SAE J1390 pdf download
SAE J1390 pdf download.Engine Cooling Fan Structural Analysis.
Three levels of fan structural analysis are included in this practice:
1. Initial Structural Integrity
2. Invehicle Testing
3. Durability Test Methods
The Initial Structural Integrity section descnbes analytical and test methods used to predict potential resonance and, therefore, possible fatigue accumulahon.
The In-vehicle (or machine) section enumerates the general procedure used to conduct a fan strain gage test. Various considerations that may affect the outcome of strain gage data have been described I of the user of this procedure to adaptdiscard depending on the particular application.
The Durability Test Methods section describes the detailed test procedures that may be used depending on type of fan, equipment availability, and end objective.
Each of the previous levels builds upon information derived from the previous level, Engineering judgment is required as to the applicability of each level to a different vehicle environment or a new fan design.
This SAE Recommended Practice is applicable to medium and heavy-duty trucks. buses. construction equipment, industrial, and agricultural equipment. It does not necessarily include passenger cars and light trucks.
1.1 Purpose—The purpose of this document is to identify the general methodology for the structural analysis of engine cooling fans, and to provide expanded information on subset practices within the general methodology, such that a user of this practice can adapt specific subsets related to a vehicle class.
2. References
2.1 ApplIcable Publications—The following publications form a part of the specificabon to the extent specified
herein, Unless otherwise indicated, the latest revision of SAE publications shall apply.
2.1.1 SAE PuBucAlloNs—Avallable from SAE, 400 Commonwealth Drive. Warrendale, PA 15096-0001.
SAE Ji 099—Technical Report on Low Cycle Fatigue Properties Ferrous and Non-Ferrous of Materials
SAE J1 1 16—Categories of Off-Road Sell-Propelled Work Machines
SAE Ji 234—Specification Definitions—Off-Road Work Machines
SAEJ1474—Heavy-Duty Nonmetallic Engine Cooling Fans—Material. Manufacturing and Test Considerations
SAE J)ISO 61 65—Earthmoving machines—Basic Types—Vocabulary
3. Initial Structural Integrity
3.1 Scope—It is necessary to identify and attempt to evaluate the characteristics of an application which can have an effect on f an durability. Failures almost always occur in fatigue, so careful attention should be paid to avoid resonance or forced vibration of the fan, This section considers vibrational inputs, fan natural frequencies, and operating speed as part of the initial structural Integrity analysis. A f an application fact sheet (Figure 1) is recommended as a form to communicate between user and fan supplier.
3.1.1 A resonant condition may occur when the natural frequencies of the fan as determined from 3.3 Is coincident with either of the vibrational input frequencies or their harmonics, as calculated in 3.2.
Therefore, it is desirable to separate these frequencies, including the upper and lower harmonics, whenever possible. In addition, torsional vibrations, auxiliary equipment, driveline vibrations, etc. may cause vratory inputs to the fan which cannot be predicted in equation form.
3.2 VIbrational Inputs
3.2.1 Without verification by in-vehicle testing, the potential critical speeds and frequencies that can affect the fan can only be predicted. Two potential frequencies of vibration are the harmonics of the piston firing frequency Equation 1 and the harmonics of the fan rotational frequency assooated with obstructions that cause a nonuniform or pulsating flow as the fan rotates (Equation 2).
3.3Fan Natural Frequencies
3.3.1 The resonant frequencies and location of the node lines of the fan should be measured for each mode of vibration. This can be done by using a shaker table, accelerometers, strain gages, or by observation. Theresonant frequencies may be for both rectilinear and torsional modes of vibration. Each resonant frequencyof a fan can be affected by the following:
a. The shape of the fan mounting surface, which may affect the relative spring constant of the systemand should be duplicated as closely as possible.
b. The torque of the mounting bolts may also affect the relative spring constant.
c. Dimensional variations from fan to fan，including material tolerances,may affect both the relative spring constant and the vibrating mass.
When using means other than the actual installation for driving the vibrating mass，caution should beexercised with the excitation level as the natural resonant frequencies can be masked by the high excitationlevels of an over driven forced vibration.
The maximum stress may not occur at the resonant frequency.lt may occur at a beat frequency betweenthe resonant frequencies of two different modes of vibration, i.e., a combination of rectilinear and torsionalexcitation.
