# Chapter 13: Engine friction and lubrication¶

## Example 13.1 Page No 423¶

In [1]:
#Input data
d=0.08		            #The diameter of bore in m
L=0.075		            #The length of the stroke in m
l=0.152		            #The connecting rod length in m
h=0.062		           #Skirt length of the piston in m
Fr=8000		            #Compressive force in the connecting rod in N
p=3000		           #The pressure in the cylinder kPa
y=0.004*10**-3	       #The clearence between piston and cylinder wall in m
U=0.006		           #The dynamic viscosity of the lubricating oil in pa.s
u=8.2		           #The piston speed in m/s

#Calculations
import math
ts=(U*u)/y	                       #The shear stress in N/m**2
A=pi*d*h	                       #Contact area between the piston and the cylinder in m**2
Ff=ts*A		                       #Friction force on the piston inN
r=L/2.0		                       #Crank length in m
Ft=Fr*sin(A)	#The side thrust in N

#Output
print"The friction force on the piston ",round(Ff,0),"N"
print"The thrust force on the cylinder wall is",round(Ft,0),"N"

The friction force on the piston  192.0 N
The thrust force on the cylinder wall is 1916.0 N


## Example 13.2 Page No 424¶

In [3]:
#Input data
d=0.065		#The cylinder bore diameter in m
L=6.0		#The length of the stroke in cm
l=12.0		#The length of the connecting rod in cm
p=50.0		#The pressure in the cylinder in bar
q=90.0		#The crank position in power stroke of the cycle for one cylinder in degrees
Ff=900.0		#Friction force in N
o=0.2		#Wrist pin off set in cm

#Calculations
r=L/2.0		#The crank length in cm
sineA=r/l
cosA=(1-(sineA)**2)**(1/2.0)
Fr=(((p*10**5*(pi/4.0)*d**2)-Ff)/cosA)/1000.0
Ft=Fr*sineA	    #The side thrust on the piston in kN
sineA1=(r-o)/l	#The value of sine
cosA1=(1-(sineA1)**2)**(1/2.0)
Fr1=(((p*10**5*(pi/4.0)*d**2)-Ff)/cosA1)/1000.0
Ft1=Fr1*sineA1  #The side thrust in kN

#Output
print"(a) The force in the connecting rod ",round(Fr,3)," kN"
print"The side thrust on the piston =",round(Ft,2),"kN"
print"(b) The side thrust on the piston =",round(Ft1,3)," kN"

(a) The force in the connecting rod  16.206  kN
The side thrust on the piston = 4.05 kN
(b) The side thrust on the piston = 3.765  kN