Sliding structure for shaft member with improved abrasion resistance and injector

An injector having a needle which is inserted into a nozzle supplied with a fuel for injection, is made up of a shaft member retained slidably in a guide hole formed in the nozzle wall and displaced in the axial direction to switch between fuel injection and termination of fuel injection;

• wherein a plurality of labyrinth grooves are formed in both axial end portions of the side surface of the shaft member which are located in an area, which are always in slidable contact with a side surface of the guide hole,
• wherein an intermediate portion of the shaft member between said axial end portions has a substantially constant outer diameter that is free of grooves, and
• wherein a distance between an end of the shaft member and a first groove of the labyrinth grooves nearest to the end of the shaft member is 0.1 to 0.8 mm.

An injector having a needle, which is inserted into a nozzle supplied with a fuel for injection and is displaced in the axial direction to switch between fuel injection and termination of fuel injection,

• a valve chamber provided with a valve body for isolating a back pressure chamber from a low-pressure source provided in a low-pressure flow path for releasing to the low-pressure source fuel in the back pressure chamber, to which a high-pressure fuel is supplied and which generates a back pressure of the needle, and
• a piston, which is made up of a shaft member that presses against the valve body, and is retained slidably in a guide hole, wherein a plurality of labyrinth grooves are formed in both axial end portions of the side surface of the shaft member which are located in an area, which are always in slidable contact with a side surface of the guide hole, and wherein an intermediate portion of the shaft member between said axial end portions has a substantially constant outer diameter that is free of grooves, and
• wherein a distance between an end of the shaft member and a first groove of the labyrinth grooves nearest to the end of the shaft member is 0.1 to 0.8 mm.