Understanding Bosch High-Pressure Fuel Pumps: How They Work

Bosch high-pressure fuel pumps are used in modern diesel-powered vehicles, including pickup trucks, cars, and SUVs. They are a key component of common-rail fuel injection systems, which are found in almost all new road vehicles produced in the US and Europe. Bosch offers different types of high-pressure fuel pumps, such as the CP3 and CP4, which supply up to 29,000 psi of pressure. These pumps play a crucial role in optimizing fuel mixture preparation, minimizing fuel consumption, and ensuring seamless performance in various weather conditions.

Common-rail injection systems

The common-rail injection system consists of a high-pressure pump, a high-pressure rail, and individual injectors for each cylinder. The high-pressure pump delivers fuel to the connected rail under high pressure. The high-pressure rail is the hydraulic component that connects the pump and injectors. From here, the fuel is distributed to the individual injectors, which are integrated into each engine cylinder. The injection timing and fuel quantity are calculated and controlled individually for each cylinder, allowing for flexible injection timing and pressure.

The common-rail injection system with piezo injectors by Bosch enables the flexible injection of fuel at pressures up to 2,700 bar. The piezo injector injects the amount of fuel required for economical combustion, regardless of the driving situation. This system also features the "Digital Rate Shaping" strategy (DRS), which reduces the delay between pre-injection and main injection, resulting in a smoother combustion process with reduced noise, emissions, and fuel consumption.

Bosch's common-rail injection system is designed to meet the increasing requirements for diesel engine injection systems, including higher pressures, faster switching times, and flexible adaptation of the injection pattern to suit operating conditions. The system's flexibility, efficiency, and cost-effectiveness make it a popular choice for various applications, including passenger cars, light-duty vehicles, and off-highway machinery.

Direct injection

Bosch high-pressure fuel pumps are used in direct injection systems to deliver the required pressure. The pump compresses the fuel supplied by the electric fuel pump to a pressure of up to 250 bar for the HDP5evo pump and 350 bar for the HDP6 pump. The high-pressure fuel is then pumped through and stored in a rail that feeds the injectors, instead of directly feeding an injector. This allows for multiple injection events, variable timing, and precise control.

The Bosch high-pressure pump is made of stainless steel and welded construction, with intelligent design and minimized use of material. It is designed to comply with future legislation and suitability for higher demands on the engine due to increased system pressures. The pump also improves acoustic properties due to optimized demand control and outlet valve, reducing Noise, Vibration, and Harshness (NVH).

Bosch high-pressure fuel pumps for direct injection are available for various vehicle makes and models, including Land Rover, Jaguar, Chevrolet, Volkswagen, Ford, and Audi. These pumps are made of high-grade materials for enhanced durability and performance in all weather conditions.

Mixture preparation

The Bosch high-pressure pump (HDP) is designed to optimise mixture preparation. The HDP provides high pressure for optimum mixture preparation, with system pressures of up to 350 bar. The HDP5evo and HDP6 are two variants of the HDP.

The HDP5evo compresses fuel supplied by the electric fuel pump to a pressure of up to 250 bar. This pressure is achieved through the use of an optimised demand control and outlet valve, which also improves the acoustic properties of the pump.

The HDP6 delivers fuel at a pressure of 350 bar, which is required for high-pressure injection. The high-pressure injectors on the fuel rail meter the fuel with precision and at high pressure, directly optimising mixture preparation in the combustion chamber.

The electronic engine control unit (ECU) is responsible for adjusting the optimal mixing ratio between air and fuel, as well as the timing of injection. The air supply for the motor is just as important for the combustion of the air-fuel mixture as the fuel itself.

In the context of direct injection, fuel is injected separately from the air, directly into the combustion chamber. This is in contrast to earlier methods where fuel and air were mixed before entering the combustion chamber. As soon as the fuel leaves the nozzle of the injector, it ignites and creates power.

Fuel pump construction

Bosch high-pressure fuel pumps are constructed with intelligent design, minimised use of materials, and sophisticated manufacturing methods, resulting in a stainless-steel/welded construction. The HDP5evo and HDP6 high-pressure pumps are examples of these fuel pumps that play a crucial role in meeting future legislation and engine demands.

The HDP5evo high-pressure pump is designed to compress fuel supplied by the electric fuel pump to a pressure of up to 250 bar. This pump is driven by the need to improve acoustic properties and reduce noise, vibration, and harshness (NVH).

On the other hand, the HDP6 high-pressure pump increases the pressure of the fuel delivered by the electric fuel pump to 350 bar, which is necessary for high-pressure injection. This pump optimises mixture preparation directly within the combustion chamber.

Bosch fuel pumps are manufactured on the same production lines, adhering to rigorous quality standards, to guarantee a long and dependable service life. They are also put through end-of-line function testing to ensure the highest quality and performance.

The construction of Bosch high-pressure fuel pumps, with their attention to detail, advanced manufacturing techniques, and rigorous testing, ensures seamless performance, durability, and reliability in various vehicle applications.

Injector interface

The high-pressure injector provides the interface between the fuel rail and the combustion chamber. It is designed to meter and atomize the fuel such that a specific air-fuel mixture with optimum combustion characteristics is achieved in the combustion chamber. The high-pressure injectors are fitted to the fuel rail and they meter and atomize the fuel very rapidly and at high pressure for optimum mixture formation directly in the combustion chamber.

The fuel rail supplies the injectors with fuel with minimal pressure fluctuations between individual injections. The fuel-supply module's task is to pump the fuel volume out of the tank to the fuel rail using a certain pressure. The high-pressure pump plays an important role in complying with future legislation and suitability for higher demands on the engine due to increased system pressures of up to 350 bar.

The high-pressure pump compresses the fuel supplied by the electric fuel pump to a pressure of up to 250 bar. The high-pressure pump improves acoustic properties due to optimized demand control and outlet valve. The high-pressure injectors on the fuel rail meter the fuel with great precision and at high pressure. This optimizes mixture preparation directly in the combustion chamber.

The fuel injector injects the fuel so that it forms a homogeneous mixture with the added air. The fuel injectors, which are mounted on the fuel rail, continuously dose the required fuel quantity into the intake manifold according to the spray pattern and with the highest precision. The air-fuel mixture is generated outside of the combustion chamber in the intake manifold. The fuel injector sprays the fuel before the inlet valve. During the intake stroke, the mixture flows through the open inlet valve into the combustion chamber.

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