Unit Injector is an integrated direct fuel injection

Fuel injection

Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....

 system for diesel engine

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

s, combining the injector

Injector

ʎ̩An injector, ejector, steam ejector, steam injector, eductor-jet pump or thermocompressor is a pump-like device that uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid to velocity energy which creates a low pressure zone that dɯaws in and...

 nozzle

Nozzle

A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....

 and the injection pump

Injection pump

An Injection Pump is the device that pumps fuel into the cylinders of a diesel engine or less typically, a gasoline engine. Traditionally, the pump is driven indirectly from the crankshaft by gears, chains or a toothed belt that also drives the camshaft on overhead-cam engines . It rotates at half...

 in a single component. The pump is usually driven by a shared camshaft

Camshaft

A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...

.

History

In 1911 a patent was issued in Great Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

 for a unit injector resembling those in use today to Frederick Lamplough.
Commercial usage of unit injectors in the U.S. began in early 1930s on Winton

Winton Motor Carriage Company

The Winton Motor Carriage Company was a pioneer United States automobile manufacturer based in Cleveland, Ohio. Winton was one of the first American companies to sell a motor car.-1896:...

 engines powering locomotives, boats, even US Navy submarines,, and in 1934, Arthur Fielden was granted U.S. patent No.1,981,913 on the unit injector design later used for the General Motors

General Motors

General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...

 two-stroke diesel engines. Most mid-sized diesel engines used a single pump and separate injectors, but some makers, such as Detroit Diesel

Detroit Diesel

As a corporation, Daimler Trucks North America has decided to rename the company "DETROIT".Detroit Diesel Corporation is an American-based diesel engine producer headquartered in Detroit, Michigan, USA...

became well-known for favouring unit injectors.

In 1994, Robert Bosch GmbH

Robert Bosch GmbH

Robert Bosch GmbH is a multinational engineering and electronics company headquartered in Gerlingen, near Stuttgart, Germany. It is the world's largest supplier of automotive components...

 supplied the first electronic Unit Injector for commercial vehicles, and other manufacturers soon followed.

Today, major manufacturers include Robert Bosch GmbH

Robert Bosch GmbH

Robert Bosch GmbH is a multinational engineering and electronics company headquartered in Gerlingen, near Stuttgart, Germany. It is the world's largest supplier of automotive components...

, CAT

Caterpillar Inc.

Caterpillar Inc. , also known as "CAT", designs, manufactures, markets and sells machinery and engines and sells financial products and insurance to customers via a worldwide dealer network. Caterpillar is the world's largest manufacturer of construction and mining equipment, diesel and natural gas...

, Cummins

Cummins

Cummins Inc. is a Fortune 500 corporation that designs, manufactures, distributes and services engines and related technologies, including fuel systems, controls, air handling, filtration, emission control and electrical power generation systems...

, Delphi Corp.

Delphi (auto parts)

Delphi Automotive PLC is an automotive parts company headquartered in Troy, Michigan, USA. Delphi is one of the world's largest automotive parts manufacturers and has approximately 146,600 employees ....

, Detroit Diesel

Detroit Diesel

As a corporation, Daimler Trucks North America has decided to rename the company "DETROIT".Detroit Diesel Corporation is an American-based diesel engine producer headquartered in Detroit, Michigan, USA...

 and the Delphi Corp. acquired Lucas Automotive

Lucas Industries plc

Lucas Industries plc was a famous British manufacturer of components for the motor industry and aerospace industry. It was based in Birmingham. It was listed on the London Stock Exchange and was once a constituent of the FTSE 100 Index...

.

Design and technology

Design of the Unit Injector eliminates the need for high pressure fuel pipes, and with that their associated failures, as well as allowing for much higher injection pressure to occur. The unit injector system allows accurate injection timing, and amount control as in the common rail

Common rail

Common rail direct fuel injection is a modern variant of direct fuel injection system for petrol and diesel engines.On diesel engines, it features a high-pressure fuel rail feeding individual solenoid valves, as opposed to low-pressure fuel pump feeding unit injectors...

 system .

The Unit Injector is fitted into the engine cylinder head

Cylinder head

In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...

, where the fuel is supplied via integral ducts machined directly into the cylinder head. Each injector has its own pumping element, and in the case of electronic control, a fuel solenoid valve as well. The fuel system is divided into the low pressure (<500 kPa

KPA

KPA may refer to:* Kenya Ports Authority* Kiln phosphoric acid, a dry process to produce phosphoric acid at high temperature in a kiln* Kilopascal , a unit of pressure* Known-plaintext attack, a method of cryptanalysis* Korean People's Army...

) fuel supply system, and the high pressure injection system (<2000 bar

Bar (unit)

The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...

).

Operation principle

The basic operation can be described as a sequence of four separate phases: the filling phase, the spill phase, the injection phase, and the pressure reduction phase.

A low pressure fuel delivery pump

Fuel pump

A fuel pump is a frequently essential component on a car or other internal combustion engined device. Many engines do not require any fuel pump at all, requiring only gravity to feed fuel from the fuel tank through a line or hose to the engine...

 supplies filtered diesel fuel into the cylinder head

Cylinder head

In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...

 fuel ducts, and into each injector fuel port of constant stroke pump plunger injector, which is overhead camshaft

Overhead camshaft

Overhead cam valvetrain configurations place the engine camshaft within the cylinder heads, above the combustion chambers, and drive the valves or lifters in a more direct manner compared to overhead valves and pushrods...

 operated.
Fill phase: The constant stroke pump element on the way up draws fuel from the supply duct in to the chamber, and as long as electric solenoid valve

Solenoid valve

A solenoid valve is an electromechanical valve for use with liquid or gas. The valve is controlled by an electric current through a solenoid: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports...

 remains de-energized fuel line is open.
Spill phase: The pump element is on the way down, and as long as solenoid valve remains de-energized the fuel line is open and fuel flows in through into the return duct.
Injection phase: The pump element is still on the way down, the solenoid is now energized and fuel line is now closed. The fuel can not pass back into return duct, and is now compressed by the plunger until pressure exceeds specific "opening" pressure, and the injector nozzle needle lifts, allowing fuel to be injected into the combustion chamber

Combustion chamber

A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...

.
Pressure reduction phase: The plunger is still on its way down, the engine ECU

Engine control unit

An engine control unit is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running...

 de-energizes the solenoid when required quantity of fuel is delivered, the fuel valve opens, fuel can flow back into return duct, causing pressure drop, which in turn causes the injector nozzle needle to shut, hence no more fuel is injected.

Summary: The start of an injection is controlled by the solenoid closing point, and the injected fuel quantity is determined by the closing time, which is the length of time the solenoid remains closed. The solenoid operation is fully controlled by the engine ECU.

Additional functions

The use of electronic control allows for special functions; such as temperature controlled injection timing, cylinder balancing (smooth idle), switching off individual cylinders under part load for further reduction in emissions and fuel consumption, and multi-pulse injection (more than one injection occurrence during one engine cycle).

Further development and applications

In 1993, CAT

Caterpillar Inc.

Caterpillar Inc. , also known as "CAT", designs, manufactures, markets and sells machinery and engines and sells financial products and insurance to customers via a worldwide dealer network. Caterpillar is the world's largest manufacturer of construction and mining equipment, diesel and natural gas...

 introduced "Hydraulically-actuated Electronic Unit Injection" (HEUI), where the injectors are no longer camshaft

Camshaft

A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...

 operated. First available on Navistar's

Navistar International

Navistar International Corporation is a United States-based holding company that owns the manufacturer of International brand commercial trucks, MaxxForce brand diesel engines, IC Bus school and commercial buses, Workhorse brand chassis for motor homes and step vans, and is a private label...

 7.3 litres (445.1 cu in), V8

V8 engine

A V8 engine is a V engine with eight cylinders mounted on the crankcase in two banks of four cylinders, in most cases set at a right angle to each other but sometimes at a narrower angle, with all eight pistons driving a common crankshaft....

 diesel engine

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

. HEUI uses engine oil pressure to power high pressure fuel injection, where usual method of unit injector operation is the engine

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

 camshaft.

Unit injector fuel systems are being used on wide variety of vehicles and engines; commercial vehicle

Commercial vehicle

A commercial vehicle is a type of motor vehicle that may be used for transporting goods or passengers. The European Union defines "commercial motor vehicle" as any motorised road vehicle, which by its type of construction and equipment is designed for, and capable of transporting, whether for...

 from manufacturers such as Volvo

Volvo Trucks

Volvo Trucks is a global truck manufacturer based in Sweden, owned by Volvo Group - AB Volvo it is the world's second largest heavy-duty truck brand....

, Cummins

Cummins

Cummins Inc. is a Fortune 500 corporation that designs, manufactures, distributes and services engines and related technologies, including fuel systems, controls, air handling, filtration, emission control and electrical power generation systems...

, Detroit Diesel

Detroit Diesel

As a corporation, Daimler Trucks North America has decided to rename the company "DETROIT".Detroit Diesel Corporation is an American-based diesel engine producer headquartered in Detroit, Michigan, USA...

, CAT

Caterpillar Inc.

Caterpillar Inc. , also known as "CAT", designs, manufactures, markets and sells machinery and engines and sells financial products and insurance to customers via a worldwide dealer network. Caterpillar is the world's largest manufacturer of construction and mining equipment, diesel and natural gas...

, and passenger vehicles from manufacturers such as Land Rover

Land Rover

Land Rover is a British car manufacturer with its headquarters in Gaydon, Warwickshire, United Kingdom which specialises in four-wheel-drive vehicles. It is owned by the Indian company Tata Motors, forming part of their Jaguar Land Rover group...

 and Volkswagen Group

Volkswagen Group

Volkswagen Group is a German multinational automobile manufacturing group. , Volkswagen was ranked as the world’s third largest motor vehicle manufacturer and Europe's largest....

, among others.
The Volkswagen Group mainstream marques

Marqués

Marqués and Márquez may mean:People*A. H. de Oliveira Marques*Anderson Luís de Azevedo Rodrigues Marques, Brazilian footballer*Fernando Marqués, Spanish footballer...

 use unit injector systems (branded "Pumpe Düse", commonly appreviated to "PD") in their Suction Diesel Injection

Suction Diesel Injection

The SDI engine is a design of naturally aspirated direct injection diesel engine developed and produced by Volkswagen Group for use in cars and vans, along with marine engine and Volkswagen Industrial Motor applications....

 (SDI) and Turbocharged Direct Injection

Turbocharged Direct Injection

TDI or Turbocharged Direct Injection is a design of turbodiesel engines, which feature turbocharging and cylinder-direct fuel injection, developed and produced by Volkswagen Group. These TDI engines are widely used in all mainstream Volkswagen Group marques of passenger cars and light commercial...

 (TDI) diesel engine

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

s.

• In North America
  North America
  North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
  
  , the Volkswagen Jetta
  Volkswagen Jetta
  Although the Golf had reached considerable success, in the North American markets, Volkswagen observed that the hatchback body style lacked some of the appeal to those who preferred the traditional three-box configuration...
  
  , Golf
  Volkswagen Golf
  The Volkswagen Golf is a small family car manufactured by Volkswagen since 1974 and marketed worldwide across six generations, in various body configurations and under various nameplates – as the Volkswagen Rabbit in the United States and Canada , and as the Volkswagen Caribe in Mexico .The...
  
  , and New Beetle
  Volkswagen New Beetle
  -Specifications:*Dimension:**Length: **Width: **Height: **Wheelbase: **Curb weight: *Max speed: 177–210 km/h *Acceleration : 6.5-13.2 sec-Body styles:-Engine choices:-Safety:...
  
   TDI 2004-2006 are Mk4 Pumpe Düse (newer models use Mk5 BEW engines and older models use ALH engines).

Volkswagen Group major-interest truck

Truck

A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...

 and diesel engine maker Scania AB also use the unit injector system, which they call "Pumpe-Düse-Einspritzung", or "PDE".