Motors: expansible chamber type – Plural relatively movable or rigidly interconnected working... – Condition responsive means for modifying working member...
Reexamination Certificate
1998-09-24
2001-10-30
Lopez, F. Daniel (Department: 3745)
Motors: expansible chamber type
Plural relatively movable or rigidly interconnected working...
Condition responsive means for modifying working member...
C414S708000
Reexamination Certificate
active
06308612
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic levelling control system for a loader type vehicle and particularly to an improved hydraulic system for controlling the attitude of a material handling unit supported on a boom, during raising and during lowering of the boom.
Loader type vehicles generally include a boom pivotally carried on the vehicle with a material handling unit pivoted on the free end of the boom. Generally, the boom is raised and lowered on the vehicle by a boom cylinder having fluid supplied thereto through a boom control valve while the material handling unit is pivoted on the end of the boom through a unit cylinder having fluid supplied thereto through a unit valve. Fluid is generally supplied to the respective control valves from a reservoir through a pump.
In the absence of any self-leveling function, it is necessary for the operator of the loader type vehicle to operate both the boom valve and the unit valve one with each hand or foot, to maintain the material handling unit level while raising or lowering the boom. This operation is not only difficult but also requires the strict attention of the operator.
Hydraulic leveling systems have heretofore been made such as disclosed in U.S. Pat. No. 3,563,137, in which fluid exiting from the rod end of the boom cylinder during raising of the boom, is passed through a valve type flow divider that directs one portion of the inlet flow to the piston end of the unit cylinder while dumping a remaining portion of the inlet flow to drain, to level the unit during raising of the boom. This patent also discloses an embodiment in which the boom control valve was modified to provide a boom-raise, unit-leveling position and a boom-lower, unit-leveling position, in addition to the customary boom-raise and boom-lower positions. In that embodiment, the boom control valve was operative to pass fluid existing from the piston end of the boom cylinder during lowering of the boom through a second flow divider valve arranged to direct one portion of the flow to the rod end of the unit cylinder and to dump the remaining portion to drain. Valve type flow dividers divide flow from an inlet into separate streams at two outlets to in accordance with the pressure drop through two orifices and can operate reliably only when the pressure at the inlet is substantially greater than the pressure at either outlet. During lowering of the boom, a portion of the fluid from the piston end of the boom cylinder is passed to the rod end of the bucket cylinder. The area of the piston end of the boom cylinder is usually very large as compared to the area of the rod end of the unit cylinder and, under some operating conditions, the pressure at the piston end of the boom cylinder is too low as compared to the pressure required at the rod end of the bucket cylinder, to reliably move the bucket when the latter is loaded.
U.S. Pat. No. 5,447,094 discloses a leveling circuit using a valve type flow divider for controlling leveling of the bucket during raising of the boom and a motor type flow divider for controlling leveling of the bucket during lower of the boom. While this hydraulic leveling system operates during both raising and lowering of the boom, the motor type flow divider significantly increases the cost of the leveling system. Further, motor type flow dividers divide fluid in a fixed ratio and are not adjustable to change the fixed ratio to accommodate different size boom and unit cylinders such as are used in different loader-type vehicles.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an hydraulic control system for controlling the orientation of the material handling unit on a boom, and which is operative in an automatic leveling mode to reliably control leveling of the unit during both raising and lowering of the boom.
Another object of this invention is to provide an hydraulic control system in accordance with the foregoing object, and which will automatically disengage from the automatic leveling mode when the unit valve is operated to tilt the unit.
Another object of this invention is to provide an hydraulic control system for controlling the orientation of material handling unit supported on a boom in accordance with the foregoing object, and which will automatically disengage from the unit leveling mode and allow the boom to continue at the same speed, during either raising or lowering of the boom, when the unit cylinder bottoms out in either direction.
Another object of this invention is to provide an hydraulic control system in accordance with the forgoing object, and which is adjustable to enable use of the system on different material handling equipment having boom and unit cylinders with different displacement ratios.
In the present invention, an hydraulic control system is provided which is operable in an automatic leveling mode, to control leveling of a material handling unit mounted on the free end of a boom during both raising and lowering of the boom, using a proportional flow divider/combiner valve having a primary inlet and a first and second secondary outlets. In the automatic leveling mode, when the boom control valve is moved to a boom raise position, fluid from the fluid pressure inlet of the boom control valve is supplied to the boom-raise chamber and fluid from the boom-lower chamber of the boom cylinder is passed to the primary inlet of the flow divider/combiner valve which divides the flow into a first stream that is passed to the tilt-down chamber of the unit cylinder and a second stream which is returned to the reservoir through the boom control valve, to level the unit during raising the boom. When the boom control valve is moved to a boom-lower position, hydraulic fluid from the fluid pressure inlet of the boom control valve is supplied to the tilt-up chamber of the unit cylinder and to the second secondary passage of the flow divider/combiner valve, and fluid from the tilt-down chamber of the unit cylinder is passed to the first secondary passage of the flow divider/combiner valve. The streams from the first and second secondary passages are combined in a preset ratio in the flow divider/combiner valve and supplied to the boom-lower chamber of the boom cylinder, to maintain the unit in a preset attitude with respect to the ground, during lowering of the boom.
The control system includes valve means operable to change the operation from an automatic leveling mode to a manual mode and enable raising and lowering of the boom and tilting of the unit upwardly and downwardly independently of each other, under the control of the respective boom and unit control valves.
REFERENCES:
patent: 3563137 (1971-02-01), Graber
patent: 4408518 (1983-10-01), Diel
patent: 4465089 (1984-08-01), Inhofer
patent: 4531536 (1985-07-01), Kosarzecki
patent: 4561342 (1985-12-01), Calvert
patent: 4683802 (1987-08-01), Prokop et al.
patent: 4709618 (1987-12-01), Zongker
patent: 4723478 (1988-02-01), Diel
patent: 4799851 (1989-01-01), Swanson
patent: 4815357 (1989-03-01), Truehart
patent: 5447094 (1995-09-01), Geyler, Jr.
patent: 5669282 (1997-09-01), Tanino
patent: 5797310 (1998-08-01), Casey et al.
Sun drawings “High Capacity Flow Divider/Combiner”, pp. 7-15, submitted Sep. 9, 1994.
Emanie Faraidoon Fred
Frey Brian Andrew
Delta Power Company
Lopez F. Daniel
Pillote Vernon J.
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