Basic Principles of Power Harrell, Chapter 6

Goals Terminology Levers and their influence on torque Relation between torque and power Method by which an engine develops torque and power Identify three terms used in ag power and machinery that describe power Describe the two ways by which agricultural tractors are rated for power and how each can be measured Interpret engine performance test data in accordance with power and torque

Force Energy that is exerted by one source upon another with a tendency to change the action of the one being acted upon There is no motion involved in the expression of force Weight expresses the mass that must be overcome based on the actions of gravity (1 lb = 0.4536 kg) Force required to hold mass in place against the force of gravity is expressed as a Newton (9.81 kilograms of force) What is the force required to support 205 kg of weight?

Work Involves the action of force to move a body at rest Involves both force and distance, which can be calculated Work = distance X force (results in ft lbs of force in standard, or Joules in metric, which is a Newton meter) If a football weighs 1 lb, how much work must be performed to throw it 25 yards?

Torque Term used to describe a rotating or twisting force Requires the use of a lever Identifies the amount of twisting or turning effort that is applied by using a lever to achieve rotation Torque = force X length of lever (ft. lbs. or N*m) Torque is influenced by the length of the lever Cable or chain drum must also be considered when using hoists, so weight X drum radius length of crank lever

Engine Torque The internal combustion engine: piston inside a closed cylinder, connecting rod, crankshaft Combustion and expansion of gases creates force that pushes the piston Length of the crankshaft throw is half the stroke Calculate: Lb of Force X length of throw To convert Lb Ft. to lb inches, multiply by 12

Power The term Power is used to express the rate at which work is being performed (time) Formula: work/time or Force X distance time Figure 6-8

Horsepower The term horsepower is a description of the amount of work that an average horse can produce in a specific period of time. 1 hp = 33,000 ft lb/min So….. Formula: HP = force X distance time x 33,000

Types of Power Drawbar Power Power takeoff (PTO) power Brake Power Belt power (old tractors)

Drawbar Power Drawbar power refers to the power that a tractor will produce when pulling a load attached to a drawbar. Example, the size of tractor can be determined for pulling a six bottom plow if you know: With of cut of each bottom in inches Speed of travel in mph Depth of plowing in inches Classification of soil See page 107

Drawbar Power Plow speed = 4.5 mph or 396 ft/min Plow depth = 8 in Cut width = 14 in 6 bottoms (plowshares) 14 in/bottom X 6 bottoms X 120 lb pull/1 inch of cut = 10,080 lb Force X distance time X 33,000 ft lb/min 10, 080 lb X 396 ft 1 min X 33,000 ft lb/min

PTO Horsepower 540 rpm 540/1000 rpm

Brake Power Power which an engine or motor delivers when measured at the output shaft Generally considered the same as PTO in a tractor Drawbar power is generally 15% less than PTO or brake power

Belt Power Old rating used with old tractors

Measuring Power Use a dynamometer Places a load on a rotating output shaft in a controlled manner Tachometer – measures the number of revolutions per minute which the crankshaft and friction wheel rotate PTO dynamometer – commonly used in tractor shops

Interpretation of Data Sales literature discussed by a salesman Technician must also determine if a piece of equipment is meeting specs Performance test data is usually represented as test curves on a graph Temperature and altitude (elevation) will affect performance Increased ambient temperature decreases performance Increased elevation decreases performance

Summary Measuring and determining power is important There are different ways to measure power in agricultural equipment Loss of power indicates a problem in the equipment that should be repaired