Technical Role Of Oil Pumps And Vehicle Structural System
A company manufactures a range of transmission oil pumps for heavy earthmoving vehicles. The journal bearings in the pump are finished with a grinding process. Unfortunately, increased pump performance requirements have led to many early service failures. It is emphasized that journal bearing surface problems are the only possible cause of failure. The journal bearing on the gearbox pump is manufactured on a production grinder and finished to company specifications Ra = 1.6 μm, and the usual roughness obtained from the workshop is Ra = 0.8 μm. The initial failure of the journal bearing occurred on the drive shaft of the pump and caused the pump to fail due to the total wear on the opposite side of the bronze bushing.
Manufacturers reduce the surface roughness of bearings by machining the pump journal on a tool room grinder. This resulted in improved service performance and no further failures were reported. However, the tool room grinder is not suitable for mass production, so the production grinder should operate in the same or similar roughness level as the tool room grinder, and reach a roughness level of Ra = 0.6 μm.
This roughness machining initially seemed successful until further pump failures were reported again. Shocked by this, the manufacturer continues to produce pumps with a target roughness level Ra = 0.3 μm on the tool room grinder. Recently, a new type of computer numerically controlled (CNC) grinder has been introduced to the production line, and its life has been reported to have improved.
The following case studies are designed to study the differences between the ground and make some assumptions about service performance.
Turbine Lubricant System
During normal operation, the main oil pump installed on and driven by the turbine shaft draws oil from the main tank (MOT) and then discharges it to the bearing oil system at high pressure. Lube oil pressure is usually kept constant at 100–150 kPa, depending on the specific turbine and bearing design. During the start and stop operation of the turbine, when the rotor and main oil pump do not reach the rated speed, an externally driven auxiliary oil pump is required to supply oil
The main tank (MOT) is equipped with a steam extractor to keep the oil tank atmosphere free of oil vapor, and a filter is provided to trap suspended impurities. The oil used in the bearing lubricant system is cooled in a turbine oil cooler to control the bearing oil / metal temperature. Thereafter, the oil passes through the oil filter to provide dust-free lubricating oil for the bearings. Then, the oil that has passed through the filter is introduced into the bearing through the lubricating oil pressure reducing regulator through the lubricating oil supply main pipe. The lubricating oil flows back from the lubricating oil to the bearing by gravity and returns to the MOT through the lubricating oil header, where any heavy impurities that may be absorbed by the oil during the circulation process will settle out.
Oil Pumps Details of the various oil pumps used are described in the following paragraphs.
Main lubricant pump
In order to ensure the supply, the main lubricating oil pump is directly driven by the main rotary line. On older equipment, this is a gear driven positive displacement pump. On modern equipment, the large amount of oil required (about 100 liters per second) makes centrifugal pumps economically usable; a typical example is shown in Figure 2.55.
This pump is not a self-priming pump and requires a suction pressure of approximately 3-4 bar.
To ensure a safe supply of lubricating oil, the oil from the main oil pump discharge port will pass through an oil turbine. The tanker is mounted on top of the tank and drives a submersible centrifugal pump. The pump delivers oil to the main pump suction port.
AC and DC motor driven auxiliary oil pumps
The AC and DC auxiliary oil pumps that supply oil to bearings under start-up and normal shutdown or emergency shutdown are centrifugal pumps with submerged suction ports. They are also suspended from the top of the tank, and their arrangement is very similar to that of Figure 2.56, except that the oil turbine is replaced by an AC or DC motor. The AC pump delivers oil to the lube oil line, supplies oil to the oil filter and cooler at a pressure of approximately 3 bar, and primes the main oil pump. The DC pump feeds the same piping system as the AC pump, or feeds oil directly into the bearing piping at a pressure of about 1.5 bar. The capacity of each pump is about 70-120 liters / second.
Jacking oil pump and filling pump
The jacking oil pump delivers approximately 300 bar of oil to each bearing. The pump used is a motor-driven positive displacement pump, or a multi-plunger pump or a two-shaft gear pump.
This arrangement uses a gear pump for each bearing, or a motor / pump unit for one or two bearings. The pump needs positive suction pressure. The multi-plunger pump is supplied by a lubricating oil manifold, and the gear pump has a motor-driven positive displacement two-shaft gear pump.
In some designs, the rotating gear is equipped with a separate jacking oil pump. The pump is a motor-driven positive displacement two-shaft gear pump; the discharge pressure is the same as other jacking oil pumps.
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