Hydraulic auto-tensioner for engine accessory

A hydraulic auto-tensioner for use with an engine accessory, comprising:

• a cylinder containing hydraulic oil and including a bottom portion having an upper surface formed with a sleeve fit-in hole;
• a sleeve having a lower end portion press-fitted in the sleeve fit-in hole;
• a rod having a lower end portion slidably inserted in the sleeve and defining a pressure chamber in the sleeve;
• a return spring incorporated between a spring washer provided at an upper part of the rod and the upper surface of the bottom portion of the cylinder and biasing the cylinder and the rod in a direction in which the rod protrudes from the cylinder;
• a tubular spring cover provided on the spring washer and covering an upper part of the return spring;
• a seal member incorporated in an upper side opening of the cylinder and having an inner periphery kept in elastic contact with an outer periphery of the spring cover, thereby defining a reservoir chamber between the cylinder and the sleeve, an oil passage being defined between fitting surfaces of the sleeve and the sleeve fit-in hole such that the reservoir chamber communicates with the pressure chamber through the oil passage;
• and
• a check valve mounted in the lower end portion of the sleeve and configured to be closed, thereby disconnecting the pressure chamber from the oil passage, when a pressure in the pressure chamber becomes higher than a pressure in the reservoir chamber,
• wherein the sleeve has a lower end face in abutment with a bottom surface of the sleeve fit-in hole, the bottom surface of the sleeve fit-in hole having:
• an annular inner peripheral surface portion;
• an annular outer peripheral surface portion surrounding the annular inner peripheral surface portion and located at a higher level than the annular inner peripheral surface portion;
• and
• an oil sump surrounded by the annular inner peripheral surface portion.