Grease lubricator, particularly for construction machine

In a grease lubricator including

• a work chamber having a length and being defined by a chamber wall extending along said length;
• a delivery piston accommodated in said work chamber for executing delivery strokes and return strokes therein;
• said delivery piston having a delivery piston head;
• first driving means for causing said delivery piston to execute said delivery strokes and said return strokes;
• a supply port connectable to a grease container and having a supply port opening provided in said chamber wall;
• said supply port merging into said work chamber through said supply port opening and being closable by said delivery piston during the delivery strokes thereof;
• a delivery port connectable to a machine location to be lubricated and having a delivery port opening through which said delivery port merges into said work chamber;
• said delivery port opening being situated downstream of said supply port opening as viewed in a direction of said delivery strokes;
• a closure element having open and closed positions for respectively establishing and interrupting communication between said work chamber and said delivery port;
• biasing means for resiliently maintaining said closure element in said closed position;
• and
• an adjusting abutment situated at an end of said work chamber and limiting a length of said delivery strokes;
• the improvement comprising
• (a) a compressing portion forming a length portion of said work chamber and being situated downstream of said supply port opening;
• (b) a delivery portion forming a length portion of said work chamber and adjoining said compressing portion downstream thereof;
• said compressing portion having a diameter greater than a diameter of said delivery portion;
• (c) grease return means for returning grease from said compressing portion into said supply port;
• said grease return means including blocking means for maintaining communication between said compressing portion and said supply port solely as long as said delivery piston head is situated in said compressing portion during the delivery strokes and a sufficiently high pressure prevails in said compressing portion;
• (d) biasing means for resiliently maintaining said closure element in said closed position;
• said biasing means having a biasing force set such that said closure element assumes said open position from said closed position at the earliest when said delivery piston head, during the delivery stroke, has reached said delivery portion and has blocked off said delivery portion from said compressing portion;
• (e) a limiting face situated in said work chamber and separating said compressing portion from said delivery portion;
• (f) a holding element attached to said delivery piston;
• (g) an external piston forming part of said grease return means;
• said external piston being situated in said work chamber and being displaceable relative to said delivery piston along a path limited by said limiting face and said holding element;
• and
• (h) second driving means for causing said external piston to execute strokes in a direction of said delivery strokes of said delivery piston;
• a force applied by said second driving means to said external piston being less than a force applied by said first driving means to said delivery piston;
• the force of said second driving means being set such that said external piston overcomes a pressure derived from a compressible medium in said work chamber to arrive into engagement with said limiting face.