Dry sump

"Scavenge pump" redirects here. For pushing exhausted gas-charge out of the cylinder, seeScavenging (automotive).

Schematic diagram of a basic dry-sump engine lubrication system. The oil collects in sump (1), is withdrawn continuously by scavenge pump (2) and travels to the oil tank (3), where gases entrained in the oil separate and the oil cools. Gases (6) are returned to the engine sump. Pressure pump (4) forces the de-gassed and cooled oil (5) back to the engine's lubrication points (7).

Adry-sumpsystem is a method to manage the lubricatingmotor oilinfour-strokeand largetwo-strokepistondriveninternal combustion engines.The dry-sump system uses two or moreoil pumpsand a separate oil reservoir, as opposed to a conventionalwet-sumpsystem, which uses only the mainsump(U.S.: oil pan) below the engine and a single pump. A dry-sump engine requires apressure relief valveto regulate negative pressure inside the engine, so internal seals are not inverted.

Dry-sumps are common on largerdiesel enginessuch as those used in ships, as well as gasoline engines used inracing cars,aerobatic aircraft,high-performancepersonal watercraftand motorcycles. Dry sump lubrication may be chosen for these applications due to increased reliability, oil capacity, reduction of oil starvation under highg-loads and/or other technical or performance reasons. Dry sump systems may not be suitable for all applications due to increased cost, complexity, and/or bulk, among other factors.

Design

Engines are both lubricated and cooled by oil that circulates throughout the engine, feeding variousbearingsand other moving parts and then draining, via gravity, into the sump at the base of the engine. In the wet-sump system of nearly all productionautomobileengines, the oil that's not actively circulating is stored in the sump, which is large enough for this purpose. A pump collects oil from the sump and directly circulates it back through the engine. In a dry-sump system, the oil still falls to the base of the engine, but into a much shallower sump, where one or more scavenge pumps draw it away and transfer it to a (usually external) reservoir, where it is both cooled andde-aeratedbefore being recirculated through the engine by a pressure pump. The sump in a dry-sump system is not actually dry; it is still wet from oil draining from the engine. The reservoir is usually tall and narrow and specially designed with internal baffles, and an oil outlet (supply) at the very bottom for uninhibited oil supply even during sloshing.

The dry pump operation consists of a pressure stage and a scavenging stage. Although the term "stages" is commonly used to describe the work of the multiple pumps, they typically run in parallel rather than in series as might be implied by the term. The pressure stage draws oil from the bottom of the reservoir and passes it through the filter and into the engine itself.An adjustable pressure regulator ensures that the oil pressure is kept stable at different engine speeds. The dry-sump system requires at least two pumps - one pressure and one scavenge - and sometimes as many as four or five scavenge pumps are used to minimize the amount of oil in the engine. The pressure pump and scavenge pumps are frequently mounted on a common crankshaft, so that a single pulley at the front of the system can run as many pumps as the engine design requires. It is common practice to have one scavenge pump percrankcasesection; however, in the case ofinverted engines(typicallyaircraft engines) it is necessary to employ separate scavenge pumps for eachcylinder bank.Therefore, an invertedV enginewould have a minimum of two scavenge pumps and a pressure pump in the pumpstack.

Dry sump systems may optionally be designed to keep the engine's crankcase at lower than atmospheric pressure (vacuum), by sealing the crankcase and allowing the scavenge pumps to draw out both oil and gases.An equilibrium pressure will be reached when the rate of gases entering the crankcase (blow-by gases past the piston rings, but also air leaks and oil vapor) equals the rate of gas removal from the scavenge pump capacity beyond what's required to remove just the oil. Alternatively, the crankcase may be kept near atmospheric pressure by venting it to the oil reservoir, which in turn is vented into the engine's air intake, or to outside air.

Advantages

A dry-sump system offers many advantages over a wet-sump. The primary advantages include:

• Prevention of the engine experiencing oil starvation during highg-loads when oil sloshes, which improves engine reliability. Most engines can be damaged by even brief periods of oil starvation. This is the reason why dry-sumps were invented, and is particularly valuable inracingcars,high performancesports cars, andaerobatic aircraftthat regularly experience high accelerations. Oil slosh occurs in dry-sump systems too, but it is much easier to design a remote reservoir to tolerate high amounts of slosh, by being tall and narrow, and having large baffles.
• Increased oil capacity by using a large external reservoir, which would be impractical in a wet-sump system.
• Improvements to vehicle handling and stability. The vehicle'scenter of gravitycan be lowered by mounting the (typically very heavy) engine lower in the chassis due to a shallow sump profile. A vehicle's overallweight distributioncan be modified by locating the external oil reservoir away from the engine.
• Improved oil temperature control. This is due to increased oil volume providing resistance to heat saturation, the positioning of the oil reservoir away from the hot engine, and the ability to include cooling capabilities between the scavenger pumps and oil reservoir and also within the reservoir itself.
• Improved oil quality. When oil sloshes against the crankshaft and other high-speed spinning parts, it causes a "hurricane that whips the oil in a wet-sump engine into an aerated froth like a milkshake in a blender".Aerated oil protects engine components far less effectively. A dry-sump system minimizes oil aeration, and also de-aerates oil far more effectively by pumping it first into a remote reservoir.
• Increased engine power. In a wet-sump engine, oil slosh against spinning parts causes substantial viscousdragwhich createsparasitic power loss.A dry-sump system removes oil from the crankcase, along with the possibility of such viscous drag. More complex dry-sump systems may scavenge oil from other areas where oil may pool, such as in the valvetrain. Power can be further increased if the dry-sump system is designed to create a vacuum inside the crankcase, which reduces air drag (or 'windage') on moving parts as well.
• Improved pump efficiency to maintain oil supply to the engine. Since scavenge pumps are typically mounted at the lowest point on the engine, the oil flows into the pump intake by gravity rather than having to be lifted up into the intake of the pump as in a wet-sump. Furthermore, scavenge pumps can be of a design that is more tolerant of entrapped gasses than the typical pressure pump, which can lose suction if too much air mixes into the oil. Since the pressure pump is typically lower than the external oil tank, it always has a positive pressure on its suction regardless of cornering forces.
• Having the pumps external to the engine makes them easier to maintain or replace.

Disadvantages

Dry-sump engines have several disadvantages compared to wet-sump engines, including;

• Dry-sump systems add cost, complexity, and weight.
• The extra pumps and lines in dry-sump engines require additional oil and maintenance.
• The large external reservoir and pumps can be tricky to position around the engine and within the engine bay due to their size.
• Aswrist pinsand pistons rely on the oil being splashed around in the crankcase for lubrication and cooling respectively, these parts might have inadequate oiling if too much oil is pulled away by the pump. Installing piston oilers can circumvent this issue, but do so with additional cost and complexity for the engine.
• Inadequate uppervalvetrainlubrication can also become an issue if too much oil vapor is being pulled out from the area, especially with multi-staged pumps.

Common engine applications

Dry-sumps are common on largerdiesel enginessuch as those used for ship propulsion, largely due to increased reliability and serviceability. They are also commonly used in racing cars and aerobatic aircraft, due to problems withg-forces,reliable oil supply, power output and vehicle handling. The Chevrolet Corvette Z06 has a dry sump engine which requires initial oil change after 500 miles.

Motorcycle engines

The dry-sump lubrication is particularly applicable to motorcycles, which tend to be operated more vigorously than other road vehicles. Although motorcycles such as theHonda CB750(1969) feature a dry-sump engine, modern motorcycles tend to use a wet-sump design. This is understandable with across-the-frameinline four-cylinder engines,since these wide engines must be mounted fairly high in the frame (for ground clearance), so the space below may as well be used for a wet-sump. However, narrower engines can be mounted lower and ideally should use dry-sump lubrication.

Several motorcycle models that use dry-sumps include;

• The classic Britishparallel twinmotorcycles, such asBSA,TriumphandNorton,all used dry-sump lubrication. Traditionally, the oil tank was a remote item, but some late-model BSAs, and the Meriden Triumphs, used "oil-in-the-frame" designs.
• The Triumph Rocket 3, an inline three-cylinder, water-cooled, DOHC engine.
• TheYamaha TRX850270-degree parallel twin motorcycle has a dry-sump engine. Its oil reservoir is not remote, but integral to the engine, sitting atop the gearbox. This design eliminates external oil lines, allowing simpler engine removal and providing faster oil warm up.
• TheYamaha XT660Z(and R/X models) use a dry-sump design where the bike's frame tubing is used as the oil reservoir and cooling system
• TheYamaha SR400/500uses a dry-sump design where the bike's frame tubing doubles as the oil reservoir and cooling system.
• Harley-Davidsonhas used dry-sump type lubricating oil systems in their engines since the 1930s.
• TheRotaxenginedAprilia RSV Mille,and theAprilia RST1000 Futuraboth incorporate a dry-sump, along with sister bikes, the SL1000 Falco and ETV1000 Caponord.
• All BMW K-series motorcycles with inline-4 engines.
• TheHonda NX650, XR500R, XR600R, XR650R and XR650Lfour-stroke dirt bikes utilize a dry-sump with the oil in the frame tubing.
• TheSuzuki DR-Z400has a 2L dry-sump with oil in the frame tubing.
• Chennai builtRoyal Enfieldprior to 2007. Royal Enfield dry sump designs were completely phased out by 2012.

See also

• Wet sump

External links

• "Why do some engines use a dry sump oil system?".HowStuffWorks.April 2000.Retrieved2006-11-16.
• "Technical Explanation The Dry Sump System".ARE.Retrieved2016-08-03.
• "Wet Sump vs Dry Sump - Engine Oil Systems".YouTube.com.EngineeringExplained. 2017-01-04.Retrieved2017-01-04.