This invention relates to boom-type vehicles, and more particularly to a frame leveling speed control arrangement for a boom-type vehicle.
A boom-type vehicle such as an extendible boom forklift typically includes a boom pivotably mounted to a frame. Hydraulic cylinders are interposed between the boom and the frame for moving the boom between its raised and lowered positions. The frame carries a set of wheels, and one or more frame leveling cylinders are interposed between the frame the wheels for leveling the frame when it is desired to raise the boom.
It is an object of the present invention to provide a system for insuring that a brake is applied when the boom reaches a predetermined angle relative to the frame. It is a further object of the invention to provide relatively slow movement of the frame leveling cylinder when the boom reaches a predetermined position relative to the frame. A still further object of the invention is to provide a system for preventing movement of the vehicle and for providing controlled movement of the frame leveling cylinder when the boom attains a predetermined angle relative to the frame.
In accordance with one aspect of the invention, a boom-type vehicle includes a frame carrying a set of ground-engaging wheels, and a frame leveling arrangement interposed between the frame and the wheels for leveling the frame relative to the ground. A boom is pivotably mounted to the frame, and a position sensing arrangement is interposed between the boom and the frame for sensing the angle of the boom relative to the frame. The frame leveling arrangement includes a leveling speed control responsive to the position sensing arrangement for enabling the leveling arrangement to operate at a first speed of operation when the angle of the boom relative to the frame is below a predetermined threshold, and to operate at a second speed of operation less than the first speed when the angle of the boom relative to the frame is above the predetermined threshold. A hydraulic cylinder arrangement is preferably interconnected between the boom and the frame for providing pivoting movement of the boom relative to the frame. The position sensing arrangement may be in the form of a movable member interconnected with the boom and movable in response to the movement of the boom relative to the frame, and a sensing member mounted to a portion of the cylinder arrangement interconnected with the frame, such that the position of the movable member relative to the sensing member changes according to the angle of the boom relative to the frame. The movable member may be in the form of a rod having a first end pivotably interconnected with the boom and a second end spaced therefrom. The sensing member may be in the form of a proximity switch operable to detect the second end of the rod when the angle of the boom relative to the frame reaches the predetermined threshold. The frame leveling arrangement may be in the form of a hydraulic cylinder arrangement interconnected between the frame and the wheels. The leveling speed control features a shiftable flow restricting arrangement interconnected with the hydraulic cylinder arrangement. The shiftable flow restricting arrangement may be in the form of a flow restrictor in the flow path of the hydraulic frame leveling cylinder arrangement and a check valve which is shiftable in response to actuation of the proximity switch to direct fluid flow through the flow restrictor when the angle of the boom relative to the frame reaches the predetermined threshold.
In accordance with another aspect of the invention, a boom-type vehicle includes a frame carrying a set of ground-engaging wheels, and a brake mechanism interconnected with the wheels for selectively preventing rotation of the wheels relative to the frame. A frame leveling arrangement is interposed between the frame and the wheels for leveling the frame relative to the ground. A boom is pivotably mounted to the frame, and a position sensing arrangement is interposed between the boom and the frame for sensing the angle of the boom relative to the frame. A brake actuator is responsive to the position sensing arrangement for automatically applying the brake mechanism when the angle of the boom relative to the frame exceeds a predetermined threshold. The position sensing arrangement is preferably as summarized above, and the brake actuator is responsive to actuation of the proximity switch for automatically applying the brake mechanism.
In a particularly preferred embodiment, the position sensing arrangement is interconnected with both the brake actuator and the leveling speed control arrangement. In this manner, the brake mechanism is automatically applied when the boom attains a predetermined angle relative to the frame and, simultaneously, the leveling speed control arrangement is operable to restrict fluid flow to and from the frame leveling cylinder arrangement for reducing the speed of operation of the frame leveling cylinder arrangement. This combination of automatic brake actuation and leveling speed control insures that the vehicle remains stationary and the frame can only be leveled at a relatively slow speed when the boom is at or above a certain angle relative to the frame.
The invention also contemplates a method of operating a boom-type vehicle, substantially in accordance with the foregoing summary.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.