SELF-LEVELLING MOBILE SUPPORTING CHASSIS

Abstract: A work platform-supporting device is held by legs extendable by hydraulic rams and retractable by its own weight. A sensing device including a pendulum (43) attached by a stem (45) to a universal joint (46) controls the movement of the rams. Two pairs of control valves located at 90 DEG to each other are attached to the stem (45). One pair of control valves reacts to the pitch of the platform while the other pair reacts to the roll of the platform. These valves are attached to a hinge mechanism, which is connected to the stem by a ball joint (67). When the sensing device and the platform are level the valves are in a neutral position. When the platform becomes inclined the pendulum moves to a vertical position thus activating the valves. The valves allow hydraulic fluid to flow into the ram on the downhill side of the platform and the ram on the uphill side retracts allowing hydraulic fluid to return to the hydraulic fluid reservoir. The valves have built-in dampers and the pendulum is immersed in a viscous fluid (42).

Description: SELF-LEVELLING MOBILE SUPPORTING CHASSIS —BACKGROUND OF THE INVENTION-- This invention relates self levelling mobile supporting chassis. This invention has particular application to self propelled self levelling mobile supporting chassis which carry an elevating work platform and are commonly known as cherry pickers or power ladders and for the purposes of illustration reference will be made hereinafter to such applications. Cherry pickers are often used in the horticultural industry to carry a person along rows of fruit trees for picking fruit from their upper portions or for pruning the branches which are not accessible from the ground. Typically these machines have a pair of hydraulically driven wheels which are independently speed controlled from a boom supported operators platform thus providing a high degree of manoeuvrability. The controls also include boom elevating controls. Typically the further supporting wheel or wheels are arranged as castor wheels to enable the machine to be steered by the independent speed control of the driven wheels . While such machines operate effectively on flat ground or gentle slopes any slope beyond about 5 degrees poses a danger to the operator as the stability of the cherry picker is compromised as the work platform is raised and the centre of gravity of the machines shifts downhill. In addition to the risk of rollover there is a severe reduction of manoeuvrability due to the weight reduction imposed on the uphill drive wheel. Furthermore as the machine tilts the steering axis of the caster wheel or wheels is tilted off vertical and this causes the castor wheel to run downhill. This adds to the traction problems of the uphill drive wheel. Attempts have been made to provide self levelling work platforms such as described in US Patent No. 5082085. However such proposals provide only limited usefulness and mostly require significant operator control. —SUMMARY OF THE INVENTION— This invention in one aspect aims to alleviate at least one of the above disadvantages. In another aspect this invention aims to provide self levelling apparatus and self levelling chassis which can be used advantageously. With the foregoing in view, this invention in one aspect resides broadly in a self levelling mobile chassis including: - a wheel supported chassis having a pair of opposed wheels adjacent one end thereof which are independently height adjustable with respect to the chassis; selectively operable height adjusters operable for independent adjustment of the height adjustable wheels; roll control means for monitoring tilting off level of the chassis about a longitudinal roll axis; pitch control means for monitoring tilting off level of the chassis about a transverse pitch axis, and the roll and pitch control means independently but cumulatively controlling the height adjusters. Preferably the wheels supporting the chassis include a wheel set remote from the height adjustable wheels and about which wheel set the chassis may roll. This may be achieved by having laterally spaced wheels mounted on a beam axle which is pivotable about a central trunnion mounting. Alternatively the wheel set may be a single centrally disposed wheel or closely spaced centrally disposed wheels. The wheel set may also be a pair of fixed spaced apart wheels. However in such instance the levelling would occur about the fixed wheel which is uppermost and this would limit the range of slopes on which the apparatus could be used. It would also introduce asymmetrical stability problems which would be undesirable. It is also preferred that the wheel set be arranged to trail freely behind a steering axis to automatically follow the steering effected by differential rotation of the height adjustable wheels. Suitably the mobile supporting chassis is self propelled and supports a boom assembly pivotally connected to the supporting chassis for pivotal movement about an axis which is normally horizontal for raising and lowering the outer end of the boom assembly and suitably the sensitivity of the wheel adjusters is such that the outer end of the boom during normal operation of the mobile supporting chassis across undulating terrain is maintained within a vertical projection of the wheels. It is also preferred that the height adjustable wheels be independently hydraulically driven and that the height adjustment of the adjustable wheels is achieved by the use of hydraulic rams. Further it is preferred that independent controls be provided for the driven wheels for steering and that the hydraulic controls for the hydraulic rams be controlled by movement of a pendulum or other level sensing means, such as mercury switches or other electrical sensors for automatic levelling of the supporting chassis. In a preferred embodiment of the invention the hydraulic rams which control the height adjustable wheels are single acting hydraulic rams and the height adjustment is achieved by selectively forcing oil into the respective ram to lower the selected wheel relative to the chassis, and to enable oil to be forced therefrom under the weight of the chassis to enable the selected wheel to move upwards. This enables a simple arrangement of hydraulic control valves to be mechanically actuated by a pendulum to achieve the independent but cumulative control required. Preferably the control means includes a pair of valves comprising a three-way control valve for each wheel for pitch control and another pair of valves comprising a further three-way control valve for each wheel for roll control, the respective pairs of valves being arranged for ganged operation by movement of level sensitive means in a transverse and fore and aft direction respectively. In this arrangement, one pair of three-way control valves, hereinafter the roll control valves, is operable upon movement of the control spindles thereof in a transverse direction, for roll control, to supply fluid to one ram and simultaneously drain fluid from the other to lower one adjustable wheel and raise the other to correct the sensed roll. The other pair of three-way control valves, hereinafter the pitch control valves, is operable upon movement of the control spindles thereof in a longitudinal direction, for pitch control, to simultaneously supply fluid to or drain fluid from both rams to cause them to lower or be raised to correct the sensed change in pitch. As the roll and pitch controls are independent but cumulative one of the rams may be fed fluid from the roll control and simultaneously drained of fluid by the pitch control. This can maintain an equilibrium in that ram so that the effect is that if when travelling along level ground one adjustable wheel encounters a ditch or mound it will move independently to maintain support of the chassis in normal attitude as it passes through the ditch or over the mound. If the adjustable wheels encounter a slope they will move automatically one up one down to maintain support of the chassis in normal level attitude as it passes along the slope. If this automatic adjustment causes the chassis to simultaneously pitch forward or backward the pitch control valves will cause fluid to be supplied simultaneously to both rams or be drained from both rams to maintain a normal chassis attitude. These operations can occur simultaneously such as by the sensing pendulum swinging at an angle which bisects the transverse and longitudinal directions and operating both pitch control valves and roll control valves simultaneously. In a further aspect this invention resides broadly in hydraulic level controlling apparatus for automatically controlling roll and pitch movements of a body having a pair of laterally spaced ram assemblies operable separately to roll the body or in unison to pitch the body, the apparatus including: - a pendulum suspended for free swinging movement from the body; a first pair of three-way hydraulic roll control valves simultaneously operable by movement of the pendulum in a transverse direction for effecting extension of one ram assembly and retraction of an opposing ram assembly for effecting roll corrections, and a second pair of three-way hydraulic pitch control valves simultaneously operable by movement of the pendulum in a longitudinal direction for simultaneously effecting extension or retraction of both said ram assemblies. Suitably the pendulum includes a weight at its lower end which is suspended in an oil bath for damping the movement thereof. The pitch and roll control valves could be positioned in any desired configuration and be operated by linkages which translate movement of the pendulum to the controls thereof or by electrical actuators actuated in response to position switches associated with the pendulum. Alternatively the position switches may be proximity sensors for sensing the position of the pendulum and if desired mercury switches may be used to monitor the tilt in lieu of the pendulum. Preferably however the pitch and roll control valves are spool valves arranged in respective pairs at right angles to one another and having the spools of each pair actuated directly by longitudinal and transverse movement of the pendulum. In a further aspect this invention resides broadly in a self propelled self levelling mobile supporting chassis including: - a chassis; a centrally disposed castor wheel suspended fixedly adjacent one end of the chassis; a pair of laterally spaced hydraulically driven wheels adjacent the other end of the chassis which are independently height adjustable with respect to the chassis; selectively operable height adjusting ram assemblies operable for independent height adjustment of the height adjustable wheels; a pendulum suspended by the chassis for free swinging movement; a first pair of three-way hydraulic roll control valves simultaneously operable by movement of the pendulum in a transverse direction for effecting extension of one ram assembly and retraction of the opposing ram assembly; a second pair of three-way hydraulic pitch control valves simultaneously operable by movement of the pendulum in a longitudinal direction for simultaneously effecting extension or retraction of both said ram assemblies, and control means for controlling the speed of the hydraulically driven wheels for effecting steering of the self propelled self levelling mobile supporting chassis. —BRIEF DESCRIPTION OF THE DRAWINGS— In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a typical embodiment of the invention, wherein: - FIG. 1 is a side view of a elevating work platform according to this invention; FIG. 2 illustrates the configuration of the wheel mountings; FIG. 3 is a plan view of the wheel supported chassis; FIG. 4 is a diagrammatic side view of the self levelling control apparatus; FIG. 5 is a diagrammatic inverted plan view of the self levelling control apparatus, and FIG. 6 illustrates the hydraulic circuit connections between the self levelling control apparatus and the wheel height adjusting rams. —DESCRIPTION OF THE PREFERRED EMBODIMENT— The self propelled mobile platform or cherry picker 10 illustrated in Fig. 1 includes a supporting chassis 11 supported by a pair of spaced apart height adjustable front wheels 12 and a single centrally disposed castor wheel 13. The latter may pivot to a trailing position about its support axis 14 to self steer in either direction of travel of the cherry picker 10. A boom assembly 15 is supported at the trailing end of the chassis 11 and has a boom 16 which carries the work platform 17 at its outer end. The boom 16 is pivoted at its rear end about a horizontal pivot 18 such that the work platform 17 may be raised and lowered. A hydraulic ram 20 is utilised for selectively raising and lowering the boom 11 and a stabilising boom 21 is used to suspend the pivotable work platform 17 in an operative attitude at the end of the boom 16. The front wheels 12 include hub mounted hydraulic motors 22 which may be operated by controls 23 supported on the work platform 17. These controls also include controls for raising and lowering the boom 16. The chassis 11 supports a drive motor 24 driving a hydraulic pump 25 which is utilised to drive the hydraulic motors 22 as well as the other rams 20 and 21 and the rams 30A and 30B which control the height adjustment of the respective front wheels 12, as illustrated in Fig. 2. It will be seen that each front wheel 12 is carried on a leading link 31 which is pivotly connected to the chassis 11 by a horizontal pivot connection 32 such that the front wheels 12 may be raised or lowered with respect to the chassis 11. The rams 30 are single acting rams which utilise a single supply line 34 which leads to a manifold or accumulator controlled by automatic levelling means for either supply or return of fluid to and from the respective ram 30 to effect downward or upward movement of the respective wheel in relation to the chassis 11. It will be seen in this embodiment that the leading links 31 supporting the front wheels 12 form forward extensions of spaced chassis rails 35. The links 31 are connected thereto at their lower edges by the pivots 32. The chassis rails 35 and the links 31 are cut away at their adjacent upper ends to enable the links 31 to move upwardly to a position illustrated at 36 and being the maximum upward movement of the front wheels 12 relative to the chassis 11. Such upward movement of the wheel is accompanied by retraction of the ram 30 and the return of hydraulic fluid from the rams 30 through the line 34. Furthermore, the wheels may move downwardly a similar amount upon extension of the hydraulic ram 30. Either of the front wheels 12 may be selectively raised or lowered from their normal position illustrated in Fig. 2 so as to maintain the chassis 11 in a substantially horizontal attitude so that the boom assembly 15 extends vertically. Thus elevation of the boom 16 is effected in a vertical direction so as not to compromise the fore and aft stability of the cherry picker through its traversing an incline or negotiating a mound or other undulation. Actuation of the hydraulic rams 30 is controlled by the control means illustrated in Figs. 3 - 5 which automatically maintains the chassis of the cherry picker in a normal level attitude. The control means 40 which is suitably mounted low in the machine such as beneath the chassis 11 as illustrated in Fig. 1 includes a housing 41 which acts as a container for oil 42 which acts as an oil bath within which the end mass 43 of a pendulum assembly 44 may swing, its movement being damped by the oil 42. The pendulum shaft 45 is supported at its upper end by a universal joint 46 connected to the upper wall 47. The upper wall also supports respective pairs of control valves 48 and 49 adapted to control the rams 30 for effecting roll and pitch controls. The control valves 48 are mounted in pairs so that one of each pair may control a respective one of the rams 30. The control valves 48 which control movement of the wheels about the roll axis are located laterally of the pendulum shaft 45 so that as the pendulum swings laterally relative to the chassis as it begins to roll, the spools 50 of the roll control valves 48 will be moved from a central position to either side thereof to either direct hydraulic pressure into the ram or to enable the hydraulic fluid in the ram to be drained therefrom. In the central position the spools 50 prevent flow of hydraulic fluid to or from the control valves 48. The three-way valves 51, 52, 55 and 56 each consists of a vale body and a sliding spool. The body contains three ports opening into the spool gallery. The centre port is connected to the hydraulic rams and the other two are connected to the pressurised fluid supply and to the fluid reservoir. When the spool is in the central position all ports are closed and fluid is locked in the ram. As the spool moves in one direction it exposes the pressurised port and allows oil to flow into the ram. In the opposite direction the spool exposes the reservoir port and allows oil to drain from the ram. In Fig. 5 the hydraulic circuit is drawn with the high pressure lines thicker than the return lines. Furthermore, the active lines from the control valves 48 and 49 to the manifolds or accumulators 53 and 54 at which the cumulative control is effected is shown dotted. In this embodiment, it will be seen that the three-way valve 51 and 52 forming the pitch control valves 49 are connected in parallel to the manifolds 53 and 54 such that simultaneous actuation thereof in the same direction by the pendulum assembly 44 will cause either supply of high pressure fluid to each manifold 53 and 55 or will open each manifold 53 and 55 to drain through the return manifold 55. However the three-way valves 56 and 57 forming the roll control valve 48 are configured oppositely such that simultaneous actuation of the valves 56 and 57 in one direction by lateral movement of the pendulum 44 will open the manifold 54 to a high pressure supply such as indicated in dotted line at 58 while the other line 59 from the valve 56 will be open the manifold 53 to the return manifold 55. This will cause one hydraulic ram 30 to extend and the other hydraulic ram 30 to retract as illustrated. Should the pitch of the chassis begin to change, the pendulum 45 will move fore and aft and will actuate the valves 51 and 52 to either connect the manifolds 53 and 54 to the high pressure manifold 60 or alternatively to the return manifold 55 as required to effect the change in pitch. The line 34 from the hydraulic ram associated with the control valve 56 will then be open to drain through the connection 59 as well as through the connection 61 through the pitch control valve 52. This will enable the ram 30B to retract. At the other side of the chassis, the hydraulic ram 30B connected by line 34 to the roll control valve 57 will be open to the high pressure manifold 60 through the line 58 and the return manifold 55 through the line 62. This action will substantially prevent further extension of the ram 30A while maintaining or increasing retraction of the ram 30B. This action will continue until the pitch is controlled. It will be seen that the connection between the pendulum shaft 45 and the spools 50 includes lateral and longitudinal push/pull rods 65 and 66 mounted by rod ends 67 to the shaft 45. These rod ends provide spherical type universal joints at the shaft connections. Ball end actuators 68 are provided on each spool 50 and these locate in a channel 69 suspended by a respective spring steel levers 70 suspended from the upper wall 47 of the housing 41 for pivotal movement about axes at right angles to one another as illustrated. The levers 70 extend down beyond the channels 69 to connect adjustably to the threaded push/pull rod 65 or 66, the connection 71 thereto being a further rod end type universal connection. The spring steel levers provide a degree of give between the shaft 45 and the spools and the universal connections permit the pendulum to pivot freely within the bounds required for actuation of the spools 50. In use, as the machine 10 moves onto a transverse slope it is necessary that one drive wheel 12 move up and the other down to keep the chassis level. For this purpose movement of the pendulum controls the oil flow to feed hydraulic fluid to the downhill side ram 30 and simultaneously drain fluid from the uphill ram 30. If the machine 10 confronts rising ground the pitch control drains from both rams simultaneously until the chassis 11 is level. Conversely on falling ground both rams are filled together. If the machine 10 moves onto a transverse slope and move up the slope hydraulic fluid is fed to the downhill side ram 30 and hydraulic fluid is drained from the uphill ram 30. The pitch control valves will simultaneously operate to drain fluid from both rams 30 and the cumulative result of the hydraulic feed is that the chassis will be maintained level. It will be realised that the above has been given only by way of illustrative example of this invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is defined in the appended claims.

Claims: —CLAIMS— 1. A self levelling mobile chassis including:- a wheel supported chassis having a pair of opposed wheels adjacent one end thereof which are independently height adjustable with respect to the chassis; selectively operable height adjusters operable for independent adjustment of the height adjustable wheels; roll control means for monitoring tilting off level of the chassis about a longitudinal roll axis; pitch control means for monitoring tilting off level of the chassis about a transverse pitch axis, and the roll and pitch control means independently but cumulatively controlling the height adjusters. 2. A self levelling mobile chassis as claimed in claim 1, wherein the wheels supporting the chassis include a centrally disposed castor wheel supported adjacent the end of the chassis remote from the height adjustable wheels. 3. A self levelling mobile chassis as claimed in claim 1 or claim 2, wherein the height adjustable wheels are driven wheels and a boom assembly is pivotally connected to the supporting chassis for pivotal movement about a normally horizontal axis. 4. A self levelling mobile chassis as claimed in claim 3, wherein the boom assembly supports an operators platform having controls for elevating the boom and independent speed controls for the height adjustable height adjustable wheels. 5. A self levelling mobile chassis as claimed in any one of the preceding claims, wherein the height adjustable wheels are independently hydraulically driven and the height adjustment of the adjustable wheels is achieved by the use of hydraulic rams. 6. A self levelling mobile chassis as claimed in any one of the preceding claims, wherein single acting hydraulic rams control the height adjustable wheels and the height adjustment is achieved by selectively forcing oil into the respective ram to lower the selected wheel relative to the chassis, and by enabling oil to be forced therefrom under the weight of the chassis to enable the selected wheel to move upwards. 7. A self levelling mobile chassis as claimed in claim 6, wherein the hydraulic control valves controlling the rams include a three-way control valve for controlling each wheel for pitch control and a further three-way control valve for each wheel for roll control, the respective pitch and roll control valves being arranged for ganged operation by movement of level sensitive means. 8. Hydraulic level controlling apparatus for automatically controlling roll and pitch movements of a body having a pair of laterally spaced ram assemblies operable separately to roll the body or in unison to pitch the body, the apparatus including: - a pendulum suspended for free swinging movement from the body; a first pair of three-way hydraulic roll control valves simultaneously operable by movement of the pendulum in a transverse direction for effecting extension of one ram assembly and retraction of an opposing ram assembly for effecting roll corrections, and a second pair of three-way hydraulic pitch control valves simultaneously operable by movement of the pendulum in a longitudinal direction for simultaneously effecting extension or retraction of both said ram assemblies. 9. Hydraulic level controlling apparatus as claimed in claim 8 wherein the pendulum includes a weight at its lower end suspended in an oil bath and the pitch and roll control valves are spool valves arranged in respective pairs at right angles to one another and having the spools of each pair actuated directly by longitudinal and transverse movement of the pendulum. 10. A self propelled self levelling mobile supporting chassis including:- a chassis; a centrally disposed castor wheel suspended fixedly adjacent one end of the chassis; a pair of laterally spaced hydraulically driven wheels adjacent the other end of the chassis which are independently height adjustable with respect to the chassis; selectively operable height adjusting ram assemblies operable for independent height adjustment of the height adjustable wheels; a pendulum suspended by the chassis for free swinging movement; a first pair of three-way hydraulic roll control valves simultaneously operable by movement of the pendulum in a transverse direction for effecting extension of one ram assembly and retraction of the opposing ram assembly; a second pair of three-way hydraulic pitch control valves simultaneously operable by movement of the pendulum in a longitudinal direction for simultaneously effecting extension or retraction of both said ram assemblies, and control means for controlling the speed of the hydraulically driven wheels for effecting steering of the self propelled self levelling mobile supporting chassis. 11. A self levelling mobile chassis as claimed in any one of claims 1 to 7, wherein the the roll and pitch control means is as claimed in claim 8. 12. A self propelled and self levelling work platform substantially as hereinbefore described and or illustrated.

Inventors: BARTLETT DAVID JOSEPH, RAFFELS PETER JOHN, BARTLETT, DAVID, JOSEPH, RAFFELS, PETER, JOHN
Applicants: BARTLETT DAVID JOSEPH, RAFFELS PETER JOHN, BARTLETT, DAVID, JOSEPH, RAFFELS, PETER, JOHN
Application year: 1998
Main classification: A01D46
IPC codes: B60G17