Dry sump


A dry-sump system is a method to manage the lubricating motor oil in four-stroke and large two-stroke piston driven internal combustion engines. 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 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, aerobatic aircraft and high-performance 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.

Mechanism

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 engines, a pump collects this oil from the sump and directly circulates it back through the engine. In a dry-sump, the oil still falls to the base of the engine, however instead of collecting in a reservoir-style oil sump, it falls into a much shallower sump, where one or more scavenge pumps draw it away and transfer it to a reservoir, where it is both cooled and de-aerated before being recirculated through the engine by a pressure pump. 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 it is necessary to employ separate scavenge pumps for each cylinder bank. Therefore, an inverted V engine would have a minimum of two scavenge pumps and a pressure pump in the pump stack.
The main purpose of the dry-sump system is to contain all the stored oil in a separate tank, or reservoir. This reservoir is usually tall and round or narrow and specially designed with internal baffles, and an oil outlet at the very bottom for uninhibited oil supply. The dry-sump oil pump is a minimum of 2 stages, with as many as 5 or 6. One stage is for pressure and is supplied the 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. The remaining stages "scavenge" the oil out of the dry-sump pan and return the oil to the top of the tank or reservoir. If an oil cooler is used usually it is mounted inline between the scavenge outlets and the tank. The dry-sump pump is usually driven by a Gilmer or High Torque Drive timing belt and pulleys, off the front of the crankshaft, at approximately one half crank speed. The dry-sump pump is designed with multiple stages to ensure that all the oil is scavenged from the pan and also to allow removal of excess air from the crankcase.

Advantages

A dry-sump system offers many advantages over a wet-sump. The primary advantages include:
Dry-sump engines have several disadvantages compared to wet-sump engines, including;
Dry-sumps are common on larger diesel engines 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-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 the Honda CB750 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, 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;