Agricultural Mechanics PDF - Operation and Service of Power Trains

# AGRICULTURAL MECHANICS ## 8204-A ### OPERATION AND SERVICE OF POWER TRAINS #### PRINCIPLES OF POWER TRANSFER When something is to be moved, the easiest and most convenient way is usually found. When the first cave-dwellers wanted to move a large rock, they probably used the first simple machine ca...

# AGRICULTURAL MECHANICS ## 8204-A ### OPERATION AND SERVICE OF POWER TRAINS #### PRINCIPLES OF POWER TRANSFER When something is to be moved, the easiest and most convenient way is usually found. When the first cave-dwellers wanted to move a large rock, they probably used the first simple machine called a lever. A tree branch was stuck under a large rock. A smaller rock was placed under the branch as close to the large rock as possible. Force was applied through the branch to try to get the large rock to roll. The small rock became a fulcrum (pivot point) and the branch became a lever. The twisting action or pressure that caused the large rock to roll was the torque. Stated another way, torque is the turning effort that produces rotation or tended to produce rotation. Today, torque is measured by the pounds of force or pull applied a given distance from the pivot point. For example: One hundred pounds of force is applied six foot from a pivot point. Therefore, 600 foot-pounds of torque tries to cause rotation (100 lbs of force x 6 ft = 600 ft-lbs of torque). The mechanical advantage of a lever is the ratio of the length of the lever on the force side of the pivot point to the length of the lever on the resistance side. If force remains the same and the pivot point is moved closer to the resistance, the mechanical advantage will increase. Also, the closer the pivot point to the resistance, the further the force end of the lever must be moved. Therefore, the slower the action to move the resistance or weight. The cave- dwellers had one problem with their simple machine. It was not a continuous process. As their needs changed, other simple machines were developed. Other simple machines include: the wheel and axle, the pulley, the inclined plane, the screw, and the wedge. - **AXLE AND PULLEY** - Weight - Force - **PULLEYS** - Weight - Force - **INCLINE PLANE** - Weight - Force - **SCREW** - Force - **WEDGE** - Force The same simple principles are used today with science and technology to design and build modern agricultural equipment. This allows work to be performed continuously and efficiently. # INTRODUCTION TO POWER TRAINS Most modern engines operate most efficiently at approximately 2,200 RPM. A typical 150 horsepower engine will produce approximately 300 foot-pounds of continuous torque measured at the flywheel. A question may arise. With a lever 6 feet long with 50 pounds of force applied, a person could produce 300 foot-pounds of torque. Why can't he or she pull the same load as a 150 horsepower tractor? (For a full explanation of measuring engine horsepower and torque, refer to student topic # 8203-A). The difference is continuous torque, speed, momentum, and increasing torque. - **A power train converts the high speed, lower torque rotation of the crankshaft into a low speed, high torque rotation of the wheels to pull a load. In effect, the functions of a power train are:** - 1) connect and disconnect the power from the engine, - 2) allow for selection of speed ratios, - 3) provide a means for reversing direction of travel, - 4) equalize power to all drive wheels for turning, and - 5) start and stop the PTO shaft. - **Power is transmitted from one point to another through the power train in one of three methods:** - Friction - Moving Fluids - Gears #### Friction Drives Children use the friction method of transmitting power when they peddle their tricycle. They apply a downward force with their legs through the peddles on the crank, to the front wheel, and on to the floor. The floor is stationary. The friction between the wheel and the floor caused the tricycle to move. If they hit a slick spot or are in the sand pile, the tricycle will not move. Even though power is exerted, there is a lack of friction between the wheel and the floor or the ground. The same principle of friction drives is used when one wheel, or roller is allowed to touch another wheel. Force is applied to one wheel or the driver wheel causing it to turn. The friction between the two wheels causes the second wheel to turn or be the driven wheel, but rotate in the opposite direction. #### Fluid Drives Fluid drives were probably one of the first power transmitting tools developed other than the simple lever. The water wheel was turned by the force of running water against a series of paddles or buckets. Modern versions of fluid drives include fluid couplings, torque convertors, and hydrostatic transmissions. Fluid drives use the flow of hydraulic oil directed against a turbine wheel with vanes or other objects causing them to move. #### Gear Drives Gear drives are the most common way to transmit power. When the teeth of two gears are in mesh, all slippage is eliminated. For this reason, gears are widely used for high power applications. Different types and cuts of gears can: 1) change speed and direction of power; and 2) transfer, and increase or decrease torque. A chain drive is a variation of the gear drive. The sprockets (gears) are separated and thus can not be meshed. Instead, the sprockets are connected by a continuous chain with links. These links mesh with the teeth on the sprockets and eliminate slippage. The driving sprocket transmits power to the driven sprocket through the chain. #### Gear, Pulley and Sprocket Ratios and Shaft Speeds Recall the principle of the lever and the fulcrum used to move the rock. The same principle holds true with gears, pulleys or sprockets in power trains. The torque developed between gears, pulleys or sprockets and the speed they rotate is proportional to the distance from the center shaft to the teeth or friction surface. Therfore, a smaller driver equals less speed, but more torque. A large driver equals more speed and less torque. Gear, pulley, or sprocket ratio is the measure of the changes in speed and torque in the gear train. Defined another way; gear ratio describes the ratio of the number of teeth on one gear (or diameter of pulley) to that of the other in the set. If both the driver and the driven gear have 20 teeth each, there would be a 1 to 1 gear ratio. A 1 to 1 ratio would cause no change in the speed or torque between the driver gear and the driven gear. **Example:** The smaller gear has 12 teeth and the other has 24 teeth. The expression of the gear ratio in the set would depend upon the direction of power flow. If the driver gear is the smaller and has 12 teeth, then the gear ratio would be 12:24 or 1 to 2. Remember a smaller driver gear produces less speed and more torque in the driven gear. If the driver gear shaft rotates at 500 RPM, then the driven shaft speed would be 250 RPM or a 2 to 1 speed ratio. If 300 foot-pounds of torque are applied by the driver shaft, 600 foot-pounds would be supplied out of the driven shaft. In the above illustration, the driver gear would make one revolution while the driven gear makes only one-half revolution. When the power flow is reversed, the larger 24 teeth gear would become the driver. Remember a larger driver equals more speed and less torque in the driven. If the driver rotated at 500 RPM, the driven shaft or output shaft of the 12 teeth gear would turn at 1,000 RPM. This would produce a 24:12 or 2 to 1 gear ratio and a 1 to 2 speed ratio. The 300 foot-pounds input torque would decrease to 150 foot-pounds on the output shaft. This gives the basis for the relationship that torque is inversely related to speed (RPM). Gears, pulleys or sprockets are used to provide an increase or decrease in the speed ratio The torque will also increase or decrease by the inverse ratio. Depending upon the size of gears, pulleys or sprockets used, many different ratios are possible. #### PURPOSE OF THE CLUTCH The first part of the power train system is commonly recognized as the clutch. Its main function is to connect the power from the engine or other power source with the transmission or rest of the system. The clutch disconnects the power, permitting it to run free of a load. The clutch mechanism also allows a load to be gradually applied to the power source. Most clutches use friction to transmit power to the machine. The friction is caused by touching two surfaces together. These surfaces are made of steel or some other material that will withstand the heat and wear created by friction. #### OPERATION OF A BASIC CLUTCH Two disks or other surfaces are mounted on two separate shafts opposite each other. If there is space between the two disks, one will rotate while the other is still. When the two surfaces come into contact with each other, friction begins. Both shafts will turn as a single unit. The basic disk clutch used in many agricultural trucks and tractors, and automotive applications uses the flywheel attached to the crankshaft as one disk. The other is the clutch disk connected to the transmission input shaft. - **Clutch Engaged** - Both disks are tuming - **Clutch Disengaged** - Only one disk is tuming #### PARTS AND OPERATION OF A BASIC DISK CLUTCH - **Engaging Position** - The operator releases the clutch pedal. The clutch pedal linkage moves the release bearing back allowing the clutch levers to pivot. This allows heavy springs to push the clutch pressure plate toward the clutch disk. The clutch disk which is not turning is located between the pressure plate and the flywheel. Spring pressure on the pressure plate increases friction between the clutch disk and the flywheel. When the clutch pedal is fully released, the clutch disk is held tightly between the pressure plate and the flywheel and all three turn as a unit. - **Disengaging Position** - The operator depresses the clutch pedal. Linkage pushes the release bearing against the clutch levers. The clutch levers pivot and pull the pressure plate away from the clutch disk and compress the clutch springs. The pressure plate and flywheel continue to turn as a unit. Because of air clearance and lack of friction, the clutch disk connected to the rest of the power train stops turning. For proper operation, clearances and adjustments must be within manufacturers' specifications. The phrases "riding the clutch" or "slipping the clutch" refer to a situation when the operator is holding the clutch in a half engaged/half disengaged position for a long time. This causes excessive slippage, friction and wear on all clutch parts. Also excessive friction causes excessive heat. Excessive heat can cause clutch springs to weaken and the clutch plate and disk to warp. The clutch surfaces will wear away even with normal use. Linkages must be periodically adjusted to maintain proper operation. The amount of free travel and the adjustment varies with make and model of the equipment. It is recommended that an appropriate operator's and/or technical manual be used when making adjustments. #### TYPES OR CLASSIFICATIONS OF CLUTCHES Clutches are classified by the way they are operated and the type of clutch assembly. - **Disk or Plate Clutch... Wet or Dry** - For many years, the most common clutches found on farm tractors, trucks and automobiles were single-disk dry type clutches. This type of clutch operates through mechanical linkages by a hand or foot pedal. Dry disk type clutches are air cooled. Many modern clutch assemblies now use multiple plates and disks. This allows for increased surface area for the increased friction in high speed high horsepower operations. Increased friction also increases heat. Multi-disk wet type clutches operate in an oil bath or spray. Modern technology allows special clutch disks to be cooled with oil, but not slip under a load. Metal pressure springs are also being replaced by hydraulic pistons or cylinders as a means of applying pressure against the pressure plates. - **Overrunning Clutch** - This type of clutch allows engagement in one direction. One half of the unit can free wheel in the opposite direction of rotation. Overrunning clutches are often used as safety clutches on agricultural equipment. They allow the driven part of the system to continue to rotate or "overrun" until momentum has stopped when the driver side of the power train is slowed, disengaged or stopped. Overrunning clutches are common in equipment such as hay balers grinder/mixers which have large driven flywheels and in electrical starter drives.. - **Magnetic Clutch** - Magnetic clutches use magnetic force to pull and hold the driver and driven side together. This allows them to rotate as one unit. Electro-magnetic clutches are commonly used on A/C compressors and small engine powershafts. - **Expanding Shoe Clutch** - This type of clutch has an inner shoe that expands by mechanical linkage or centrifugal force to contact the outer part in order to transmit torque. Expanding shoe clutches are commonly used on chain saw drives and other small engine applications. - **Belt Clutch** - Belt clutches operate simply by tightening or loosening the tension on the belts to control the amount of friction. Linkage moves the driver, driven, or a third idler pulley back and forth. Belt guides are often used to maintain correct belt position while disengaged. clutches are very common on many types of belt driven agricultural equipment. #### MAJOR WAYS IN WHICH CLUTCHES OPERATE - **Mechanically operated clutches use linkages and springs to engage and disengage the clutch mechanism. The most common is the standard linkage. The movement of the clutch pedal or lever is carried through linkage to disengage the clutch. The clutch remains engaged under normal operation by spring pressure. The second type of mechanical linkage is the over- center linkage as illustrated. The pedal or lever is locked into the engaged position when the linkage is moved beyond the center position against a stop. In this position the linkage has mechanical advantage. The clutch is disengaged when the linkage is moved away from the stop position and beyond on-center.** - **Hydraulically operated clutches use a clutch pedal or lever attached to a master cylinder. The master cylinder (which is a small piston pump) is then connected by a hose or pipe to a smaller slave cylinder. The slave cylinder is attached to the clutch linkage. The master cylinder piston pushes hydraulic fluid through the hose to move the slave cylinder piston. The slave cylinder piston movement then operates the clutch linkages.** - **Other types of hydraulically operated clutch systems use pressure supplied from the main hydraulic pump. The clutch pedal or lever movement opens or closes a hydraulic valve to apply or release hydraulic pressure to the slave cylinder or piston.** - **Electrically operated clutches use an electro-magnetic field. Direct action clutches are operated by a simple on/off electrical switch. Closing a switch sends current through the coil and sets up a magnetic field. The clutch facing of the driven side is drawn against the facing of the driver side or rotor. To disengage the clutch, the switch is turned off to collapse the magnetic field. (See magnetic clutch illustration in the types of clutches section.) An indirect-action clutch also contains a coil. The coil is located in the driving member. The driven side of the clutch contains a magnetizable metal and dry graphite lubricant. The current is controlled by a rheostat switch. The amount of current supplied to the coil determines the strength of the magnetic field and its attraction to the driven side. With full current, the two units are locked together by magnetic pull and turn as one unit. The two parts are not in physical contact with each other. With only limited current, the driven side of the clutch is allowed to purposely "slip" because of a weaker magnetic field. This system can then operate as a variable speed clutch. There is no heat build-up because the two surface do not come in contact with each other.** #### TRANSMISSIONS There are two main purposes of the transmission. First, it provides a means to select various speed ratios for different travel speeds. Secondly, it provides a means of reversing the direction of travel of the vehicle. All three means of transmitting power: friction, gear, and fluid are used separately or in combinations in the different types of transmissions. There are three major types of transmissions. They are: 1) mechanical transmissions, 2) hydraulically assisted mechanical transmissions, and 3) hydraulic transmissions. Each will be discussed separately in this topic. #### Mechanical Transmissions use a series of different sized spur gears on parallel input and output shafts to provide the various speed ratios. Shifting is done by hand or foot through mechanical linkage. Mechanical transmissions can be divided in three types for further discussion and clarification. - **Sliding Gear Transmissions** are usually the simplest in design. They have an input shaft from the clutch and an output shaft to the differential mounted in parallel. Different sized straight cut spur gears are in fixed positions on the shafts. Certain other gears rotate freely on the shafts. Additional gears are splined to the shafts and can slide back and forth. A third idler shaft can be positioned next to the input and output shafts. The idler shaft and gears provide a means of reserving the direction of rotation in the output shaft. All rotation in the gears and shafts must be completely stopped before shifting starts, or grinding and clashing of the teeth will occur. A simple three speed sliding gear transmission is illustrated below. In this transmission, gears F, G, H, E, and D are in a fixed position on the shafts. Gear C is free to rotate on the output shaft. Gears A and B are splined to the output shaft and slide back and forth to shift gears. The different gear ratios and flow of power can be followed through the transmission as follows: - **Collar Shift Transmissions** also have parallel input and output shafts, but with all power gears in constant mesh. The power gears themselves are not shifted, but a smaller shifting collar. This permits the use of stronger helical cut spur gears for high speed high power applications. Helical cut spur gears are quieter operating and allow more actual teeth contact area for the same width gear. The power gears are free to rotate on the shafts when the transmission is in neutral and in certain speed ratios. A smaller shifter gear is splined to the shaft and is located next to each free rotating power gear. To engage the selected gear ratio, the small shifting collar is moved over to lock the smaller shifter gear and the power gear together. The rotation of shafts and gears of a collar shift transmission must also be stopped to prevent grinding or clashing of gear teeth during shifting. - **Synchromesh or Synchronized Transmissions** are basically constant mesh collar shift transmissions with a few extra devices. Synchronizers are used in conjunction with the shifting collars to equalize or "synchronize" the rotating speed of the mating gears before they engage. A friction facing connected to the shifter collar comes in contact with a friction facing on the driven gear as shifting starts. As contact is made, friction increases and starts the selected gear to rotating on the shaft. Friction increases as the shift collar moves closer until the selected driven gear and the driver shifter gear are turning at the same speed. The shifter collar teeth can then engage the teeth of the driven gear without clashing and grinding while the shafts are turning. This allows "on the go" shifting of mechanical transmissions as long as the clutch is disengaged. Several different synchronizer designs are used. The disk and plate type synchronizer uses alternating friction disk and plates. Half are attached to the driven gear and half are attached to the driven shifter collar. Illustrated below is a common block or cone type synchronizer assembly. #### Hydraulic Assisted Transmissions are mechanical transmissions controlled or shifted by hydraulics. Gears are in constant mesh with one another. Some gears are fixed to the shaft, others are free to rotate until locked. The gear train transmits the power flow while hydraulic clutches and brakes control the power. Hydraulic assisted transmissions can normally be shifted from one consecutive gear to the next "on the go" without disengaging the main engine clutch. This is because of the alternating friction disk and plate clutch, and brake assemblies that replace the shifter collars. The disks are splined to the driver gears and the plates to the driven gears. Hydraulic pressure applied against a piston engages a clutch or applies a brake. Releasing hydraulic pressure disengages a clutch or releases a brake. There are two types of hydraulic assist transmissions. One is a basic parallel countershaft transmission. It uses spur gears similar to a collar shift or synchromesh transmission. Hydraulic clutch and brake packs are used instead of shift collars and synchronizers to start the gear to turning and lock it to the shaft. Pressure is released from one clutch and applied to the next clutch in the gear train by shifting appropriate hydraulic valves. The shifting mechanism often has a split second time delay to prevent sudden jerky shifting. The second type of hydraulic assisted transmission is a planetary transmission. It is first necessary to explain the action of a planetary assembly before discussing a planetary transmission. A planetary gear system is similar to our solar system. Each planet rotates on its axes as it rotates around the sun. Each planet pinion gear rotates on a separate shaft (axes) as they rotate around the center sun gear. The planet pinion gears also rotate inside a ring gear which encircles the complete assembly. All the gears are always in constant mesh with each other. The planet pinion gears are evenly spaced around the sun gear and are mounted in a planet pinion carrier. The driver (input) and driven (output) shafts can be attached to either the sun gear or the planet pinion carrier. #### Hydraulic Transmissions use mechanical power from an engine and converts it to hydraulic power in a hydraulic pump. The hydraulic power is then converted back to mechanical power in a hydraulic motor to drive or power other mechanical functions. There are two basic types of hydraulic transmissions. Hydrodynamic transmissions use hydraulic fluids pumped at high speeds, but at relatively low pressures. Hydrostatic transmissions use hydraulic fluids pumped at high pressure, but at low speeds. In either case, it is the hydraulic fluid that transmits the power, not a mechanical linkage or gears. Recall the previous discussion of how hydraulic fluid forced against the vanes caused a turbine wheel to turn. Consider two room fans placed on a table facing each other with one fan turned on. The air blast from the fan that is turned on will hit the curved blades on the second fan causing it to turn. These two principles combined make up a fluid coupler which is the simplest form of a hydrodynamic drive. Two fluid filled cup or bowl shaped housings are positioned face to face next to each other. Each half has fins or vanes inside. One side is the driver member and the other is the driven member. Hydraulic fluid is forced by centrifugal force to the outside edge of the driver side cup (pump side) as it rotates. The fluid then hits the fins of the turbine or driven side of the coupler and starts it turning. The faster the driver side turns, the more fluid is pumped. The fluid then feeds back to the pump side and the cycle starts over. If the pumping continues, the turbine side will soon be turning at approximately the same speed as the pump side. #### DIFFERENTIAL The differential has two primary and one secondary functions. First, it transmits power "around the corner" through the use of a bevel gear assembly. A smaller bevel pinion gear on the differential drive shaft is connected to the transmission. The larger bevel ring gear is connected to the axle shafts. This allows the power transmitted through the crankshaft and transmission to turn 90° to the drive wheels. The second primary function is to allow each drive wheel or axle to rotate at a different speed and still propel its own load as a vehicle makes a turn. This is accomplished as smaller bevel pinions rotate on their shafts (also called spider shafts) which are connected to the differential housing. Two larger bevel gears are connected to the axle shafts. The bevel pinions "walk" the outside bevel gear and axle around the corner as the differential housing and ring gear rotates and the vehicle turns. Differential action can be a disadvantage if one wheel or drive mechanism looses traction. The majority, if not all, power will go to the axle with the least resistance. This is the case when a tractor pulling a plow suddenly runs into a muddy or sandy spot in the field. Because of the loss of traction on one wheel, it will spin faster because of the lack of resistance to the ground. The other axle and drive wheel will slow down proportional or even stop turning. Many vehicle differentials are equipped with a differential lock. It can automatically or manually be engaged to lock both bevel gears together so both axles can turn as a unit. The wheel that is getting good traction will then turn at the same speed as the pinion ring gear to pull the tractor out of the mud. The secondary function and benefit of the differential assemble is a further reduction in RPM and increase in torque provided by the power train. In some vehicles such as light, middle, and heavy duty trucks, different gear ratio options are available for the differential. Selection would depend upon the primary intended use such as "a farm and ranch pick-up or truck" pulling heavy trailers on country roads vs an "over the road highway truck." For example, a 1 to 4.11 gear ratio would provide lower speed and higher torque to the drive wheel at a given engine RPM. AI to 3.55 gear ratio would provide slightly higher speeds, but provide less pulling torque at the same engine RPM. #### FINAL DRIVES The final drive assemblies are normally considered the last part of a power train. They provide the "final" reduction in speed and increase in torque to the drive wheels or other driven assemblies. Recall that the crankshaft of the engine may be rotating at 2,200 RPM and producing approximately 300 foot-pounds of torque. Each previous part of the power train has done its part to reduce the RPM and increase the torque. The drive wheel axles may now only rotate a few RPM and be producing many thousand foot-pounds of torque. This would depend upon the gear and speed ratios used in the transmission, differential and final drives. Not all power trains will use final drives. Straight axles may come directly out of the differential. This is the case with most automobiles and trucks. However, most agricultural tractors and other power equipment will use one of the three types of final drives. The final drive assemblies may be located: 1) in the transmission/differential housing, 2) in separate housings next to the differential, or 3) in housings at the end of the axle. - **Pinion Drives** - Pinion drives use a small pinion spur gear. The small spur gear is attached to the differential output shaft. The smaller pinion gear meshes with a larger spur gear that is attached to the shaft to which the wheel is connected. The larger spur gears are often called the "bull" gears in pinion type final drives. - **Planetary Drives** - Planetary final drives use planetary assemblies that were discussed previously. Planetary final drives are used extensively on high horsepower low speed vehicles. This allows the advantages of the high torque loads being spread evenly over several planet pinion gears instead of just one gear as is the case with a pinion drive assembly. The drive axle shaft is connected to the planet pinion carrier. Some planetary final drives may be located next to the differential housing and are called "inboard planetaries." Others are located on the end of the axle housing and are called "outboard planetaries." - **Chain Drives** - The third type of final drive is called chain drives. They use a small sprocket on the driver side of the final drive assemble and a larger sprocket on the driven side. The sprockets are connected by a heavy link chain. This allows the driver and driven shafts to be located different distances apart for different applications. Chain drives are usually limited to lower horsepower applications such as high-clearance spray rigs, and special purpose high-clearance equipment for vegetable and fruit production, etc. #### TORQUE DIVIDER Tractors, trucks, and automobiles that are equipped with true "four-wheel drives" or "mechanical front wheel drives (MFWD)" have an additional power train component. Some type of torque divider housing is needed to divide the torque from the transmission output shaft. Part of the torque must be supplied to the front drive axle differential and part to the rear. Torque dividers (also know as drop boxes or transfer cases) will contain the proper gear ratios if the front and rear drive tires are different sizes. The torque divider may also be equipped with some type of clutch or shifting mechanism to engage or disengage power to the front differential. This will depend upon whether the vehicle is equipped with full or part time four- wheel drive. Many of the new MFWD equipped tractors are equipped with hydraulically operated clutch assemblies so that the front axle drive can automatically engage and disengage on the go. #### POWER TAKE OFF The power take-off (PTO) is actually an attachment or extension of the power train of a tractor. It is used to connect the rotating power of the engine to auxiliary equipment. There are three basic classifications of PTO systems used on tractors. - **Transmission-Driven PTOs** are driven from gears in the transmission and only operate when the engine clutch is engaged. When the engine clutch is disengaged, the forward or reverse travel of the tractor is stopped along with power to the PTO. The clutch must be disengaged and travel completely stopped before the PTO can be shifted in or out. - **Continuous-Running PTOs** have two clutch disks in the clutch assembly, but only one set of control linkage. One clutch disk is for the transmission and the other is for the PTO. The first half of the clutch pedal action operates the transmission clutch while the second half operates the PTO clutch. The clutch pedal is depressed half way to stop travel of the tractor while the PTO remains turning. Pressing the clutch all the way stops both. With a continuous-running PTO, the transmission cannot be shifted while the PTO is operating. - **Independent PTOs** have a separate clutch and controls for both the transmission and the PTO. Each can operate completely independent of each other. Besides the three classifications of PTO systems used on tractors, they can operate at two different speeds. Lower horsepower tractors operate at 540 RPM while larger tractors operate at 1000 RPM when the engine is at rated speeds. Some mid-size tractors may be equipped to operate at both PTO speeds. In 1965, the American Society of Agricultural Engineers and the International Standards Organization established industry PTO standards. Different brand tractors and equipment within specific horsepower ranges are compatible and can be safely attached. This prevents a light duty 540 RPM implement from being attached to a large tractor operating at 1,000 RPM which could cause serious damage and possible bodily injury. #### PTO STANDARDS - **Type I: 540 RPM PTO** - 6 spline shaft... 1 3/8" in diameter - For equipment requiring 85 PTO HP or less - **Type II: 1,000 RPM PTO** - 21 spline shaft... 1 3/8" in diameter - For equipment requiring 85 to 150 PTO HP - **Type III: 1,000 RPM PTO** - 20 spline shaft... 1 3/4" in diameter - For equipment requiring over 150 PTΟ ΗΡ #### POWER TRAIN LUBRICANTS Power train lubricants can be divided into: 1) gear oils, 2) automatic transmission/hydrostatic transmission fluids, 3) transmission/hydraulic fluids, and 4) lubricating greases. The type of lubricant used will depend upon the application. Different lubricants/fluids have different additives, characteristics, and requirements. Below is a partial list: - **Viscosity Ratings** - Different viscosity oils (resistance to flow) are required because of the wide variation in both ambient and power train operating temperatures. - **Foam Inhibitors** - Violent churning and high rate of flow in some applications can cause oil to foam and fill with air. Air does not lubricate and can be compressed allowing metal surfaces to come in contact with each other and increase wear. - **Extreme Pressure Properties** - The oils and lubricants must adhere to the surfaces. In high torque applications, extreme friction and sliding pressures applied in many gear combinations can cause the lubricates to be "pushed or squeezed" out. - **Anti-rust and Corrosion Inhibiters** - Grit and scale from internal rust and corrosion can increase scoring and wear between precise bearing and gear surfaces. - **Seal/Gasket Conditioners** - Lubricants and additives must be compatible with gaskets and seals made of rubber and other materials. Special conditioners can help the seal and gaskets remain soft and pliable without deteriorating. - **Oxide Inhibiters** - Lubricants and their additives must be chemically stable so that they do not go through a chemical breakdown, oxidize, and form sludge. The type of power train lubricant/hydraulic fluid used in agricultural tractors and equipment often depends upon the design of the power train component itself. Over the years, various designs have been used. Some of these designs include: 1) A separate dry clutch housing; transmission, differential, and final drives all housed in another single compartment using a common lubricant; and the hydraulic system either separate or as a part of the power train system. 2) Separate compartments and lubricants for the wet clutch; transmission, differential, and final drives; with hydraulic fluid supplied by the wet clutch compartment. 3) Three compartment units that are divided into: torque converter and wet clutch; transmission, differential, and final drives; and the PTO which supplies the hydraulic fluid. 4) Separate and/or common compartments with a common power train lubricant and hydraulic fluid. #### Gear Oils Gear oils are used primarily to lubricate mechanical transmissions, differentials, final drives, steering assemblies, and other gear boxes. The gears may range from simple low speed straight cut spur gears to high speed spiral bevel hypoid gears. As the gear type, size, and torque load changes, so does the lubrication requirements. Gear oils have two major classifications. The first is the Society of Automotive Engineers (SAE) classification which is based on viscosity alone. The viscosity rating is based on the number of seconds it takes a measured quantity of oil to flow through a standardized small orifice at a specified temperature. The SAE classification numbers for gear oils are higher than the SAE numbers for engine oils. However, the gear oils are not necessarily that much higher in viscosity. The common SAE 90 gear oil has approximately the same viscosity as SAE 40 engine oil. Many oil suppliers now have available multi-viscosity gear oils such as SAE 80/90/140. The gear oils used in most agricultural applications have a higher viscosity rating than do hydraulic oils. The second classification is the American Petroleum Institute (API) rating which tells how severe of operating conditions the gear oil is suitable for. The API gear oil service classifications range from API GL-1 to API GL-6 (inclusive). API GL-1 & 2 gear oils are used in standard transmissions, worm axle gears, and gear boxes operating under low pressures and speeds. Anti rust, oxide, and foam additives may be used. Because of low torque applications, friction reducers and extreme pressure additives are not included. API GL-3 classification is used in manual transmission and spiral bevel gear applications under moderate conditions. API GL-4 & 5 gear oils are used in moderate to severe high speed high torque conditions with hypoid cut gears. API GL-6 gear oils are recommended for the most severe high speed high torque applications. Single gear oils meeting or exceeding several classifications are available from many oil suppliers. Friction reducers and extreme pressure additives are used in API GL-3 through GL-6 gear oils. #### Automatic Transmission Fluids - The function of automatic/hydrostatic transmission fluids are somewhat different. They must serve as the medium to transmit power and to transfer heat in addition to lubricate internal parts. The original automatic transmission fluid specification was Type A. In the 1960s, specifications were upgraded by Ford Motor Co. and were called Type F. The latest specifications called DEXRON were issued by General Motors. It has been adopted by most manufacturers, but the other classifications are still in use. Special seal conditioners are added because of all the seals, gaskets, and adhesives used in automatic and hydrostatic transmissions and the extreme heat build-up. #### Transmission/Hydraulic Oils - Hydraulic oils must also transmit power, lubricate internal parts and transfer heat. Because of