An eight-cylinder diesel engine has a front main bearing with a journal diameter of 3.500 in and a unilateral tolerance of ‒0.003 in. The bushing bore diameter is 3.505 in with a unilateral tolerance of +0.005 in. The bushing length is 2 in. The pressure-fed bearing has a central annular groove 0.250 in wide. The SAE 30 oil comes from a sump at 120°F using a supply pressure of 50 psig. The sump’s heat-dissipation capacity is 5000 Btu/h per bearing. For a minimum radial clearance, a speed of 2000 rev/min, and a radial load of 4600 lbf, find the average film temperature and apply Trumpler’s criteria in your design assessment.
The average film temperature.
The design of bearing by use of Trumpler’s criterion.
Answer to Problem 16P
The average film temperature
The design is not successful.
Explanation of Solution
Write expression for minimum thickness.
Here, bore diameter is
Write expression for journal radius.
Write expression for radial clearance ratio.
Write expression for effective length
Here, length of bearing is
Write expression for slenderness ratio.
Write expression for nominal pressure.
Write expression for viscosity.
Here, viscosity is
Write expression for Somerfield number.
Here Somerfield number is
Write expression for temperature rise in oil.
Here, the supply pressure is
Write expression for average temperature.
Here, sump temperature is
Write expression for heat lost
Here, the density of lubricant is
Write expression for average film temperature
Conclusion:
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
The, nominal pressure
Therefore, Trumpler’s design criterion is not satisfied.
Trial (A):
Refer to figure 12.1 “Viscosity-temperature chart in SI units” to obtain the value of viscosity,
Substitute
Refer to figure 12-13 “Viscosity-temperature chart in SI units” obtain the value of viscosity,
Substitute
Refer to chart 12-18 “Coefficient of friction variable” to obtain the value of coefficient of friction variable
Refer to chart 12-16 “Minimum film thickness and eccentricity ratio” to obtain the value of eccentric ratio
Substitute
Substitute
Trial (B):
Refer to figure 12.1 “Viscosity-temperature chart in SI units” to obtain the value of viscosity,
Substitute
Refer to figure 12-13 “Viscosity-temperature chart in SI units” to obtain the value of viscosity for oil SAE 30 as
Substitute
Refer to chart 12-18 “Coefficient of friction variable” to obtain the value of coefficient of friction variable
Refer to chart 12-16 “Minimum film thickness and eccentricity ratio” to obtain the value of eccentric ratio
Substitute
Substitute
Trial (C):
Refer to figure 12.1 “Viscosity-temperature chart in SI units” obtain the value of viscosity as
Substitute
Substitute
Refer to chart 12-18 “Coefficient of friction variable” to obtain the value of coefficient of friction variable
Refer to chart 12-16 “Minimum film thickness and eccentricity ratio” to obtain the value of eccentric ratio
Substitute
Substitute
Trial (D):
Refer to figure 12.1 “Viscosity-temperature chart in SI units” to obtain the value of viscosity as
Substitute
Substitute
Refer to chart 12-18 “Coefficient of friction variable” to obtain the value of coefficient of friction variable
Refer to chart 12-16 “Minimum film thickness and eccentricity ratio” to obtain the value of eccentric ratio
Substitute
Substitute
Write average film temperature.
Substitute
Thus, the average film temperature is
Substitute the
Thus, the heat loss is
Refer to chart of “Minimum film thickness variable and eccentricity ratio” obtain the value of film thickness variable
Write expression for minimum film thickens.
Solve Equation (XII) for
Substitute
Thus, the minimum radial clearance is
Write expression for minimum film thickness using Trumpler’s criteria.
Substitute
Write expression for maximum temperature of the lubricant.
Here, the sump temperature is
Substitute
Since the maximum temperature is less than the given temperature
Thus, the design is not successful.
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Chapter 12 Solutions
Shigley's Mechanical Engineering Design (McGraw-Hill Series in Mechanical Engineering)
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