Injection timing control device for distributor-type fuel injection pump

Claim 1

In a fuel injection pump for internal combustion engines of the type including a pump plunger, a rotary element coupled to said plunger for rotation at speeds dependent on engine speed, a semi-fixed element having an end face disposed in camming engagement with said rotary element and allowed to make a pivotal movement through a limited angle, the rotary element being adapted to carry out simultaneous rotating and reciprocating motion to cause a corresponding simultaneous rotating and reciprocating motion of the pump plunger for suction and pressure delivery of fuel, a first hydraulic actuatable element having a predetermined pressure applying area and connected to said semi-fixed element, a second hydraulic actuatable element having a larger pressure applying area than said first hydraulic actuatable element and disposed on an extension of the axis of said first hydraulic actuatable element, means for prohibiting displacement of said second hydraulic actuatable element toward said first hydraulic actuatable element beyond a prescribed range, a first spring interposed between said two hydraulic actuatable elements and urging them in a direction opposite to each other, and a pressure source for supplying a hydraulic pressure which is a function of engine speed to said first and second hydraulic actuatable elements at pressure applying areas thereof, wherein said pressure applying areas of said first and second hydraulic actuatable elements are each arranged on end faces of the respective hydraulic actuatable elements remote from said first spring, and whereby displacement of said first hydraulic actuatable element toward said second hydraulic actuatable element causes an advance in the injection timing of the pump, the improvement comprising: coupling means coupled to said first and second hydraulic actuatable element for permitting relative movement of said first and second hydraulic actuatable elements within a prescribed distance and for causing common movement of said first and second hydraulic actuatable elements when said prescribed distance is exceeded; and a second spring having one end arranged stationary and another end permanently urging said second hydraulic actuatable element in a direction away from said first hydraulic actuatable element; said second hydraulic actuatable element being kept in a most biased position by said spring until said hydraulic pressure which is a function of engine speed reaches a predetermined value to bias said first hydraulic actuatable element in an injection timing advancing direction through said coupling means; and wherein the following relationships are satisfied simultaneously: P(A.sub.2 -A.sub.1)>KS and PA.sub.1 ≧F where A 1 =pressure applying area of said first hydraulic actuatable element, A 2 =pressure applying area of said second hydraulic actuatable element, P=pressure acting upon the pressure applying areas of said first and second hydraulic actuatable elements, S=maximum allowable displacement of said second hydraulic actuatable element, F=setting load of said first spring, and K=spring constant of said second spring.