Accessory drive device for engine

An engine accessory drive system comprising:

• a drive shaft;
• a driven shaft coupled to an engine accessory;
• an endless transmission member looped around the drive shaft and the driven shaft;
• a first tensioner disposed on a slack side of the endless transmission member and configured to push and bias the endless transmission member to apply tension to the endless transmission member;
• and
• a second tensioner disposed on a tight side of the endless transmission member and configured to push and bias the endless transmission member to apply tension to the endless transmission member, wherein
• the second tensioner has a damping function to damp pushing force applied to the second tensioner by the endless transmission member in a direction opposite to a biasing direction,
• the first tensioner has a damping function to damp pushing force applied to the first tensioner by the endless transmission member in a direction opposite to a biasing direction,
• each of the first tensioner and the second tensioner is a hydraulic tensioner having a plunger configured to bias the endless transmission member in the biasing direction by utilizing a hydraulic fluid supplied to a pressure chamber, and a spring which biases the plunger in the biasing direction, and the hydraulic tensioner being configured to damp the pushing force by utilizing the hydraulic fluid leaked from the pressure chamber when the plunger is pushed by the endless transmission member in the direction opposite to the biasing direction,
• biasing force of the first tensioner is set to be smaller than biasing force of the second tensioner, and
• a spring constant of the spring included in the second tensioner is set to be greater than a spring constant of the spring included in the first tensioner.