Dry-sump Lubrication
   HOME

TheInfoList



OR:

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, deterge ...
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 of the piston, one up and one down, in one revolution of the crankshaft in contrast to a four-stroke engine which re ...
reciprocating
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 comb ...
s. The dry sump system uses two or more oil pumps and a separate oil reservoir, as opposed to a conventional
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 su ...
system, which uses only the main sump (
U.S. The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 states and a federal capital district, Washington, D.C. The 48 contiguous ...
: oil pan) below the engine and a single pump. A dry sump engine requires a
pressure relief valve A relief valve or pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system; excessive pressure might otherwise build up and create a process upset, instrument or equipment failure, explosion, or f ...
to regulate negative pressure inside the engine so that internal seals are not inverted. Dry sump lubrication is common on larger
diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...
s 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. In North America, the term is commonly used to describe all forms of automobile sport including n ...
,
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, whic ...
, high-performance
personal watercraft A personal watercraft (PWC), also called Jet Ski or water scooter, is a primarily recreational watercraft that is designed to hold only a small number of occupants, who sit or stand on top of the craft, not within the craft as in a boat. P ...
, and
motorcycles A motorcycle (motorbike, bike; uni (if one-wheeled); trike (if three-wheeled); quad (if four-wheeled)) is a lightweight private 1-to-2 passenger personal motor vehicle Steering, steered by a Motorcycle handlebar, handlebar from a saddle-style ...
. Dry sumps 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 sumps 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 nearly all production
automobile A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, peopl ...
engines, oil that is not actively circulating is stored in the sump. A pump collects oil from the sump and directly circulates it back through the engine. In a dry-sump system, oil still collects at the base of the engine, but into a much smaller 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 reservoir is usually tall, narrow, and designed with baffles and an oil outlet at the very bottom for uninhibited oil supply even during sloshing. Dry sump 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 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 sump. 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 per
crankcase A crankcase is the housing in a reciprocating engine, piston engine that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, res ...
section; however, in the case of inverted engines (typically
aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Aircraft using power components are referred to as powered flight. Most aircraft engines are either piston engines or gas turbin ...
s), 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 categoriz ...
. 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 one pressure pump. Dry sump systems may optionally be designed to keep the engine's crankcase at lower than atmospheric pressure (i.e. a partial
vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...
) 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 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 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, whic ...
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. * 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 barycenter or balance point) is the unique point at any given time where the weighted relative position of the distributed mass sums to zero. For ...
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 t ...
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 lubricates 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 sloshing against spinning parts causes substantial viscous drag, which in turn 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 In aerodynamics, firearms ballistics, and automobiles, windage is the effects of some fluid, usually air (e.g., wind) and sometimes liquids, such as oil. Aerodynamics Windage is a force created on an object by friction when there is relative m ...
') 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 system. 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; * Added cost, complexity, and weight. * Additional oil and maintenance required by the additional pumps and lines. * Difficulty in positioning the external reservoir and pumps around the engine, and within the engine bay, due to their size. * As wrist pins and 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 adds further cost and complexity. * Inadequate upper
valvetrain A valvetrain 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) into the combu ...
lubrication if too much oil vapor is being pulled out from the area, especially with multi-staged pumps.


Common applications

Dry sumps are common on larger
diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...
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 g-force or gravitational force equivalent is a Specific force, mass-specific force (force per unit mass), expressed in Unit of measurement, units of standard gravity (symbol ''g'' or ''g''0, not to be confused with "g", the symbol for ...
s, reliable oil supply, power output, and vehicle handling. The C6, C7, and C8 generations of the Chevrolet Corvette Z06 use dry sump lubrication, which necessitates an initial oil change after .


Motorcycle engines

Dry sump lubrication is particularly useful for motorcycles, which tend to be operated more vigorously than other road vehicles. Although many motorcycles such as the
Honda CB750 The Honda CB750 is an air-cooled, Transverse engine, transverse, Straight-four engine, in-line-four-cylinder-engine motorcycle made by Honda over several generations for year models 1969–2008 with an upright, or Types of motorcycles#Standard, ...
(1969) feature dry sump engines, modern motorcycle engines tend to use a wet sump design (particularly
transverse Transverse may refer to: *Transverse engine, an engine in which the crankshaft is oriented side-to-side relative to the wheels of the vehicle *Transverse flute, a flute that is held horizontally * Transverse force (or ''Euler force''), the tangen ...
inline-four engines, which are wider and 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 should ideally use dry-sump lubrication. Several motorcycle models that use dry sumps include: * 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 Prod ...
-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) fr ...
and the Aprilia RST1000 Futura, along with their sister bikes the SL1000 Falco and ETV1000 Caponord. * All BMW K-series motorcycles with inline-4 engines. * Classic British parallel twin motorcycles, such as those made by BSA, Triumph, and Norton. Traditionally, the oil tank was a remote item, but some late-model BSAs and Meriden Triumphs had the frame tubing double as the oil reservoir. * Harley-Davidsons, since the 1930s. * The Honda NX650, XR500R, XR600R, XR650R and XR650L, with the oil in the frame tubing. *
Chennai Chennai, also known as Madras (List of renamed places in India#Tamil Nadu, its official name until 1996), is the capital city, capital and List of cities in Tamil Nadu by population, largest city of Tamil Nadu, the southernmost states and ...
-built Royal Enfields prior to 2007. Royal Enfield dry sump designs were completely phased out by 2012. * The Suzuki DR-Z400, with the oil in the frame tubing. * The Triumph Rocket 3. * The
Yamaha TRX850 The Yamaha TRX850 is a Sport bike, 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 ...
. Its oil reservoir is not remote, but integral to the engine, sitting atop the gearbox. This design eliminates external oil lines, allowing for simpler engine removal and faster oil warm-up. * The Yamaha XT660Z/R/X and Yamaha SR400/500, with the frame tubing serving as the oil reservoir and cooling system.


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 su ...


References


External links

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