V. Machines (A,B,C,J) Dennis Buckmaster [email protected]

https://engineering.purdue.edu/~dbuckmas/

OUTLINE

• Internal combustion engines • Hydraulic power circuits • Mechanical power transmission

References

•

Engineering Principles of Agricultural Machinery, 2 nd ed.

2006. Srivastava, Goering, Rohrbach, Buckmaster. ASABE.

•

Off-Road Vehicle Engineering Principles

. 2003. Goering, Stone, Smith, Turnquist. ASABE.

Other good sources

• •

Fluid Power Circuits and Controls: Fundamentals and Applications.

2002. Cundiff. CRC Press.

Machine Design for Mobile and Industrial Applications.

1999. Krutz, Schueller, Claar. SAE.

Free & Online

http://hydraulicspneumatics.com/learning resources/ebooks ASABE members can access ASABE texts & Standards electronically at: http://elibrary.asabe.org/toc.asp

Engines

• Power and Efficiencies • Thermodynamics • Performance

Engine Power Flows

Power & Efficiencies

• Fuel equivalent P fe,kW = (Hg kJ/kg ∙ṁ f,kg/h )/3600 [Hg = 45,000 kJ/kg for No. 2 diesel] • Indicated P i,kW = p ime,kPa D e,l N e,rpm /120000 • Brake P b,kW = 2 πT Nm N e,rpm /60000 • Friction P f = P i -P b

Power &

Efficiencies

• Indicated Thermal E it = P i /P fe • Mechanical E m = P b /P i • Overall (brake thermal) E bt = P b /P fe = E it *E m • Brake Specific Fuel Consumption BSFC= ṁ f,kg/h /P b,kW

Dual Cycle



Related equations

• Compression ratio = r r = V 1 /V 2 • Displacement D e,l = (V 1 -V 2 )*(# cylinders) = π(bore cm ) 2 (stroke cm )*(# cyl)/4000 • Ideal gas p 1 V 1 /T 1 = P 2 V 2 /T 2 • Polytropic compression or expansion p 2 /p 1 = r n

[n = 1 (isothermal) to 1.4 (adiabatic), about 1.3 during compression & power strokes]

Related equations

• Air intake ṁ a,kg/h

= .03D

e,l N e,rpm ρ a,kg/cu m η v,decimal

•

From Stoichiometry (fuel chemistry) A/F = air to fuel mass ratio = 15:1 for cetane

What is the displacement of a 6 cylinder engine having a 116 mm bore and 120 mm stroke?

For this same engine (7.6 l displacement, 2200 rpm rated speed), what is the air consumption if it is naturally aspirated and has a volumetric efficiency of 85%? Assume a typical day with air density of 1.15 kg/m 3 .

With a stoichiometric air to fuel ratio based on cetane, at what rate could fuel theoretically be burned?

Consider the this same (595 Nm, 137 kW @ 2200 rpm) engine which has a high idle speed of 2400 rpm and a torque reserve of 30%; peak torque occurs at 1300 rpm. Sketch the torque and power curves (versus engine speed).

Torque (Nm) Power (kW) Speed (rpm)

Consider the this same (595 Nm, 137 kW @ 2200 rpm) engine which has a high idle speed of 2400 rpm and a torque reserve of 30%; peak torque occurs at 1300 rpm. Sketch the torque and power curves (versus engine speed).

Torque (Nm) Power (kW) Speed (rpm)

Alternative fuels

What has to be similar?

• Self Ignition Temperature • Energy density • Flow characteristics • Stoichiometric A/F ratio

Power Hydraulics

• Principles • Pumps, motors • Cylinders • Pressure compensated & load sensing systems • Electrohydraulics introduction

About Pressure

• 14.7 psia STP (approx __ in Hg) • Gage is relative to atmospheric • Absolute is what it says … absolute & relative to perfect vacuum • What causes oil to enter a pump?

• Typical pressures: – Pneumatic system – Off-road hydraulic systems 21

Liquids Have no Shape of their own

22

Liquids are Practically Incompressible

23

Pascal’s Law

• Pressure Exerted on a Confined Fluid is Transmitted Undiminished in All Directions and Acts With Equal Force on Equal Areas and at Right Angles to Them.

24

Application Principles

1 lb (.45kg) Force 10 lbs (4.5kg) 10 sq in (6.5cm2) Piston Area 1 sq in (.65cm2) Piston Area 1 psi (6.9kpa)

25

Hydraulic “lever”

26

Types of Hydraulic Systems

Open Center Closed Center

The control valve that regulates the flow from the pump determines if system is open or closed.

Do not confuse Hydraulics with the “Closed Loop” of the Power Train. (Hydro) 27

Trapped Oil Flow in Neutral 28

Extend

29

Retract

30

Neutral Again

31

Pumps

Pump Inefficiency

• Leakage: you get less flow from a pump than simple theory suggests.

– Increases with larger pressure difference • Friction: it takes some torque to turn a pump even if there is no pressure rise – Is more of a factor at low pressures

Efficiency of pumps & motors

• E m – mechanical efficiency < 1 due to friction, flow resistance • E v – volumetric efficiency < 1 due to leakage • E o • E o =overall efficiency = E = Power out/power in m * E v

Flow

Q

gpm

= D

cu in/rev

N

rpm

/231

Speed

Flow

Q

gpm

= D

cu in/rev

N

rpm

/231

Speed

Torque Required

T

inlb

= D

cu in/rev

∆P

psi

/(2 π)

Pressure Rise

Torque Required

T

inlb

= D

cu in/rev

∆P

psi

/(2 π)

Pressure Rise

Flow Theoretical pump Effect of leakage Relief valve or pressure compensator Pressure

Flow Constant power curve Pressure

P

hp

= P

psi

Q

gpm

/1714

Example pump problems 1a. If a pump turns at 2000 rpm with a displacement of 3 in 3 /rev, theoretically, how much flow is created?

1b. If the same pump is 95% volumetrically efficient (5% leakage), how much flow is created?

Example pump problems 1a. If a pump turns at 2000 rpm with a displacement of 3 in 3 /rev, theoretically, how much flow is created?

1b. If the same pump is 95% volumetrically efficient (5% leakage), how much flow is created?

Example pump problems 2a. If 8 gpm is required and the pump is to turn at 1750 rpm, what displacement is theoretically needed?

2b. If the same pump will really be is 90% volumetrically efficient (10% leakage), what is the smallest pump to choose?

Example pump problems 2a. If 8 gpm is required and the pump is to turn at 1750 rpm, what displacement is theoretically needed?

2b. If the same pump will really be is 90% volumetrically efficient (10% leakage), what is the smallest pump to choose?

Example pump problems 3a. A 7 in 3 /rev pump is to generate 3000 psi pressure rise; how much torque will it theoretically take to turn the pump?

3b. If the same pump is 91% mechanically efficient (9% friction & drag), how much torque must the prime mover deliver?

Example pump problems 3a. A 7 in 3 /rev pump is to generate 3000 psi pressure rise; how much torque will it theoretically take to turn the pump?

3b. If the same pump is 91% mechanically efficient (9% friction & drag), how much torque must the prime mover deliver?

Example motor problem If a motor with 2 in 3 /rev displacement and 90% mechanical and 92% volumetric efficiencies receives 13 gpm at 2000 psi … a. How much fluid power is received?

b. What is it’s overall efficiency?

c. How fast will it turn?

d. How much torque will be generated?

Example motor problem If a motor with 2 in 3 /rev displacement and 90% mechanical and 92% volumetric efficiencies receives 13 gpm at 2000 psi … a. How much fluid power is received?

b. What is it’s overall efficiency?

c. How fast will it turn?

d. How much torque will be generated?

Example motor problem If a motor with 2 in 3 /rev displacement and 90% mechanical and 92% volumetric efficiencies receives 13 gpm at 2000 psi … a. How much fluid power is received?

b. What is it’s overall efficiency?

c. How fast will it turn?

d. How much torque will be generated?

Cylinders

Force balance on piston assembly: P 1 * A 1 P 2 * A 2 F external

Example cylinder problem • • • • 3000 psi system • 2” bore cylinder • Extends 24 inches in 10 seconds • Q: max force generated max work done power used flow required 51

Example cylinder problem • Tractor source with 2500 psi and 13 gpm available • Return pressure “tax” of 500 psi • Cylinder with 3” bore, 1.5” rod diameters • Q1: How much force will the cylinder generate?

• Q2: How long will it take to extend 12 inches?

•

Pressure builds due to resistance

• A fixed displacement pump delivering flow with the capability of 3000 psi does not always deliver 3000 psi!

• How much pressure does a pump deliver?

• What limits pressure delivered?

Load Sensing Advantage

Open Center

Pump size & speed sets flow Relief valve sets pressure

Pressure compensated Pump

Pressure Compensated Circuit

Load Sensing Advantage

Open Center

Pump size & speed sets flow Relief valve sets pressure

Closed Center, Pressure Compensated

Compensator adjusts displacement & flow Compensator sets pressure

LOAD SENSING CIRCUIT

Load Sensing Advantage

Open Center

Pump size & speed sets flow Relief valve sets pressure

Closed Center, Pressure Compensated

Compensator adjusts displacement & flow Compensator sets pressure

Load Sensing

Compensator adjusts displacement & flow Load sensing compensator sets pressure

HYDRAULIC PLUMBING - SIZE

Pulse Width Modulation

Spool valve

Typical Valve Performance

Power Transmission

Transmissions transform power

a torque for speed tradeoff

Gears

Planetary Gear Sets

Belt & Chain Drives

• Speed ratio determined by sprocket teeth or belt sheave diameter ratio

FIRST GEAR

FIRST GEAR First gear speeds … if … Input shaft: 1000 rpm Main countershaft: 1000 (22/61) = 360 rpm Ratio = input speed/output speed = 1000/360 = 2.78

Ratio = output teeth/input teeth = 61/22 = 2.78

Secondary countershaft: 360 rpm (41/42) = 351 rpm Output shaft: 351 rpm (14/45) = 109 rpm RATIO: input speed/output speed = 1000/109 = 9.2

Product of output teeth/input teeth = (61/22)(42/41)(45/14) = 9.2

Example gear problem • If 50 kW @ 2400 rpm drives a pinion gear with 30 teeth and the meshing gear has 90 teeth (assume 98% efficiency)… • Q1: What is the speed of the output shaft?

• Q2: How much power leaves the output shaft?

• Q3: How much torque leaves the output shaft?

Example planetary gear problem If the sun of a planetary gear set turns at 1000 rpm, what speed of the ring would result in a still planet carrier? Teeth on gears are sun: 20 and ring: 100.

Example belt problem If a belt drive from a 1750 rpm electric motor is to transmit 5 hp to a driven shaft at 500 rpm and the small sheave has a pitch diameter of 4” … Q1: What should the pitch diameter of the other pulley be?

Q2: Which shaft gets the small sheave?

Q3: How much torque does the driven shaft receive?

P hp = T ft-lb N rpm /5252

THE END

 • Skip what follows

Electricity

Voltage = Current * Resistance V

volts

= I

amps

* R

ohms V I R

Power = voltage times current P

Watts

= V

volts

*I

amps

Three Types of Circuits

Series Same current, voltage divided Parallel Same voltage, current divided Series / Parallel

+ 12 v.

-

Example 12 V DC problem A 12 V DC solenoid a hydraulic valve has a 5 amp fuse in its circuit.

Q1: What resistance would you expect to measure as you troubleshoot its condition?

Q2: How much electrical power does it consume?

Example 12 V DC problem Q1: Identify specifications for a relay of a 12 V DC lighting circuit on a mobile machine if the circuit has four 60W lamps.

Q2: Would the lamps be wired in series or parallel?

Good luck on the PE Exam!

• My email address: [email protected]

• My web page: https://engineering.purdue.edu/~dbuckmas/ Note … ASABE members can access ASABE texts electronically at: http://elibrary.asabe.org/toc.asp