The pump circulates coolant throughout the system while the engine is running. If the drive belt fails, the water pump will not function. It is one of the reasons it’s so important to always check the status of the belt during maintenance. The water pump uses centrifugal force to send coolant to the outside while it spins, drawing coolant from the center continuously. The pump inlet is located close to the center so that coolant returning from the radiator strikes the pump vanes, which then fling the coolant to the outside of the pump to enter the engine. Coolant leaving the pump first flows through the engine block and cylinder head, then through the radiator and finally back to the pump.
Normally the shaft has a tubular section and is made in one- or two-piece construction. The two-piece arrangement is supported at the mid point by a rubber mounted bearing.
The following points are considered for selecting bearings during motor design
Weights and forces involved
Magnetic pull as a result of unsymmetrical air gaps
Dynamic forces due to inaccurate adjustment
Pitch errors in gears
Potential thrust loads
Heavy loads are usually left to roller bearings and lighter loads are carried by ball bearings. Directions of all these loads will have direct relevance on your choice of bearing.
For example, cylindrical rollers can carry high radial loads but virtually no axial loads. Other bearings such as angular contact ball bearings can carry radial and axial loads.
The prescribed shaft speed will have a direct effect on the choice of lubricant, bearing size, cage design, internal clearance and shield/seal types. Induction motors and pulse modulation motors can produce electrical pitting or ribbing on bearing raceways, hence insulated bearing options are to be considered.
Coupling with gears or belts
The type of motor connection will produce load on the motors bearings. A coupling drive can produce forces in various directions; hence alignment is of key importance here.
In many cases a roller bearing with a degree of shaft float is used at the drive end and at the other a ball bearing, hence fixing the float direction and magnitude. A belt or gear take off can place higher loads than a coupling.
Vertical mounting arrangements
Motors, which are to be operated vertically, should have special consideration. Bearing arrangement is vital in vertical mounting, as are lubricant requirements.
High humidity or damp conditions will require the bearing to have seals or shields. Solid contamination such as dust, mud, wood chips, metal flakes and other solid material will also require the bearing to have shields or seals. It should be born in mind that where solid contamination is high then secondary forms of sealing are desirable.
Bearings generate their own heat but most heat will come from the rotor. Either air, oil or water can be used to cool the bearing however when there is the possibility of a high temperature gradient from the inner ring to the outer ring then special attention should be paid to the internal clearance. If no care is taken preloading could occur which will quickly lead to bearing failure.
In high vibration conditions cylindrical roller bearings provide the most resistance although special care should be taken over cage selection.
Some applications require low noise bearings in which case deep groove bearings coupled with low noise grease provide the best solution. Bearing clearance can also have an effect here.
The life of a bearing is defined as the number of revolutions (or the number of operating hours at a given constant speed) the bearing can endure before the first sign of fatigue. The service life of a bearing depends to a large extent on the operating conditions while procedures used to mount and maintain it are equally important.
Grease lubrication should always be used where possible in motor applications. It simplifies maintenance and prolongs bearing life. Where speeds and temperatures are high then oil lubrication should be considered.
Motor maintenance normally consists of:
Servicing of the stator windings
Lubrication of the bearings
Monitoring of the motor performance
Permanently lubricated bearings that have shields or seals fitted do not require any relubrication, thus these are maintenance free.
The accuracy of the equipment will determine the accuracy of the precision grade of the bearings. For high precision bearings (normally associated with high speeds) the seating areas on the shaft need to be machined to corresponding levels of surface finish and roundness + concentricity.
ROLLING-ELEMENT BEARINGS USED IN ELECTRIC MOTORS
|Load direction (magnitude)
|Tapered roller bearing
|Uniaxial (high), radial (high)
|Axial (low), radial (moderate)
|Cylindrical roller bearing
|Angular-contact ball bearing
|Axial (moderate), radial (moderate)
|Spherical-roller thrust bearing
|Uniaxial (moderate to heavy)
|Toroidal roller bearing
There are three classifications of centrifugal pumps: radial flow, mixed flow and axial flow based on the direction the fluid enters the inlet (eye) of the impeller, see figure 1.2. Radial and mixed flow pumps are either single or double suction designs.
For the most part, Alternators are relatively small and lightweight. The alternators found in most passenger cars and light trucks are constructed using an aluminum outer housing, as the lightweight metal does not magnetize.
This is important since aluminum dissipates the tremendous heat generated by producing the electrical power and since the rotor assembly produces a magnetic field.
If you closely inspect an alternator, you’ll find it has vents on both the front and back side. Again, this aids in heat dissipation.
A drive pulley is attached to the rotor shaft on the front of the alternator. When the engine is running, the crankshaft turns the drive belt, which in turn spins the pulley on the rotor shaft.
In essence, the alternator transfers the mechanical energy from the engine into electrical power.
Overrunning Alternator Pulley Units feature a robust, proven design based on sprag one-way clutch technology.
This unique design helps extend auxiliary drive belt service life for even the most severe customer specifications. Overrunning Alternator Pulley Units also help reduce belt load and optimize the front-end system.
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