Grubaugh, Elston K.

Valco, Thomas D.

Texas A&amp;M Repository

II -.,;LCf- 8'2-3Mf".1uJ L-2047GEAR SELECTION AND ENGINE SPEEDElston K. Grubaugh and Thomas D. Valco*Fu I consumption is largely determined by theway a tractor is operated. Drawbar load, enginespeed, the gear used, amount of turning and amountof engine idle time can cause fuel consumption tovary more than 30 percent for a given task.To operate efficiently, a tractor engine should beoperat d at its rated capacity. Diesel, gasoline andLP-ga tractors all operate most efficiently underheavy loads when the throttle is wide open. Dieseltractor have the added advantage of greater"lugging" ability, the ability to pull at slowerengine speeds when the tractor and implement arebogg d down. The gear selection process for dieseltractors is the same as the gasoline or LP-gas trac-tors. Select the highest gear at which the engine willoperate at its rated speed when pulling heavy loads.Exce sive black smoke from a diesel engine meansthat it is lugging too hard and wasting fuel. Over-loading any tractor causes excessive fuel consump-tion and rapid engine and drive-train wear. Over-load occur when the tractor engine cannot reach itsfull rated peed. In these situations, shift to a lowergear.To determine if the tractor is overloaded, slow theengine to half throttle while the tractor is movingacross the field under load. Then move the throttle toits wide-op n position. If the engine quickly reachesits rated operating speed, the tractor is notoverloaded.Many field operations, such as spraying andplanting, do not require full-rated tractor horse-power. A imilar ituation exists when implementssized for a smaller tractor are used with high horse-power tractor. Additionally, many operations mustbe perform d at a fixed field speed. For light or part-load operations, consider shifting to a higher gearand slowing the engine speed to maintain the de-sired field speed. Slower engine speeds improve fuelefficiency.*Extension agricultural engineers-mechanization, The TexasA&M University System.21:2The "gear up - throttle down" concept can bedemonstrated with Nebraska Tractor Test data. l Inthe Nebraska tests, the tractor was tested formaximum drawbar horsepower in a gear selected bythe tractor manufacturer. In the same gear, the trac-tor was tested pulling 50 percent of the maximumpower run load. Then, the tractor was tested in ahigher gear and at a reduced engine speed to main-tain the same pull and travel speed as in the secondrun.During the third run, most tractors tested used be-tween 15 and 30 percent less fuel than during thesecond run, even though the same amount of workwas performed. Throttle setting and gear selectionwere the only factors changed.The "gear up - throttle down" practice usuallycan be used when loads require less than two-thirdsof the tractor's power. Generally, it is safe to reduceengine speed by 20 to 25 percent of the rated speed.Check the operator's manual for specific recom-mendations for your tractor.When using the practice of "gear up - throttledown," remember not to overload or lug the engine.A simple rule for diesel tractors pulling light loads isto select a gear and engine speed in which the ex-haust smoke is not excessive. You can also test for anoverload by using the throttle test mentioned pre-viously. Most diesel engines can stand moderateoverloads at part speed. Remember, however, thedrawbar power required remains the same when youshift up and reduce speed. Power is a combination ofspeed and torque. Sustained high torque loads,resulting from either excessive load and weight orincorrect gear and speed selection, can damage trans-mission and other drive-train components.Also, remember that when engine speed is re-duced, power take off (PTO) speed is corresponding-ly reduced. In addition, with reduced engine speed,reaction time of the tractor hydraulic system isslower.1 "Nebraska Tractor Test Data," Department of AgriculturalEngineering, University of Nebraska, Lincoln, NE 68583.Table 1. Tractor and operation comparisonSmall Large Largekactor kactor kactorThrottle setting Full Full ReducedPercent load 100% 50% 50%Drawbar horsepower 55.79 56.67 56.72Fuel consumption 4.49 5.23 4.20(gallons/hour)Fuel efficiency 12.54 10.91 13.55(horsepower hours/gallon)Nebraska tractor tests indicate that a large dieseltractor operated at reduced engine speed for lightdrawbar loads may actually use less fuel than asmaller tractor working at its rated capacity.Table 1 compares the performance of a largetractor rated at 110 drawbar horsepower and asmaller tractor rated at 56 draw bar horsepower on aload requiring 55 drawbar horsepower. Data inTable 1 indicate that the large tractor geared up andthrottled down had the highest fuel efficiency -13.55 horsepower hours per gallon. This is a reduc-tion of about 1 gallon per hour over full throttle op-eration of the large tractor and 0.29 gallon per hourover the small tractor. A large tractor properlymatched to a light load may save fuel compared to asmaller tractor operating at full load.Many tractor operators think that because a dieseltractor is turbocharged it should be operated at full-rated speed. If full draw bar horsepower is not re-quired, this is not justified.Fuel consumption and fuel efficiency vary widelyfor specific tractors. Fuel efficiency (horsepowerhours per gallon) is the amount of work the tractorproduces per gallon of fuel used. This measure is notinfluenced by engine size and can be used to compareefficiencies of tractors with different horsepowers.By keeping accurate records of the fuel usage ofyour tractors under a variety of operating condi-tions' you can make decisions concerning the mostefficient operation of the machine. Also, goodrecords can indicate when tune ups or repairs areneeded.Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socioeconomic level,race, color, sex, religion, handicap or national origin.Cooperative Extension Work in Agriculture and Home Economics, The Texas A&M University System and the United States Departmentof Agriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, 1914, as amended, and June 30, 1914.5M - 8-82, New ENG 6-3

Gear Selection and Engine Speed.

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Gear Selection and Engine Speed.

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Gear Selection and Engine Speed.

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