Fuel Pump: Description and Operation

PURPOSE
The fuel pump delivers high volume fuel to the injector rail to provide the injectors with a constant supply of fuel.

Fuel Pump (Typical):

CONSTRUCTION
The roller-cell pump consists of a cylindrical hollow chamber in which an eccentrically fitted rotor disc rotates. This is fitted with metal rollers which are held in pocket-shaped recesses around the circumference.
A check valve is incorporated in the fuel outlet and a pressure limiter valve is located on the pressure side of the fuel pump housing with a return passage to the fuel inlet side.

Since the fuel pump is located within the fuel tank the electric motor is well cooled, while also avoiding problems with lubrication and seal seepage. There is no danger of explosion because there is never an ignitable mixture in the common housing for pump and motor.

Roller Pump (Located In Fuel Pump):

OPERATION
When the rotor disc rotates, the rollers are pressed outwards by centrifugal force and act as a circulating seal. A pumping action is created by the circulating rollers which draw in fuel at the inlet port and force the fuel through the discharge port into the fuel system.
When the pump is shut off, the check valve in the fuel outlet will close, prohibiting fuel from returning to the fuel tank via the fuel pump. The check valve maintains a pressure in the fuel lines called "rest pressure".

The fuel pump operates during engine cranking and when the engine is running. If the engine stops while the ignition is on, the injection ECU shuts off power to the fuel pump to reduce the risk of fire in the event of an accident.

In order to maintain a constant pressure in the fuel system under all possible operating conditions, the pump supplies substantially more fuel than the engine would ever need at any engine load.