MECH 605 Mechanical CAD

Basic Sketch Of Motor• How Do We Describe The Physics Of Operation?• How Much Power Will It Make With R&D’s Steam

Source?

Inlet Port

ExhaustPort

Side View

MECH 605 Mechanical CAD

Basic Piston Expander DesignRear View

½ Stroke

Bore

Basic KinematicsLinkage

MECH 605 Mechanical CAD

Piston Engine Kinematics

)sin(sin

coscos

sinsin

1

l

r

lrx

lr

x

θ φ

Rod length l

½ Stroke r

olumeClearanceVV

PistonAreaA

xlrAVV

c

p

pc

)(

MECH 605 Mechanical CAD

Power TransmissionFBD Of Piston

φ

F Rod

F Side

Fp

TanFF

SinFF

Cos

FF

CosFF

PistonAreaA

APF

ps

rods

prod

rodp

p

pcylinderp

MECH 605 Mechanical CAD

Torque Developed From Rod Loading On Crankshaft

F Rod

F Side

Fp

F Side

F Gas

r

)(

CosTanSinrFT

CosTanrFSinrFT

TanFF

CosrFSinrFT

p

pp

ps

sp

MECH 605 Mechanical CAD

How Do We Evaluate Cylinder Pressure To Obtain Power?

• Thermodynamics Portion Of The Analysis• Need To Make Some Basic Simplifying

Assumptions:– Consider The Cylinder The Control Volume– First Pass Assume No Heat Transfer

• Adiabatic – No Heat Transfer• Reversible Process - Isentropic• Simple Valve Operation

MECH 605 Mechanical CAD

Thermodynamic Analysis• Assuming A Closed Adiabatic System:

– Ideal Gas Behavior

– Simple Valve Operation

0

012

Q

SS

Wuu

V

VTT

V

VPP

k

k

12

1

2

112

2

112

)(

)(

MECH 605 Mechanical CAD

Engine ThermodynamicsWhat’s Happening In The Cylinder?

1 Intake Opens2 Top Dead Center3 Intake Closes3-4 Adiabatic Expansion4 Exhaust Opens5 Bottom Dead Center6 Exhaust Closes

2 3

4

5

1

CylinderPressure

CylinderVolume

6

k

V

VPP )(

2

112

MECH 605 Mechanical CAD

Next Steps• Utilize The Kinematics and Thermodynamics

To Complete Simulation Provided On Web Site

• Simulation Will Evaluate: – Output Torque– Component Loading– Cylinder Pressures and Temperatures

• Utilize Component Loading In Stress Analysis Of Various Parts

MECH 605 Mechanical CAD

Assemblies / Family Tree’s

• Assemblies And Sub Assemblies Should Reflect The Assembly Process

• The Lower Level Parts Should Reflect The Assembly They Are Used On

• The Family Tree Is A Graphical Representation Of The Parts Used In The Assembly And How They Are Assembled

MECH 605 Mechanical CAD

Family Tree

R e a r B e a ring

F o rw ard B e a ring

C ra n k S h a ft

C ra nk S up p o rt

C ra n k S u p po rt A sse m b lyS u b -A sse m b ly

P is ton P in

C o nn e ctin g R od

P is ton

P is to n A sse m b lyS u b -A sse m b ly

S c re w #2

S c re w #1

C y lin de r H ea d G a ske t

C y lin d er H e ad

C y lin d e r B lo ck

R e a r C ran k C a se

M isc P a rts A tta ch edD u rin g F in a l A sse m b ly

1 .5 " B ore E ng ineT o p L eve l A sse m b ly