LN-3 Agricultural Machinery AG31001 Elements of mechanical rotary power transmission most common in agriculture Mechanical Rotary Power Transmission Dr. Peeyush Soni Associate Professor Department of Agricultural & Food Engineering Indian Institute of Technology Kharagpur 1. 2. 3. 4. 5. Bearings and Seals V-belt drives Chain and Sprocket drives Universal joints Power-Take-Off drives soni@iitkgp.ac.in P Soni (AgFE-IIT) P Soni (AgFE-IIT) Mechanical rotary power transmission Mechanical rotary power transmission Bearings on agricultural implements… Required to operated under extremely dusty or dirty conditions Development of suitable bearings, seals and lubricants has been a real challenge Sealed, factory-lubricated ball bearings (with no provision of re-lubrication) Bearings and Seals … are extensively used on most harvesting equipment. High initial cost is justified by reduced R&M cost and daily servicing time Provision of re-greasing may have some merit where excessive heat breaks down the grease; however, there are issues of: § using incorrect grease type, § contamination of grease from dirt on the fitting or the gun, § collection of dirt/dust around the seal lips … needed on axles of ground driven rotating components as well as in power-transmission systems Load capacities of Anti-friction Bearing (Ball/Roller/Taper/Needle) 3 P Soni (AgFE-IIT) Mechanical rotary power transmission Self-alignment of bearings on open shafts is an important feature in agricultural operations … to compensate for manufacturing tolerances and variable deflection of supporting members Self aligning mountings: Plain cast-iron sleeve body fitted loosely in a hole in a plate to a sphericalOD ball bearing held in stamped flanges Turnnion support for bearing housing Bushing (Plain Bearing) Bearings Anti-friction (Rolling Contact) Rolling elements placed between the Consisting of a shaft rotating in a hole, comprising just a bearing surface and no rolling elements. There are several turning and stationary races prevent specific styles: bushing, journal bearing, sleeve bearing sliding friction. Two main types: solid sleeve Flanged bushing bushing Bronze bushed journal bearing Self aligning support Not capable of taking thrust load, unless supported with circumferential ribs or endflanges Clenched (or clinched) bushing Ball bearing: designed primarily for radial loading Roller bearing: High radial load capacity but no end-thrust. Suitable for low-speed (axle of see d drill). They’re more sensitive than ball bearings for misalignment, dirt and grit. Needle b earing: roller bearing with more number of small-dia rollers without a cage or spacer. Exceptionally high load capacity at low peripheral speeds. Well suited to applications involving oscillating motion. Needle bearing Special bearing: a) Disk harrow bearing: Heavy radial and thrust loads at low speeds, and operate under dirt. Self-aligning mounting and effective seals are must. Bronze, Oil-impregnated metal, Hardened steel, Available with either square or round holes. b) Tine-bar bearing: on the reel of a sideWhite cast iron, Oil-soaked wood, Plastics delivery hay rake Tapered roller bearing: Takes both radi al and thrust loads depending on taperness P Soni (AgFE-IIT) Mechanical rotary power transmission P Soni (AgFE-IIT) Single V-belt Mechanical rotary power transmission Multiple V-belt Banded V-belt These matched sets are used on drives having high power requirements, and pulsating loads Matched set of conventional belts with a thin tie band connecting their tops. Tying together… • minimizes lateral belt whip, • improves load distribution among the belts V-Belt Drives MercedesBenz Serpentine Belt Diagram • Extensively used in agricultural machinery applications where it is not necessary to maintain exact speed ratios. P Soni (AgFE-IIT) Mechanical rotary power transmission V-belt transits a given power with less shaft pull than a flat-belt drive, because V-belt wedges into the sheave grooves V-belt can be operated with small arcs of contact (as in close-center shaft arrangements) with large shaft-speed ratios In agriculture, a single belt often drives several components (Serpentine drive). V-belt permits considerable latitude in possible orientation and arrangement of shafts V-belt in Agriculture vs Industry Prefix H: distinguishes agricultural V-belts from industrial V-belts. Agril V-belt loadings can be higher than their corresponding industrial application Cross-sectional sizes of both kinds are the same; but construction of agri V-belts is stronger and rugged (to withstand • excessive shock loads, • heavy pulsating loads, and • harsh working conditions) 3 types of V-belts, esp. designed for agricultural machines 1. Agricultural V-belt Trapezoidal section. Included angle ~ 300 - 400 P Soni (AgFE-IIT) 2. Agricultural double V-belt 3. Adjustable speed V-belt Mechanical rotary power transmission P Soni (AgFE-IIT) Adjustable-pitch V-belt sheave has provision for moving one face axially w.r.t. the other face, thus changing the radius at which the belt operates Mechanical rotary power transmission Mechanics of V-Belt Drives Agricultural V-Belt Cross-Sectional Dimensions V-belt transmits power by virtue of difference in belt tension between the point at which it enters a sheave and the point at which it leaves ΔT is developed through friction between the belt sidewalls and the sides of sheave groove. The wedging effect (as the belt is pulled into groove bcoz of belt tension) greatly increases the potential driving force. As a belt tends to conform to the sheave curvature, outer section stretches and inner section is compressed. Neutral axi s is determined by the position of the load-carrying cords within the belt crosssection. Neutral Axis establishes the pitch-diameter of sheave Tension difference (ΔT) or Effective Pull, that is required to transmit the load at each driven sheave − ASAE Standard S211.5 P Soni (AgFE-IIT) Mechanical rotary power transmission = 1000. P Soni (AgFE-IIT) Mechanical rotary power transmission Tension Ratio (R) If R is too great, belt slippage will be excessive For properly designed drive, slippage should not exceed 1 to 2% If R is too small, unnecessarily high tensions will be needed for a given effective pull, thereby reducing belt life The maximum allowable Coefficient k tension ratio (Ra) reflecting friction and wedging effect = P Soni (AgFE-IIT) = k~0.512 Arc of contact, rad (=deg x π/180) • Gears: Constant speed-ratios, Close-center, Intersecting or crossing shafts, Enclosed for protected lubrication • Chain drives: Parallel shafts with moderate center distance, Constant speed-ratios, Usually open for external oiling Chain & Sprocket Drives For V-belt and V-sheave, θ=π, most assumed Raπ =5 When arc of contact is less (θ<π), Ra is also less, thus requiring higher values of tensions for a given effective pull or power 15 Mechanical rotary power transmission Advantages of Chain Drives Chain Nomenclature • Chain drives, unlike belt drives, do not slip or creep. • There is no power loss due to slippage; therefore, chain drives are more efficient than belt drives. • Chain drives are more compa ct than belt drives. A chain drive, for a given capacity, is narrower than a belt, and the sprockets are smaller in diameter than the belt sheaves. • Chain drives are more practical for slow speed drives. • Chains can operate effectively at high temperatures. • Chains do not dete riorate due to oil, grease, sunlight, or age. • Chains withstand chemicals a nd abrasive conditions. • Chains can operate in wet conditions. • Chains are effective when several shafts are to be driven from a single sha ft, as positive timing between the driven shafts is usually re quired. • Chain drives are simpler and less costly than gear drives. Limitations of Chain Drives • Chain drives cannot be used where the drive must slip. • Chain drives cannot accept much misalignment. • Chain drives usually require frequent lubrication. • Chain drives are noisy and can cause v ibration within the machine. • Chain drives do not have load capacities or service life characteristics equa l to those of gear drives. P Soni (AgFE-IIT) Mechanical rotary power transmission P Soni (AgFE-IIT) Mechanical rotary power transmission Sprocket Nomenclature Types of drive chain common on farm machines § § § § Strands: 2, 3, 4 Standard-pitch roller chain v = 0.5 to 20 m/s Well-suited for heavy loads requiring a compact drive Oil-bath lubrication is needed for high -speed operation Not suited for Agril machines; several times as expensive as steel detachable chains Double-pitch roller chain § § Multiple Strands Chain § Uses the s ame diameter pins, bushing and rollers, same thickness of link plates as standard-pitch roller chain, but the side plates have twice the pitch They have same strength and precision as corresponding standard-pitch chains, but less mass; Less expens ive than that the s tandard-pitch Double-pitch d rive chain is used in place of standar d roller chain when speeds are low, loads are light, and center distances are excessively long Detachable link chains § § § § § Used both for transmitting power and in conveyors and elevators Least expensive type of chain Well-suited for moderate loads at speed < 2 – 2.5 m/s They are s.t. more wear than r oller chains due to loose-fitting, open hooks. They are not lubricated Melleable-cast-iron, detachable link chain P Soni (AgFE-IIT) Mechanical rotary power transmission P Soni (AgFE-IIT) Pressed-steel, detachable link chain Mechanical rotary power transmission Load capacity of chains: In general, it is based upon the rate of wear rather than the ultimate strength. As chain wears, the pitch length i ncreases, and the chain rides farther out on the sprocket teeth Wear is due to hinge action as chain engages or leaves a sprocket Rate of wear is directly related to chain speed, and inversely related to chain length à That’s why speed-ratios should not exceed 10 to 1 (std. pitch roller chain) 6 to 1 (other chains) Overload Safety Devices for rotary drives Pull required for a given power and speed, In many types of farm machinery, a single power source drives various components that have widely differing power requirements, and subject to varying degrees of possible overload Required pull, N − P Soni (AgFE-IIT) = 1000. Mechanical rotary power transmission Overload Safety Devices 3 General types of safety devices commonly used in rotary drives: A. Shear Devices A-1: Shear key between shaft and hub Simple and relatively inexpensive Sheared element must be replaced after each overload Not suitable for drives where frequent overload occurs Shear devices can be designed for almost any desired load rating (selection of material and size of pin) § Removal of the hub from the shaft is necessary to replace shear key § § § § Shearing of replaceable member Principle of inclined plane Usually brass key with tapered shaft and bore Friction P Soni (AgFE-IIT) P Soni (AgFE-IIT) Mechanical rotary power transmission A-2: Diametral shear pin through hub and shaft (gives double shear) Mechanical rotary power transmission A-3: Flange-mounted shear pin parallel to shaft T Shaft, 2r, D Hub, 2r1, D1 This shear-pin is the most easily replaced, but the unit is more costly than a diametral pin Pin, d The torque at which a flangemounted shear pin will fail is The torque at which a diametral shear pin will fail is Double shear =2 ( 4 Shaft Torque, N-m distance of shear plane from the shaft center i.e. shaft dia P Soni (AgFE-IIT) Mechanical rotary power transmission Shear-pin dia = ( 4 Shaft Torque, N-m Distance b/w Shear-pin dia shaft center and shear-pin center ) P Soni (AgFE-IIT) Mechanical rotary power transmission ) Driving shaft B. Jump Clutch Spring loaded corrugated coupling C. Friction Devices Driven shaft A properly designed belt drive can serve as a friction safety device! Although its performance is affected by variations in belt tension and belt slip It has automatic-resetting feature It has rounded, mating jaws or corrugations that are held together by an adjustable spring. A B Spring adjusment Single-plate clutches with two friction surfaces Part A is keyed to driving shaft, and part B (driven) is free to rotate on the shaft when overload occurs. Spring pressure is adjusted to drive normal loads, but slip when overload When load exceeds the setting of the unit (torque limiter), operator is warned audibly Jump clutches are more expensive than shear devices, and not suited to large loads (due to excessive physical size required) Spiral jaw clutch P Soni (AgFE-IIT) Friction clutches are very effective in protecting a drive from high-frequency peak torques Principle of friction clutch But excessive slipping overheats the friction plates When jumping, they impose high shock loads upon the drive system P Soni (AgFE-IIT) Mechanical rotary power transmission A universal joint (or Cardan) is a joint or coupling in a rigid shaft that allows the shaft to "bend" in any direction Mechanical rotary power transmission Some Terminology α Joint angle ω1 Input (driving) angular velocity (rad/s) ω2 Output (driven) angular velocity (rad/s) β1 Angle of rotation (momentary) of Input shaft from initial posi tion (rad) β2 Angle of rotation (momentary) of Output shaft from initial positi on (rad) Universal Joints spider 1. Single joint 2. Multiple joint combinations 28 Source: https://www.crawlpedia.com/u_joints .htm P Soni (AgFE-IIT) Mechanical rotary power transmission Single joints The basic parts of universal joint Angles of rotation of the two shafts ( 1, 2) are related to the joint angle (α) tan = tan cos α k tan = tan ( cos Universal joint under a straight mo tion Peak lag occurs when the input shaft is past 450 plus by an amount equal to half the peak lag (indicated by broken line in lower half) The spin of the cross makes a huge difference in the speed of the output shaft. The cross has 2 kinds of motion: rotation and spin. When the cross is spinning as well as rotating, the velocity of the output shaft will have an added effect. For the first 900 of the input shaft rotation, the green axis spins to its maximum angle. The forward s pin aids and changes the o utput shaft rotation − 1) Source: www.learnengineering.org 2 Forward spin of the shaft during the first 90 0 1 But for the next 90 degrees, it shoul d spin back to the initial zero position. The reverse spin will have an opposite effect on the output shaft rotation. P Soni (AgFE-IIT) Peak lead occurs when the input shaft is at 1350 minus by an amount equal to half the peak lag (indicated by broken line in upper half) ( The ends of universal joint turn in different planes. The shaft connecting the green ends should spin to accomplish this movement Angular displacement of the output shaft during 180 degrees turn Mechanical rotary power transmission A single joint operating at an angle, does NOT deliver uniform angular output velocity ω2 The output shaft has a fluctuating speed. More the angle between the shafts more will be the speed fluctuation. P Soni (AgFE-IIT) Motion and Torque characteristics of a single joint Mechanical rotary power transmission If a single joint is deflected by angle α (joint angle) and rotated by ß1 then the output shaft differs from rotation angle of the input shaft. Wh en there is a joint angle, motion of the output yoke doesn’t follow the motion of the i nput yoke in terms of ang ular displacement, velocity, and acc eleration. The amount of variation b/w the input and output motions depends on the operating angle (joint angle). The angular displacement of the output yoke ( 2) during one revolution lags and leads the input yoke twice. The maximum angular acceleration/ deceleration coincides with the maximum lag and lead angles, respectively P Soni (AgFE-IIT) Mechanical rotary power transmission ) P Soni (AgFE-IIT) Mechanical rotary power transmission ω2 cos = ω1 1 − sin 2 . cos 2 Angular velocities ratio The max speed of driven (output) shaft = 2 1 = 1 − sin2 = 1 The min speed of driven (output) shaft Condition for equal speeds of the shafts tan The max fluctuation of output speed max(ω 2) - m (ω2 ) Angular Acceleration of the output Shaft P Soni (AgFE-IIT) Mechanical rotary power transmission Exercise: Two shafts are connected by a universal joint. The driving shaft rotates at a uniform speed of 1200 rpm. Determine the greatest permissible angle between the shaft axes so that the total fluctuation of speed does not exceed 100 rpm. Also calculate the maximum and minimum speeds of the driven shaft. P Soni (AgFE-IIT) Mechanical rotary power transmission P Soni (AgFE-IIT) ω2 = ± cos max(ω2) - ω2 = ω1α 2 ω2 cos . sin 2 . sin = 1. (1 − sin 2 . cos 2 )2 Max angular Acceleration of the output Shaft, at corresponding 2 sin 2 Mechanical rotary power transmission Exercise: cos 1 = (2 − sin 2 Two shafts with an included angle of 160° are connected by a Hooke’s joint. The driving shaft runs at a uniform speed of 1500 rpm The driven shaft carries a flywheel of mass 12 kg and 100 mm radius of gyration. Find the maximum angular acceleration of the driven shaft and the maximum torque required. P Soni (AgFE-IIT) Mechanical rotary power transmission 1 ) Multijoint Combinations Bearing loads on input and output shafts with Z-Arrangement When 2 univers al joints are connec ted in series, the angular displacement and velocity fluctuations will cancel (condition of equal speeds) IF (a) the joint angles are equal (output and input shafts make equal angles with the intermediate shaft), and (b) the axes of the output and input shafts are coplanar Driveline-center part stressed in bending Double Universal Joint Constant velocity ratio: Double Hooke’s Joint If a constant velocity input gives fluctuating output, a fluctuating input will gi ve a constant velocity output. Thus, the double universal joint acts as a constant velocity joint. Use of double uni versity joint in eliminating jerky motion Source: www.lear nengineering.com P Soni (AgFE-IIT) Mechanical rotary power transmission P Soni (AgFE-IIT) Mechanical rotary power transmission Bearing loads on input and output shafts with W-Arrangement In W-arrangement, an additional force, “S“ is introduced, caused by the additional moments TZII acting in the same direction. Input and output shaft stressed in bending Power-Take-Off Drives P Soni (AgFE-IIT) Mechanical rotary power transmission Lift Arms PTO Adapters & Extenders Lift Rods Lower Lift Links Sway Chain PTO Adapter, Clamp Type, 1-3/4" 20 Spline Female, 1-3/8" 21 Spline Male P Soni (AgFE-IIT) Mechanical rotary power transmission power take-off PTO external shaft on the rear of the tractor to provide rotational power to implements (ISO:500 definition) Swinging drawbar P Soni (AgFE-IIT) Mechanical rotary power transmission Standardization of PTO Drives Why standardization? Easy attachment and interchangeable use of PTO-driven implements with various makes and models of tractors ASAE and ISO Standards ISO 500: rear-mounted PTOs on agricultural tractors with a track width of more than 1 150 mm Independently controlled PTO (introduced in 1940 ) greatly increased its versatility in comparison with the Transmission-driven PTO PTO used extensively on: ü ü ü ü ü ü Harvesting equipment (trailed / mounted) Sprayers Rotary or vibratory tillage implements Pull-type field forage choppers Corn pickers Stalk cutters and shredders P Soni (AgFE-IIT) Mechanical rotary power transmission The tractor rear PTO is classified into four types PTO type Nominal diameter, mm Number and type of splines Nominal PTO rated rotational speed, rpm Recommended power at rated engine speed , kW 1 35 [1⅜] 6 straight 540 <65 2 35 [1⅜] 21 involute 1000 <130 3 45 [1¾] 20 involute 1000 <300 4 57.5 22 involute 1000 <450 P Soni (AgFE-IIT) Mechanical rotary power transmission ASAE Standard S203.8 540 rpm Type-1 1000 rpm Type-2 1000 rpm Type-3 Shaft dia, mm 35 [1⅜] 35 [1⅜] 45 [1¾] A, mm 356 406 508 C, mm 330 - 432 330 - 432 432 - 533 D, mm 152 - 305 152 - 305 203 - 254 B, mm -25 to +127 -25 to +127 -25 to +127 5: P TO 6: master shield 7: Drawb ar External, straight-sided spline dimensions — Type 1 (source: ISO:500-3) P Soni (AgFE-IIT) External, involute spline dimen sions — Type 2 (source: ISO:500-3) Mechanical rotary power transmission Telescoping PTO shaft with integral safety shield Standardized locations for the PTO shaft and drawbar hitch point on agricultural tractors. Hitch point is directly beneath the extended center line of the PTO shaft P Soni (AgFE-IIT) Mechanical rotary power transmission PTO Drives with TWO & THREE Universal Joints Fixed-length shaft b/w front 2 joints; Telescopic shaft b/w 2 re ar joints e.g. ASAE Standard dimension 356 (14”) shaft is used with 540 rpm PTO having 356 mm from h-point to the end of PTO shaft ◙ ◙ A Angle between implement and tractor P Soni (AgFE-IIT) Mechanical rotary power transmission The dim A is greater for Type-2, 3 PTOs (1000 rpm); so the problem of unequal angles is minimized or eliminated for the higher PTO speed systems P Soni (AgFE-IIT) Angles in u-joints, Two u-joint drive Angles in front u-joints, Three u-joint drive Front joint Second joint Front joint 00 0 0 0 0 300 16 14 12 18 500 27 23 21 29 700 38 32 33 37 900 50 40 54 39 Mechanical rotary power transmission Second joint PTO Drive with Offset If the driven shaft of implement is offset from the centerline of PTO shaft so that the normal joint angle of one or both the intermediate shafts is > 15 – 20 0 from the PTO shaft, serious fluctuations may occur during sharp turns Two possible arrangements for obtaining the offset: 1. Joints phased 2. Joints not phased Telescopic shaft Both theoretically provides uni form velocity of driven shaft when the implement and tractor are in line. Fixed shaft 1. Joints phased 2. Joints not phased Provides much less fluctuations on sharp turns – due to having smaller maximum joint angles Plan views of two arrangements of a 3 u-joint offset PTO drive P Soni (AgFE-IIT) Mechanical rotary power transmission