motores

Richard Prystupa

MotoresMotores

MotoresMotores (Modulo 160401a (Modulo 160401a)) Es un dispositivo mecánico en el cual la energía Es un dispositivo mecánico en el cual la energía

química de la oxidación del combustible es química de la oxidación del combustible es convertida en energía calorífica, la cual a su vez es convertida en energía calorífica, la cual a su vez es convertida en energía mecánica.convertida en energía mecánica.

La relación es normalmente desde 7:1 hasta 15:1 por La relación es normalmente desde 7:1 hasta 15:1 por peso (aire/combustible).peso (aire/combustible).

?QUE ES TORQUE??QUE ES TORQUE?

Es la fuerza aplicada en una palanca que hace rotar Es la fuerza aplicada en una palanca que hace rotar alguna cosa, provocando un momento torsional.alguna cosa, provocando un momento torsional.

Expresado en lb*pie, lb*plgs, o Newton-metros.Expresado en lb*pie, lb*plgs, o Newton-metros. Tq = F x distancia del radio en pieTq = F x distancia del radio en pie

Lectura del torqueFuerzaTornillo o tuerca conectada

empieza a torcerse

QUE ES POTENCIA?QUE ES POTENCIA?

Es cuán rápido podemos realizar el trabajo.Es cuán rápido podemos realizar el trabajo. 1 HP = 746 Watts1 HP = 746 Watts 1 HP = 550 lb. pie./sec.1 HP = 550 lb. pie./sec. HP = HP = T x RPMT x RPM 52525252

¿Cuál es la ál es la unidad de unidad de potencia?potencia?

Si

RANGO DE CABALLOS DE FUERZA DE UN RANGO DE CABALLOS DE FUERZA DE UN MOTORMOTOR (p. 8)(p. 8)

CABALLOS DE FUERZA INDICADOCABALLOS DE FUERZA INDICADO Son los caballos de fuerza calculados teóricamente.Son los caballos de fuerza calculados teóricamente. No se encuentran previstas las perdidas por No se encuentran previstas las perdidas por

fricción o bombeo, o la energía necesaria para fricción o bombeo, o la energía necesaria para mover otros accesorios.mover otros accesorios.

CABALLOS DE FUERZA POR FRICCION CABALLOS DE FUERZA POR FRICCION (CFFr)(CFFr)

Es la energía perdida por fricción y bombeo.Es la energía perdida por fricción y bombeo. (Ej. Transmisión, rodamientos, poleas, bombas)(Ej. Transmisión, rodamientos, poleas, bombas) FHP = IHP – BHP (CFFr= CFI – CFF)FHP = IHP – BHP (CFFr= CFI – CFF)

CABALLOS DE FUERZA DE FRENOCABALLOS DE FUERZA DE FRENO

Es la energía existente Es la energía existente medida en el extremo medida en el extremo del cigüeñal (Volante).del cigüeñal (Volante).

Este es el desarrollo de Este es el desarrollo de los caballos de fuerza los caballos de fuerza existente en el motor en existente en el motor en operación.operación.

BHP = IHP – FHP. BHP = IHP – FHP. (CFF= CFI-CFFr)(CFF= CFI-CFFr)

PRESIONPRESION

Es una fuerza por unidad de área. Es una fuerza por unidad de área. EjEj. lbs.*Plgs. lbs.*Plgs22 o kPa (1 lb*Plgs o kPa (1 lb*Plgs22 = 6.9 kPa) = 6.9 kPa)

VACIOVACIO (p. 9) (p. 9)

Es la presión por debajo de la presión atmosférica. Es la presión por debajo de la presión atmosférica. (14.7 lbs*Plgs(14.7 lbs*Plgs22 o 0 psig @ sea level). o 0 psig @ sea level).

PRESION ATMOSFERICAPRESION ATMOSFERICA

Es debido al peso de la atmósfera sobre la superficie de la Es debido al peso de la atmósfera sobre la superficie de la tierra que a nivel del mar existe 14.7 lbs*Plgstierra que a nivel del mar existe 14.7 lbs*Plgs22 atmosférica. atmosférica.

Atmósfera

Aceleración

de la gravedad

16 400 pies sobre el nivel del mar.

Pr = 7.7 Lbsa*Plgs2

A nivel del mar

Pr = 14.7 Lbsa*plgs2

Presión ejercida sobre unidad unidades de área.

RELACION CILINDRO CARRERARELACION CILINDRO CARRERA (p. 10)(p. 10)

CILINDROCILINDRO El diámetro interior del cilindroEl diámetro interior del cilindro Medido a una precisión de .001”Medido a una precisión de .001”

CARRERACARRERA Es el desplazamiento del pistón Es el desplazamiento del pistón

desde el PMS al PMI o viceversa.desde el PMS al PMI o viceversa.

Øint

Carrera

PMI

PMS

DESPLAZAMIENTO DEL MOTORDESPLAZAMIENTO DEL MOTOR

Ej. Ej. Cilindro = 4.001”Cilindro = 4.001”Carrera = 3.480”Carrera = 3.480”Motor de 8 cilindrosMotor de 8 cilindros

¿¿Cual es el Cual es el desplazamiento cúbico del desplazamiento cúbico del MotorMotor??

V = ∏r² x HV = ∏r² x HV = 3.14 (2) ² x 3.480” x # V = 3.14 (2) ² x 3.480” x # cil.cil.V = 349.865 PlgsV = 349.865 Plgs33 o o 350 Plgs350 Plgs33..

PMS

CARRERA

PMI

CILINDRO

MOTOR CUADRADOMOTOR CUADRADO (p. 10) (p. 10)

Cuando el diámetro interior del cilindro es igual a la carrera.Cuando el diámetro interior del cilindro es igual a la carrera.

4”

4”

MOTOR SOBRECUADRADOMOTOR SOBRECUADRADO Cuando el Cuando el ØØint.int. del cilindro es mayor que la carrera, por del cilindro es mayor que la carrera, por

consiguiente, el pistón tiene menos recorridoconsiguiente, el pistón tiene menos recorrido.. Son encontrados típicamente en motores automotriz y altas Son encontrados típicamente en motores automotriz y altas

aceleraciones.aceleraciones. Típicamente son de motores pequeños – 327, 350, 400 GMTípicamente son de motores pequeños – 327, 350, 400 GM

4”

3”

MOTOR SUBCUADRADOMOTOR SUBCUADRADO

Cuando el Cuando el ØØint.int. del cilindro es menor quela carrera. del cilindro es menor quela carrera. Grandes torques de salida a bajas rpm.Grandes torques de salida a bajas rpm. Son hallados sobre grandes, pequeños motores en movimiento. Son hallados sobre grandes, pequeños motores en movimiento. Motores de bloques grandes – 396, 427, 454 son determinados Motores de bloques grandes – 396, 427, 454 son determinados

por su peso y dimensiones externas, no el desplazamiento en por su peso y dimensiones externas, no el desplazamiento en PlgsPlgs33..

3”

4”

VOLUMEN DE LA HOLGURAVOLUMEN DE LA HOLGURA

Es el volumen remanente sobre el pistón, Es el volumen remanente sobre el pistón, cuando este esta en el PMS.cuando este esta en el PMS.

Pistón @ PMS Holgura

Carrera

COMPRESSION RATIOCOMPRESSION RATIO Is how much air/fuel mixture is compressed by Is how much air/fuel mixture is compressed by

volume.volume. It is the ratio of the total volume of the cylinder and It is the ratio of the total volume of the cylinder and

combustion chamber clearance at BDC compared combustion chamber clearance at BDC compared to the clearance volume at TDC.to the clearance volume at TDC.

What would the compression ratio be in this example?

COMPRESSION RATIOCOMPRESSION RATIO

What would the compression ratio be in this example?

15:1

VOLUMETRIC EFFICIENCYVOLUMETRIC EFFICIENCY (p. 11) (p. 11)

The ratio expressed as a percentage of the The ratio expressed as a percentage of the volume of atmospheric air drawn into the volume of atmospheric air drawn into the cylinder on the intake stroke (cylinder on the intake stroke (4 stroke4 stroke natural natural aspirationaspiration) compared to the displacement.) compared to the displacement.

VEVE = = Actual OutputActual Output x 100 x 100

Theoretical OutputTheoretical Output

SCAVENGE EFFICIENCYSCAVENGE EFFICIENCY

It is the ratio expressed as a percentage of the fresh It is the ratio expressed as a percentage of the fresh air contained in the cylinder to the total volume of air contained in the cylinder to the total volume of air and exhaust gases in the cylinder at the time the air and exhaust gases in the cylinder at the time the port closes.port closes.

Associated with two-stroke engines. Associated with two-stroke engines.

THERMAL EFFICIENCYTHERMAL EFFICIENCY

States how well the engine changes fuel energy States how well the engine changes fuel energy into mechanical energy.into mechanical energy.

Most engines are about 25 to 35% efficient. (Most Most engines are about 25 to 35% efficient. (Most goes out the exhaust).goes out the exhaust).

BASIC ENGINE OPERATION BASIC ENGINE OPERATION (p. 12) (p. 12)

INTERNAL COMBUSTION ENGINESINTERNAL COMBUSTION ENGINES Fuel is burnt inside the engine in the cylinders.Fuel is burnt inside the engine in the cylinders.

INTERNAL COMBUSTION ENGINESINTERNAL COMBUSTION ENGINES

The 3 main requirements to allow fuel to burn in an engine are: The 3 main requirements to allow fuel to burn in an engine are: Fuel, Air and Ignition.Fuel, Air and Ignition.

INTERNAL COMBUSTION ENGINESINTERNAL COMBUSTION ENGINES

The compression process generates heat, in some The compression process generates heat, in some cases it is enough to ignite the mixture without a cases it is enough to ignite the mixture without a spark. (Diesel engine).spark. (Diesel engine).

INTERNAL COMBUSTION ENGINESINTERNAL COMBUSTION ENGINES Upon the power stroke, the piston transfers the Upon the power stroke, the piston transfers the

energy to the connecting rod which then is energy to the connecting rod which then is transferred to the crankshaft into rotary motion.transferred to the crankshaft into rotary motion.

Four Stroke (Cycle) EnginesFour Stroke (Cycle) Engines (p. 13 – Fig. 8) (p. 13 – Fig. 8)

On a 4 cycle engine, it takes 720 degrees of the On a 4 cycle engine, it takes 720 degrees of the crank to rotate to complete 1 cycle.crank to rotate to complete 1 cycle.

Four Stroke (Cycle) EnginesFour Stroke (Cycle) Engines

On the On the intake strokeintake stroke, the intake valve opens before , the intake valve opens before the piston reaches TDC (valve overlap) and begins the piston reaches TDC (valve overlap) and begins to move downwards pulling air/fuel mixture into the to move downwards pulling air/fuel mixture into the cylinder.cylinder.


Slightly past BDC, the intake valve closes and the Slightly past BDC, the intake valve closes and the piston moves upward compressing the air/fuel piston moves upward compressing the air/fuel mixture.mixture.


The air/fuel mixture is ignited at TDC (both valves The air/fuel mixture is ignited at TDC (both valves are still closed – are still closed – compression strokecompression stroke).).


The piston moves past TDC as complete burning of The piston moves past TDC as complete burning of the air/fuel mixture begins to take place.the air/fuel mixture begins to take place.

The expanding gases push the piston downward in The expanding gases push the piston downward in the cylinder producing power (the cylinder producing power (power strokepower stroke).).


Slightly before the piston reaches BDC, the exhaust Slightly before the piston reaches BDC, the exhaust valve opens and the piston pushes the burned gases valve opens and the piston pushes the burned gases out of the cylinder as it moves up (out of the cylinder as it moves up (exhaust strokeexhaust stroke).).


As the piston nears TDC, the exhaust valve starts As the piston nears TDC, the exhaust valve starts closing and the intake valve starts opening and the closing and the intake valve starts opening and the cycle begins again. This is known as cycle begins again. This is known as valve overlapvalve overlap and occurs at the end of the exhaust stroke.and occurs at the end of the exhaust stroke.

TWO STROKE (CYCLE) ENGINESTWO STROKE (CYCLE) ENGINES (p.15-fig. 9)(p.15-fig. 9)

Two stroke engines complete one cycle in 360 Two stroke engines complete one cycle in 360 degrees.degrees.

2 stroke engines may use valves or ports.2 stroke engines may use valves or ports.

TWO STROKE (CYCLE) ENGINESTWO STROKE (CYCLE) ENGINES

When the piston is moving downward, spent When the piston is moving downward, spent gases begin leaving the piston cylinder.gases begin leaving the piston cylinder.


The air/fuel mixture begins entering the The air/fuel mixture begins entering the cylinder close to the bottom of the strokecylinder close to the bottom of the stroke . .

TWO STROKE (CYCLE) ENGINESTWO STROKE (CYCLE) ENGINES As the piston starts moving upward, air/fuel is still As the piston starts moving upward, air/fuel is still

entering the piston chamber but is stopped early in entering the piston chamber but is stopped early in the stroke.the stroke.

The remainder of the stroke is used to compress the The remainder of the stroke is used to compress the air/fuel mixture in the piston chamber.air/fuel mixture in the piston chamber.


Near TDC, the mixture is ignited and the expanding Near TDC, the mixture is ignited and the expanding gases begin to push the piston downwards.gases begin to push the piston downwards.


Near the end of the cycle, the exhaust valve (or port) Near the end of the cycle, the exhaust valve (or port) opens and the spent gases begin exhausting.opens and the spent gases begin exhausting.

2 stroke engines need to be artificially aspirated to force 2 stroke engines need to be artificially aspirated to force out the exhaust gases and to push in the fresh air/fuel mix.out the exhaust gases and to push in the fresh air/fuel mix.


The intake valve (or port) opens while the piston is The intake valve (or port) opens while the piston is still moving downward and the cycle begins again.still moving downward and the cycle begins again.

TWO STROKE vs. FOUR STROKETWO STROKE vs. FOUR STROKE

simpler and lighter simpler and lighter do not have valves do not have valves fire once every revolution, fire once every revolution,

(~75% more hp than 4 (~75% more hp than 4 stroke)stroke)

can work in any can work in any orientation orientation

not as efficient as 4 strokenot as efficient as 4 stroke

fire once every two fire once every two revolutions revolutions

More efficient than 2 strokeMore efficient than 2 stroke Better fuel consumptionBetter fuel consumption No mixing oil/fuelNo mixing oil/fuel

CRANKSHAFT ROTATIONCRANKSHAFT ROTATION

Is determined as if viewing the engine from the Is determined as if viewing the engine from the main power takeoff or flywheel end. main power takeoff or flywheel end. (Rear)(Rear)

If the engine turns to the right its rotation clockwise If the engine turns to the right its rotation clockwise (CW).(CW).

If engine rotates to the left its rotation is If engine rotates to the left its rotation is counterclockwise (CCW).counterclockwise (CCW).

NUMBERING OF CYLINDERSNUMBERING OF CYLINDERS

FIRING ORDERFIRING ORDER (p. 17) (p. 17)

FIRING ORDERFIRING ORDER

The position of the crankshaft throws and the lobes The position of the crankshaft throws and the lobes on the camshaft determine the firing order of an on the camshaft determine the firing order of an engine.engine.

The order is designed to give an even number of The order is designed to give an even number of pulses throughout the complete rotation of the pulses throughout the complete rotation of the crankshaft.crankshaft.

This is the sequence of order for the cylinders to This is the sequence of order for the cylinders to receive ignition.receive ignition.

RUNNING MATESRUNNING MATES (Fig. 11) (Fig. 11)

This applies to This applies to four stroke engines onlyfour stroke engines only because because every cylinder fires in one complete revolution every cylinder fires in one complete revolution (360 degrees) on 2 stroke engines.(360 degrees) on 2 stroke engines.

Running mates refer to pistons which reach TDC Running mates refer to pistons which reach TDC simultaneously, but only one fires. (720simultaneously, but only one fires. (720˚ cycle)˚ cycle)

Assists in balancing of the crank and pistons.Assists in balancing of the crank and pistons.

Running mate arrangements:Running mate arrangements: 4 cyl. Inline engine: 1-4, 2-3.4 cyl. Inline engine: 1-4, 2-3. 8 cyl. Inline engine: 1-8, 2-7, 3-6, 4-5.8 cyl. Inline engine: 1-8, 2-7, 3-6, 4-5. V 6 engine: 1-6, 2-5, 3-4.V 6 engine: 1-6, 2-5, 3-4.

RUNNING MATES (Crankshaft Throws)RUNNING MATES (Crankshaft Throws)

ENGINE CLASSIFICATIONENGINE CLASSIFICATION (p. 18) (p. 18)

Engines are classified by:Engines are classified by: cylinder and crankshaft arrangements.cylinder and crankshaft arrangements. valve arrangement.valve arrangement. position of camshaft.position of camshaft. cooling methods.cooling methods. induction methods.induction methods. engine speeds.engine speeds. operating (stroke) cycle.operating (stroke) cycle. ignition methods and type of fuel consumed.ignition methods and type of fuel consumed.

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