There are many and diverse types of apparatus which function to move an object in various directions. Among these apparatus are included power operated implements such as buckets, booms and bulldozer blades which are usually mounted on a vehicle and manipulated by a plurality of individual controls. The operator must give a great deal of attention to selectively moving the various levers, buttons, or the like into their proper modes of operation in order to correspondingly maneuver the various hydraulic motors or jacks which control the complex movement of the implement.
For example, while two separate levers can be utilized for individually operating a pair of valves in a hydraulic system and thereby directing fluid selectively to the opposite ends of a pair of hydraulic jacks, there is frequently the need to simultaneously move the jacks in the same direction or in opposite directions at the same rate. This is difficult to accomplish when the operator is also maneuvering the vehicle or manipulating a separate control element since two hands are usually required. On the other hand, if an attempt is made to mechanically connect each of the levers with both of the control valves so that the two jacks can be simultaneously extended or retracted with one lever or can be simultaneously moved in opposite directions with the other, then movement of one lever would disadvantageously move the other. In addition, it is usually desirable that both control levers be automatically returned to a neutral or jack-holding position upon manually releasing them, and yet when operating an individual lever the effort which is required should be minimal. It is thus apparent that a complex coupling problem is involved when connecting both levers to both valves.
While it would appear to be desirable to utilize a single control lever to position a pair of hydraulic jacks through a suitable control valve arrangement, it is not always easy to relate the required hand movement with the desired implement movement. Furthermore, operator movement of a universally pivotable single control lever can easily lead to unequal rates of movement of the jacks to the point of requiring correctional manipulation of the lever at a crucial operating time.
Reference is herein made to U.S. Pat. No. 3,705,631 issued Dec. 12, 1972 to D. H. Seaberg, and U.S. Pat. No. 3,795,280 issued Mar. 5, 1974, the latter of which is assigned to the assignee of the present invention, which relate to control arrangements and associated hydraulic control circuits for selectively actuating separate hydraulic jacks for lifting, tilting and angling a bulldozer blade on a tractor. While such controls have been well received by the industry, it takes a special degree of dexterity and alertness to operate them. Particularly, it is difficult to correctly manipulate an electrical switch disposed on or adjacent to the single control lever. As a result, the operator will occasionally move the switch in the wrong direction or hold it engaged an excessively long period. As a consequence, one of the hydraulic jacks might well be at the end of its stroke so that the additional fluid flow being directed thereto by the inadvertent engagement of the switch must be exhausted at the relatively high pressure setting of the system relief valve. As is well known in the art, any prolonged exhausting of fluid against the system relief valve pressure is undesirable from many standpoints.
Another problem is that these lever control arrangements cannot always be disposed immediately adjacent to the control valves. As a result they must cooperate with various hydraulic or electrical piloting devices to remotely actuate the control valves and to thereby affect operating economies for certain member placement advantages on the vehicle.