Series Self-Leveling Valve

This invention relates generally to controls for hydraulic power systems and more specifically to directional control valves that selectively effect automatic leveling of a bucket on the front end of a loader or similar device during movement of the boom arm to which the bucket is attached.

It is conventional practice to provide a hydraulic cylinder and separate control valve for manipulating the bucket of a front end loader and a second cylinder and companion valve for aiding in raising and lowering the boom of a loader. In the absence of any self-leveling function, it is necessary for the operator of the loader to operate both valves, one with each hand, to maintain the bucket level while raising the boom. This operation is not only difficult but also requires the strict attention of the operator. The advantages of a self-leveling system are obvious and there have been numerous types of systems on the market for many years.

One of the more common methods, such as shown in U.S. Pat. No. 3,987,920 to Parquet, is a mechanical linkage tied to the frame of the loader which tilts the bucket, maintaining it level as the boom is raised or lowered.

Another common method, which is strictly hydraulic, is illustrated in U.S. Pat. No. 3,251,277 to Stacey. In this patent the fluid displaced from the boom cylinder is directed to the bucket cylinder by actuation of the boom spool alone. This type of system requires a matching of volumes so that the volume displacement from the boom cylinder will extend the bucket cylinder the precise distance to hold the bucket level as the boom is raised. This type of system is more expensive and bulky since it requires an unduly large bucket cylinder.

Another method is illustrated in U.S. Pat. No. 3,811,587 to Seaberg which utilizes a pair of hydraulic motors mechanically tied together with the larger motor located in the boom cylinder circuit while the smaller motor is located in the bucket circuit. As flow passes through the boom circuit, a proportionally smaller flow is forced through the bucket circuit.

Another self-leveling system is shown in U.S. Pat. No. 3,563,137 to Graber wherein the flow exiting the boom cylinder passes through a flow divider, dumping a portion to drain while directing the remaining portion to the bucket cylinder to maintain a level condition while raising the boom.

In the last mentioned patent, the excess oil is removed from the self-leveling circuit by a proportional flow divider dumping to drain, however, such a system can only be used in a conventional parallel circuit as distinguished from a series circuit. A parallel circuit, as illustrated in the last mentioned patent, provides a source of pump pressure to each valve spool in a parallel path. A series system such as U.S. Pat. No. 3,251,277 to Stacey provides a pump power passage in series through the particular valve in the system. In a series type valve, if an upstream valve is moved to an operative position, there is no pump pressure to the remaining downstream valves since the power passages are in series.

Series type valves are normally not adaptable to a self-leveling function with the exception of the last mentioned patent to Stacey wherein the boom cylinder is located downstream from the bucket cylinder.

In the present invention which is a series circuit, a flow divider is utilized in the boom discharge flow path with a portion going to the bucket cylinder while the remaining flow passes back to the valve to the boom return motor port. This last mentioned flow through the boom return port provides downstream oil for the bucket cylinder if the operator attempts to override the self-leveling function while the boom cylinder is moving. The present invention gives a downstream valve in a series circuit the added capacity of functioning during the movement of the blocking upstream valve.

It is therefore the principal object of the present invention to provide a series type self-leveling system that directs only the necessary portion of the boom-displaced fluid to actuate the bucket cylinder and maintain a level condition while still allowing the bucket cylinder to override the self-leveling function if desired.

Another object of the present invention is to provide a series type control valve assembly including separate valves for controlling boom and bucket cylinders and a flow divider for directing a portion of fluid returning from the boom cylinder into the bucket cylinder so as to provide an automatic self-leveling function.

Another object of the present invention is to provide a self-leveling system which is simple in design and less expensive than parallel systems.

Another object of the present invention is to provide an inexpensive flow divider valve which can be plumbed into a conventional non-self-leveling system so as to achieve automatic self-leveling.

A further object of the present invention is to provide a self-leveling system which utilizes the same directional control valve as non-self-leveling systems.

Other object and advantages of the present invention are described in or will become apparent from the following detailed description and accompanying drawings of the preferred embodiment.

The drawing is a partially schematic representation of the hydraulic controls for a front end loader including longitudinal sectional views of the control valves with the boom and bucket valves in neutral position.

With reference to the drawing, the overall self-leveling system is generally referred to by reference numeral 10. The system includes boom and bucket cylinders 12 and 14, respectively, which are controlled by boom and bucket directional control valves 11 and 13. Boom 15, which can be of many types, is pivotally mounted to the base frame member 17 of the loader while bucket 16 is attached to the end of boom 15 and bucket cylinder 14. Positioned between the control valves 11 and 13 and the boom and bucket cylinders 12 and 14, respectively, is a flow divider valve 20, as seen in the drawing. Boom and bucket valves 11 and 13 are located in a common valve body 18 in a series type flow path.

Control valves 11 and 13 are supplied pump pressure from pump 22 through inlet cavity 24. Connected with pump inlet cavity 24 is a conventional system relief valve 26 which when the system pressure is exceeded in cavity 24, relief valve 26 opens dumping pressure into reservoir cavity 30.

Boom valve spool 28 is positioned in a bore 29 which passes through valve body 18. From left to right, bore 29 first intersects reservoir cavity 30, return cavity 32, motor port cavity 34, power passage 36, pump inlet cavity 24, open center passage 38, power passage 40, motor port cavity 42, return cavity 32 and reservoir cavity 30. Power passages 36 and 40 are always open to pump inlet cavity 24 via passages 98 (symbolically shown). Attached to the right end of spool 28 is a conventional centering spring mechanism 44 which returns the valve spool to its neutral position as indicated in the drawing. Bucket valve spool 46 is positioned in a bore 47 which also passes through valve body 18. Bucket spool bore 47, from left to right, first intersects reservoir cavity 30, motor port cavity 48, power passage 50, open center cavity 54, downstream open center cavity 56, power passage 58, motor port cavity 60 and reservoir cavity 30. Power passages 50 and 58 are always open to open-center cavity 54 via passages 99 (symbolically shown). U-shaped reservoir cavity 30 drains to reservoir 62 at all times regardless of the positions of valve spools 28 and 46. Attached to the right end of valve spool 46 is a common centering spring 64 covered by a conventional vented cap 66.

Boom valve spool 28 includes, from left to right, valve spool lands 68, 70, 72 and 74, while bucket valve spool 46 includes valve spool lands 76, 78, 80 and 82, respectively.

Flow divider valve 20 includes an inlet cavity 84 which supplies a shuttle spool 85 through a pair of lateral openings 86 in the center of the spool. Located in the left and right ends, respectively, of spool 85 are fixed orifices 87 and 88 which are sized to create whatever flow proportion is desired. Shuttle spool 85 is slidably positioned in a bore which intersects boom motor port cavity 89 on its left end and bucket motor port cavity 90 on its right end. In a static condition, spring 94 urges spool 85 against a stop 83, threaded into the body of valve 20. The tapered ends of shuttle spool 85 function as variable orifices governed by the pressure drop across fixed orifices 87 and 88, respectively. A detailed description of the function of shuttle spool 85 is given in U.S. Pat. No. 3,563,137, mentioned above.

The divided flow from flow divider valve 20 is split into two flow paths, with the first exiting boom motor port cavity 89 to boom motor port 42, and the second flow path exiting cavity 90 across check valve 91 to bucket motor port 60.

Also located in flow divider valve 20 is an unloading valve spool 92 which in the absence of pressure in cavity 90 is held in a closed position by spring 93, as shown in the drawing.

The self-leveling system 10 of the present invention would typically be used on a front end loader with a series type hydraulic system, as distinguished from the more complex load-responsive or other type variable flow systems.

The boom and bucket control valves 11 and 13, are conventional valves normally used in a more basic system which does not self-level. In such a system, the boom and bucket valves 11 and 13 would be connected only to their respective cylinders 12 and 14.

With boom and bucket spools 28 and 46 in their neutral positions as indicated in the drawing, there is no pressure build-up in inlet cavity 24 since the pump flow freely passes through open center passages 38, 54 and 56 back to reservoir 62. If it is the intent of the operator to raise the boom 15 while maintaining the bucket 16 in a level position; boom valve spool 28 is moved to the right to the raised position, as indicated at the left end of the spool 28. In the raise position, spool land 70 blocks flow through open center passage 38 causing pressure to build in inlet cavity 24 while the left edge of land 70 opens power passage 36 to motor port 34 (via passage 98) allowing pump pressure to enter the cap end of boom cylinder 12. As the boom begins to raise, the discharge flow from the rod end of cylinder 12 enters inlet cavity 84 of the flow divider valve 20. From cavity 84, fluid enters the center of shuttle spool 85 through lateral openings 86 and exits in a split path through the two fixed orifices 87 and 88 at the opposite ends of the spool 85. Since the shuttle spool 85 is initially located in its most rightwardly position against stop 83, due to the force of spring 94, the initial flow will all be across orifice 87. However, as soon as flow begins across orifice 87, the spool will shift leftwardly due to the imbalance of forces acting on the opposite ends of the spool caused by a pressure drop across orifice 87, and allow flow to begin across orifice 88, into cavity 90. Regardless of the amount of flow into the divider valve or the pressure levels it reaches, the shuttle spool 85 will proportionally divide or split the flows into cavities 89 and 90, respectively, with the proportion being preset by the comparative orifice sizes of orifices 87 and 88. In other words, if it is desirous to obtain one-third of the flow to bucket cylinder 14, and two-thirds of the flow to boom motor port 42, the orifices 87 and 88 will be accordingly sized.

As the boom 15 continues to rise, the flow is split at flow divider valve 20, with a portion of the flow passing to the cap end of bucket cylinder 14 via cavity 90, across check valve 91. The other split flow in cavity 89 flows back through boom motor port 42. The left edge of land 74 on the boom spool opens port 42 to return cavity 32, which in turn is open to reservoir 62 as long as bucket spool 46 has its open center cavities 54 and 56 open.

The flow exhausting from the rod end of bucket cylinder 14 enters flow divider valve 20 through cavity 97 and passes to reservoir 62 across unloading valve spool 92 as long as there is pressure in cavity 90. If bucket cylinder 14 attempts to overspeed and cavitate due to the weight in the bucket, the pressure in the cap end of cylinder 14 drops to zero which is felt in cavity 90, allowing unloading spool 92 to shift to the right due to spring 93 and block the flow from the rod end of bucket cylinder 14 to drain, thereby stopping movement of the cylinder until pressure again builds in the cap end.

If during the raising of the boom 15, the operator decides to override the self-leveling function, and say dump the bucket as the boom is rising; the operator would move the bucket spool to the left from its neutral position, as shown in the drawing. Land 80 on the bucket spool would block the open center flow through cavities 54 and 56, thereby building pressure in cavity 54 upstream of the bucket spool 46 since there is return flow entering motor port 42 from the flow divider valve 20. This split flow from cavity 89 which normally is passed to drain across the open center cavity 54 of the bucket is now blocked at the open center cavity 54 and is being forced into power passage 58 (air passage 99). With spool 46 shifted to the left, the right hand edge of valve spool land 80 opens power passage 58 to motor port 60, which in turn connects with the cap end of bucket cylinder 14. The rod end of bucket cylinder 14 is open to drain either through unloading valve 92 or across a parallel line 96 which connects with motor port 48 which also is open to drain due to the position of spool land 76. Since the split flow from flow divider 20 is supplied to the return side (part 42) of the boom cylinder, there is fluid pressure available upstream of bucket spool 13 (via the edge of land 74, passage 32 and passage 38) to effect an overriding function when the boom cylinder is in a raise position. In a conventional series type circuit, this would not be possible since the actuation of any upstream valve would block the downstream valve from any positive pressure so long as the upstream valve was in an operative position. While the present invention shows the split return flow to enter a motor port 42 of the boom valve, it could also enter a separate port which connected with either a return cavity 32 or open center cavity 38.

Flow divider valve 20 has a different function when the flow direction through the valve is reversed, such as when boom spool 28 is moved to the left to its lower position. Open center flow is blocked building pressure in cavity 24 while the right edge of land 72 opens power passage 40 to motor port 42 causing pressure to flow in a reverse direction into the left end of shuttle spool 85. Pressure in cavity 89 forces shuttle spool 85 to its far right position blocking any flow to cavity 90 with all of the flow passing through cavity 84 to the rod end of boom cylinder 12. Flow divider valve 20 has now become a shut-off valve to any flow in cavity 90 that might flow to the bucket cylinder 14. While there is one flow path from the opposite ends of bucket cylinder 14 through the flow divider 20 (via passage 90, cap end of cylinder 14, rod end of cylinder 14, passage 97 and drain 62), there is also a parallel flow path to both ends of the cylinder through lines 95 and 96 which allow bucket spool 46 to independently control the bucket cylinder.