Patent Application
20100210385
The invention relates to a tensioner assembly, especially for a rotary accessory drive of an engine.
Belt drive systems are used to operate ancillary components associated with automotive engines. For example, belt drive systems are used to drive complex valve trains, balance shafts, oil pumps, high pressure fuel injection pumps and water pumps. A dedicated tensioning system is used to ensure the overall functional performance of a belt drive system given the advent of increasing packaging complexity and its influence on belt drive layout and design. A typical tensioning system includes a belt drive tensioner and a tensioner arm that engages a belt along an engagement length to create an initial required tension on the belt.
Over time, as the belt of the belt drive system wears, slack is generated. As the belt wears, it is the tensioner system that is operable to remove the slack from the system. Often, a relatively long belt is necessary, requiring a tensioning system that can control the greater potential variation in belt tightness in a long belt. One type of tensioner system is a wound coil spring with an internal friction damper operable to damp rotary motion. Another type of tensioner system is a linear coil system concentric with a hydraulic damper. In both of these types of tensioner systems, the tensioning spring operates over the same range of motion, whether rotary or linear, as the damper.
In a belt-alternator starter-type hybrid powertrain with a rotary belt drive system, a motor/generator may be controlled to start the engine by driving the engine crankshaft via the belt. The belt may be subjected to large dynamic forces. The tensioner system must adequately dampen these forces while tensioning the relatively long belt.
A tensioner assembly for an endless drive element is provided that utilizes rotary motion and linear damping with decoupled tensioning and damping components. The drive element may be a belt or chain. The tensioner assembly includes a rotatable element in contact with a span of the drive element and rotatable via the drive element, and a first linkage supporting the rotatable element for rotation thereon. The rotatable element may be a pulley, a sprocket or a gear. A torsion spring operatively connects the first linkage to a base for pivoting about a pivot point with respect to the base. The torsion spring is configured to bias the rotatable element in a direction to tension the drive element. A linear damper is operatively connected to the first linkage at a distance from the pivot point, such as by a second linkage or lever arm, and is grounded to the base for damping pivoting motion of the first linkage. Thus, the torsion spring and the damper are decoupled from one another and are able to operate over different ranges of motion. A range in flexibility of the tensioning function is achieved by selecting a spring force appropriate for expected operating parameters, and by selecting the length of the lever arm to maintain a relatively short damper travel range, without compromising system damping. High damping capability is provided with a relatively short damper travel range by utilizing the mechanical advantage of the lever arm. The damping element is not burdened with the structure needed to retain and retract a linear spring, as is typical for spring tensioners. The length of the damping element is not constrained by spring wire diameter, and it is therefore potentially shorter with a smaller packaging envelope. The tensioner assembly has greater flexibility in mounting and orientation within available packaging space on an engine assembly.
The tensioner assembly may be part of a rotary accessory drive for a powertrain with an engine and a motor/generator that is used to start the engine. For example, the drive element may be a belt in contact with the rotatable element, which may be a tensioner pulley, and in contact with a motor/generator pulley, and a crankshaft pulley. The tensioner assembly tensions the belt and dampens dynamic loading on the belt when the motor/generator is used to start the engine via the drive belt.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,
Referring to
Referring to
The tensioner assembly 34 has a tensioning component in the form of a torsion spring 54 and a damping component in the form of a linear damper or strut 56 that is remote from the torsion spring 54. The linear damper 56 is shown as a hydraulic damper, but could alternatively be a locking-type damper. Separating the tensioning component (i.e., spring 54) from the damping component (i.e., damper 56) as described herein increases packaging flexibility and permits the hydraulic damper 56 to be reduced in size.
The torsion spring 54 is wound concentric with the pivot axis P and has a first end portion 55 secured to the body portion 46 and a second end portion 57 secured to the base 41. Although a wound spring 54 is shown, a torsion bar-type rotary spring may also be used. The torsion spring 54 is wound to exhibit a spring force SF that resists dynamic belt forces on the tensioner pulley 40, represented by belt forces F, that are applied to the spring 54 via the first linkage 45. Unlike typical torsion spring tensioner assemblies, there is no damping element positioned between the body portion 46 and the base 41 operable to resist relative motion of the body portion 46 and base 41. Instead, damping is provided by a linear hydraulic damper 56 that is connected with the body portion via a link arm 58, also referred to as a lever arm or a second linkage. The link arm 58 is angularly spaced from center axis C of the pulley 40 about the pivot axis P. The link arm 58 is pivotably attached to a first portion 60 of the damper 56 at a pivot point PP. Thus, the damper 56 is spaced a distance D from the pivot point P. A second portion 62 of the damper 56 is fixed to the base 41 via third linkage 64, and is thus grounded to the engine casing 13 of
When the first linkage 45 is urged to pivot about pivot axis P due to belt forces F that overcome the torsion spring force SF, causing the first linkage 45 to pivot from a first position shown in phantom as 45A to a second position shown in solid in
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.
