Electro-hydraulic control circuit for backhoe

Claim 1

In a vehicle having a hydraulic fluid source and equipped with a backhoe having a swing mount, a swing motor operatively connected between the vehicle and the swing mount for pivoting said swing mount about an upright axis relative to the vehicle, a boom pivotal about a horizontal axis on the swing mount, a boom motor connected between the swing mount and the boom, a dipper stick pivotally carried on the free end of the boom, a dipper motor connected between the dipper stick and the boom, a bucket pivotally carried on the free end of the dipper stick, and a bucket motor operatively connected between the bucket and the dipper stick, the improvement comprising: swing, boom, dipper and bucket valves for independently directing fluid pressure from said source to the associated one of said motors; said swing valve and said bucket valve having a spool and a servo-motor for controlling the position of the spool within the associated valve; solenoid-actuated valve means connected to each servo-motor for selectively directing fluid pressure from said source to each of said servo-motors; a first potentiometer operatively connected to the spool of said swing valve and providing a resistance related to the displacement from neutral of the swing valve spool; a manually operable swing control means including a second potentiometer for providing a resistance related to the position of the swing control means from a given position; a third potentiometer operatively connected between the swing mount and the vehicle for providing a resistance related to the displacement from a given position of the swing mount relative to the vehicle; a first bridge circuit including said first, second and third potentiometers with said first potentiometer being in one arm of the bridge circuit and second and third potentiometers being in another arm of the bridge circuit; a first comparator in said first bridge circuit for detecting an imbalance between said one arm and said another arm and for energizing said solenoid valve means for said swing valve in response to a detected imbalance, whereby the swing mount will be moved to a position corresponding to the position manually provided for the swing control means; a fourth potentiometer operatively connected to the spool of said bucket valve and providing a resistance related to the displacement from neutral of the bucket valve spool; a manually operable bucket control means including a fifth potentiometer for providing a resistance related to the position of the bucket control means from a neutral position; a second bridge circuit including said fourth and fifth potentiometers located in different arms thereof; a second comparator in said second circuit for detecting an imbalance between said different arms and for energizing said solenoid valve means for said bucket valve in response to a detected imbalance, whereby the bucket valve spool will be initially displaced from its neutral position an amount corresponding to the displacement of the bucket control means from its neutral position.