[3] Operation A: The PCV remains open during the plunger’s downward stroke, allowing low-pressure fuel to be drawn into the plunger chamber by way of the PCV. B: If the valve remains open because current is not applied to the PCV, even after the plunger begins its upward stroke, the fuel that was drawn in returns via the PCV, without being pres- surized. C: When current is applied to the PCV in order to close the valve at the timing that accommo- dates the required discharge volume, the return passage closes, causing pressure in the plunger chamber to rise. The fuel then passes through the delivery valve (check valve) to the rail.
As a result, an amount of fuel that corresponding to the plunger lift after the PCV closes becomes the discharge volume, and varying the timing of the PCV closure (plunger pre- stroke) varies the discharge volume, thus regulating rail pressure. A’: After surpassing the maximum cam lift, the plunger begins its downward stroke, causing pressure in the plunger chamber to decrease. At this time, the delivery valve closes, thus stopping the pumping of the fuel. In addition, because current to the PCV valve is cut off, the PCV opens, allowing low-pressure fuel to be drawn into the plunger chamber. Thus, the pump assumes condition “A”.
Suction process Delivery process Discharge volume Q= π d 2 (H-h) 4 Cam lift H h Pre-stroke PCV operation Valve closed Valve open Pump operation Reducing discharge volume Discharging required dischrge volume Increasing dischargevolume PCV Rail Delivery valve Plunger A B C A' φ d Q000087E 7