CONSTRUCTION EQUIPMENT MACHINE WITH IMPROVED BOOM SUSPENSION

Abstract

A construction equipment machine of the loader type is provided and has at least a chassis, a traction arrangement and a loader arrangement. The loader arrangement includes a loader boom structure which is controlled through a two way boom hydraulic cylinder system, and a boom suspension system through which a lift-side of the boom cylinder system may be connected to a hydraulic pressurized accumulator while the drop-side of the boom cylinder system is connected to a tank return line. The tank return line has a flow limiter for limiting the flow of hydraulic oil in the direction from the drop-side of the boom cylinder system to the tank.

Description

BACKGROUND AND SUMMARY

The invention relates to the field of construction equipment machines of the loader type, such as skid-steer loaders, wheel loaders, articulated wheel loader, back-hoe loaders and telescopic handlers.

Construction equipment machines of the loader type have in common that they feature at least a chassis, a traction arrangement and a loader arrangement. The loader arrangement comprises a loader boom structure, which is moveable with respect to the chassis, for example though an articulation around a boom axis, and a loader tool, which may as well be articulated with respect to the loader boom at a distal end thereof around a tool axis which is parallel to the boom axis. The position of the boom with respect to the chassis is controlled through a two way boom hydraulic cylinder system and, where the tool is moveable with respect to the boom, the position of the tool with respect to the boom is controlled through a two way tool hydraulic cylinder system.

In the following text, the lift movement of the boom refers to an upward movement of the boom and the drop movement of the boom to a downward movement of the boom. The lift movement of the tool refers to an upward movement of tip of the tool and the drop movement of the tool to a downward movement of the tip of the tool, with respect to the articulation axis of the tool on the boom. The lift and drop-sides of the hydraulic cylinder systems refer to the hydraulic chamber(s) to which it is necessary to send hydraulic pressure in order to generate to corresponding movement.

In most cases, conventional skid-steer loaders, wheel loaders, articulated wheel loader, and back-hoe loaders feature a boom structure having two parallel loader arms, and each hydraulic cylinder system for the boom and for the tool comprises two two-way-cylinders connected in parallel. On the other hand, conventional telescopic handlers have a single telescopic loader arm and the hydraulic cylinder system for the boom may comprise one or two two-way-cylinders, not counting the specific cylinder for controlling the telescopic movement of the arm. In any case, various tools may attached to the loader boom, such as a loader bucket, a fork for handling pallets, etc . . . In some cases, the tool is attached directly to the boom structure, or it is attached indirectly via a tool attachment mechanism.

The traction arrangement for such machines may comprise a set of wheels, all driven or not, or a set of tracks. The traction arrangement may feature deflectable wheels for steering the machine, or may rely on the skid steer principle. Articulated loaders are steered through the controlled articulation of their chassis.

Whereas excavators are mostly static machine, that is to say that, in a typical working cycle, the machine is not significantly displaced, construction equipment machines of the loader type are essentially machines which are used to carry loads from one place to another. Therefore, the typical work cycle of a loader is to pick up a load, to move from a first location to a second location, to discharge the load, and to come back from the second location to the first location to pick up the next load. The loader may be operated on uneven terrains, and there has appeared the need to provide a boom suspension system so that especially the pitching movement of the chassis of the machine does not affect too strongly the load carried by the loader tool, in order to prevent the load from falling off the tool.

Such suspension systems are well known and they usually are designed so that a lift-side of the boom cylinder system may be connected to a hydraulic pressurized accumulator while the drop-side of the boom cylinder is connected to a tank return line. Such boom suspension arrangements are usually disconnectable because, when they are operative, the boom structure cannot be effectively controlled in the drop direction due to the fact that the drop-side of the hydraulic cylinder system is connected to the tank return line, and therefore no effective working hydraulic pressure can be sent to the drop-side. Therefore, when the boom suspension system is operative, the boom can be lowered only thanks to the action of gravity, and, for example, the lowering movement will be strongly dependent on the weight of the load carried by the loader tool, without any precise control by the machine operator.

Also, loader type machines are often equipped with a self level system which automatically maintains the orientation of the tool when the boom is lifted, in order to avoid that the content of the loader tools falls off the tool due to the change in orientation of the boom. Various systems are known, and some of them are based on connecting the drop-side of the boom cylinder system to the drop-side of the tool cylinder system. Due to the fact that, when the boom suspension system is operative, the drop-side of the boom cylinder system is connected to the tank, such self leveling systems are inoperative when the boom suspension system is operative.

Due to the above consequences of the known boom suspension designs, such systems need to be deactivated very frequently and can in fact only be activated during certain parts of a typical working cycle of a loader type machine, for example only when the vehicle is carrying a previously loaded load from one point to the other. Such systems are preferably deactivated during the loading phase, the unloading phase, and the return travel phase from the unloading location to the loading location.

Therefore, there is a need to improve existing boom suspension systems. Preferably, the boom suspension system should be designed so that, in many cases, the boom suspension system can be kept operative during the whole typical work cycle of a loader. Also, preferably, the operation of such boom suspension system should be compatible with the operation of a self level suspension system.

The invention provides, according to an aspect thereof, for a construction equipment machine of the loader type, of the type having at least a chassis, a traction arrangement and a loader arrangement, wherein the loader arrangement comprises a loader boom structure which is moveable with respect to the chassis and which holds a tool assembly, wherein the position of the boom with respect to the chassis is controlled through a two-way boom hydraulic cylinder system, and wherein the loader arrangement has a boom suspension system through which a lift-side of the boom cylinder system may be connected to a hydraulic pressurized accumulator while the drop-side of the boom cylinder system is connected to a tank return line, characterized in that the tank return line has a flow limiter for limiting the flow of hydraulic oil in the direction from the drop-side of the boom cylinder system to the tank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are respectively a side view and a top view of a conventional skid-steer loader.

FIGS. 3 and 4 are each a schematic representation of a part of the hydraulic power circuit for the loader boom arrangement for a construction machine according to two embodiments of the invention.

DETAILED DESCRIPTION

On FIGS. 1 and 2 is shown one example of a loader type construction equipment machine: a conventional compact skid steer loader. A compact skid steer loader 10 has a short chassis 12 on top of which is arranged a cabin 14 for accommodating an operator. In this embodiment, the skid steer loader is a wheeled machine having a left pair of wheels 16 and a right pair of wheels 18. Being a compact machine, the front wheels of the machine are approximately located vertically under the front end of the cabin 14 and the rear wheels are located approximately under the rear end of the cabin 14. The chassis 12 has a rear overhang 20 for accommodating the engine of the machine.

The machine 10 has a loader arrangement, The loader arrangement has a loader boom structure 22 which comprises a pair of parallel loader arms 24 oriented longitudinally and which are articulated at their rear extremity 26 around a horizontal boom axis 28 on rear vertical pillars 30 which extend upwards from the chassis on both lateral sides of the rear overhang 20. In machines know as “radial lift”, the loader arms 24 are articulated at the top extremity of these vertical pillars 30, which is approximately above the mid-height of the cabin 14. The invention would also apply to so-called “vertical lift” machines where the loader arms are not simply articulated but connected at their rear extremity to the rear end of the machine through a multilink mechanism. The loader arms 24 extend forwardly on both sides of the cabin 14 towards the front of the machine.

At the front extremity of the loader aims 24, the loader arrangement comprises a tool assembly comprising an attachment plate 32 on which it is possible to adapt various tools depending on the work to be performed. On FIGS. 1 and 2, the tool is a conventional loader bucket 38. The attachment plate 32 is pivotally connected to the loader arms 24 around a horizontal tool axis 34, and extends transversally across the width of the machine in front of the cabin 14, of the chassis 12 and of the front wheels. The tool 38 is therefore articulated with respect to the loader boom 22, at a distal end thereof, around a tool axis 34 which is parallel to the boom axis 28. It is to be noted that, in some applications, a tool may be fitted to the boom structure in a fixed manner.

The loader boom structure is actuated by a hydraulic boom cylinder system, here comprising two boom cylinders 35, to displace the loader arms 24 with respect to the chassis between a low position shown in dashed lines on FIG. 1 to a high position showed in solid lines. The boom cylinders 35 are for example connected by one extremity to the rear pillars 30 and at their other extremity to an intermediate part of the loader arms. Similarly, the tool assembly can be actuated angularly with respect to the boom structure around the tool axis by a hydraulic tool cylinder system, here comprising two tool cylinders 36, between a high position and a low position.

As best seen on FIG. 3, each of the boom and tool cylinders 36, 36 is preferably a two-way cylinder where a piston, connected to a rod, slides inside the body of the cylinder, thereby defining two variable volume chambers 351, 35d, 361, 36d. Each cylinder thereby has a lift chamber 351, 361 and a drop chamber 35d, 36d so that the cylinders will tend to lift or drop the boom or the tool respectively when the corresponding chamber is fed with pressurized fluid, the other chamber being connected to the tank of a hydraulic circuit of the machine.

It can be noted that, in the particular embodiment shown, the boom cylinders 35 are located under the boom articulation axis 28, so that an extension of the-boom cylinders 35 causes a lift of the boom, while the tool cylinders 36 are located over the tool articulation axis 34, so that an extension of the tool cylinders causes the tool to drop. Other configurations could be possible.

In a skid steer machine, the propulsion is achieved thanks to separate left and the right propulsion units. Each propulsion unit has its own motor, its own transmission, and its own ground engaging element. The ground engaging element is, in the case of the embodiment show on FIGS. 1 and 2, a pair of synchronous wheels, that is to say a pair of wheels which are of the same diameter and which are at all times driven at the same speed in the same direction. In most cases, the motor is a hydraulic motor which drives both wheels, for example through a chain drive. The motor could also be an electric motor and/or it could be provided one motor for each wheel, Also, while the ground engaging element is here represented as a pair of wheels, it could be well replaced by an endless track mechanism. The steering of the machine is simply achieved by controlling the left and the right propulsion units at the same speed to drive straight in the forward or rearward direction, or by controlling the difference in speed of the left and right propulsion units to drive the machine to the left or to the right.

On FIG. 3 is represented schematically part of a hydraulic circuit which can be used for controlling the boom cylinder systems 35,

In this embodiment of the invention, it can be seen that the hydraulic circuit comprises a boom control directional valve 40 which has a first and a second ports 42, 44 which are hydraulically connected respectively to the boom cylinder system lift chambers 351 and to the boom cylinder system drop chambers 35d, by a lift boom circuit 46 and a drop boom circuit 48 respectively. The boom control valve 40 can selectively connect in a proportional way the first and second ports 42, 44 to a source of pressurized fluid or to a tank of the machine's hydraulic circuit to control the extension or retraction of the cylinders, thereby controlling the lift or drop of the boom. The source of pressurized fluid is generally an engine driven pump equipped with pressure regulating means for regulating the maximum pressure which can be delivered through the control valve 40 to the boom cylinder system. The boom control valve 40 can be a pilot operated valve. In the shown configuration, the lift chambers 351 are the extension chambers of the boom cylinders 35, while the drop chambers 35d are the retraction chambers of the boom cylinders 35.

In parallel to the lift boom circuit 46 and to drop boom circuit 48, it is provided a boom suspension arrangement 50. On the lift-side of the boom cylinder system, the boom suspension arrangement 50 comprises a hydraulic accumulator 52 which can be selectively connected to the boom lift circuit 46 through an accumulator line 54. An electrically controlled two position and two port lift-side valve 56 is located on the accumulator line 54 to control the communication between the accumulator 52 and the boom lift circuit 46. In a first position, the lift-side valve 56 allows only the passage of hydraulic fluid from the accumulator 52 to the boom lift circuit 46. In the reverse direction, only a limited flow of oil may then flow through a valve by-pass 58 which is for example provided with a throttle 60. The lift-side valve 56 is biased towards that first position. When the lift-side valve 56 is electrically set to its second position, the flow through valve 56 is substantially unlimited in both directions. The presence of the by-pass 58 is then insignificant. On the drop-side of the boom cylinder system 35, the boom suspension arrangement 50 also comprises an electrically controlled two position and two port drop-side valve 64 which is located on a dedicated tank return line 62 connected to the drop boom circuit 48. The drop-side valve 64 controls the communication between the drop-side of the boom cylinder system 35 and a hydraulic tank 66. In a first position, the drop- side valve 64 allows only the passage of hydraulic fluid from the tank 66 to the boom drop circuit 48, The drop-side valve 64 is biased towards that first position. When the drop-side valve 64 is electrically set to its second position, the flow through valve 64 is substantially unlimited in both directions. Such an arrangement is well known to the man in the art. Operation of the boom suspension is essentially as follows: when both valves 56, 64 are in the first position, the boom suspension is not operative. When both valves 56, 64 are in their second position, the boom can move up and down thanks to the varying capacity of the pressurized accumulator 52, and thanks to the fact that the drop-side is connected to the tank 66 and therefore does not interfere with that possibility of movement.

According to the invention, the boom suspension system further comprises, on the tank return line 62, a flow limiter 68 for limiting the flow of hydraulic oil at least in the direction from the drop-side 35d of the boom cylinder 35 to the tank 66.

The aim of the flow limiter 68 is to allow the flow to the tank to such an extent that the drop-side of the boom cylinder system is not hydraulically locked, thereby permitting free movement. On the other hand, this flow is limited by the flow limiter to such an extent that, when the boom suspension is operative and the boom control valve 40 is set to send hydraulic pressure to the drop-side of the boom cylinder system, the pressure loss due to this flow in the tank return line 62 should not exceed a certain percentage of the nominal maximum operating pressure of the hydraulic circuit. In other words, even with the boom suspension active, i.e. even with the drop-side valve 64 in its second position, the maximum pressure available for the drop-side 35d of the boom cylinder system should remain above a certain percentage of the nominal maximum pressure of the source of pressurized fluid. Therefore, as that percentage of pressure is available, the loader boom arrangement can be controlled downwards with sufficient strength and precision to achieve the required working efficiency.

Preferably, the flow limiter 68 limits the flow of hydraulic oil in the direction from the drop-side 35d of the boom cylinder 35 to the tank at a rate lower than the possible flow rate in the reverse direction. This allows to strongly limit the risk of cavitation at the drop-side boom cylinder system by not limiting too much the reverse flow. In fact, in the shown embodiment, the flow of oil in the tank return line is not substantially limited in the reverse direction.

In the shown embodiment, the flow limiter 68 is a unidirectional flow limiter comprising a check valve 70 hydraulically in parallel with a throttle 72.

The exact dimensioning of the flow limiter 68 is of course dependant on many factors. In one application on a skid steer loader, the source of pressurized fluid is a pump driven by a diesel engine, the pump delivering 36 cubic centimeters per revolution. The hydraulic circuit feeding the control valve 40 is equipped with a pressure regulator having a nominal minimal setting at 207 bars. The boom lift and boom drop circuit 46, 48 and the accumulator and tank return lines 54, 62 have a diameter of one half of an inch (12.7 mm). In such application, it has been found that a throttle 72 having a diameter of 1.9 mm on the tank return line 62 is well suitable and allows maintaining approximately 90 percent of the nominal maximum pressure available for the drop-side of the boom cylinder system 35. Of course, if a lower percentage of the nominal maximum pressure is deemed acceptable in view of the application, a throttle of wider cross section could be used.

In the shown embodiment, it can be seen that the tank return line 62 is a dedicated return line for the boom suspension system which does not go through the boom control valve 40. Therefore, the tank return line 62 may be shut off when the boom suspension system is not operative.

In a second embodiment of the invention which is shown on FIG. 4, the hydraulic circuit is equipped self level system 74 through which the drop-side 35d of the boom cylinder system 35 may be connected to the drop-side 36d of the tool cylinder system 36. Such seif level system 74 is well known to the skilled man in the art and it is for example sold by EATON Corporation under model number 39055. It functions in fact as a flow divider which sends a predefined part of the oil coming out of the drop-side 35d of the boom cylinder system 35 to the drop-side 36d of the tool cylinder system 36, the rest of the oil being sent back to the tank through the boom control valve 40. The aim of such system is to automatically correct the absolute angular position of the tool with respect to the ground when the angular orientation of the boom changes due to its movement with respect to the chassis. Basically, this system changes the orientation of the tool with respect to the boom in the opposite way to the change of orientation of the boom with respect to the chassis.

In this embodiment of the invention, it can be seen that the hydraulic circxiit comprises, in addition to the elements already described in relation to FIG. 3, a tool control directional valve 76 which has a first and a second ports 78, 80 which are hydraulically connected to respectively the tool cylinder lift chambers 361 and the tool cylinders drop chamber 36d, by a lift tool circuit 82 and a drop tool circuit 84 respectively. The tool control valve 76 can selectively connect the first and second ports 78, 80 to a source of pressurized fluid or to a tank of the machine's hydraulic circuit to control the extension or retraction of the cylinders 36, thereby controlling the lift or drop of the tool. The tool control valve 76 can be a pilot operated valve. In the shown configuration, the. lift chambers 361 are the retraction chambers of the cylinders 36, while the drop chambers 35d are the extension chambers of the cylinders 35.

The self level system 74 has four ports 86, 88, 90, 92, and is in fact inserted in the boom drop circuit 48, which is interrupted and divided in two parts by the self level system 74. A cylinder-side of the boom drop circuit 48 is connected to a first port 86, while a control-valve-side of the boom drop circuit 48 is connected to a second port 88. A third port 90 is connected to the tool drop circuit 84 and a fourth port 92 is connected to the tool lift circuit 82.

Very schematically, the operation of the self level system is as follows, without a boom suspension arrangement. When pressurized fluid is sent via the boom control valve 40 to the lift-side 351 of the boom cylinder system 35, causing an upward movement of the boom, the oil contained in the drop-side of the boom cylinder system is expelled towards the boom drop circuit 48 and enters into first port 86 of the self level system 74. There, a first part of this oil exits through port 88 and is driven by the boom drop circuit 48, through the boom valve 40, towards a tank. The second part of the oil exits through port 90 towards the tool drop circuit 84. If it is assumed that the tool control valve 76 is then closed, this second part of the oil expelled of the boom cylinder system thus enters the drop-side. of the tool cylinder system 36 and causes an inverse rotation of the tool with respect to the boom.

Such system cannot operate when a traditional boom suspension is operative. Indeed, under such conditions, the drop-side of the boom cylinder system is connected to the tank, so that substantially all the oil which is expelled from the boom drop chambers exits through the dedicated tank return line 62 rather than going through the boom drop circuit 48.

To the contrary, with a boom suspension system as in the invention, the flow limiter 68 creates a backpressure in the boom drop circuit which is sufficient to allow a proper functioning of the self level system, at least to a certain extent. Therefore, the invention is all that more useful in the context of a loader arrangement having a self level system.

Claims

1. Construction equipment machine of the loader type, of the type having at least: a chassis anda traction arrangement anda loader arrangement,

2. Construction equipment machine according to claim 1, wherein the flow limiter limits the flow of hydraulic oil in the direction from the drop-side of the boom cylinder to the tank at a rate lower than the possible flow rate in the reverse direction.

3. Construction equipment machine according to claim 1, wherein the flow of oil in the tank return line is not substantially limited in the direction from the tank to the drop-side of the boom cylinder.

4. Construction equipment machine according to claim 1, wherein the flow limiter is a unidirectional flow limiter comprising a check valve hydraulically in parallel with a throttle.

5. Construction equipment machine according to claim 1, wherein the tank return line is a dedicated return line for the boom suspension system which may be shut off when the boom suspension system is not operative.

6. Construction equipment machine according to claim 1, wherein the loader boom structure is articulated with respect to the chassis around a boom axis.

7. Construction equipment machine according to claim 1, wherein the tool assembly is articulated with respect to the loader boom at a distal end thereof around a tool axis, and in that the angular position of the tool assembly with respect to the boom is controlled through a two way tool hydraulic cylinder system.

8. Construction equipment machine according to claim 7, wherein the loader arrangement has a self level system through which the drop-side of the boom cylinder system is adapted to be connected to the drop-side of the tool cylinder system.

9. Construction equipment machine according to claim 1, wherein at least one of the hydraulic cylinder systems comprises two two-way-cylinders arranged in parallel.

10. Method for operating a construction equipment machine of the loader type having at least: a chassis,a traction arrangement anda loader arrangement, wherein the loader arrangement comprises a loader boom structure which is moveable with respect to the chassis and which holds a tool assembly, wherein the position of the boom structure with respect to the chassis is controlled through a two way boom hydraulic cylinder system, and wherein the loader arrangement has a boom suspension system through which a lift-side of the boom cylinder system is adapted to be connected to a hydraulic pressurized accumulator while the drop-side of the boom cylinder system is connected to a dedicated tank return line which is adapted to be shut off when the boom suspension system is not operative,wherein the method comprises:connecting the drop side of the boom cylinder system to a source of pressurized fluid through a directional boom control valve,simultaneously maintaining the drop side of the boom cylinder connected to the tank by the dedicated return line and limiting the flow of oil to the tank in that the tank return line thanks to a flow limiter for limiting the flow of hydraulic oil in the direction from the drop-side of the boom cylinder system to the tank.

11. The method as set forth in claim 10, wherein the flow limiter limits the flow of hydraulic oil in the direction from the drop-side of the boom cylinder to the tank at a rate lower than the possible flow rate in the reverse direction.

12. The method as set forth in claim 10, wherein the flow of oil in the tank return line is not substantially limited in the direction from the tank to the drop-side of the boom cylinder.

13. The method as set forth in claim 10, wherein the flow limiter is a unidirectional flow limiter comprising a check valve hydraulically in parallel with a throttle.

14. The method as set forth in claim 10, wherein the dedicated return line for the boom suspension system is shut off when the boom suspension system is not operative.

15. The method as set forth in claim 10, wherein the tool assembly is articulated with respect to the loader boom at a distal end thereof around a tool axis, and in that the angular position of the tool assembly with respect to the boom is controlled through a two way tool hydraulic cylinder system. wherein the loader arrangement has a self level system through which the drop-side of the boom cylinder system is adapted to be connected to the drop-side of the tool cylinder system. and wherein the method includes operating simultaneously both the boom suspension system and self leveling system by maintaining the drop side of the boom cylinder connected to the tank by the dedicated return line and limiting the flow of oil to the tank in the tank return line thanks to the flow limiter for limiting the flow of hydraulic oil in the direction from the drop-side of the boom cylinder system to the tank.