Patent ID: 7845896
Filing Date: 2010-12-07
Classification: B66F,E02F,F15B

Abstract:
1. In a loader including a frame supported on front and rear axles carrying front and rear sets of wheels, a hydraulically operated extension arm mounted to the frame for swinging vertically between lowered and raised positions, an extensible and retractable hydraulic cylinder coupled between said frame and said extension arm for selectively moving said arm between said lowered and raised positions, a first supply line coupled to a piston rod side of said hydraulic cylinder, a second supply line coupled to a piston side of said hydraulic cylinder, a pressurized hydraulic fluid source, a hydraulic fluid tank, at least one mechanically switchable control device coupled, on the one hand, to said first and second supply lines and coupled, on the other hand, to said fluid source and fluid tank and being selectively operable for controlling the flow of hydraulic fluid to and from said hydraulic cylinder, a load sensor located on said loader for monitoring a load condition on the loader and operable for creating an electrical load signal representing said load condition, and an electronic control unit coupled to said load sensor for receiving said electrical signal and comparing it with a critical load stored in memory in said electronic control unit and for generating a control signal representing a difference between said load signal and said critical load, the improvement comprising: a load holding valve including a pressure limiting valve located in said second supply line and normally preventing flow toward said control device from said hydraulic cylinder: first and second control pressure lines respectively connecting the rod and piston sides of said hydraulic cylinder to said pressure limiting valve such that the respective pressures therein act in a direction tending to open said pressure limiting valve; one of a connecting line or a discharge line having a first end coupled to said first supply line, with said connecting line having a second end coupled to said second supply line, and with said discharge line having a second end coupled directly to said tank; an electrically operable variable restriction device being coupled in said one of said connecting line or discharge line for establishing a variable restricted flow path away from said first supply line and including a proportional electrical controller connected for receiving said control signal from said electronic control unit and being operable in response to said control signal for gradually reducing a restriction afforded by said restricted flow path when said sensed load increases toward a value equal to said critical load.