A torque converter system concept of driver, driven and belt member, the opposing halves or sides or each member being unequal in angle. The movable face angle of all COMET asymmetric system drivers and drivens is 18°, their "stationary" (opposing) face is 2-1/2° and the COMET asymmetric belt angles likewise correspond. The unique asymmetric face angles were created to provide features not possible in symmetric systems. In this special system concept, both the driven's and the driver's movable faces and the driven's torque sensing cam/spring mechanism all are on the same side..."outboard" of the belt. Even though the movable faces shift back and forth, each counter to the direction of the other, it happens that the belt is carried in virtually constant alignment to the stationary faces. Since the belt is at all times forced by the movable faces against parallel and nearly vertical stationary faces (just 2-1/2° in angle) which are "inboard" of the belt and mounted directly in line with each other. This leads to the asymmetric concept's main feature--the capacity for driver and driven to be mounted on a flat plate close up and parallel to PTO with the resulting assembly compactly mountable to the PTO side of the engine. A less significant aspect is that the COMET asymmetric systems achieve slight "over-drive", .90:1 or 10% over-drive.
CENTER DISTANCE (C.D.): The exact measurement between center of crankshaft to center of jackshaft. Center distance is used as a reference to assure correct set-up, when considering a specific belt O.C. and any particular driver and driven pair's diameter. There always is only one correct C.D. setting for a given driver/belt/driven assy.
DRIVE BELT: The drive belt links the driver pulley to the driven pulley. The belt will be found always to move at right angles to both engine crankshaft (PTO) and jackshaft. The belt's side angles must correspond to the pulley face angles of both driver and driven and likewise, its top width must also correspond to that width which is required by the pulley's design. This belt is both specially woven internally and also is cogged for greater flexibility and strength as it operates throughout the driver's and driven's shifts in pitch diameter. No substitute belt is acceptable. Great care must also be exercised that the correct length ("O.C") of belt is used. Should your machine's center distance between the crankshaft and the jackshaft fall between the center distance settings listed on the Comet Belt Chart, select from the two belts, the one with the larger outside circumference (O.C.) for best wear and to avoid machine "creep" during idling.
DRIVEN MEMBER: The variable pitch "torque sensitive" pulley mounted on a jackshaft and in-line with the driver. Larger in diameter than the driver and frequently called the torque converter, its greater diameter multiplies available torque, that results in a corresponding reduction in RPM...of the vehicle's driving wheel(s)...in relation to the RPM of the engine. Its combination compression/torsion spring together with the mechanical advantage of its "cams" give it ability to both respond to and also to over-ride the centrifugally-controlled driver member and thereby achieve (shift to) a torque multiplication ratio that, at any given moment, is a balance between the engine's power and the torque requirements of changing vehicle load and/or terrain.
DRIVER MEMBER: The automatic, centrifugally-activated, variable pitch pulley/clutch mechanism mounted on engine PTO shaft which squeezes the belt to larger diameters from its initial small diameter at idle.
JACKSHAFT: The auxiliary or counter shaft which must be parallel to the engine's PTO shalt and onto which the driven member is mounted, in-line with the driver...the driven may instead be mounted on an input shaft to reverse or reduction gear box or occasionally directly to the load.
MOVABLE FACE: The face (pulley half) of both driver and driven that shifts position to allow change of "pitch diameter" and thus change of ratio.
O.C. - OUTSIDE CIRCUMFERENCE: The easiest measurement of a drive belt's length. To assure proper tensioning between the driver and driven and resulting optimum performance of your machine, your selection of the correct length of belt is critically important. Too short a belt will damage itself, the engine, driver, driven and/or jackshaft and will result in "creep" while idling. Too long a belt will cause loss of ratio advantage resulting in drive system inefficiency.
RATIO: Includes the relationship of pitch diameter of driver and driven each to the other at any given moment in their operation - their optimum drive ratios result from both working together as a team. (Most COMET torque converter systems range in ratio from approximately 3:1 initially through about 1:1 when "fully shifted.") In a broader sense, the over-all ratio of the drive train also includes the sprocket or gear ratio and is determined by multiplying these separate ratios each times the other. Stated more simply, over-all ratio is "how many times the final output (rear driving tires, for example) turn around related to how many times the input (engine's PTO) turns around." Ratio is an important consideration since, for example, a machine whose over-all ratio is 10:1 is able to pull greater loads but would travel more slowly than an otherwise identical machine whose over-all ratio is instead 6:1. Conversely. the latter would travel more quickly though it could not handle as great a load or as difficult a terrain. Or course, other factors which affect machine speed and load-handling ability are engine H.P. & RPM and also the driving tire's diameter.
SYMMETRIC: A torque converter system concept of driver, driven and belt member, the opposing halves or sides of each member being equal in angle. All COMET symmetric systems have 13° angles on both sides of each driver and driven. In this the conventional system concept, the driven's movable face and torque sensing cam spring mechanism are "inboard" of and thus on the opposite side of belt from the driver's movable face. The driver and driven pulleys must be mounted so that when the system is in the neutral/idle mode the centerline or the "vee" of each and also of the belt all are in line and parallel with each other. Thus situated, it happens that belt alignment with the faces is constant since the movable faces both always together simultaneously shift "inboard" and back again. Ratio range of these systems is typically about 3:1 to 1:1.
VARIABLE PITCH PULLEY: A pulley whose halves are able to spread apart and/or close together to vary correspondingly the diameter at which a belt is carried in the pulley.
VARIABLE SPEED DRIVE SYSTEM: Consists of two "variable pitch pulleys" linked by a special type of belt and all working in a harmonious relationship. Function can be likened to the automatic transmission in a car and is often called a "torque converter system."
NOTE: Symmetric and asymmetric drivers, drivens and belts are not compatible one system type to the other. Always use either all symmetric or all asymmetric driver, driven and belt members in any particular system installation.
Page Last Updated: 01/08/2020
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