Engine accessory drive with belt tensioner and same plane idler

A belt tensioner for a starter generator drive is provided. The belt tensioner comprises a carrier having a pivot defining a first pivot axis at a first end and a carrier arm extending from the pivot to terminate in a second end. An idler pulley is rotatably mounted to the carrier for rotation about the first pivot axis and a tensioner pulley is rotatably mounted to the carrier at the second end of the carrier arm for rotation about a second axis. The second axis extends parallel to and is arcuately moveable relative to, the first pivot axis. A tensioner is in communication with the second end of the carrier arm for biasing the carrier arm and the tensioner pulley against a drive belt for tensioning the drive belt engaged by the idler pulley and the tensioner pulley.

FIELD OF THE INVENTION

This invention relates to internal combustion engines and, more particularly, to an engine accessory drive and drive belt tensioner for such drive.

BACKGROUND

Belt Alternator Starter (“BAS”) powertrain systems for hybrid vehicles differ from conventional, non-hybrid systems in that the torque to turn the accessory drive belt and related accessories is not always generated from the engine crankshaft through the crankshaft pulley. During engine operation, the engine crankshaft provides torque for rotating a Motor Generator Unit (“MGU”), or electric starter generator unit, generally providing for taut and slack sides of the drive belt on opposite sides of the MGU pulley. During engine starting using the MGU, however, the MGU drives the accessory drive belt and related accessories causing the slack side of the belt to switch to the opposite side of the MGU pulley. Accordingly, belt tensioners are generally required in such systems as are idler pulleys that are used to shorten drive belt spans to minimize the potential for drive belt slack.

During engine driven operation of the MGU and other accessories, the loads placed on the drive belt are determined by the power required to drive the accessories, including the MGU unit. The accessory drive loads are relatively light and, accordingly, require moderate to low belt tensioning to avoid belt slippage. On the other hand, during engine starting using the MGU, the MGU must supply power to rotate the engine (crankshaft, pistons, camshafts, etc.) as well as the accessories. MGU driven engine starts require a significantly higher level of belt tensioning to control motion on the slack side of belt and assure that the belt will not slip. Because of packaging requirements it is common to provide separate tensioner and idler arms and pulleys with different pivot locations to attain the necessary drive belt geometry.

SUMMARY

In an exemplary embodiment, a belt tensioner for an engine mounted, belt driven component is provided. The belt tensioner comprises a carrier having a pivot defining a first pivot axis at a first end and extending from the pivot to terminate at a second end. An idler pulley is rotatably mounted to the carrier for rotation about the first pivot axis. A tensioner pulley is rotatably mounted to the carrier at the second end for rotation about a second axis. The second axis extends parallel to and is arcuately moveable relative to, the first pivot axis. A tensioner assembly is in communication with the second end of the carrier for biasing the carrier and the tensioner pulley against a drive belt for tensioning the drive belt engaged by the idler pulley and the tensioner pulley.

In another exemplary embodiment, an accessory drive for an engine having a belt-driven, electric starter-generator unit for driving and being driven by the engine is provided and comprises a first driven pulley connected with an engine crankshaft and rotatable therewith. A second driven pulley, connected with an electric starter-generator unit is mounted to the engine. A drive belt connects the first driven pulley and the second driven pulley for driving either pulley from the other pulley. A drive belt tensioner assembly comprises a carrier having a pivot at a first end, defining a first pivot axis, mounted to the engine for pivotal motion thereon and extending from the pivot to terminate in a second end. An idler pulley rotatably mounted to the carrier for rotation about the first pivot axis and to carry the drive belt thereon and a tensioner pulley rotatably mounted to the carrier at the second end for rotation about a second axis that extends parallel to, and is arcuately moveable relative to, the first pivot axis. A tensioner assembly is mounted to the engine and connected to the second end of the carrier to bias the carrier and the tensioner pulley about the first pivot axis for tensioning the drive belt.

In yet another exemplary embodiment, an engine system having a belt-alternator starter accessory drive system is provided and comprises an engine, a first driven pulley connected with a crankshaft and rotatable therewith and a second driven pulley connected with an electric starter-generator unit mounted to the engine. A drive belt connects the first driven pulley and the second driven pulley for driving either pulley from the other pulley. A drive belt tensioner assembly comprises a carrier having a pivot at a first end, defining a first pivot axis, mounted to the engine for pivotal motion thereon and extending from the pivot to terminate in a second end, an idler pulley rotatably mounted to the carrier for rotation about the first pivot axis and to carry the drive belt thereon and a tensioner pulley rotatably mounted to the carrier at the second end of the carrier for rotation about a second axis that extends parallel to, and is arcuately moveable relative to, the first pivot axis. A tensioner assembly is mounted to the engine and connected to the second end of the carrier to bias the carrier and the tensioner pulley about the first pivot axis for tensioning the drive belt.

DESCRIPTION OF THE EMBODIMENTS

In accordance with an exemplary embodiment,FIG. 1illustrates an engine10, for a hybrid vehicle (not shown) having a Belt Alternator Starter (“BAS”) accessory drive system12. The BAS accessory drive system12includes an engine drive pulley14mounted for rotation on the end of an engine crankshaft16. An electric starter generator unit, or Motor Generator Unit (“MGU”)18, includes an electric machine that can be driven to act as an electric generator and produce electric power, or use electric power to drive the engine10as a starter. MGU18, operative as a starter or a generator, is mounted on the engine10at a lateral distance from the engine drive pulley14and includes an MGU drive pulley20mounted for rotation on the shaft22of the MGU rotor. An air conditioner compressor24may also be mounted on the engine10and includes an air compressor drive pulley26mounted for clutched rotation on the shaft28of the air conditioner compressor24. In addition, a water pump30is mounted on the engine10and similarly includes a water pump drive pulley32mounted for rotation on the shaft34of the water pump30. Other similarly mounted accessory components, such as an air pump (not shown) or a power steering pump (not shown), for instance, may also be associated with the BAS accessory drive system12. A drive belt36is connected between and engages all of the pulleys14,20,26,32for rotating together the engine crankshaft, the MGU, the air conditioner compressor, the water pump and any other optional accessories.

The MGU18serves both as a generator when the engine is running and producing mechanical power needed to spin the electric machine and convert the mechanical power into electrical power in a generating mode, and as a starting motor when the engine is off, the vehicle is operating in a hybrid mode, and the electric machine is used to spin the motor in a starting mode. The MGU18is driven by drive belt36in the generating mode but drives the belt in the starting or cranking mode. In the generating mode, the upper run36′ of the drive belt36is tight while the lower run36″ is slack. The situation is reversed during the starting or cranking mode so that the upper run36′ is slack, while the lower run36″ is tight. To properly tension the drive belt36, the BAS accessory drive system12includes one or more tensioners and idler pulleys in order to prevent slippage of the drive belt when the MGU18is in either the driven or driving mode.

In an exemplary embodiment, a drive belt tensioner assembly38has an arm39having a first end40that is mounted at pivot42to a support boss44extending from the housing of the MGU18. The pivot42allows pivotal motion of the tensioner arm39about an associated pivot axis46. A second end of the tensioner arm39includes a tensioner pulley50mounted for rotation about an axis52that is parallel to the pivot axis46of the pivot42. The tensioner pulley50of the tensioner assembly38is biased against the upper run36′ of the drive belt36by a biasing member (not shown) and operates through a range of rotation “α” to maintain a desired level of tension in the upper run36′ when the MGU is operating in the starting or cranking mode.

Referring toFIGS. 1-4, a centrally located drive belt tensioner assembly52is mounted to the BAS accessory drive system12and may be constructed as a pre-assembled unit. The drive belt tensioner assembly52includes a one-piece carrier54having a first end56that is mounted by pivot assembly58to a support boss (not shown) located on the engine assembly10. The pivot assembly58allows pivotal motion of the one-piece carrier about an associated pivot axis60. The pivot assembly may include a pivot mount61having a bearing assembly62disposed about its circumference and configured to support idler pulley64for rotation about the pivot axis60. The bearing assembly62may include a counter balancing limiter66that extends into an arcuate slot68in the one piece carrier and operates to limit the rotation of the one piece carrier54about the pivot axis60, as well as balancing clamping forces on the pivot assembly58when the tensioner/idler assembly52is mounted to the engine assembly10.

Mounted to the second end70of the one piece carrier54of the drive belt tensioner assembly52is a tensioner assembly72in the form of a hydraulic strut74comprising a damped central hydraulic cylinder76surrounded by a compression coil spring78. Tensioner assembly72is connected at an upper eye80to the second end70of the carrier54and extends to a lower eye82that, in assembly, is pivotally secured to a fixed support (not shown) of the engine10by the lower eye pivot mount84. The lower eye pivot mount84allows pivotal motion of the tensioner assembly72about an associated lower eye pivot axis86. The tensioner assembly72is configured so that the compression coil spring78continuously biases against the upper and lower eyes80,82so as to bias the central hydraulic cylinder76in an extending direction toward which the central hydraulic cylinder is internally designed to move freely. However, the central hydraulic cylinder76includes internal velocity sensitive damping (not shown) that limits the rate of compression caused by forces which may act against it.

In an exemplary embodiment, a second tensioner pulley88is rotatably mounted to the one piece carrier54of the drive belt tensioner assembly52, intermediate of the first and second ends56,70respectively. The second tensioner pulley88rotates about pulley shaft90that is fixed to the carrier54. The second tensioner pulley88of the drive belt tensioner assembly52biases the lower run36″ of the drive belt36due to the biasing force exerted on the second end70of the one piece carrier54and operates through a range of rotation “γ” to maintain a desired level of tension in the lower run36″ when the MGU18is operating in the driven mode; under power from the crankshaft16. Additionally, the idler pulley64, while not directly exerting a biasing force on the drive belt36, operates to segment the long belt span between the MGU drive pulley20and the water pump drive pulley32thereby increasing the effectiveness of the tensioner assembly38.

During normal operation of the engine assembly10(crankshaft driven MGU18), the drive belt tensioner assembly52tensions drive belt span36″ with a force, determined by the spring rate of the compression coil spring78, sufficient to take up any slack in the belt run while the tensioner assembly38rides against the drive belt36on the opposite side of the MGU drive pulley20on the tensioned belt span36′. The positions of the tensioner assembly38and the tensioner idler assembly52remain relatively constant during normal, steady-state engine operation and the tensioner forces applied to the drive belt36are relatively moderate, though sufficient to control both belt runs36′ and36″ during such operation when the engine is driving the various accessories and the MGU18. In this manner the forces that are acting on the bearing systems of the various pulleys and accessories are subject to moderate loads sufficient only to drive the accessories and the MGU18from the engine drive pulley14.

During rapid engine speed changes during transient operation of the engine assembly10or, upon transition of the MGU18from the driven mode to the cranking or starting mode the biasing force of the compression coil spring78is insufficient to hold the second tensioner pulley88in position against the force generated on the lower belt run36″. Under the latter, relatively short period of operation of the BAS accessory drive system12, the central hydraulic cylinder76applies a hydraulic damping force to the coil spring78that restrains contraction of the tensioner assembly72to a slow rate of change, thus applying velocity sensitive damping to the BAS accessory drive system12through the drive belt tensioner assembly52. The central hydraulic cylinder76thus applies a restraining force opposing movement of the second tensioner pulley88resulting from the increase in torque applied on the belt36in the lower belt run36″ so that the second tensioner pulley88is allowed to move at only a very slow rate. In this operational mode, the initial position of the second tensioner pulley is changed a relatively small amount during the relatively short engine starting cycle in which the belt tension in the lower run36″ is significantly increased. At the same time, the tensioner pulley50is pivoted downwardly,FIG. 1, into the upper span36′ as necessary to take up the increased slack in the run while the engine is being started.

The arrangement of the drive belt tensioner assembly52is such that the second tensioner pulley88exerts a force on the drive belt36that is directed generally horizontally to the engine drive pulley14and, consequently, the engine crankshaft16. A horizontal force is preferred to a vertically acting force in order to minimize the effects of wear on the crankshaft bearings (not shown). By providing a mechanism that includes a hydraulically damped tensioner pulley88married with a drive belt idler pulley64, the drive belt tensioner assembly52reduces the space required in the BAS accessory drive system12, which may be referred to as the “belt clearance zone”, thereby allowing for ease of packaging the BAS accessory drive system12as well as reducing part count and reducing complexity. By driving all rotatable engine accessories on a single belt, which is provided for by the drive belt tensioner assembly52the capability of packaging engine driven accessories in a single belt plane is also realized. Elimination or avoidance of a second drive belt plane (two drive belts located in spaced axial relationship to one another) may reduce the length of an engine assembly10by several inches allowing for improved vehicle packaging opportunities.

Although the invention has been described primarily with reference to a BAS hybrid engine system is has been contemplated that there are applications for the invention in non-BAS systems that may require a high degree of short-term drive belt tensioning such as in higher performance engines in which rapid speed excursions may frequently be expected and, therefore the invention should not be limited to the descriptive embodiments included herein.