Surprisingly, the circulation of oil in an internal combustion engine is achieved by the oil pump. The oil pump is a part of an engine lubrication system that pumps oil under pressure. It pumps oil from the sump through the galleries to the rotating bearing, the sliding pistons and the camshaft of the engine.
The primary purpose for the system is to pressurized oil lubricating oil to circulate within the engine moving parts. The pumped oil also maintained the temperature of the engine.
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Today we’ll be looking at the definition, functions, working, diagram, types as well as failures of oil pumps in an internal combustion engine.
Oil Pump Definition
The oil pump is a mechanical device that is used in an engine to circulate oil to the moving parts like bearing, camshaft, and pistons in order to avoid wear and tear of the parts. It is one of the essential parts of an engine lubrication system that must not go wrong or faulty else breakdown will occur.
The functions of an oil pump in an automobile include:
- Transferring of oil to the engine essential parts of the engine under pressure.
- Ease movement of the engine lubricant around the engine.
- Offers direction to the movement of the oil through the galleries to various parts.
- Helps to return the hot oil to the coolant oil in the reservoir.
- Keeps the oil circulation within the engine constants.
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The oil pump is inevitable in an engine for lubrication as engines need to be properly lubricated when it’s running. The oil pump is usually a gear-driven from the crankshaft which start pumping oil immediately the engine is running. In some oil-free engines like a two-stroke, oil injectors are not used.
From a strainer, oil passes into the oil pump and then flows through the heat exchanger, where it’s cooled. The cooled oil then flows through the galleries to the moving parts of the engine before returning to the sump. If an engine is designed with an injector, a small portion of oil is diverted to it.
Oil which is injected into the cylinder seals the space between the cylinder wall and the piston rings. This prevents the compressed air from escaping through the pistons, which increase the overall efficiency of the engine.
An engine oil pressure generates up to 10 psi per every 1000 revolutions per minute (rpm) which is about 55-65psi. The pressure of the crankshaft journal and bearing is much higher than 50, 60 psi which is set by the relative pump’s relief valve and will reach hundreds of psi.
This high pressure is produced by the relative speeds in feet per second of the crankshaft journal and not rpm. The bearing, the bearing width, oil viscosity, and temperature, balanced against the bearing clearance (the leakage rate) are considered.
Low-speed engines are designed with relatively large journals with modest pump and size and pressure. This is because pump pressure does not fill in the hole and refresh the oil in the annular space faster than the leak expels it.
Low pressure indicates that leakage from the bearings is higher than the pump delivery rate.
Read: Understanding Engine Lubrication System
Watch the video to have a better understanding of how oil pump works:
In an automobile dashboard, there is a gauge pressure indicator or warning lamp that indicate the condition of the oil pumped. it could be high oil pressure or low oil pressure depending on the oil in the engine or the engine status.
The high oil pressure occurs in the front or main engine resulting in blowing away the oil plugs out. High oil pressure means extreme high pressure on cold start-up, which occurs due to the design of the engine.
Low oil pressure can cause damage to the engine. it causes the engine components to begin to fail, starting from the cam carrier bearings which is the top portion of the engine. that is, the top parts will starve with lubrication. If pistons have crown jects, low pressure could cause liner/piston nip. The crankshaft and connecting rod may also seize due to low oil pressure.
Low oil pressure can be caused by the followings:
- Worn or defective oil pump or broken pressure relief valve spring.
- Low oil or no oil in the engine.
- Worn main bearings.
- Oil gallery fracture or blockage.
Types of the oil pump
Below are the three types of oil pump used in engines and how they work:
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Rotor oil pump
A rotor type of oil pump is also called a gerotor pump. It contains an inner gear that turns inside the outer rotor. The inner rotor features one less lobe than the outer one, and it’s mounted slightly off-centre of the outer rotor. This forces the outer rotor to spin at about 80% of the speed of the inner gear.
The bellow-like pumping action is created which pulls oil from the inlet port and pushes it towards the outlet port. In the rotor type of oil pump, close tolerance is required for good pumping continuality. The pump is mounted in the crankcase.
Twin Gear Pump
The twin gear pump is also known as an external pump. It is mounted inside the oil pan on the bottom of the engine. it uses two of intermeshing gears to pump oil. A shaft drives the first gear and the second gear is driven by the first gear. The shaft that drove the first gear is usually connected to the crankshaft, camshaft or distributor shaft.
The gear teeth trap oil and carry it around the outside gear from the pickup tube inlet to the outlet. There is a tight clearance between the gears which prevents the oil from flowing backwards to the inlet. Finally
Front cover oil pump
The front cover oil pump is also known as an internal or external pump. It’s often mounted in front of the engine cover. Its working is similar to that of the rotor pump which uses an inner drive gear and outer rotor. In this case, the inner drive is mounted directly on the crankshaft.
The direct-drive approach helps to avoid the requirement of a separate pump drive shaft. The pump turns at same rpm with the engine. For this reason, more pressure generated at idle than a camshaft or distributor driven pump. Front cover types of oil pumps are used on most overhead cam engines, and also seen in late model pushrod engines.
One limitation of this oil pump is that the oil has to travel a further distance from the oil pan to the pump. This slowdown the flow of oil when the engine is cold and is first started.
Read: Components of an internal combustion engine
Common Failure on Oil Pump
The failing of an oil pump could cause serious damage to a vehicle, most especially if the driver did not know its failure symptoms. Well, drivers are notified when a problem occurs in the engine, oil light indicator on the car’s dashboard turned on which alert there is a problem. Below are the failure symptoms of an oil pump:
Low oil pressure: faulty or worn oil pump won’t be able to properly pump oil through the system. This will result in low oil pressure and could cause damage to the engine. although there are several symptoms of low oil pressure which is stated earlier in this pose.
Increased in engine working temperature: oil act as a cooling agent in a vehicle’s engine as it reduces friction. The engine will be at normal temperature when the pump is in good condition as the flow of oil is constant. But, when the flow of the engine oil is slow or stop, the parts are continued to be lubricated by hot oil which is not allowed to flow.
Noise: hydraulic lifter in a vehicle begins to make noise if not properly lubricated. When the oil pump is in good condition and oil is properly circulated these tend to be silent. The lifters are extremely expensive to be replaced which is why it’s important engine never lack oil.
That’s it for this article “oil pump in internal combustion”. I hope the knowledge is attained, if so, kindly comment, share and recommend this site to other technical students. Thanks!