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A dry-sump system is a method to manage the lubricating
motor oil Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines. They typically consist of base oils enhanced with various additives, particularly antiwear additives, deterg ...
in
four-stroke A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directio ...
and large
two-stroke A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of ...
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
driven
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
s. The dry-sump system uses two or more oil pumps and a separate oil reservoir, as opposed to a conventional wet-sump system, which uses only the main
sump A sump is a low space that collects often undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers. Sump can also refer to an area in a cave ...
(U.S.: oil pan) below the engine and a single pump. A dry-sump engine requires a pressure relief valve to regulate negative pressure inside the engine, so internal seals are not inverted. Dry-sumps are common on larger diesel engines such as those used in ships, as well as gasoline engines used in
racing cars Auto racing (also known as car racing, motor racing, or automobile racing) is a motorsport involving the racing of automobiles for competition. Auto racing has existed since the invention of the automobile. Races of various sorts were organise ...
,
aerobatic aircraft An aerobatic aircraft is an aerodyne (a heavier-than-air aircraft) used in aerobatics, both for flight exhibitions and aerobatic competitions. Most fall into one of two categories, aircraft used for training and by flight demonstration teams, wh ...
, high-performance personal watercraft and motorcycles. Dry sump lubrication may be chosen for these applications due to increased reliability, oil capacity, reduction of oil starvation under high g-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 various bearings and other moving parts and then draining, via gravity, into the sump at the base of the engine. In the wet-sump system of most production
automobile A car or automobile is a motor vehicle with Wheel, wheels. Most definitions of ''cars'' say that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, pe ...
engines, 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 and de-aerated before 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. A 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. Dry-sump designs frequently mount the pressure pump and scavenge pumps on a common crankshaft, so that one 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 per crankcase section, however in the case of inverted engines (
aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many ...
) it is necessary to employ separate scavenge pumps for each
cylinder bank The engine configuration describes the fundamental operating principles by which internal combustion engines are categorized. Piston engines are often categorized by their cylinder layout, valves and camshafts. Wankel engines are often categorize ...
. Therefore, an inverted
V engine A V engine, sometimes called a Vee engine, is a common configuration for internal combustion engines. It consists of two cylinder banks—usually with the same number of cylinders in each bank—connected to a common crankshaft. These cylinder ...
would have a minimum of two scavenge pumps and a pressure pump in the pump ''stack''. Although the term "stages" is commonly used to describe multiple scavenge pumps, they typically run in parallel, rather than in series as the term might imply. The pressure stage draws oil from the bottom of the reservoir, and along with an adjustable pressure regulator, supplies the oil under pressure through the filter and into the engine. 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 high g-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 in
racing In sport, racing is a competition of speed, in which competitors try to complete a given task in the shortest amount of time. Typically this involves traversing some distance, but it can be any other task involving speed to reach a specific goa ...
cars, high performance sports cars, and
aerobatic aircraft An aerobatic aircraft is an aerodyne (a heavier-than-air aircraft) used in aerobatics, both for flight exhibitions and aerobatic competitions. Most fall into one of two categories, aircraft used for training and by flight demonstration teams, wh ...
that 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's
center of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weight function, weighted relative position (vector), position of the distributed mass sums to zero. Thi ...
can be lowered by mounting the (typically very heavy) engine lower in the chassis due to a shallow sump profile. A vehicle's overall
weight distribution Weight distribution is the apportioning of weight within a vehicle, especially cars, airplanes, and trains. Typically, it is written in the form ''x''/''y'', where ''x'' is the percentage of weight in the front, and ''y'' is the percentage in the ...
can 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 viscous drag which creates parasitic 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 Windage is a term used in aerodynamics, firearms ballistics, and automobiles. Usage Aerodynamics Windage is a force created on an object by friction when there is relative movement between air and the object. Windage loss is the reduction in ...
') 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 performance-enhancing features of dry-sump lubrication can hurt a car's day-to-day driveability. A good example is the classic
Mercedes-Benz 300SL The Mercedes-Benz 300 SL (chassis code W 198) is a two-seat sports car which was produced by Mercedes-Benz as a gullwinged coupe (1954–1957) and roadster (1957–1963).Werner Oswald: ''Mercedes-Benz Personenwagen 1945–1985''. Motorbuch Ve ...
, a car that was designed for racing but sold to the general public and used on-road. The car had high oil capacity and a dry-sump system to cope with continuous high-speed running while racing. Owners found in general use, however, that the oil never achieved the correct
operating temperature An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
because the system was so effective at cooling the oil. A makeshift solution was devised to deliberately block the oil cooler airflow to boost the oil temperature. * The large external reservoir and pumps can be tricky to position around the engine and within the engine bay due to their size. * As wrist pins and pistons rely for lubrication and cooling respectively, on the oil being splashed around in the crankcase, 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 upper
valvetrain A valvetrain or valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture (or air alone for direct-injected engines) ...
lubrication 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 larger
diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...
s such 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 with
g-force The gravitational force equivalent, or, more commonly, g-force, is a measurement of the type of force per unit mass – typically acceleration – that causes a perception of weight, with a g-force of 1 g (not gram in mass measure ...
s, 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 the Honda CB750 (1969) feature a dry-sump engine, modern motorcycles tend to use a wet-sump design. This is understandable with across-the-frame inline 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 British
parallel twin A straight-twin engine, also known as an inline-twin, vertical-twin, or parallel-twin, is a two-cylinder piston engine whose cylinders are arranged in a line along a common crankshaft. Straight-twin engines are primarily used in motorcycles; ot ...
motorcycles, such as BSA,
Triumph The Roman triumph (Latin triumphus) was a celebration for a victorious military commander in ancient Rome. For later imitations, in life or in art, see Trionfo. Numerous later uses of the term, up to the present, are derived directly or indirectl ...
and
Norton Norton may refer to: Places Norton, meaning 'north settlement' in Old English, is a common place name. Places named Norton include: Canada * Rural Municipality of Norton No. 69, Saskatchewan *Norton Parish, New Brunswick **Norton, New Brunswick, a ...
, 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 3-cylinder, water-cooled, DOHC engine. * The
Yamaha TRX850 The Yamaha TRX850 is a sports motorcycle with a 10-valve DOHC 849 cc 270° parallel-twin engine. First released in Japan in 1995, a version for the European market was available from 1996 to 2000. Design and development The TRX has a half ...
270-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. * The Yamaha 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 * The Yamaha SR400/500 uses a dry-sump design where the bike's frame tubing doubles as the oil reservoir and cooling system. *
Harley-Davidson Harley-Davidson, Inc. (H-D, or simply Harley) is an American motorcycle manufacturer headquartered in Milwaukee, Wisconsin, United States. Founded in 1903, it is one of two major American motorcycle manufacturers to survive the Great Depressi ...
has used dry-sump type lubricating oil systems in their engines since the 1930s. * The
Rotax Rotax is the brand name for a range of internal combustion engines developed and manufactured by the Austrian company BRP-Rotax GmbH & Co KG (until 2016 BRP-Powertrain GmbH & Co. KG), in turn owned by the Canadian Bombardier Recreational Produc ...
engined
Aprilia RSV Mille The Aprilia RSV Mille is a sport motorcycle manufactured by Aprilia from 1998 to 2003. It was offered in three versions, RSV Mille, RSV Mille R, and RSV Mille SP. The first RSV Mille (ME) was made from 1998 to 2000, the updated RSV Mille (RP) fro ...
, and the
Aprilia RST1000 Futura The Aprilia RST1000 Futura is a sport touring motorcycle that was produced by Aprilia from 2001 to 2004. It is equipped with a 113 horsepower (85 kW) four-stroke 60° V-twin engine with electric-start, liquid cooling and electronic fuel-inj ...
both incorporate a dry-sump, along with sister bikes, the SL1000 Falco and ETV1000 Caponord. * The Honda NX650, XR500R, XR600R, XR650R and XR650L four-stroke dirt bikes utilize a dry-sump with the oil in the frame tubing. * The
Suzuki DR-Z400 The Suzuki DR-Z400 is a Dual-sport_motorcycle, dual-sport motorcycle manufactured by Suzuki beginning in 2000. It is powered by a single-cylinder, , carbureted, liquid-cooled four-stroke engine. Kawasaki motorcycles, Kawasaki marketed a private l ...
has a 2L dry-sump with oil in the frame tubing. * Chennai built Royal Enfield prior to 2007. Royal Enfield dry sump designs were completely phased out by 2012.


See also

*
Wet sump Within piston engines, a wet sump is part of a lubrication system whereby the crankcase sump is used as an integral oil reservoir. An alternative system is the dry sump, whereby oil is pumped from a shallow sump into an external reservoir.Wet sum ...


References


External links

* * * {{Automotive engine Engine lubrication systems Engine technology