Beam pumping unit and design method for beam pumping unit

A beam pumping unit, comprising:

• a set of beams;
• a walking beam arranged above the set of beams, wherein a middle part of the walking beam forms a first pivotal connection having a first pivotal center with the set of beams, a first portion is extended over a first side of the first pivotal center, a second portion is extended over a second side of the first pivotal center, a donkey head is mounted at the first portion, a walking beam tail seat is mounted at the second portion, and a distance from a donkey head suspension point to the first pivotal center is A;
• a rotating arm arranged behind and below the first pivotal center, wherein the rotating arm has a first position formed as a rotating center and a second position revolving around the rotating center by a radius R, wherein the rotating arm is vertically oriented and directly coupled to a power source such that the power source outputs torque directly to the rotating arm without an intermediate transmission;
• a drive rod, wherein a lower part of the drive rod and the second position form a second pivotal connection having a second pivotal center, and an upper part of the drive rod and the walking beam tail seat form a third pivotal connection having a third pivotal center, wherein the rotating arm is configured to pivot about a vertical axis through an angular displacement to drive the drive rod in a substantially vertical plane;
• a straight line distance between the third pivotal center and the first pivotal center is C;
• the second pivotal center makes a circular motion around the rotating center at a rotating angle θ to drive the walking beam to swing at a preset magnitude of angle δ, and then the donkey head is driven to conduct up-down reciprocating motion;
• the third pivotal center is set higher than the rotating center;
• wherein
• a stroke of the beam pumping unit is greater than 7,620 mm;
• and
• 58°<δ≤72°.