Endless drive arrangement and improved two-armed tensioning system for same

An endless drive arrangement, comprising:

• a crankshaft;
• a secondary drive device;
• an endless drive member connecting the crankshaft and the secondary drive device;
• a tensioner, including
• a first tensioner arm that has a first tensioner pulley rotatably mounted thereto, wherein the first tensioner pulley is engaged with a first span of the endless drive member on a first side of the secondary drive device, wherein the first tensioner arm is movable about a first tensioner arm axis;
• a second tensioner arm that has a second tensioner pulley rotatably mounted thereto, wherein the second tensioner pulley is engaged with a second span of the endless drive member on a second side of the secondary drive device, wherein the second tensioner arm is movable about a second tensioner arm axis;
• a tensioner biasing member that is positioned to apply a tensioner biasing force to bias the first and second tensioner arms in respective first and second free arm directions;
• and
• a second tensioner arm stop that is positioned to limit the movement of the second tensioner arm in a direction opposite the second free arm direction, wherein the second tensioner arm stop is positioned such that, in use, the second tensioner pulley is engaged with the endless drive member while the second tensioner arm is engaged with the second stop throughout a selected range of operating conditions, and wherein
• TR
• TL
• >
• hF
• 
• 
• 2
• hF
• 
• 
• 1
• where
• TR=TR2−TR3,
• TL=TR4−TR5,
• TR2=the moment arm relative to the second tensioner arm axis of a force T2 exerted on the second tensioner pulley by a first portion of the second span of the endless drive member,
• TR3=the moment arm relative to the second tensioner arm axis of a force T3 exerted on the second tensioner pulley by a second portion of the second span of the endless drive member,
• TR4=the moment arm relative to the first tensioner arm axis of a force T4 exerted on the first tensioner pulley by a first portion of the first span of the endless drive member,
• TR5=the moment arm relative to the second tensioner arm axis of a force TS exerted on the first tensioner pulley by a second portion of the first span of the endless drive member,
• hF1=the moment arm relative to the first tensioner arm axis of a force FL exerted on the first tensioner arm by the tensioner biasing member, and
• hF2=the moment arm relative to the second tensioner arm axis of the force FL exerted on the second tensioner arm by the tensioner biasing member.

An endless drive arrangement for an engine, comprising:

• a crankshaft pulley connected to a crankshaft;
• a secondary drive device pulley connected to a shaft of a secondary drive device;
• an endless drive member that is engaged with the crankshaft pulley and with the secondary drive device pulley, wherein the endless drive arrangement is operable in a first mode in which the crankshaft pulley drives the endless drive member and the secondary drive device pulley does not drive the endless drive member such that tension in a first span of the endless drive member is lower than tension in a second span of the endless drive member, and in a second mode in which the secondary drive device pulley drives the endless drive member in isolation or in addition to the crankshaft pulley;
• and
• a tensioner, including a first tensioner arm that has a first tensioner pulley rotatably mounted thereto, wherein the first tensioner pulley is engaged with the first span of the endless drive member, wherein the first tensioner arm is movable about a first tensioner arm axis;
• a second tensioner arm that has a second tensioner pulley rotatably mounted thereto, wherein the second tensioner pulley is engaged with the second span of the endless drive member, wherein the second tensioner arm is movable about a second tensioner arm axis;
• a tensioner biasing member that is positioned to bias the first and second tensioner arms in respective first and second free arm directions, wherein the first tensioner pulley is disposed on a first side of the first tensioner arm axis, and the tensioner biasing member is positioned to apply the tensioner biasing force on a second side of the first tensioner arm axis, and wherein the second tensioner pulley is on a first side of the second tensioner arm axis, and the tensioner biasing member is positioned to apply the tensioner biasing force on a second side of the second tensioner arm axis;
• a first tensioner arm stop surface that is positioned to limit the movement of the first tensioner arm in a direction opposite the first free arm direction, and
• a second tensioner arm stop surface that is positioned to limit the movement of the second tensioner arm in a direction opposite the second free arm direction,
• wherein, due at least to the configuration of the first and second tensioner arms, the position of the first tensioner arm axis, the position of the second tensioner arm axis, the wrap of the endless drive member about the first and second tensioner pulleys, and the position of the second tensioner arm stop surface, the second tensioner arm has a preload torque in static equilibrium of about 1 Nm to about 15 Nm arising from a combination of torques applied by at least the endless drive member and the tensioner biasing member, wherein the preload torque urges the second tensioner arm into engagement with the second tensioner arm stop surface such that, when the endless drive arrangement operates in the first or second mode, the second tensioner arm remains engaged with the second tensioner arm stop surface and the first tensioner arm remains spaced from the first tensioner arm stop surface where transient torque on the second tensioner arm acts against the preload torque but is below the preload torque, and wherein, when the endless drive arrangement operates in the first or second mode, the first tensioner arm remains engaged with the first tensioner arm stop surface and the second tensioner arm remains spaced from the second tensioner arm stop surface where transient torque on the second tensioner arm acts against the preload torque and is sufficiently above the preload torque.