The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 03, 1979
Filed:
Apr. 19, 1978
Howard L Johnson, Joliet, IL (US);
Caterpillar Tractor Co., Peoria, IL (US);
Abstract
A hydraulic system including a pressure and flow compensated pump, a source of pilot fluid under pressure, a plurality of hydraulic circuits each including a work performing device, a plurality of controls, one for each circuit, each including a pilot operated flow valve for connecting the associated work performing device to the pump and an operator positioned valve connected to the pilot source for selectively directing pilot fluid to the corresponding flow valve, the work performing devices and the flow valves being connected in parallel. The system further includes a supply margin valve having pressure responsive surfaces respectively connected to the pump and to the work performing devices for providing a control signal to the pump to cause the same to supply fluid at a pressure equal to the pressure required by the work performing devices plus a predetermined margin and a first demand margin valve having pressure responsive surfaces respectively connected to the pump and to the work performing devices for decreasing the pressure of pilot fluid directed to some, but not all, of the operator positioned valves when the predetermined margin is not met. There is further included a second demand margin valve having pressure responsive surfaces respectively connected to the pump and to the work performing devices for decreasing the pressure of the pilot fluid directed to at least one of the others of the operator positioned valves when the predetermined margin is not met by more than a predetermined amount so that the first demand margin valve will decrease pilot pressure to certain of the valves before the second demand margin valve decreases pilot pressure to the other of the valves.