the hydraulic control hoses; and (5) the simplified drive assembly provide the lift truck with an unobstructed window approximately 40 inches wide furnishing significantly improved forward visibility. Accordingly, the lift truck may be guided more efficiently by the operator. The drive assembly also includes a delayed carriage lift feature whereby the guide rods 96 connected to the dead chains 92 cooperate with the guide sleeves 98 mounted to the mast section 18 to maintain the relative position of the carriage assembly 28 on the inner mast section 20 whenever the lift is in a negative configuration. Accordingly, relative movement only takes place between the first and second mast sections 16, 18 and the second and third mast sections 18, 20 when in a negative configuration. Consequently, the boat is moved in a negative configuration at a 2-1 speed ratio. This relatively slow ratio allows better control when the operator's view is slightly obscured by, for example, the boat and the dock. In contrast, when the lift is in a positive configuration, the stops 100 at the ends of the guide rods 96 abut and engage the guide sleeves 98 so that the carriage assembly 28 moves relative to the third mast section 20. This relative movement is completed in conjunction with the relative movement between the first and second mast sections 16, 18 and the second and third mast sections 18, 20. Accordingly, in the positive lift configuration, a 3- 1 speed ratio is obtained. This additional speed of operation improves productivity and is only provided when the boat is in full view and therefore may be more easily controlled by the operator. The carriage assembly 28 includes pivotally mounted forks 30 with relatively widely spaced pivot points. The forks 30 also include an inside strut arrangement that cooperates with the wide pivot points to significantly enhance the durability of the design. The forks 30 also have a unique composite construction. More specifically the forks include a curved upper surface member 80 that reduces stress concentrations and spreads the load over a larger area of the boat being handled. Additionally, a rubber jacket 82 specially contoured to fit the forks 30 serves to cushion the boat on the forks and prevent the underlying metal structure of the forks from directly contacting both the boat and the rack or trailer upon which the boat may be placed or from which it may be removed. A unique hydraulic sideshifter circuit 110 is also provided. The circuit is of a relatively simple design and advantageously is fully responsive to a single operator control 124. The circuit 110 serves to fully coordinate the movement of the forks 30 to the right or left as desired when placing or picking up a boat. The circuit also serves to prevent any possibility of passing a fork under the boat when laterally shifting the boat by stopping the movement of both forks when one of the forks 30 reaches its limit of travel. The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The preferred embodiment was chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended Claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.

Claims: Claims 1) A lift truck for transporting, lifting and lowering a load, comprising; an upright assembly mounted to said lift truck; a carriage assembly mounted for movement along a path on said upright assembly and including means for engaging and supporting said load; drive means for said upright assembly and carriage assembly, said drive means moving said carriage assembly at a first, relatively slow speed over a first portion of said movement path and at a second, relatively fast speed over a second portion of said movement path. 2) The lift truck set forth in Claim l, wherein said upright assembly includes first, second and third telescoping mast sections, said carriage assembly being mounted for movement along said third mast section. 3) The lift truck set forth in Claim 2, wherein said drive means includes an actuating means for operatively connecting said first and second mast sections, a first flexible member for operatively connecting said first and third mast sections and a first sheave means mounted to said second mast section with said first flexible member being played over said first sheave means. 4) The lift truck set forth in Claim 3, wherein said drive means further includes a second flexible member operatively connecting said second mast section and said carriage assembly and a second sheave means mounted to said third mast section with said second flexible member being played over said second sheave means. 5) The lift truck set forth in Claim 4, wherein said drive means further includes a guide rod connected to said second flexible member, a guide sleeve mounted to said second mast section for receiving said guide rod and stop means provided at one end of said rod for engaging said guide sleeve whereby movement of said carriage means is controlled along said upright assembly. 6) The lift truck set forth in Claim 3, wherein said actuating means comprises a pair of hydraulic cylinders mounted behind said mast sections to improve visibility. 7) The lift truck set forth in Claim 1, wherein said carriage assembly includes a frame, having a pair of transversely-spaced lift brackets and a pair of vertically spaced, upper and lower fork bars, roller means rotatably mounted on said lift brackets for engaging the upright assembly, and a pair of forks for supporting said load, each fork being independently pivotally mounted to said upper fork bar. 8) The lift truck set forth in Claim 7, wherein each fork includes an inwardly depending strut having a rearwardly directed surface for bearing against said lower fork bar. 9) The lift truck set forth in Claim 7, further including a jacket that fits snugly around each fork, said jacket being constructed from rubber material reinforced with polyester cord. 10) The lift truck set forth in Claim 7, further including means for shifting said forks from side-to-side relative to said carriage assembly in a coordinated manner in the same direction and at the same speed. 11) The lift truck set forth in Claim 10, further including means for stopping shifting movement of said forks when one of said forks reaches its limit of travel. 12) An upright assembly for a lift truck, comprising: first, second and third mast sections connected in telescoping relation to each other; a carriage assembly mounted on and movable along said third mast section, said carriage assembly including means for supporting a load; drive means operatively connecting said first and second mast sections; means for operatively connecting said first and third mast sections; a lift linkage for operatively connecting said carriage assembly to said second mast section; and means for mounting said upright assembly to said lift truck. 13) The upright assembly set forth in Claim 12, wherein said drive means comprises a pair of hydraulic cylinders nested behind said mast sections to increase visibility. 14) The upright assembly set forth in Claim 12, further including sheaves mounted to said second mast section and wherein said means for operatively connecting said first and third mast sections is a flexible lift chain played over said sheaves. 15) The upright assembly set forth in Claim 12, wherein said first and second mast sections comprise pairs of laterally spaced inter-connected telescopic I-beam rails, mounted in nested and overlapping relation to each other. 16) The upright assembly set forth in Claim 15, wherein said third mast section comprises a pair of laterally spaced inter-connected telescopic I-beam rails, mounted in nested and overlapping relation with said second mast section. 17) The upright assembly set forth in Claim 16, including roller means for mounting said first, second and third mast sections in nested, overlapping relation. 18) The upright assembly set forth in Claim 17, wherein said roller means provides at least three pairs of rollers engaging between said first and second mast sections and said second and third mast sections at substantially all positions of said upright assembly. 19) The upright assembly set forth in Claim 18, wherein said roller means includes a first set of four pairs of rollers for engaging between said first and second mast sections and a second set of four pairs of rollers for engaging between said second and third mast sections. 20) The upright assembly set forth in Claim 19, wherein said first set of rollers includes a first roller pair rotatably mounted adjacent one end of said first mast section, a second roller pair rotatably mounted adjacent an opposite end of said first mast section and third and fourth roller pairs rotatably mounted to a median portion of said first mast section. 21) The upright assembly set forth in Claim 19, wherein said second set of rollers includes a first roller pair rotatably mounted adjacent one end of said second mast section, a second roller pair rotatably mounted adjacent an opposite end of said second mast section and third and fourth roller pairs rotatably mounted to a median portion of said second mast section. 22) A combined upright and carriage assembly for a lift truck allowing raising and lowering of a load by manipulation of a single control actuator, comprising: an upright assembly including first, second and third telescoping mast sections; a carriage assembly mounted for movement along a path on said third mast section, said carriage assembly including means for supporting a load; and drive means for operatively connecting said upright assembly and carriage assembly together, said drive means including (a) an actuating means for operatively connecting said first and second mast sections; (b) a first flexible member for operatively connecting said first and third mast sections and first sheave means being mounted to said second mast section with said first flexible member being played over said first sheave means; and (c) a second flexible member for operatively connecting said second mast section and said carriage assembly and second sheave means being mounted to said third mast section with said second flexible member being played over said second sheave means. 23) The combined upright and carriage assembly set forth in Claim 22, further including a guide rod connected to one end of said second flexible member and a guide sleeve mounted to said second mast section, said guide rod ' being received in free sliding engagement in said guide sleeve so as to prevent relative movement between said carriage assembly and said third mast section during relative movement between said second and third mast sections. 24) The combined upright and carriage assembly set forth in Claim 23, further including stop means mounted to a distal end of said guide rod, said stop means serving to abut against said guide sleeve and provide engagement to cause relative movement of said carriage assembly along said third mast section during relative movement between said second and third mast sections. 25) A carriage assembly for an upright assembly of a lift truck, comprising: frame means; means for mounting said frame means for movement along said upright assembly of said lift truck; forks for supporting a load on said carriage assembly; means for pivotally mounting said forks to said frame means; and means for selectively driving said forks about said pivotal mounting means. 26) The carriage assembly set forth in Claim 25, wherein said frame means includes a pair of transversely-spaced lift brackets and a pair of vertically spaced upper and lower fork bars. 27) The carriage assembly set forth in Claim 26, wherein said mounting means includes roller means rotatably mounted to said lift brackets that engage said upright assembly. 28) The carriage assembly set forth in Claim 26, wherein said forks are independently pivotally mounted to said upper fork bar, each fork including an inwardly depending strut having a rearwardly directed surface for bearing against said lower fork bar. 29) The carriage assembly set forth in Claim 28, wherein each fork includes a box beam foundation supporting a curved upper surface support member. 30) The carriage assembly set forth in Claim 29, further including a jacket that fits snugly around said box beam foundation and curved upper surface support member, said jacket being constructed from rubber material. 31) The carriage assembly set forth in Claim 30, wherein said jacket of rubber material is reinforced with polyester cord. 32) The carriage assembly set forth in Claim 30, wherein said jacket is held in position on a fork by means of a band clamp adjacent the heel of said fork. 33) The carriage assembly set forth in Claim 32, further including a skid plate mounted beneath the heel of said fork. 34) A sideshifter circuit for shifting forks of a lift truck to the left or right, comprising: a single operator control; a first actuator for positioning one fork; a second actuator for positioning a second fork; a pressurized fluid source; means for feeding fluid from said pressurized fluid source to said actuators; and valve means for coordinating operation of said actuators and insuring that said forks are moved together in the same direction at substantially the same speed in response to said single operator control. 35) The sideshifter circuit set forth in Claim 34, further including means for stopping movement of said forks when one of said forks reaches its limit of travel. 36) The sideshifter circuit set forth in Claim 34, wherein said single operator control actuates a directional control valve. 37) The sideshifter circuit set forth in Claim 36, wherein said valve means includes a valve housing, containing four piloted check valves and one shuttle check valve, operatively positioned in said feeding means between said directional control valve and said first and second actuators. 38) The sideshifter circuit set forth in Claim 37, wherein said valve housing includes two directional control valve ports connected by said feeding means to said directional control valve, said shuttle check valve being connected across said directional control valve ports. 39) The sideshifter circuit set forth in Claim 38, further including .means for feeding fluid as a pilot signal from said shuttle check valve to said piloted check valves. 40) The sideshifter circuit set forth in Claim 39, wherein said valve housing further includes two actuator ports and two diverter ports, one piloted check valve controlling fluid flow through each of said actuator ports and diverter ports. 41) The sideshifter circuit set forth in Claim 40, wherein said first and second -actuators are cylinders including a base end and a rod end, said feeding means connecting one actuator port to said rod end of said first actuator and the other actuator port to said rod end of said second actuator. 42) The sideshifter circuit set forth in Claim 41, wherein said feeding means connects one diverter port to said base end of said first actuator and the other diverter port to said base end of said second actuator.

Inventors: HANSELL JEFFREY C, SHAFE JACK, SIMPSON CLARK C, HANSELL, JEFFREY, C., SHAFE, JACK, SIMPSON, CLARK, C.
Applicants: CLARK EQUIPMENT CO, CLARK EQUIPMENT COMPANY
Application year: 1991
Main classification: B66B9
IPC codes: B66F9