High-pressure pump with fuel quantity control valve

The high pressure pump is a fuel pump with 3 pistons and the following tasks:

• Increase fuel pressure (range from 50 to 200 bar)
• Deliver fuel to rail.

The high pressure pump is bolted onto the rear end of the vacuum pump. The high pressure pump drive shaft is connected to the vacuum pump drive shaft, which is driven by the timing chain.

The fuel-quantity control valve is mounted on the high-pressure pump. The fuel-quantity control valve is controlled using a pulse-width-modulated signal. While the fuel-quantity control system is active the DME digital engine electronics system uses various pulse-duty factors to regulate operation of the fuel-quantity control valve. The rail pressure is adjusted to the specified level calculated in the DME digital engine electronics ECU.

Fig 1: Identifying High-Pressure Pump With Fuel Quantity Control Valve

Courtesy of BMW OF NORTH AMERICA, INC.

The high-pressure pump generates pressure to maintain a constant level in the rail. Two valves are employed to maintain the pressure within the fuel rail at the required level:

• Fuel quantity control valve
• Rail pressure regulating valve.

The correct rail pressure is set depending on the situation at the time using one of the following three possible control types:

• Volumetric flow regulation by the flow regulating valve:

  The flow regulating valve only allows the amount of fuel to flow into the high pressure pump from the low-pressure side that is required in order to generate the required fuel rail pressure. In this scenario, the cylinders in the high pressure pump are not completely filled with fuel. Increasing the current results in progressively higher levels of rail pressure. The rail pressure regulating valve is supplied with so much current that it stays closed.

• Pressure regulation by the rail pressure regulating valve (e.g. in the overrun phase):

  The high-pressure pump provides a constant supply of highly-pressurized fuel to the rail. The rail pressure regulating valve reduces the fuel quantity in the low pressure fuel system if too much is delivered to the rail. Increasing the current results in progressively higher levels of rail pressure. The fuel quantity control valve is thereby closed.

• Combined closed-loop control with simultaneous regulation from the rail pressure regulating valve and the fuel-quantity control valve:

  For very low fuel injection rates of less than 4 mg (when idling), it is necessary for the rail pressure regulating valve to remove some fuel from the high-pressure fuel system. The reason is that the high-pressure pump cannot run with zero delivery. This means that the high-pressure pump continues to supply the high-pressure fuel system with fuel, even when the fuel-quantity control valve is closed. This would lead to excessive rail pressure and thus to a control deviation. The excess rail pressure is counteracted by continuously changing between the "fuel quantity control" and "pressure regulation" control types.

These control strategies come into play under the following conditions:

• During engine starts: Full delivery
• When the engine is running: Load-dependent change between 3 control types

Fig 2: Identifying High Pressure Pump

Courtesy of BMW OF NORTH AMERICA, INC.

The rail pressure is set by the 3 control types depending on the load. As a result the high pressure pump delivers the exact fuel quantity required by the engine. The high-pressure pump's output is reduced, simultaneously reducing the engine's fuel consumption.